in previous papers , we have shown that 
 heteroatom - substituted chiral 
 [ d1]methyllithiums , the smallest organometallic compounds , 
 can be prepared in homochiral form by tin  lithium exchange 
 from the respective tributylstannyl derivatives at low temperatures . they differ in their chemical as well as in their macro- and microscopic 
 configurational stability , depending on the heteroatom , the solvent , 
 and the temperature used . the oxygen - substituted chiral methyllithiums 1a(1 ) and 1b(1 ) are the macroscopically configurationally most 
 stable ones , followed by 1c(2 ) and 1d(3 ) ( figure 1 ) . the other oxygen - substituted ones are chemically 
 unstable but microscopically configurationally stable on the time 
 scale of a rearrangement . the silyloxy- and germyloxy - substituted 
 ones 1e and 1f undergo retro - brook rearrangements 
 ( 1,2-wittig rearrangements ) with retention of configuration . the ( allyloxy)methyllithiums 1 g isomerize 
 ( 2,3-wittig rearrangement ) with inversion of configuration , and the 
 phosphate1h rearranges ( phosphate  phosphonate 
 rearrangement ) with retention of configuration . the chiral ( dibenzylamino)methyllithiums ( 1i ) are the most stable of all 
 nitrogen - substituted ones but not completely even at 95 c . 
 at the same temperature , compound 1j is configurationally 
 less stable than 1i.(5 ) homochiral 
 isocyanomethyllithium ( 1k ) racemizes completely at 95 
 c when generated in the presence of benzaldehyde as electrophile . the phosphoric acid amide 1l undergoes 
 a phosphoramidate-aminophosphonate rearrangement with 
 retention of configuration . chloro[d1]methyllithium 1 m decomposes quickly but is macroscopically 
 configurationally stable for its short lifetime . this paper addresses the configurational stability 
 of chiral thio- 
 and bromo[d1]methyllithiums as compared to oxy- and chloromethyllithiums 
 to study the influence of going from heteroatoms of the second ( oxygen ) 
 and third ( chlorine ) row elements to ones of the third ( sulfur ) and 
 fourth ( bromine ) one , respectively . the hoffmann test of -(phenylthio)butyllithium 
 and -bromopentyllithium and secondary 
 -thiobenzyllithium established 
 configurational stability of the 
 former at 120 and 110 c , respectively but instability 
 of the latter at 78 c on the time scale of their addition 
 to ( s)-n , n - dibenzylphenylalaninal . the configurationally most stable 
 -thioalkyllithiums are tertiary ones with a carbamoyl substituent 
 at the sulfur atom . theoretical calculations 
 for methyllithiums substituted with a heteroatom being an element 
 of the third or a higher row show that they are configurationally 
 less stable than those of the second row because of the increasing 
 ease of planarization of the carbanionic center . thus , sulfur- and selenium - substituted alkyllithiums are 
 configurationally less stable than the oxygen - substituted ones . the same is true for phosphorus versus nitrogen 
 and silicon versus carbon - substituted chiral methyllithiums . investigations of the structure of many -heteroatom - substituted 
 alkyllithiums and mechanistic studies on the enantiomerization of -thioalkyllithiums 
 have been performed . reich has recently published an excellent 
 perspective of his structural work on organolithium reagents using 
 low - temperature nmr spectroscopy . anticipating 
 that chiral thio[d1]methyllithiums would not be macroscopically 
 configurationally stable , but only microscopically at best , we decided 
 to intercept them after generation at low temperatures by intramolecular 
 reactions . two types were used , the thiophosphate -mercaptophosphonate and the thia -- wittig rearrangement involving short - lived thioalkyllithiums . the 
 former was found to follow a retentive course with microscopically 
 configurationally stable ( from 78 to 0 c ) ( dialkoxyphosphinyl)thioalkyllithiums 
 as intermediates and the latter an invertive one at the carbanionic 
 center . -allylthioalkyllithiums as intermediates of the thia -- wittig 
 rearrangement were found to be configurationally stable , but -benzylthioalkyllithiums 
 were found to be unstable and partially enantiomerized prior to the 
 rearrangement . furthermore , ikemoto et 
 al . studied the effect of solvents and additives on the steric course 
 of oxy -- wittig rearrangement of the chiral 1,3-diphenyl-1-propenyloxy-2-propen-1-yl 
 carbanion . they found that the marked differences on the enantiomeric 
 ratios obtained with different solvents can be ascribed to the extent 
 of ion separation , which depends on the nature of solvent / additive . the substrates for testing the configurational 
 stability of chiral ( diisopropoxyphosphinyl)thiomethyllithiums , the 
 diisopropyl s - tributylstannylmethyl thiophosphates , 
 were prepared according to scheme 1 . here and 
 in all other cases , reactions were first optimized in the unlabeled 
 series and then applied to the labeled ones . tributylstannylmethanol 
 ( 2 ) was converted via its lithium alkoxide at 78 
 c to mesylate 3 , which 
 was used directly to alkylate the triethylammonium salt of diisopropyl 
 thiophosphate ( 4 ) . similarly , the deuterated enantiomers 
 ( s)- and ( r)-[d1]5 were prepared from ( r)- and ( s)-tributylstannyl[d1]methanol of 99% ee , respectively , obtained by an improved procedure ( see 
 the experimental section ) . to generate the 
 short - lived dipole - stabilized ( diisopropoxyphosphinyl)thiomethyllithium 
 ( 6 ) , thiophosphate 5 was transmetalated 
 in thf at 78 c with meli added dropwise every 3 s. normally , 
 alkyllithiums were added with a syringe equipped with a needle to 
 vigorously stirred reaction mixtures . in analogy to previous results , 
 we assume tin  lithium exchange whenever used here in this paper 
 to generate heteroatom - substituted methyllithiums to follow a retentive 
 course . it was found by reich and phillips and others that 
 tin  ate complexes form in quantities detectable by nmr spectroscopy 
 under special conditions , e.g. , the presence of hmpa as additive in 
 thf , increasing the number of phenyl substituents at tin , and low 
 temperature ( 80 c ) . furthermore , tributyltin compounds 
 are not favorable for the formation of ate complexes , which are substantially 
 less reactive than lithium reagents . ate complexes play 
 only a minor role here , if at all , and that salt free species of heteroatom - substituted 
 methyllithiums are produced . the migration of the phosphinyl group 
 from the sulfur to the carbon atom , a thermodynamically driven reaction , 
 gives phosphonate 7 . addition of acoh 2 min later , workup , 
 and chromatographic purification furnished mercaptomethylphosphonate8 in 60% yield . as no starting 
 material could be detected , transmetalation and the ensuing rearrangement 
 must be rapid reactions . when the experiment was performed at 0 c , 
 it furnished merely 33% of the desired mercaptophosphonate , although 
 no starting material was left . to determine the ee in the labeled 
 series , mercaptophosphonate8 was derivatized with ( r)-1-(1-naphthyl)ethyl isocyanate 
 to give thiocarbamates 10 ( scheme 2 ) . its h nmr spectrum displayed well - separated signals 
 for the diastereotopic hydrogens of the sch2p group , allowing 
 evaluation of the ee of the deuterated mercaptomethylphosphonates . 
 with this information in hands , thiophosphates ( s)- and ( r)-[d1]5 were rearranged 
 at temperatures ranging from 95 to 0 c , plausibly assuming 
 a retentive course as in the case of a secondary phosphinylthioalkyllithium . the yields and the enantiomeric excesses of 
 the mercaptomethylphosphonates [ d1]8 are given 
 in table 1 . the rearrangement in et2o at 0 c gave 
 racemic [ d1]8 ; however in thf a product with 
 23% ee ( entries 3 and 1 ) . the reason for the stronger influence of 
 et2o compared to thf on the ee is not clear , but possibly 
 attributable to the differing degree of solvation of lithium . the best result in terms of a combination of 
 yield ( 68% ) and ee ( 51% ) was obtained in thf with n - buli at 95 c ( entry 5 ) . in summary , these results 
 show that chiral ( phosphinylthio)methyllithiums [ d1]6 are microscopically configurationally labile down to 95 
 c on the time scale of the thiophosphate--mercaptophosphonate 
 rearrangement . three systems with differing lifetimes for the intermediate thiomethyllithiums 
 amenable to thia -- wittig rearrangement were investigated . the 
 required stannanes 12a  c were accessed 
 from thiols 11a  c , t - buona , and tributylstannylmethyl mesylates3 in yields of 82% to 92% ( scheme 3 ) . lithium exchange in thf at 95 
 c with n - buli produced thiomethyllithium 13a ( scheme 4 ) . the ensuing thia -- wittig 
 rearrangement furnished lithium thiolate 14a , which would 
 give on acidic workup and extraction 3-butenethiol . its boiling point of 7080 c is too low to allow 
 direct isolation of small amounts ( < 1 mmol ) . therefore , a substoichiometric 
 amount of cf3co2h ( 0.33 equiv relative to n - buli ) was added 10 min after the addition of n - buli , followed by excess ( r)-1-phenylethyl isocyanate , 
 to convert thiol 15 for determination of yield and evaluation 
 of ee in the labeled series to thiocarbamate 16 in 83% 
 overall yield . the two diastereotopic hydrogens at c-1 formed an ab 
 system in the h nmr spectrum ( dmso - d6 , 600 mhz ) , which collapsed to two broadened singlets at 2.79 
 and 2.82 ppm on decoupling of protons at c-2 . similarly , deuterated 
 stannanes ( r)- and ( s)-[d1]12a were rearranged using either thf or et2o as solvent at temperatures ranging from 95 to 0 c 
 ( table 2 ) . the data show that the yields and the ee are significantly 
 better 
 for thf than et2o . in analogy to the results for secondary 
 allythioalkyllithiums obtained by brickmann and brckner , we assume that the rearrangement proceeds with 
 inversion of configuration at the carbanionic center . surprisingly , chiral thiomethylithiums [ d1]13a are configurationally stable on the time scale of thia -- wittig 
 rearrangement below 95 c in thf and ee of thiol obtained 
 at 0 c was still 71% . it decreased only from 95% to 
 71% by going from 95 to 0 c in thf as solvent . next , the microscopic configurational stability of benzylthiomethyllithiums 
 ( 13b ) on time scale of -rearrangement was addressed . benzylthiomethylstannane 12b was transmetalated with n - buli in thf already at 30 c , as a higher 
 activation energy was expected than for allyl analogue ( scheme 5 ) . as before , the rearranged lithium thiolate was 
 converted to thiocarbamate 18 via thiol 17 . when the same reaction was performed with stannane ( r)-[d1]12b at 50 c ( reaction 
 time : 20 min ) , the yield of thiocarbamates [ d1]18 was 59% . when thiomethyllithium ( s)-[d1]13b was generated at 78 c and quenched with cf3co2h after 10 min , only benzyl methyl sulfide was detected 
 besides tetrabutyltin by h nmr spectroscopy ( 400 mhz ) 
 in the crude product . the following conclusions can be drawn from 
 these three experiments . first , benzylthiomethyllithium ( 13b ) undergoes thia -- wittig rearrangement down to 50 c . 
 at lower temperatures , the activation energy , at least that for dearomatization 
 corresponding to resonance energy of benzene of 36 kcalmol , can not be overcome . second , this high activation 
 energy increased the lifetime of intermediates 13b and 
 their chances to enantiomerize , compared to those for allylthiomethyllithium 
 ( 13a ) . third , chiral benzylthio[d1]methyllithium is microscopically 
 configurationally unstable on the time scale of thia -- wittig 
 rearrangement . the chemical stability of benzylthiomethyllithium 
 toward thia -- wittig 
 rearrangement at 78 c enabled us to investigate its 
 microscopic and macroscopic configurational stability . first , meli 
 was added to a solution of unlabeled stannane 12b in 
 thf , followed by benzaldehyde as our standard electrophile for chiral 
 [ d1]methyllithiums 10 min later . workup after 5 min and 
 flash chromatography furnished ( )--benzylthio alcohol 19 in 77% yield ( scheme 6 ) . the ( r)-mosher ester derived from ( s)--methoxy--(trifluoromethyl)phenylacetyl 
 chloride [ ( s)-mtpacl , ( s)-mosher 
 chloride ] was prepared and investigated by h nmr spectroscopy . the sch2 group of each diastereomer displayed a well - separated 
 ab part of an abx system , enabling the determination of ee with an 
 estimated accuracy of 3% at best at deuterium bearing carbon atom 
 in the labeled series . to address macroscopic configurational stability 
 of benzylthio[d1]methyllithium [ ( s)-13b ] , this experiment was repeated with ( r)-[d1]12b and yielded an alcohol being racemic 
 at c-1 and c-2 as deduced from the h nmr spectrum ( 400 
 mhz ) of the mixture of ( r)-mosher esters . despite 
 the short time of 1 min between addition of meli for tin  lithium 
 exchange and addition of benzaldehyde , the lifetime was long enough 
 to allow complete racemization at deuterium bearing carbon atom . to evaluate the microscopic configurational 
 stability of ( s)-13b , meli was added 
 dropwise to a solution 
 of stannane ( r)-[d1]12b and 
 benzaldehyde in thf at 78 c . the deuterated alcohol 
 ( s)-[2-d1]19 isolated in 
 24% yield , was derivatized with ( s)-mosher chloride 
 and the mixture of esters was investigated by h nmr spectroscopy . the ee at the deuterium bearing stereo center was only 16% , but significant . this time thio[d1]methyllithium ( s)-[d1]13b was immediately intercepted by benzaldehyde 
 as the electrophile . despite the short time between generation and 
 addition to carbonyl group , partial racemization of the ( very ) labile 
 thio[d1]methyllithium interfered . the yield dropped to 
 9% , but the ee increased to 26% , when the reaction was performed at 
 95 c in the presence of 2 equiv of 12-crown-4 . it was 
 hoped that this li complexing agent might influence the 
 c  li bond length and thus enantiomerization . when the reaction was performed at 50 c , 
 no thiol [ ] d1]17 formed by rearrangement could 
 be detected ( h nmr ) in the crude product besides deuterated 
 alcohol 19 ( 25% , 8% ee ) . this experiment shows that addition 
 of benzyl[d1]thiomethyllithium to benzaldehyde is ( much ) 
 faster than -rearrangement . in the former case , the lifetime 
 of the chiral carbanion is shorter and the chance to retain the configuration 
 higher . finally , the reaction was performed at 0 c and furnished 
 racemic [ d1]19 . the low yields were attributed 
 to addition of meli to benzaldehyde as competing reaction to transmetalation , 
 a general phenomenon in experiments for the determination of the microscopic 
 configurational stability of chiral heteroatom - substituted [ d1]methyllithiums . only part of 
 the starting material was consumed . in summary , benzylthio[d1]methyllithium is microscopically very labile on the time scale of 
 the addition to benzaldehyde . to lower the activation energy 
 for the thia -- wittig rearrangement 
 involving an aromatic compound , the phenyl ring was replaced by a 
 naphthyl substituent . a preliminary experiment was performed with 
 stannane 12c , which was transmetalated with n - buli at 78 c in thf and quenched after 10 min ( scheme 7 ) . no methyl 1-naphthylmethyl sulfide and only 
 a trace of starting material could be detected in the crude product 
 by h nmr spectroscopy . thiol 20 was converted 
 to thiocarbamate 21 to test its suitability for the determination 
 of the ee in the labeled series . the sch2 group displayed 
 an ab system in the h nmr spectrum ( 400 mhz ) . analogously , 
 thiomethylstannane ( s)-[d1]12c was transmetalated at 50 and 95 c , using either 
 meli ( entry 1 ) or n - buli ( entries 2 ) for tin  lithium 
 exchange ( table 3 ) . surprisingly , the ees were 
 similar for the rearrangements at 50 and 95 c . these findings demonstrate that the activation energy for isomerization 
 of naphthyl derivative 13c is significantly lower than 
 that for phenyl derivative 13b . qualitatively , dearomatization 
 of benzene could require up to 36 kcalmol , that of one benzene ring of naphthalene up to 13 kcalmol less , that is 23 kcalmol ( resonance energy of naphthalene is 59 kcalmol , as one benzene ring is retained : 5936 = 23 ) . consequently , the rearrangement of the naphthyl 
 derivative proceeded even at 95 c , while the phenyl 
 derivative rearranged only at temperatures above 50 c . 
 the reaction rate of the former was ( much ) higher than of the latter , 
 so that the lifetime of carbanion 13c was ( much ) shorter 
 than that of 13b . therefore at 50 c only 
 the benzyl - substituted thio[d1]methyllithium [ d1]13b had enough time to racemize completely , while in 
 the case of the naphthylmethyl - substituted one 80% of the molecules 
 did not enantiomerize , resulting in an ee of 60% . -haloalkyllithiums , also termed 
 lithium carbenoids , have nucleophilic and electrophilic properties , 
 depending on the solvent and the reaction temperature . lithium 
 exchange in ,-dihaloalkanes , ,-dihalocyclopropanes , or preferably dihalomethanes , at low temperatures 
 ( 78 to 120 c ) and are reacted with a variety 
 of electrophiles , especially aldehydes and ketones to obtain epoxides . chiral -chloroalkyllithiums and -chloroalkylmagnesium 
 halides have also been prepared elegantly , the latter being the configurationally 
 more stable species ( below 20 c ) . enantiopure chloro[d1]methyllithium was prepared in our group and found to be micro- 
 and macroscopically configurationally stable at 78 c , 
 but chemically very labile . here we address the configurational stability of enantiopure 
 bromo[d1]methyllithiums similarly to the chloro analogues . 
 however , the preparation of starting bromo[d1]methylstannanes 
 of ee 99% and the high propensity of brchdli to decomposition 
 were challenging obstacles on the way to success . we reasoned that 
 we could generate bromomethyllithium from bromomethyltributylstannane 
 by tin  lithium exchange and trap it in situ with benzaldehyde , 
 resulting in the formation of the lithium salt of the corresponding 
 bromohydrin . to check whether it is chemically stable and whether 
 its ( r)-mosher ester is suitable for the determination 
 of the ee in the labeled series , some exploratory experiments were 
 performed ( scheme 8) . when 
 it was converted to the lithium alkoxide in thf with meli at 78 
 c and then quenched with cf3co2h after 
 5 min , it was recovered unchanged in 95% yield . no epoxide 24 could be detected in the h nmr spectrum ( 400 mhz ) of 
 the crude product as evidenced by spiking with an authentic sample . samples of ( )-23 and ( s)-23 obtained by enantioselective reduction of phenacyl bromide 
 with ( + ) -dip - chloride were converted 
 to diastereomeric ( r)-mosher esters and investigated 
 by h nmr spectroscopy . bromomethyltributylstannane was prepared from 
 tributylstannylmethanol 
 ( 2 ) in yields of up to 91% using ph3p / nbs ( scheme 9 ) . when it was 
 transmetalated at 78 c in thf and the reaction quenched 
 with cf3co2h 30 s after the addition of 1 m 
 meli , the crude product was methyltributylstannane containing no starting 
 material . anticipating fast decomposition of bromomethyllithium , we decided 
 to do two in situ trappings using 4 equiv of benzaldehyde in admixture 
 with bromomethylstannane in dry thf at 78 c in analogy 
 to the experiments with chloromethyllithium . four equiv of meli ( 1 
 m in cumene / thf / diethoxymethane ) were added dropwise and the reaction 
 was quenched with cf3co2h after 5 and 15 min , 
 respectively . in both cases , only 25% of the starting material was 
 transmetalated , of which 80% formed bromohydrin ( )-23 in 19% yield for both experiments as evidenced byh nmr spectroscopy of the crude product . meli underwent 
 two competing reactions , tin  lithium exchange and addition 
 to benzaldehyde , which was faster and resulted in ( )-1-phenylethanol 
 as major side product . to slow down addition of meli to the electrophile 
 relative to transmetalation , acetophenone was tested as alternative 
 electrophile . the desired bromohydrin ( )-27 was 
 obtained in 13% yield along with the tertiary alcohol derived from 
 addition of meli to acetophenone , and recovered starting material . bromohydrin ( )-27 although a tertiary alcohol could 
 be converted to diastereomeric ( r)-mosher esters 
 under forcing conditions ( 50 c , 1,4-dioxane , 8 h ) . the h nmr spectrum ( 400 mhz ) showed ab systems for the ch2br groups , demonstrating the feasibility to determine the 
 ee in the deuterated series . chiral bromo[d1]methylstannane ( r)-[d1]25 was prepared from ( s)-[d1]2 at first by the procedure 
 used for the preparation 
 of the unlabeled compound in 92% yield . transmetalation and in situ 
 trapping ( with retention of configuration ) of the intermediate bromo[d1]methyllithium [ ( s)-[d1]26 ] with benzaldehyde at 78 c furnished bromohydrin 
 ( 2s)-[2-d1]23 in 11% yield 
 with an ee of 57% at c-2 , determined by h nmr spectroscopy 
 of the corresponding ( r)-mosher ester . being unsure 
 about the ee of the starting bromide , we determined it in the same 
 way as that of the chloride , using a homochiral thiol as derivatizing 
 agent and h nmr spectroscopy and found it to be 57% . this proved that the chiral bromo[d1]methylstannane was not enantiomerically pure and that it seemingly 
 produced microscopically configurationally stable bromo[d1]methyllithium , which we wanted to corroborate by more experiments . apparently , the starting bromo[d1]methylstannane racemized 
 partly under the reaction conditions for the substitution reaction , 
 under which the chloro compound was configurationally stable . bromide 
 ions in the reaction mixture replaced bromide of the substrate by 
 a sn2 mechanism , resulting in partial enantiomerization . then we switched to a modified mitsunobu reaction with ph3p / diad ( diisopropyl azodicarboxylate)/ph3phbr in toluene , optimized it , and finally obtained ( r)-bromo[d1]methylstannane of 99% ee 
 in 35% yield . chiral bromo[d1]methylstannanes with ee ranging from 77 to 99% were transmetalated 
 in the presence of benzaldehyde or acetophenone at 78 or 95 
 c . the data show that the 
 ee of the bromohydrins reflect the ee of the respective starting bromo[d1]methylstannanes being microscopically configurationally stable , 
 irrespective of whether benzaldehyde or acetophenone was used for 
 the in situ trapping ( table 4 , entries 35 ) . 
 in the case of entry 5 , the h nmr spectrum of the crude 
 product revealed the following molar ratios : ( s)-[d1]2/phcho / bromohydrin ( 2r)-[2-d1]23/bu3snch3/phch(oh)ch3 = 2:1.62:0.1:0.35:4.18 . the major portion [ 85% ; 2/(2 + 0.35 ) 
 = 0.85 ] of the starting material was recovered and only about one - third 
 ( 0.1:0.35 = 0.29 ) of the chiral bromomethyllithium as deduced from 
 the formed tributylmethylstannane gave bromohydrin . evidently , the 
 other two - thirds decomposed because of low chemical stability . when 
 acetophenone was used as electrophile , the ratios for entry 4 of table 4 in the crude product were for ( s)-[d1]2/phc(o)ch3/bromohydrin 
 ( 1r)-[1-d1]27/bu3snch3/phc(oh)(ch3)2 = 0.0:0.93:0.39:1.0:0.72 . this time transmetalation was complete as addition of meli to acetophenone 
 was slowed down compared to benzaldehyde . surprisingly , again only 
 about one - third of the bromo[d1]methyllithium generated 
 was intercepted by acetophenone . however , two - thirds decomposed apparently . we expected a higher percentage of decomposition because the lifetime 
 of brchdli will be longer in the presence of acetophenone than benzaldehyde 
 as the addition to the electrophile will be slower . we can not exclude 
 that some of the bromomethyllithiums reacted with the starting bromomethylstannanes 
 to give finally tributylmethylstannane and ethene as found for -haloalkylstannanes . these results demonstrate 
 that chiral bromo[d1]methyllithiums are microscopically 
 stable on the time scales of the addition to benzaldehyde and acetophenone , 
 but extremely labile . signals of chdbr groups in the h nmr spectra ( 400 mhz , 
 toluene - d8 ) of ( r)-mosher 
 esters derived from ( a ) ( 2s)-[2-d1]23 of 76% ee and ( b ) ( 2r)-[2-d1]23 of 99% ee ( d 96% ) . four chiral thio[d1]methyllithiums 
 with different substituents 
 at sulfur were prepared by tin  lithium exchange and their microscopic 
 configurational stability was determined relative to the thiophosphate--mercaptophosphonate 
 and thia -- wittig rearrangements , respectively ( figure 3 ) . the configurational stability of chiral thio[d1]methyllithiums is delicately influenced by their lifetime 
 depending on the substitutent at sulfur . the chances for enantiomerization 
 of a thiomethyllithium will increase with its lifetime , which is inversely 
 proportional to the rate of the rearrangement . while 13a is configurationally stable at 95 c , 13b underwent the thia -- rearrangement only down to 50 c 
 and racemized completely . in case of 13b , the microscopic 
 configurational stability was also evaluated on the time scale of 
 its addition to benzaldehyde . unfortunately , the solution structures 
 of the respective methyllithiums and their mechanism of enantiomerization 
 are unknown . hoffmann et al . and reich 
 and dykstra found for -selenium- 
 and -sulfur - substituted alkyllithiums that rotation about the 
 c  heteroatom bond is the rate - determining step of enantiomerization . lithium 
 exchange ( salt free ? ) proved to be chemically very labile but microscopically 
 configurationally stable on the time scale of the addition to benzaldehyde 
 and acetophenone at 78 c . in summary , we assume that 
 the rearrangements of 6 and 13a , c follow a retentive and invertive course , respectively , in analogy 
 to chiral , nonracemic organolithiums with the same heteroatom , but 
 an alkyl group instead of the deuterium atom . analogously , thiomethyllithium 13b and bromomethyllithium 26 add to benzaldehyde 
 with retention of configuration . . microscopic 
 configurational stability of various thio[d1]methyllithiums 
 on the time scale of rearrangements for 6 and 13a  c and on the time scale 
 of addition of 13b and bromo[d1]methyllithiums 26 to benzaldehyde . h / c ( j modulated ) nmr 
 spectra were measured at 300 k at 400.13 , 400.27 , 600.13 mhz/100.61 , 
 100.65 , 150.92 mhz , respectively . they were referenced either to residual chcl3 ( h 7.24)/toluene - d8 ( chd2 : h 2.09)/cd3od ( chd2 : h 3.31)/dmso - d6 ( chd2 : h 2.50 ) or cdcl3 ( c 77.00)/toluene - d8 ( cd3 : c 21.04)/cd3od ( cd3 : c 49.00)/dmso - d6 ( cd3 : c 39.50 ) . ir spectra 
 of films on a silicon disk were recorded on ft - ir spectrometers or 
 by using atr . optical rotations were 
 measured at 20 c with a polarimeter in a 1 dm cell . flash ( column ) chromatography was performed 
 with silica gel 60 
 ( 230400 mesh ) and monitored by tlc , carried out on 0.25 mm 
 thick plates , silica gel 60 f254 . spots were visualized 
 by uv and/or dipping the plate into a solution of ( nh4)6mo7o244h2o ( 23.0 g ) 
 and ce(so4)24h2o ( 1.0 g ) in 
 10% aq h2so4 ( 500 ml ) , followed by heating with 
 a heat gun . the two diastereomeric boronates 31 and 32 were reduced with libet3d to ( 1s)-[1-h1]- and ( 1r)-[1-h1]34 , respectively ( compound 
 numbers are taken from the literature ) . an aqueous solution of naoh ( 2.27 ml , 7.82 mmol , 3.44 m ) and a solution 
 of h2o2 ( 1.0 ml , 10.33 mmol , 30% ) were added 
 at 0 c to ( 1s)-[1-h1]34 ( 1.689 g , 3.13 mmol ) dissolved in dry thf ( 15.7 
 ml ) . after the biphasic mixture was stirred vigorously for 1 h , more 
 naoh ( 2.27 ml ) and h2o2 ( 1.0 ml ) were added . stirring was continued for another 1 h , and then water ( 18 ml ) and 
 pentaerythritol ( 600 mg ) were added . the organic phase was separated , and the aqueous phase 
 was extracted with etoac ( 3  30 ml ) . the combined organic layers 
 were washed with water ( 30 ml ) and brine ( 30 ml ) , dried ( mgso4 ) , and concentrated under reduced pressure . the residue was 
 purified by flash chromatography ( hexane / etoac , 10:1 , rf 0.48 ) to give ( s)-[d1]2 ( 826 mg , 82% , d 9698% ) . similarly , 
 ( 1r)-[1-h1]34 ( 1.617 g , 2.99 mmol ) was converted to ( r)-[d1]2 ( 731 mg , 76% , d 9698% ) . a solution of alcohol ( 0.10 
 mmol ) , dry pyridine ( 0.25 ml ) , and ( s)-mtpacl ( 0.3 
 ml , 0.15 mmol , 0.5 m in dry ch2cl2 ) in dry ch2cl2 ( 2 ml ) was left at rt ( for bromohydrins 4 h , 
 for all other alcohols 418 h ) . afterward , ch2cl2 ( 10 ml ) and hcl ( 10 ml , 1 m ) were added . the organic phase 
 was separated , washed with saturated aq nahco3 , dried ( mgso4 ) , and concentrated under reduced pressure . the crude product 
 was purified by flash chromatography to furnish oily ( r)-mosher esters . tmp ( 432 mg , 3.07 mmol ) was dissolved in 
 dry thf ( 12.4 ml ) under argon and the solution cooled to 10 
 c . n - buli ( 1.93 ml , 3.07 mmol , 1.6 m in hexane ) 
 was added . after 15 min , the solution was cooled to 78 c , 
 tributylstannylmethanol ( 2 ) ( 826 mg , 2.56 mmol ) in dry 
 thf ( 4.2 ml ) was added , and the solution was stirred for 15 min . mscl 
 ( 258 l , 3.33 mmol ) was added , the solution was stirred for 
 another 20 min , and then freshly prepared triethylammonium salt of o , o - diisopropyl thiophosphoric acid ( 3.84 mmol , 10.68 ml 
 of solution prepared from 10 mmol of phosphite in 25 ml of i - proh ) was added . the mixture was concentrated under reduced 
 pressure , and water ( 26 ml ) was added . the combined organic 
 phases were washed with water ( 30 ml ) , dried ( na2so4 ) , concentrated under reduced pressure , and purified by flash 
 chromatography ( hexane / etoac , 7:1 , rf 0.38 ) to yield thiophosphate 5 as a 
 colorless oil ( 1.014 g , 79% for two steps ) . ir ( si ) :  2958 , 
 2927 , 1253 , 979 cm . h nmr ( 400.27 
 mhz , cdcl3 ) :  4.72 ( dsept , j = 
 8.9 , 6.2 hz , 2h ) , 2.04 ( d , j = 9.0 hz , j(sn ) = 35.4 hz , 2h ) , 1.601.38 ( m , 6h ) , 
 1.36 ( d , j = 6.3 hz , 6h ) , 1.33 ( d , j = 6.3 hz , 6h ) , 1.29 ( sext , j = 7.3 hz , 6h ) , 1.040.87 
 ( m , j(sn ) = 50.8 hz , 6h ) , 0.87 
 ( t , j = 7.3 hz , 9h ) . c nmr ( 100.61 mhz , 
 cdcl3 ) :  72.1 ( d , j = 6.0 hz , 2c ) , 
 28.9 ( j(sn ) = 21.8 hz , 3c ) , 27.2 
 ( j(sn ) = 56.5 hz , 3c ) , 23.9 ( d , j = 4.2 hz , 2c ) , 23.7 ( d , j = 5.6 hz , 2c ) , 
 13.6 ( 3c ) , 9.7 ( j(sn ) = 323.4 hz , 
 3c ) , 4.5 ( d , j = 4.9 hz ) . calcd for c19h43o3pssn : c , 45.52 ; h , 8.65 ; s , 6.40 . found : 
 c , 45.93 ; h , 8.85 ; s , 6.10 . similarly , ( s)-tributylstannyl[d1]methanol { ( s)-[d1]2 } ( 826 mg , 2.56 mmol ) and ( r)-[d1]2 ( 731 mg , 2.27 mmol ) were converted to thiophosphates ( r)-[d1]5 ( 1.014 g , 79% ) and ( s)-[d1]5 ( 947 mg , 83% ) , respectively . 
 their h nmr spectra ( 400.27 mhz , cdcl3 ) were 
 identical to that for 5 except for  2.04 ( br d , j = 9.0 hz , j(sn ) = 35.4 
 hz , 1h ) . meli ( 0.52 ml , 0.52 mmol , 1 m in thf / cumene ) 
 was added to a solution of s - stannylmethyl thiophosphate 5 ( 217 mg , 0.43 mmol ) in dry thf ( 3 ml ) under argon at 78 
 c dropwise every 3 s. after 2 min , acoh ( 0.5 ml , 2 m , in thf ) 
 was added , and the solution was warmed and concentrated under reduced 
 pressure . water ( 4 ml ) was added , and the aq phase was extracted with 
 etoac ( 3  10 ml ) . the 
 residue was purified by flash chromatography ( hexane / etoac , 1:1 , rf 0.14 ) to yield mercaptophosphonate 8 as a colorless oil ( 55 mg , 60% ) . similarly , thiophosphate 5 ( 202 mg , 0.40 mmol ) was converted to mercaptophosphonate 8 ( 28 mg , 33% ) except that meli was added dropwise every 1 s and that 
 the reaction was quenched after 1 min with acoh ( 0.48 ml , 2 m , in 
 thf ) . similarly to experiment 1 , ( s)-[d1]5 ( 280 mg , 0.56 mmol ) was converted 
 to ( r)-[d1]8 ( 48 mg , 41% , 
 ee 23% ) except that the reaction was performed at 0 c and quenched 
 with acoh 15 s after the addition of meli , added dropwise every 1 
 s. the spectroscopic data were identical to that of 8 except as follows . h nmr ( 400.27 mhz , cdcl3 ) :  2.60 ( tdd , j = 13.4 , 8.2 , 2.1 hz , 1h ) , 
 1.79 ( dd , j = 8.5 , 8.2 hz , 1h ) . c nmr 
 ( 100.61 mhz , cdcl3 ) :  18.3 ( dt , j = 151.8 , 21.2 hz ) . similarly to experiment 1 , ( s)-[d1]5 ( 229 mg , 0.46 mmol ) was converted 
 to ( r)-[d1]8 ( 22 mg , 22% , 
 ee 77% ) except that the reaction was performed in et2o 
 at 95 c , using 1.05 equiv of meli . similarly to experiment 4 , ( s)-[d1]5 ( 218 mg , 0.43 mmol ) was converted 
 to ( r)-[d1]8 ( 52 mg , 56% , 
 racemic ) , except that the reaction was performed in dry et2o at 0 c . the reaction was quenched with acoh after 15 s. similarly to experiment 4 , thiophosphate 
 ( r)-[d1]5 ( 286 mg , 0.57 mmol ) 
 was converted to deuterated ( s)-mercaptophosphonate 
 ( s)-[d1]8 ( 31 mg , 25% , ee 
 61% ) except that the reaction was performed in dry thf and quenched 
 with acoh 3 min after the addition of meli . similarly to experiment 6 , ( r)-[d1]5 ( 249 mg , 0.50 mmol ) was converted 
 to ( s)-[d1]8 ( 73 mg , 68% , 
 ee 52% ) except that meli was replaced by n - buli . a solution of mercaptomethylphoshonate8 ( 76 mg , 0.36 mmol ) and ( r)-()-1-(1-naphthyl)ethyl isocyanate ( 0.62 ml , 0.72 
 mmol , ee 95% ) in dry thf ( 3 ml ) under argon was stirred for 5 h at 
 rt . afterward , water ( 0.25 ml ) was added , and the mixture was stirred 
 for another 2.5 h and concentrated under reduced pressure . the residue 
 was purified by flash chromatography ( hexane / etoac , 1:2 , rf 0.61 ) to yield thiocarbamate 10b ( 136 mg , 97% ) as a colorless oil . ir ( si ) :  3222 , 
 2980 , 2931 , 1675 , 1533 , 1238 , 1216 , 994 cm . h nmr ( 400.13 mhz , cdcl3 ) :  8.04 ( d , j = 8.3 hz , 1h ) , 7.857.75 ( m , 1h ) , 7.74 ( d , j = 7.9 hz , 1h ) , 7.557.35 ( m , 4h ) , 6.59 ( br s , 1h , 
 nh ) , 5.85 ( br s , 1h ) , 4.61 ( dsept , j = 7.7 , 6.3 hz , 
 2h ) , 3.18 ( ab - syst , jab = 15.0 hz , j = 12.9 hz , 2h ) , 1.63 ( d , j = 6.8 hz , 
 3h ) , 1.27 ( d , j = 6.0 hz , 3h ) , 1.26 ( d , j = 5.7 hz , 3h ) , 1.23 ( d , j = 6.2 hz , 3h ) , 1.21 ( d , j = 6.2 hz , 3h ) . c nmr ( 100.61 mhz , cdcl3 ) :  164.3 ( br s ) , 137.9 , 133.8 , 130.7 , 128.8 , 128.8 , 
 128.3 , 126.4 , 125.7 , 125.2 , 123.0 , 122.6 , 71.40 ( d , j = 6.7 hz ) , 71.38 ( d , j = 6.7 hz ) , 60.3 , 24.0 ( d , j = 153.2 hz ) , 23.94 ( d , j = 4.5 hz ) , 23.91 
 ( d , j = 4.4 hz ) , 23.79 ( d , j = 4.8 
 hz ) , 23.77 ( d , j = 5.2 hz ) , 21.1 ( br s ) . calcd for 
 c20h28no4ps : c , 58.66 ; h , 6.89 ; n , 
 3.42 ; s , 7.83 . found : c , 59.05 ; h , 7.14 ; n , 3.80 ; s , 8.41 . similarly , 
 ( r)-[d1]8 ( 48 mg , 0.22 mmol ) 
 was converted to ( r)-[d1]10b ( 66 mg , 73% , ee 23% ) . the h nmr spectrum ( 400.27 mhz , 
 cdcl3 ) was identical to that of 10b except 
 for  3.22 ( d , j = 13.3 hz , 0.38h ) , 3.17 ( d , j = 13.2 hz , 0.61h ) . similarly , ( s)-[d1]8 ( 31 mg , 0.14 mmol ) was converted 
 to ( s)-[d1]10b ( 50 mg , 86% , 
 ee 51% ) . the h nmr spectrum 
 ( 400.27 mhz , cdcl3 ) was identical to that of ( r)-[d1]10b except for the different integration 
 of the two doublets  3.22 ( d , j = 13.3 hz , 
 0.74h ) , 3.17 ( d , j = 13.2 hz , 0.23h ) . allylmercaptan ( 0.20 ml , 2.37 mmol ) was added 
 to a solution of t - buona ( 228 mg , 2.37 mmol ) in dry 
 thf ( 5.0 ml ) and stirred under argon for 10 min . the reaction mixture 
 was cooled to 30 c , and tributylstannylmethyl mesylate 
 ( 3 ) ( 632 mg , 1.58 mmol ) in dry thf ( 3 ml ) was added . after the mixture was stirred for 15 min , 1 m hcl ( 8 ml ) and hexane 
 ( 8 ml ) were added . the organic phase was separated and washed with 
 brine ( 20 ml ) , dried ( mgso4 ) , and concentrated under reduced 
 pressure . the residue was purified by flash chromatography ( hexane / ch2cl2 , 30:1 , rf 0.54 ) to yield tributylstannylmethyl sulfide ( 12a ) ( 500 mg , 84% ) as a colorless oil . ir ( si ) :  2956 , 2926 , 
 2853 , 1635 , 1464 , 1376 , 911 cm . h 
 nmr ( 400.27 mhz , cdcl3 ) :  5.74 ( tdd , j = 17.2 , 10.0 , 7.3 hz , 1h ) , 5.07 ( tdd , j = 10.0 , 
 1.7 , 0.8 hz , 1h ) , 5.03 ( tdd , j = 17.2 , 1.7 , 1.2 hz , 
 1h ) , 3.06 ( ddd , j = 7.3 , 1.2 , 0.8 hz , 2h ) , 1.80 ( s , j(sn ) = 41.3 hz , 2h ) , 1.601.38 
 ( m , 6h ) , 1.30 ( sext , j = 7.3 hz , 6h ) , 1.100.82 
 ( m , j(sn ) = 50.6 hz , 6h ) , 0.87 
 ( t , j = 7.3 hz , 9h ) . c nmr ( 100.61 mhz , 
 cdcl3 ) :  133.9 , 116.7 , 41.0 , 29.0 ( j(sn ) = 20.9 hz , 3c ) , 27.3 ( j(sn ) = 55.2 hz , 3c ) , 13.7 ( 3c ) , 9.5 ( j(sn ) = 334.7 , 319.6 hz , 3c ) , 7.5 . calcd for 
 c16h34ssn : c , 50.94 ; h , 9.08 . found : c , 51.16 ; 
 h , 9.14 . similarly , mesylates ( r)- and ( s)-[d1]3 ( 690 mg , 1.72 mmol and 635 mg , 1.59 mmol ) were converted to sulfides 
 ( s)-[d1]12a ( 537 mg , 83% ) 
 and ( r)-[d1]12a ( 375 mg , 
 63% ) , respectively . the h nmr spectra ( 400.27 mhz , cdcl3 ) were identical to that of 12 except for  
 1.78 ( br s , j(sn ) = 40.7 hz , 1h ) . benzylmercaptan ( 0.35 ml , 3.0 mmol ) was alkylated 
 with mesylate 3 ( 798 mg , 2.0 mmol ) by the procedure used 
 for the preparation of allylthiomethylstannane 12a . the 
 crude product was first heated ( 45 c , 0.5 mbar ) to remove excess 
 benzylmercaptan and then purified by flash chromatography ( hexane / ch2cl2 , 30:1 , rf 0.33 ) 
 to yield benzylthiomethylstannane 12b ( 786 mg , 92% ) as 
 a colorless oil . ir ( si ) :  2955 , 2923 , 2851 , 1493 , 1453 , 1376 , 
 1071 cm . h nmr ( 400.27 mhz , cdcl3 ) :  7.357.15 ( m , 5h , harom ) , 3.64 
 ( s , 2h , ch2s ) , 1.77 ( s , j(sn ) = 41.6 hz , 2h , ch2sn ) , 1.571.33 ( m , 6h , 3 
  ch2ch2sn ) , 1.30 ( sext , j = 7.3 hz , 6h , 3  ch2(ch2)2sn ) , 0.970.80 ( m , j(sn ) 
 = 49.6 hz , 6h , 3  ch2sn ) , 0.85 ( t , j = 7.3 hz , 9h , 3x ch3(ch2)3sn ) . c nmr ( 100.61 mhz , cdcl3 ) :  cq not detected , 
 129.0 ( 2c , carom ) , 128.3 ( 2c , carom ) , 126.6 
 ( carom ) , 42.5 ( ch2s ) , 29.0 ( j(sn ) = 20.6 hz , 3c , 3  ch2(ch2)2sn ) , 27.2 
 ( j(sn ) = 55.2 hz , 3c , 3  ch2-ch2sn ) , 13.7 
 ( 3c , 3  ch3(ch2)3 ) , 9.5 ( j(sn ) = 334.4 hz , 3c , 3  snch2(ch2)2 ) , 8.3 ( t , j(sn ) = 223.0 hz , sch2sn ) . calcd for c20h36ssn : c , 56.22 ; 
 h , 8.49 ; s , 7.50 . found : c , 56.48 ; h , 8.45 ; s , 7.26 . similarly , 
 mesylates ( r)-[d1]3 ( 1.0 
 g , 2.49 mmol ) and ( s)-[d1]3 ( 1.690 g , 4.22 mmol ) were converted to benzylthio-[d1]methylstannanes ( s)-[d1]12b ( 870 mg , 82% ) and ( r)-[d1]12b ( 1.535 g , 85% ) , respectively . their h nmr spectra ( 400.27 
 mhz , cdcl3 ) were identical to that of 12b except 
 for  1.77 ( s , j(sn ) = 41.6 
 hz , 1h ) . 1-naphthylmethanethiol ( 745 mg , 4.66 mmol ) was alkylated with mesylate 3 ( 1.240 g , 3.11 mmol ) by the procedure used for the preparation 
 of allylthiomethylstannane 12a . the combined organic 
 layers were washed with brine ( 25 ml ) and 2 m naoh ( 3  25 ml ) , 
 dried ( mgso4 ) , and concentrated under reduced pressure . the crude product was purified by flash chromatography ( hexane / ch2cl2 , 30:1 , rf 0.33 ) to yield ( 1-naphthylmethyl)thiomethylstannane 12c ( 1.219 g , 82% ) as a colorless oil . ir ( si ) :  2954 , 
 2922 , 2851 , 1510 , 1462 , 1376 , 1074 , 1016 cm . h nmr ( 400.27 mhz , cdcl3 ) :  8.198.11 
 ( d , j = 8.5 hz , 1h ) , 7.857.68 ( m , 2h ) , 7.557.42 
 ( m , 2h ) , 7.417.33 ( m , 2h ) , 4.12 ( s , 2h ) , 1.83 ( s , j(sn ) = 40.1 hz , 2h ) , 1.491.33 
 ( m , 6h ) , 1.21 ( sext , j = 7.3 hz , 6h ) , 0.980.83 
 ( m , 6h ) , 0.81 ( t , j = 7.3 hz , 9h ) . c 
 nmr ( 100.61 mhz , cdcl3 ) :  134.1 , 133.7 , 131.6 , 128.6 , 
 127.7 , 127.2 , 125.8 , 125.6 , 125.0 , 124.3 , 40.4 , 28.9 ( j(sn ) = 20.9 hz , 3c ) , 27.2 ( j(sn ) = 55.1 hz , 3c ) , 13.6 ( 3c ) , 9.5 ( j(sn ) = 319.6 hz , 3c ) , 9.1 ( j(sn ) = 214.4 hz ) . calcd for c24h38ssn : c , 60.39 ; h , 8.02 . found : c , 60.34 ; h , 7.76 . similarly , 
 mesylate ( s)-[d1]3 ( 678 mg , 
 1.69 mmol ) was converted to thiomethylstannane ( r)-[d1]12c ( 642 mg , 79% ) . h nmr ( 400.27 mhz , cdcl3 ) :  1.81 ( s , j(sn ) = 41.0 hz , 1h , chdsn ) . c nmr ( 100.61 mhz , cdcl3 ) :  8.8 ( t , j = 21.0 hz , 1c , schdsn ) . n - buli ( 0.25 ml , 0.39 
 mmol ) was added to the solution of sulfide 12a ( 131 mg , 
 0.33 mmol ) in dry thf ( 2.5 ml ) at 95 c under argon . after 10 min , 2 m cf3co2h ( 70 l , 0.13 
 mmol ) was added and the mixture was used immediately for the derivatization 
 as thiol 15 can not be isolated because of its low boiling 
 point . ( r)-(+)-1-phenylethyl 
 isocyanate ( 0,10 ml , 0.66 mmol , ee 99% ) was added at 95 c . after 
 45 min a saturated aqueous solution of nahco3 ( 10 ml ) was 
 added and the mixture was extracted with etoac ( 2  20 ml ) . the 
 combined organic phases were dried ( mgso4 ) and concentrated 
 under reduced pressure . the residue was purified by two flash chromatographies 
 ( first : hexane / etoac , 10:1 , rf 0.38 , side product derived from isocyanate 0.45 ; second : hexane / ch2cl2 , 1:1 , rf 0.29 , side product derived from isocyanate 0.68 ) to yield 
 thiocarbamate 16 ( 64 mg , 83% ) as colorless crystals . ir ( si ) :  
 3293 , 2977 , 1652 , 1520 , 1495 , 1217 , 699 cm . h nmr ( 400.27 mhz , cdcl3 ) :  7.377.18 
 ( m , 5h , harom ) , 5.77 ( tdd , j = 17.0 , 10.2 , 
 6.7 hz , 1h , ch = ch2 ) , 5.54 ( br s , 
 1h , nh ) , 5.06 ( qd , j = 17.0 , 1.6 hz , 1h , ch = ch2 ) , 5.05 ( br s , 1h , chch3 ) , 5.01 ( tdd , jci = 10.2 , 1.6 , 1.2 hz , 1h , ch = ch2 ) , 2.95 ( ab - sys , jab = 
 13.4 hz , j = 7.1 hz , 2h , ch2s ) , 2.35 ( tddd , j = 7.1 , 
 6.7 , 1.6 , 1.2 hz , 2h , ch2ch2s ) , 1.49 ( d , j = 6.9 hz , 3h , ch3ch ) . c nmr ( 100.61 
 mhz , cdcl3 ) :  142.8 , 136.3 , 128.7 ( 2c ) , 127.5 ( 2c ) , 
 126.0 , 116.3 , 51.1 , 34.5 , 29.2 , 22.0 . anal . calcd for c13h17nos : c , 66.34 ; h , 7.28 ; n , 5.95 ; s , 13.62 . found : c , 
 66.16 ; h , 7.25 ; n , 6.04 ; s , 13.40 . the h nmr spectra 
 ( 400.27 mhz , cdcl3 ) of 
 ( r)- and ( s)-[d1]16 were identical to that of 16 , except for  
 2.95 ( t , j = 7.2 hz , 1h , chd ) , 2.34 ( t , j = 6.9 hz , ch2chd ) . 
 to determine the ee of derivatives [ d1]16 the h nmr experiments were performed in dmso - d6 ( 600.13 mhz ) with irradiation at 2.24 ppm ( decoupling 
 of schdch2 ) . two broad 
 singlets (  2.79 and 2.82 ) were observed for the two diastereotopic 
 protons of the schd group . allylthio[d1]methylstannane 
 ( s)-[d1]12a ( 174 mg , 0.46 
 mmol ) was converted to thiocarbamate ( s)-[d1]16 ( 90 mg , 83% , ee 95% ) by the procedure used 
 for experiment 1 . stannane ( s)-[d1]12a ( 161 mg , 0.43 mmol ) was converted to ( s)-[d1]16 ( 95 mg , 95% , ee 91% ) by the procedure 
 used for experiment 1 except that it was performed at 78 c . stannane ( s)-[d1]12a ( 172 mg , 0.45 mmol ) was converted to ( s)-[d1]16 ( 104 mg , 99% , ee 83% ) by the procedure 
 used for experiment 1 except that it was performed at 40 c . stannane ( s)-[d1]12a ( 164 mg , 0.43 mmol ) was converted to ( s)-[d1]16 ( 73 mg , 72% , ee 71% ) by the procedure 
 used for experiment 1 except that it was performed at 0 c and 
 that the reaction was quenched with cf3co2h 
 3 min after the addition of n - bul . stannane ( r)-[d1]12a ( 189 mg , 0.50 mmol ) was converted to ( r)-[d1]16 ( 74 mg , 62% , ee 50% ) by the procedure 
 used for experiment 3 except that it was performed in dry et2o . stannane ( r)-[d1]12a ( 184 mg , 0.49 mmol ) was converted to ( r)-[d1]16 ( 51 mg , 45% , ee 20% ) by the procedure 
 used for experiment 5 except that it was performed in dry et2o . n - buli ( 0.41 ml , 0.65 mmol ) was added to a solution 
 of 12b ( 231 mg , 0.54 mmol ) in dry thf ( 3.8 ml ) at 30 
 c under argon . after 30 min , 2 m cf3co2h ( 0.11 ml , 0.22 mmol ) was added , and the mixture was used directly 
 for the derivatization . the 2-methylphenylmethanethiol 17 ( detectable by tlc : hexane / ch2cl2 , 10:1 , rf 0.54 ) was not isolated because 
 of its volatility ( bp 97 c/14 mm ) . after the mixture was stirred for 1.5 h at rt , water 
 ( 1 ml ) was added and the reaction mixture was concentrated under reduced 
 pressure . the residue was purified by flash chromatography ( hexane / ch2cl2 , 1:1 , rf 0.43 ) to yield thiocarbamate 18 ( 66 mg , 43% ) 
 as colorless crystals ; mp 9293 c ( i - pr2o ) . ir ( atr ) :  3277 , 2972 , 2926 , 1643 , 1527 , 
 1493 , 1446 , 1216 cm . h nmr ( 400.27 
 mhz , cdcl3 ) :  7.417.20 ( m , 6h , harom ) , 7.197.05 ( m , 3h , harom ) , 5.52 ( br s , 1h , chch3 ) , 5.08 ( br s , 1h , nh ) , 4.16 ( ab - sys , jab = 13.7 hz , 2h , ch2s ) , 2.33 ( s , 3h , ch3ph ) , 1.49 ( d , j = 6.9 hz , 3h , ch3ch ) . c nmr ( 100.61 
 mhz , cdcl3 ) :  co n. d. , 142.7 ( cq  arom ) , 136.6 ( cq  arom ) , 136.1 ( cq  arom ) , 130.4 ( carom ) , 129.9 ( carom ) , 128.7 ( 2c , 
 carom ) , 127.6 ( 2c , carom ) , 127.5 ( carom ) , 126.2 ( carom ) , 126.0 ( carom ) , 51.2 ( chch3 ) , 32.4 ( ch2s ) , 22.0 ( br s , ch3ch ) , 
 19.4 ( ch3ph ) . calcd 
 for c17h19nos : c , 71.54 ; h , 6.71 ; n , 4.91 ; s , 
 11.23 . found : c , 71.29 ; h , 6.77 ; n , 4.92 ; s , 11.06 . similarly , 
 ( s)-benzylthio[d1]methylstannane ( s)-[d1]12b ( 232 mg , 0.54 mmol ) was 
 converted to thiocarbamate [ d1]18 ( 92 mg , 
 59% ) except that the reaction temperature was 50 c and the 
 reaction time 20 min . the h nmr spectrum ( 400.27 mhz , 
 cdcl3 ) was identical to that of the unlabeled species 18 except for  4.17 ( s , 1h , chd ) , 4.13 ( s , 1h , chd ) 
 ( thiol [ d1]17 was racemic ) . n - buli ( 0.17 ml , 0.26 
 mmol ) was added to a solution of benzylthiomethylstannane 12b ( 92 mg , 0.22 mmol ) in dry thf ( 1.6 ml ) at 78 c under 
 argon . after 10 min , benzaldehyde ( 0.17 ml , 0.33 mmol , 2 m in dry 
 thf ) was added , followed by saturated aq nahco3 ( 3 ml ) 
 5 min later . the combined organic phases were dried ( mgso4 ) and concentrated 
 under reduced pressure . the residue was purified by flash chromatography 
 ( hexane / etoac , 10:1 , rf 0.26 ) to yield alcohol19 ( 42 mg , 77% ) as a colorless oil . h nmr ( 400.27 mhz , 
 cdcl3 ) :  7.407.18 ( m , 10h ) , 4.66 ( x - part 
 of abx - syst j = 9.2 , 3.7 hz , 1h ) , 3.71 ( s , 2h ) , 2.78 
 ( a - part of abx - syst , jab = 14.0 hz , j = 3.7 hz , 1h ) , 2.65 ( b - part of abx - syst , jab = 14.0 hz , j = 9.2 hz , 1h ) , 2.47 ( br 
 s , 1h , oh ) . similarly , stannane ( r)-[d1]12b ( 233 mg , 0.54 mmol ) was transformed 
 into alcohol ( )-[2-d1]19 ( 95 mg , 72% ) 
 by the procedure used for experiment 1 except that benzaldehyde ( 0.54 
 ml , 1.08 mmol , 2 m in dry thf ) , was added 1 min after the addition 
 of meli ( 0.27 ml , 0.82 mmol , 3 m in diethoxymethane ) . the spectroscopic 
 data of ( 2s)-[2-d1]19 were 
 identical to that of 19 except for the following . h nmr ( 400.13 mhz , cdcl3 ) :  4.59 ( 2 overlapping 
 d , j = 9.2 , 3.7 hz , 1h ) , 2.82 ( br s , 1h , oh ) , 2.68 
 ( br s , 1h , schd ) , 2.58 ( br d , j = 9.2 hz , 1h , schd ) . c nmr ( 100.61 mhz , cdcl3 ) : 
  40.4 ( t , j = 21.5 hz , 1c , schd ) . ( r)-benzylthio[d1]methylstannane [ ( r)-[d1]12b ] ( 213 mg , 0.50 mmol ) was transformed into alcohol ( s)-[d1]19 ( 30 mg , 24% , ee 16% ) by 
 the procedure used for the preparation of the racemic alcohols except 
 that the benzaldehyde ( 0.50 ml , 1.0 mmol , 2 m in dry thf ) was present 
 in the reaction mixture when meli was added dropwise every 3 s. similarly , ( r)-[d1]12b ( 228 mg , 0.53 mmol ) was transformed into 
 ( 2s)-[2-d1]19 ( 11 mg , 9% , 
 ee 26% ) by the procedure used for experiment 3 except that it was 
 performed at 95 c and that 2 equiv of 12-crown-4 were 
 present in the reaction mixture . similarly , ( r)-[d1]12b ( 237 mg , 0.55 mmol ) was transformed into 
 ( s)-[d1]19 ( 34 mg , 25% , ee 
 8% ) by the procedure used for experiment 3 , except that the experiment 
 was performed at 50 c . similarly , ( r)-[d1]12b ( 228 mg , 0.53 mmol ) was transformed into 
 ( )-[d1]19 ( 26 mg , 21% ) by the procedure 
 used for experiment 3 , except that the experiment was performed at 
 0 c . racemic alcohol 19 ( mg , mmol ) was converted to a 1:1 
 mixture of diastereomeric ( r)-mosher esters according 
 to general procedure a. the crude product was purified by flash chromatography 
 ( hexane / etoac , 10:1 , rf 0.51 ) to yield esters 19(r)-mtpa 
 ( 28 mg , 94% ) as a colorless oil . h nmr ( 600.13 mhz , cdcl3 ) :  7.487.07 ( m , 30h ) , 5.97 ( x - part of abx - syst , j = 8.2 , 5.7 hz , 1h , diastereomer a ) , 5.86 ( x - part of abx - syst , j = 9.0 , 4.8 hz , 1h , diastereomer b ) , 3.66 ( ab - syst , jab = 13.5 hz , 2h ) , 3.60 ( t , j = 1.2 hz , 3h , 3.52 ( s , 2h ) , 3.45 ( t , j = 1.2 hz , 
 3h ) , 2.87 ( a - part of abx - syst , jab = 14.4 
 hz , j = 9.0 hz , 1h , b ) , 2.83 ( a - part of abx - syst , jab = 14.4 hz , j = 8.2 hz , 1h , 
 a ) , 2.70 ( b - part of abx - syst , jab = 14.4 
 hz , j = 4.8 hz , 1h , b ) , 2.69 ( b - part of abx - syst , jab = 14.4 hz , j = 5.7 hz , 1h , 
 a ) . similarly , alcohol ( 2s)-[2-d1]19 ( 11 mg , 0.045 mmol ) , obtained by determination of 
 microscopic configurational stability of chiral benzylthiomethyllithium 
 by experiment 5 was converted to ( r)-mosher esters 
 ( s)-[d1]19(r)-mtpa ( 18 mg , 87% ) . the h nmr spectrum 
 ( 600.13 mhz , cdcl3 ) was 
 identical to that of 19(r)-mtpa 
 except for  2.85 ( d , j = 9.0 hz , 0.42h , chd ) , 2.81 ( d , j = 8.2 hz , 0.67h , chd ) , 2.68 ( 2 overlapping d , 1h , chd ) ; ee of underlying 
 alcohol 26% . n - buli ( 0.50 ml , 
 0.79 mmol ) was added to the solution of ( 1-naphthylmethylthiomethyl)tributylstannane 
 ( 12c ) ( 314 mg , 0.66 mmol ) in dry thf ( 4.6 ml ) at 78 
 c under argon . after 10 min , cf3co2h ( 0.43 
 ml , 0.87 mmol , 2 m in ch2cl2 ) was added , and 
 the mixture was extracted with etoac ( 3  10 ml ) . the combined 
 organic phases were dried ( mgso4 ) and concentrated under 
 reduced pressure . the residue was purified by flash chromatography 
 ( hexane / ch2cl2 , 10:1 , rf 0.32 ) to yield thiol 20 ( 57 
 mg , 45% ) as a colorless oil . ir ( si ) :  3050 , 2924 , 1597 , 1510 , 
 1382 , 1264 , 1248 , 1210 , 1060 cm . h 
 nmr ( 400.27 mhz , cdcl3 ) :  8.04 ( d , j = 8.5 hz , 1h ) , 7.79 ( d , j = 8.1 hz , 1h ) , 7.67 ( d , j = 8.4 hz , 1h ) , 7.557.40 ( m , 2h ) , 7.387.33 
 ( m , 1h ) , 3.94 ( d , j = 7.0 hz , 2h ) , 2.69 ( s , 3h ) , 
 1.71 ( t , j = 7.0 hz , 1h ) . c nmr ( 100.61 
 mhz , cdcl3 ) :  136.1 , 133.1 , 132.8 , 131.1 , 128.5 , 
 127.3 , 126.7 , 126.1 , 125.4 , 124.1 , 27.7 , 14.2 . calcd for c12h12s : c , 76.55 ; h , 6.42 ; s , 17.03 . similarly , ( r)-[d1]12c ( 206 mg , 0.43 mmol ) was rearranged to ( r)-[d1]20 ( 22 mg , 28% , ee 60% ) except 
 that transmetalation was performed with meli ( 3 m , in diethoxymethane ) 
 at 50 c . the h nmr spectrum ( 400.27 mhz , 
 cdcl3 ) was identical to that of 20 except 
 for  3.92 ( dt , j = 7.0 , 1.8 hz , 1h , chdsh ) , 1.69 ( d , j = 7.0 hz , 1h , chdsh ) . similarly , stannane ( r)-[d1]12c ( 208 mg , 0.43 mmol ) was rearranged to thiol 
 ( r)-[d1]20 ( 49 mg , 60% , ee 
 72% ) except that transmetalation 
 was performed with n - buli at 95 c . a solution of 
 ( r)-(+)-1-phenylethyl isocyanate ( 67 l , 0.48 
 mmol ) and thiol 20 ( 46 mg , 0.24 mmol ) in dry thf ( 1.2 
 ml ) was left for 1 h under argon at rt . water ( 1 ml ) was added , and 
 the mixture was extracted with etoac ( 3  15 ml ) . the combined 
 organic phases were dried ( mgso4 ) and concentrated under 
 reduced pressure . the residue was purified by flash chromatography 
 ( hexane / ch2cl2 , 1:1 , rf 0.37 ) to yield thiocarbamate 21 ( 39 mg , 50% ) as colorless crystals . ir ( atr ) :  3284 , 2975 , 2925 , 
 1640 , 1509 , 1446 , 1204 , 1179 , 1101 cm . h nmr ( 400.27 mhz , cdcl3 ) :  8.03 ( d , j = 8.5 hz , 1h ) , 7.78 ( d , j = 8.3 hz , 1h ) , 7.63 ( d , j = 8.4 hz , 1h ) , 7.537.39 ( m , 3h ) , 7.387.19 
 ( m , 5h ) , 5.46 ( br s , 1h ) , 5.10 ( br s , 1h ) , 4.38 ( ab - sys , jab = 13.2 hz , 2h ) , 2.65 ( s , 3h ) , 1.50 ( d , j = 6.9 hz , 3h ) . c nmr ( 100.61 mhz , cdcl3 ) : 
  c = o ( n. d. ) , 142.7 , 133.0 , 132.9 , 132.4 , 128.8 , 128.5 , 
 128.2 , 127.6 , 126.4 , 126.0 , 125.4 , 124.1 , 51.3 , 33.3 , 22.1 ( br s ) , 
 14.5 . calcd for c21h21nos : c , 75.19 ; h , 
 6.31 ; n , 4.18 ; s , 9.56 : found : c , 74.89 ; h , 6.22 ; n , 4.05 ; s , 9.56 . similarly , thiol ( r)-[d1]20 ( 49 mg , 0.26 mmol , obtained by rearrangement at 95 c 
 with n - buli ) was converted to thiocarbamate ( r)-[d1]21 ( 36 mg , 42% ) . the 
 spectroscopic data were identical to that of 21 except 
 for the following . h nmr ( 400.27 mhz , cdcl3 ) :  4.38 ( br s , 0.86h , chd ) , 4.35 ( br s , 0.14h , chd ) . c nmr ( 100.61 mhz , cdcl3 ) :  33.1 ( t , j = 21.9 hz , 1c , chds ) . ( )-23 : a solution of dibalh ( 3.98 ml , 
 5.97 mmol , 1.5 m in toluene ) was added dropwise to -bromoacetophenone 
 ( 995 mg , 5.0 mmol ) dissolved in dry et2o ( 25 ml ) at 78 
 c under argon . the reaction mixture was stirred for 2 h at 78 
 c and then 1 h at 50 c . the reaction was quenched 
 with meoh ( 0.5 ml ) and water ( 2.5 ml ) and stirred for another 30 min 
 at rt . a solution of hcl ( 12 ml , 2 m ) was added at 0 c . the 
 organic phase was separated , and the aqueous phase was extracted with 
 et2o ( 3  10 ml ) . the combined organic layers were 
 washed with water ( 15 ml ) and satd aq nahco3 ( 15 ml ) , dried 
 ( mgso4 ) , and concentrated under reduced pressure . the crude 
 product was purified by flash chromatography ( hexane / etoac , 7:1 , rf 0.43 ) to yield ( )-2-bromo-1-phenylethanol 
 [ ( )-23 ] ( 591 mg , 59% ) as a colorless oil . h nmr ( 400.13 mhz , cdcl3 ) :  7.397.29 
 ( m , 5h ) , 4.92 ( dd , x - part of an abx - syst , j = 9.1 , 
 3.5 hz , 1h ) , 3.58 ( ab - part of an abx - syst , jab = 10.4 hz , j = 9.1 , 3.5 hz , 2h ) , 2.59 ( br 
 s , 1h ) . ( s)-(+)-23 : ( + ) -dip - chloride ( 1.8 g , 5.61 mmol , dissolved in 5 ml of dry 
 thf ) was added to -bromoacetophenone ( 744 mg , 3.74 mmol , dissolved 
 in 5 ml of dry thf ) under argon at 0 c . at 0 c water ( 1 ml ) , pentaerythritol ( 916 mg , 
 6.73 mmol ) and again water ( 15 ml ) were added and the mixture was 
 stirred for another 30 min at rt . the organic phase was separated 
 and the aqueous one was extracted with et2o ( 3  15 
 ml ) . the combined organic layers were washed with water ( 2  
 10 ml ) , dried ( mgso4 ) , concentrated under reduced pressure , 
 and purified by flash chromatography ( hexane / etoac , 10:1 ) . the still 
 impure product was again dissolved in dry thf ( 10 ml ) and pentaerythritol 
 ( 680 mg , 5 mmol , dissolved in 5 ml of water ) was added . the organic phase was separated and the 
 aqueous one was extracted with et2o ( 3  15 ml ) . the 
 combined organic layers were washed with water ( 2  10 ml ) , dried 
 ( mgso4 ) and concentrated under reduced pressure . ten drops 
 of dry pyridine were added and the crude product was purified by flash 
 chromatography ( hexane / etoac , 7:1 ) to yield ( s)-(+)-2-bromo-1-phenylethanol 
 [ ( s)-(+)-23 ] as a colorless oil ( 193 
 mg , 26% ) , ee 94% ( by h nmr of ( r)-mosher 
 ester ) , [ ]d + 39.24 ( c 1.975 , ch2cl2 ) [ lit . [ ]d + 40.10 , ( c 1.81 , 
 chcl3 ) , ee 92% ] . ( )-2-bromo-1-phenylethanol [ ( )-23 ] ( 20 
 mg , 0.10 mmol ) was converted to ( r)-mosher esters 
 using general procedure a. the crude product was purified by flash 
 chromatography ( hexane / etoac,10:1 , rf 0.66 ) to yield a mixture of diastereomeric mosher 
 esters ( )-23(r)-mtpa ( 39 
 mg , 94% ) . h nmr ( 400.13 mhz , toluene - d8 ) :  7.597.55 [ m , 2h , ( r , s)-diastereomer ] , 7.517.47 [ m , 2h , ( r , r ) ] , 7.086.91 [ m , 14h , 8h of ( r , s ) , 6h of ( r , r ) ] , 6.786.75 [ m , 2h , ( r , r ) ] , 6.04 [ x - part of an abx - syst , j = 8.8 , 4.2 hz , 
 1h , ( r , s ) ] , 5.90 [ x - part of an abx - syst , j = 9.6 , 3.3 hz , 1h , ( r , r ) ] , 3.58 [ q , j = 1.0 hz , 3h , ( r , r ) ] , 3.32 [ q , j = 1.0 hz , 3h , 
 ( r , s ) ] , 3.07 [ ab - part of an abx - syst , jab = 11.1 hz , j = 8.8 , 4.2 
 hz , 2h , ( r , s ) ] , 3.01 [ ab - part of 
 an abx - syst , jab = 11.4 hz , j = 9.6 , 3.3 hz , 2h , ( r , r ) ] . similarly , ( s)-(+)-23 [ 20 mg , 0.10 
 mmol , [ ]d + 39.24 , ( c 1.98 , ch2cl2 ) ] was converted to ( r)-mosher esters ( 40 mg , 96% ) ; ee of alcohol : 94% . the h nmr spectrum was identical to that of the racemic alcohol , except 
 that the signals of the diastereomers differed in intensity . a solution of meli ( 0.60 ml , 0.60 mmol , 
 1 m in cumene / thf ) was added quickly at 78 c to the 
 ( )-bromohydrin ( )-23 ( 100 mg , 0.5 mmol ) dissolved 
 in dry thf ( 2.5 ml ) under argon atmosphere . after the mxiture was 
 stirred for 5 min , cf3co2h ( 75 mg , 0.65 ml , 
 0.65 mmol , 1.3 equiv , 1 m in dry ch2cl2 ) and 
 water ( 5 ml ) 3 min later were added . the organic phase was separated 
 and the aqueous one was extracted with et2o ( 3  15 
 ml ) . the crude product 
 did not contain phenyloxirane as determined by h nmr spectroscopy 
 after spiking with an authentic sample . the crude product was purified 
 by flash chromatography ( hexane / etoac , 7:1 , rf 0.42 ) to recover bromohydrin ( )-23 ( 95 mg , 95% ) . its rf value and h nmr spectrum were identical to that 
 of the starting material . using nbs / ph3p : a solution of ph3p ( 772 mg , 2.94 mmol ) in dry ch2cl2 ( 3 ml ) was added dropwise to nbs ( 523 mg , 2.94 
 mmol ) dissolved in dry ch2cl2 ( 5 ml ) under argon 
 at 78 c . after 10 min tributylstannylmethanol ( 2 ) ( 787 mg , 2.45 mmol ) dissolved in dry ch2cl2 ( 4 ml ) was added , and the reaction mixture was stirred rt 
 for 30 min . a few drops of meoh were added , and the mixture was concentrated 
 under reduced pressure . the residue was flash chromatographed ( hexane / ch2cl2 , 1:1 , rf 0.98 ) to yield bromomethylstannane25 ( 859 mg , 91% ) as a colorless oil . h 
 nmr ( 400.13 mhz , cdcl3 ) :  2.63 ( s , j(sn ) = 14.6 hz , 2h ) , 1.551.46 ( m , 6h ) , 
 1.30 ( sext , j = 7.3 hz , 6h ) , 1.000.95 ( m , j(sn ) = 51.4 hz , 6h ) , 0.88 ( t , j = 7.3 hz , 9h ) . similarly , ( s)-[d1]2 ( 197 mg , 0.61 mmol , prepared by an improved 
 procedure , see below ) was converted to ( r)-[d1]25 ( 205 mg , 92% , ee 60% ) . the h 
 nmr spectrum ( 400.13 mhz , cdcl3 ) was identical to that 
 of 25 except for  2.61 ( t , j = 
 1.5 hz , 1h , chd ) . when the reaction was performed in the same 
 way as before , except 
 that two instead of 1.2 equiv of ph3p / nbs were used , ( r)-[d1]2 ( 251 mg , 0.78 mmol ) were 
 converted to ( s)-[d1]25 ( 230 
 mg , 77% , ee 18% ) . using mitsunobu reaction with ph3phbr : ph3p ( 109 mg , 0.62 mmol ) , ph3phbr 
 ( 845 mg , 2.46 
 mmol ) , and stannylmethanol 2 ( 657 mg , 2.05 mmol ) were 
 dissolved in dry toluene ( 8.2 ml ) under argon . after stirring for 
 5 min at 0 c diad ( 0.71 ml , 4.47 mmol ) was added and the reaction 
 mixture was stirred for another 90 min . the mixture was purified by flash chromatography 
 ( hexane / ch2cl2 , 1:1 , rf 0.98 ) to give bromomethylstannane 25 ( 383 mg , 49% ) as a colorless oil . similarly , ( r)-[d1]2 ( 852 
 mg , 2.65 mmol , prepared by an improved procedure , see below ) was converted 
 to ( s)-d1]25 ( 491 mg , 48% , 
 ee 74% ) except that the reaction time 
 was 10 min . after the addition of methanol , the reaction mixture was 
 immediately applied to the silica column for flash chromatography . the entire procedure ( also flash chromatography ) was performed in 
 the cold room ( 3 c ) . no bath was used during concentration of 
 bromide - containing solutions under reduced pressure . similarly , 
 ( r)-[d1]2 ( 958 
 mg , 2.98 mmol ) was converted to ( s)-[d1]25 ( 521 mg , 45% , ee 94% ) as before except that the 
 reaction was performed at 10 c for 10 min . similarly , 
 ( r)-[d1]2 ( 417 
 mg , 1.30 mmol ) was converted to ( s)-[d1]25 ( 179 mg , 35% , ee 99% ) as before except that 
 the reaction was performed at 25 c for 10 min . a solution of meli ( 0.51 ml , 0.51 
 mmol , 1 m in cumene / thf ) was added quickly at 78 c to 
 the ( bromomethyl)tributylstannane 25 ( 163 mg , 0.42 mmol ) 
 dissolved in dry thf ( 2 ml ) under argon atmosphere . after 30 s , cf3co2h ( 64 mg , 0.55 ml , 0.55 mmol , 1.3 equiv , 1 m 
 in dry ch2cl2 ) was added , followed by water 
 ( 5 ml ) 1 min later . the organic phase was separated , and the aqueous 
 phase was extracted with ch2cl2 ( 3  10 
 ml ) . the combined organic layers were washed with water ( 15 ml ) , dried 
 ( na2so4 ) , and concentrated under reduced pressure . the crude product was virtually homogeneous tributylmethylstannane 
 as determined by h nmr spectroscopy , which did not contain 
 starting material . a solution of meli ( 1.85 ml , 1.85 mmol , 1 m in cumene / thf ) was 
 quickly added to a solution of bromomethylstannane 25 ( 178 mg , 0.46 mmol ) and benzaldehyde ( 194 mg , 0.93 ml , 1.85 mmol , 
 freshly distilled , 2 m in thf ) in dry thf ( 2 ml ) under argon atmosphere 
 at 78 c . after 5 min , cf3co2h 
 ( 232 mg , 2 ml , 2 mmol , 1 m in ch2cl2 ) and water 
 ( 5 ml ) were added . the organic phase was separated , and the aqeous 
 phase was extracted with ch2cl2 ( 3  10 
 ml ) , dried ( na2so4 ) , and concentrated under 
 reduced pressure . the residue was purified by flash chromatography 
 ( ch2cl2 , rf 0.46 ) to give bromohydrin ( )-23 as a colorless 
 oil ( 17 mg , 19% ) . the spectroscopic data were identical to those of 
 the authentic sample . a solution of benzaldehyde ( 198 mg , 0.94 
 ml , 1.87 mmol , freshly distilled , 2 m in dry thf ) was added at 78 
 c to the ( r)-bromo[1-d1]methylstannane 
 ( r)-[d1]2 ( 180 mg , 0.47 mmol , 
 ee 50% ) in dry thf ( 2 ml ) under argon atmosphere , followed dropwise 
 by meli ( 1.87 ml , 1.87 mmol , 1 m in cumene / thf ) . after 10 min , the 
 reaction was quenched with cf3co2h ( 240 mg , 
 2.07 ml , 2.07 mmol , 1 m in thf ) . water ( 5 ml ) was added , and the organic 
 phase was separated and the aqueous one was extracted with ch2cl2 ( 3  5 ml ) . the combined organic layers 
 were dried ( na2so4 ) and concentrated under reduced 
 pressure . the residue was purified by flash chromatography ( ch2cl2 , rf 0.43 ) to give bromohydrin ( 2s)-[2-d1]23 ( 7 mg , 11% , ee 57% ) as a colorless oil ; impure fractions 
 ( estimated product about 10 mg ) were discarded . ( r)-[d1]2 ( 157 mg , 0.41 mmol , ee 77% ) was converted to ( 2s)-[2-d1]23 ( 15 mg , 18% , ee 76% ) by procedure 
 used for experiment 1 except using 2 equiv of benzaldehyde and meli 
 ( 1 m solution obtained by dilution of 3 m meli in diethoxymethane 
 with dry thf ) which was added dropwise every 5 s. if 3 m meli in diethoxymethane 
 was used or it was added more rapidly , no product or only product 
 traces were obtained . ( r)-[d1]2 ( 161 mg , 0.42 mmol , ee 77% ) was converted to ( 1s)-[1-d1]27 ( 11 mg , 12% , ee 75% ) by the procedure 
 used for experiment 2 except that acetophenone was used as electrophile . the bromhydrine was isolated by flash chromatography ( hexane / etoac , 
 15:1 ; tlc : hexane / etoac , 10:1 , rf 0.34 ) . ( s)-[d1]2 ( 218 mg , 0.57 mmol , ee 94% ) was converted to ( 2r)-[2-d1]23 ( 10 mg , 9% , ee 94% ) by the procedure 
 used for experiment 2 . ( s)-[d1]2 ( 259 mg , 0.67 mmol , ee 94% ) was converted to ( 1r)-[1-d1]27 ( 45 mg , 31% , ee 93% ) by the procedure 
 used for experiment 3 except that the reaction was performed at 95 
 c . ( s)-[d1]2 ( 179 mg , 0.46 mmol , ee 99% ) was converted to ( 2r)-[2-d1]23 ( 13 mg , 14% , ee 99% ) 
 by procedure used for experiment 2 . they were prepared in quantitative yield from alcohols [ 1-d1]23 according to general procedure a and they 
 were purified by flash chromatography ( hexane / etoac , 10:1 , rf 0.78 ) . the two diastereomeric 
 ( r)-mosher esters obtained in quantitative yield 
 were separated by preparative tlc chromatography ( hexane / ch2cl2 , 3:1 ) in one case . the less polar one ( rf 0.56 ) was derived from ( 1r,2s)-[2-d1]23 ( 56% ee ) and 
 the more polar one ( rf 0.35 ) from ( 1s,2s)-[2-d1]23 ( 57% ee ) in quantitative yield . h nmr ( 400.13 mhz , toluene - d8 ) : 
  5.89 ( br d , j = 2.5 hz , 1h ) , 2.89 ( d , j = 2.5 hz , 1h , chd ) . h nmr ( 400.13 
 mhz , toluene - d8 ) :  5.94 ( d , j = 8.8 hz , 1h ) , 3.05 ( d , j = 8.8 hz , 1h , 
 chd ) . ( )-27 : h nmr ( 400.27 mhz , cdcl3 ) :  
 7.477.42 ( m , 2h ) , 7.397.33 ( m , 2h ) , 7.317.25 
 ( m , 1h ) , 3.71 ( ab - sys , jab = 10.4 hz , 
 2h ) , 2.52 ( br s , 1h ) , 1.67 ( s , 3h ) . [ 1-d1]27 : the h nmr spectra ( 400.27 mhz , cdcl3 ) were 
 identical to that of ( )-27 except for  3.73 
 ( br s , 0.5h , chd ) , 3.68 ( t , j = 1.4 hz , 0.5h , chd ) . the ( r)-mosher esters of ( )-27 and [ 1-d1]27 were prepared by a modified 
 general procedure as exemplified for ( 1r)-[1-d1]27mtpa-(r ) : a solution 
 of bromohydrin ( 1r)-[1-d1]27 ( 16 mg , 0.074 mmol ) , ( s)-mosher chloride ( 0.15 
 mmol , 2 equiv , 0.29 ml of a 0.53 m solution in dry 1,4-dioxane ) , and 
 dmap ( 37 mg , 0.30 mmol , 4 equiv ) in dry dioxane ( 1 ml ) was heated 
 at 50 c for 8 h ( no starting material present ) . after the solution 
 was cooled to rt , a few drops of water were added and stirring was 
 continued for 5 min . ch2cl2 ( 3 ml ) and hcl ( 3 
 ml , 1 m ) were added . the combined organic layers were 
 washed with saturated aq nahco3 , dried ( na2so4 ) , and concentrated under reduced pressure . the residue was 
 flash chromatographed ( hexane / etoac , 15:1 , rf 0.56 ) to yield ( 1r)-[1-d1]27mtpa-(r ) ( 20 mg , 62% ) . ( )-27mtpa-(r ) : h nmr ( 400.27 mhz , cdcl3 ) :  7.597.51 ( m , 
 4h ) , 7.457.35 ( m , 6h ) , 7.357.26 ( m , 8h ) , 7.237.18 
 ( m , 2h ) , 3.97 ( ab - sys , jab = 11.0 hz , 
 2h ) , 3.77 ( ab - sys , jab = 11.0 hz , 2h ) , 
 3.62 ( q , j = 1.3 hz , 3h ) , 3.57 ( q , j = 1.2 hz , 3h ) , 2.10 ( s , 3h ) , 2.02 ( s , 3h ) . ( 1r)-[1-d1]27mtpa-(r ) : 
 the h nmr spectrum ( 400.27 mhz , cdcl3 ) was 
 identical to that of ( )-27mtpa-(r ) except for  3.91 ( br s , 0.85h , chd ) , 3.81 ( br 
 s , 0.85h , chd ) and 4.00 ( br s , 0.02h ) , 3.71 ( br s , 0.03h ) ; 93% ee 
 for bromohydrin at c-1 .
thio- and bromo[d1]methyllithiums ( ee 99% ) 
 were generated 
 from the respective stannanes by tin 
 lithium exchange at temperatures 
 ranging from 0 to 95 c . 
 thio[d1]methyllithiums 6 were found to be microscopically configurationally labile 
 on the time scale of the thiophosphate--mercaptophosphonate 
 rearrangement even at 95 c . 
 thio[d1]methyllithiums 13a and 13b underwent a thia-[2,3]-wittig rearrangement 
 down to 95 c and 13b only down to 50 
 c . 
 the former were microscopically configurationally stable 
 below 95 c , and the latter racemized completely at 50 
 c . 
 chiral bromo[d1]methyllithiums are chemically 
 unstable at 78 c but microscopically configurationally 
 stable at the time scale of their addition to benzaldehyde and acetophenone .