bluuebunny/crossref_metadata_2025_split huggingface dataset:
Homo‐ und Hetero‐Metall‐Amide des Tris(tert‐butylamino)methylsilans – Polycyclen und Cluster mit Li, Na, Mg, Al und Tl
Authors: Veith Michael , Spaniol Armin , Pöhlmann Jürgen , Gross Frank , Huch Volker 
Published: July 2007

Homo and Hetero Metal Amides of Tris(tert‐butylamino)methylsilane – Polycycles and Clusters with Li, Na, Mg, Al and TlThe hydrogen atoms attached to nitrogen in tris(tert‐butyl‐amino)methylsilane (1) can be substituted by metallic main‐group elements in a quite general way. If 1 is treated with trimethylaluminium apart from the monosubstituted product MeSi(tBuNH)2(tBuNAlMe2) (2) the trisamide MeSi(tBuNAlMe2)3 (3) is obtained. In similar ways complete substitution of the amino hydrogen atoms in 1 yields the compounds MeSi[tBuNMgN(SiMe3)2]3 (6), [MeSi(tBuNLi)3]2 (10), and [MeSi(tBuNTl)3]2 (11), the later two being dimeric. If methyl‐magnesium iodide is allowed to react with 1 the intermediate MeSi(tBuNMgI)3 (4) in some instances can be isolated as the THF adduct or may react with a further equivalent of the Grignard compound to generate the complex [MgI‐(THF)5]+ [MeSi(tBuNMgI)3CH3 · THF]– (5). The aluminium compound 2 has been used to access to heterometallic amides combining aluminium and sodium as in MeSi(tBuNAlMe2)(tBuNNa)(tBuNH) (7) or magnesium and aluminium as in the dimeric compounds [MeSi(tBuNAlMe2)(tBuNH)(tBuNMgI)]2 (8) and [MeSi(tBuNAlMe2)(tBuNH)(tBuNMgMe)]2 (9). X‐ray structure analyses reveal 3 (tricyclic SiN3Al3 skeleton with Al – N distances from 2.014 to 2.025 Å), 6 (tricyclic Si‐N3Mg3 skeleton), and 7 [bicyclic SiN3AlNa skeleton with Na – N distances of 2.47(1) and 2.52(1) Å] to be monomeric even in the solid state. The compounds 8 and 9 (both pentacyclic with spiro magnesium atoms) form centrosymmetric dimers by Mg – I – Mg and Mg – (CH3) – Mg bridges, respectively. The dimers 10 and 11 are completely different in terms of chemical bonding: while in the lithium compound 10 a centrosymmetric polycycle is formed by principly ionic interactions of the lithium atoms with corresponding nitrogen atoms, the centrosymmetric dimer in 11 is held together by Tl – Tl bonds. The X‐ray structure analysis of 5 reveals the anion containing a Mg‐coordinated CH3–.
1‐Sila‐3‐alumina‐4‐aluminatacyclopentan mit Al–Al‐Bindung und C2Al2Si‐Heterocyclus
Authors: Uhl Werner , Schütz Uwe , Vester Annegret , Karsch Hans H. 
Published: July 2007

1‐Sila‐3‐alumina‐4‐aluminatacyclopentane with an Al–Al Bond and a C2Al2Si HeterocycleTetrakis[bis(trimethylsilyl)methyl]dialuminium(4) (1) with an aluminium–aluminium bond reacts in the presence of tetramethylethylenediamine (TMEDA) with the sterically highly shielded bases bis(trimethylsilyl)methyllithium or bis(dimethylphosphanyl)methyllithium to yield under deprotonation of a methyl group a carbanionic species, which is stabilized by an interaction with one of the coordinatively unsaturated Al atoms. The five‐membered heterocycle 5 is formed containing two Al, one Si and two C atoms. The Al–Al bond remains uncleaved. Interestingly, 5 crystallizes in different crystals with and without crystal ether, which were both characterized by crystal‐structure determinations. The Al–Al bond length in 5 [264.1(2) and 266.5(3) pm, respectively] is only slightly changed in comparison to the neutral starting compound 1 (266.0 pm). Under similar conditions the sterically less demanding ethyllithium leads to a β‐elimination and addition of the thereby formed LiH to one of the two Al atoms to give the recently published hydridodialuminate(5) Li(TMEDA)2+ [R2Al–AlHR2]– (2).
Metallorganische Verbindungen der Lanthanoide, 82[1]. (2,5‐Di‐tert‐butylpyrrolyl)‐Komplexe von Neodym(III), Samarium(II) und Ytterbium(II): Synthese und Röntgenstrukturanalyse von dimerem Natrium‐dichlorobis(2,5‐di‐tert‐butylpyrrolyl)(tetrahydrofuran)neodymat(III)
Authors: Schumann Herbert , Winterfeld Jörn , Hemling Holger , Kuhn Norbert 
Published: July 2007

Organometallic Compounds of the Lanthanoids, 82[1]. – [2,5‐Di‐tert‐butylpyrrolyl) Complexes of Neodymium(III), Samarium(II), and Ytterbium(II): Synthesis and X‐Ray Structural Analysis of Dimeric Sodium Dichlorobis(2,5‐di‐tert‐butylpyrrolyl)(tetrahydrofuran)neodymiate(III)NdCl3(THF)1,8 reacts with Na[pyr*
η3‐Allyl‐ und η3‐Benzyl‐Rhodiumkomplexe: Synthese, Strukturdynamik und Reaktionen mit Carbonsäuren
Authors: Werner Helmut , Schäfer Martin , Nürnberg Oliver , Wolf Justin 
Published: July 2007

η3‐Allyl and η3‐Benzyl Rhodium Complexes: Synthesis, Structure Dynamic, and Reactions with Carboxylic AcidsThe (η3‐allyl)rhodium complexes [Rh(η3‐2‐RC3H4)(PiPr3)2] (3–5) have been prepared in 70–90% yield from the in situ generated chlororhodium precursor [RhCl(PiPr3)2] (2) and 2‐RC3H4MgX. On a similar route, the corresponding ethene(phosphane) derivative [Rh(η3‐2‐MeC3H4)(PiPr3)] (9) has been obtained. Compound 9 smoothly reacts with PiPr3 and PMe3 to give 4 (R = Me) and [Rh(η3‐2‐MeC3H4)(PMe3)‐(PiPr3)] (10), respectively. In contrast to the η3‐allyl complexes which are configurationally stable, the η3‐benzyl analogues [Rh(η3‐CH2C6H4R) (PiPr3)2] (11, 12), prepared from 2 and 4‐RC6H4CH2MgCl, are highly fluctional in solution. At room temperature, an antarafacial (π‐δ‐π) as well as a suprafacial rearrangement occurs, the first one of which is frozen out at 263 K. On cooling to 193 K, the faster process (equally designated as a metallotropic shift) is also slowed down, and the rigid structure of 11 and 12 is observed. The ΔG* values for the antara and suprafacial rearrangements of 11 and 12 which have been determined from the 1H‐ and 31P‐NMR spectra at variable temperature are 60.0 ± 1.5 and 39.5 ± 1.0 kJ/mol, respectively. The η3‐benzyl compound 11 reacts even at –78°C with CO to give the monocarbonylrhodium(I) complex trans‐[Rh(η1‐CH2C6H5)(CO)(PiPr3)2] (13). Treatment of 3,4, or 11 with RCO2H (R = CF3, CH3, C6H5, C6H4‐4‐OMe, C6H4‐4‐NO2) affords the monomeric η2‐carboxylatorhodium(I) compounds [Rh(η2‐O2CR) (PiPr3)2] (14–18) almost quantitatively. If the reaction of 3 or 4 with CF3CO2H is performed at −20°C in pentane, the octahedral (η3‐allyl)hydrido complexes [Rh(η3‐2‐RC3H4)(H)(η1‐O2CCF3)(PiPr3)2] (19, 20) are isolated. The crystal structures of 12 (at 223 K) and of 15 (at 298 K) have been determined by X‐ray diffraction studies. They confirm that the η3‐benzyl ligand is highly unsymmetrically and the acetato ligand completely symmetrically bound to the [Rh(PiPr3)2] unit.
Fe(I)‐Mediated Regio‐ and Stereoselective CC/CH Bond Activation of Internal Methylene Groups of α,ω‐Diphenylalkanes
Authors: Raabe Norbert , Karraß Sigurd , Schwarz Helmut 
Published: July 2007

AbstractFor three α,ω‐diphenylalkanes the mechanistic details of the Fe+‐mediated activation of CH and CC bonds in the gas phase have been elucidated by isotopic labelling experiments. The unimolecular reactions, i.e. dehydrogenation of the alkane chain, formation of ethylene from internal methylene groups, and generation of toluene, proceed largely with high selectivity. Particularly interesting are the results for the dehydrogenation of the Fe+ complex 3‐Fe+ of 1,8‐diphenyloctane which involves to 93% the internal methylene groups C‐4/C‐5. In addition, the study of the stereoisotopomers 3c–d provides evidence for the operation of isotopically sensitive branching (“metabolic switching”) in the reaction, and the analysis of the data suggests that the selectivity of the reaction is, most likely, due to a sandwich‐type structure.
Dinuclear Paramagnetic Metallocenes Bridged by Silyl Groups — Synthesis and Intramolecular Interactions
Authors: Atzkern Hermann , Bergerat Pierre , Fritz Monika , Hiermeier Johann , Hudeczek Peter , Kahn Olivier , Kanellakopulos Basil , Köhler Frank H. , Ruhs Michael 
Published: July 2007

AbstractThe dilithium salt of the 3a,4,7a,8‐tetrahydro‐4,4,8,8‐tetra‐methyl‐4,8‐disila‐s‐indacenediyl dianion (L2−, 2) was allowed to react with the solvated metal halides MX2 (M = Ni, Co, Cr) in the presence of the cyclopentadienyl (Cp) anion to give trans‐CpMLMCp (3NiNi, 3CoCo, and 3CrCr) in yields up to 80%. The only cis isomers which could be detected were 4NiNi and 4CoCo. Similarly, the reaction of 2 with [CpVCl(PEt3)]2 gave the trans‐vanadium analogue 3VV while the successive reaction of 2 with CrCl3 (THF)3 and PEt3 yielded the bridged half‐sandwich (Et3P)Cl2CrLCrCl2(PEt3) (5CrCr). The mixed‐metal dinuclear metallocene CpFelNiCp (3FeNi) was synthesized from CpFel−, Cp− and solvated NiBr2. The molecules were characterized by mass spectrometry, elemental analyses, cyclic voltammetry, 1H, 13C, and 29SiNMR spectroscopy and solid‐state magnetic measurements. Cyclic voltammetry showed up to six electron transfers per molecule. A metal‐dependent splitting of the half‐wave potentials of up to 355 mV indicated rather strong electrostatic interaction between the metallocene units. The NMR results established unpaired spin on the ligands. Its distribution within the bridging ligand was correlated with the molecular orbital splitting and the magnetic interaction. Antiferromagnetic interaction was found for 3NiNi, 3CrCr, and 3VV with J = −11.6, −2.56, and −1.34 cm−1, respectively (H = ‐J · SA · SB). A temperature‐dependent folding of the bridging ligand was deduced from the temperature behavior of the 1HNMR signal shifts.
Ambiphile Tripod‐Komplexe: Synthese und Komplexchemie langkettiger funktionalisierter Tripod‐Liganden RC(CH2PPh2)3 mit R = Pentyl oder 8‐Nonenyl
Authors: Muth Andreas , Asam Alexander , Huttner Gottfried , Barth Annette , Zsolnai Laszlo 
Published: July 2007

Ambiphilic Tripod Complexes: Synthesis and Coordination Chemistry of Long‐Chained Functionalized Tripod Ligands RC(CH2PPh2)3 with R ‐ Pentyl or 8‐NonenylTripod ligands RC(CH2PPh2)3 with R = pentyl (3a) and R = 8‐nonenyl (3b) are accessible from the corresponding triols. By using appropriately selected activation procedures the triols 1a, b are transformed into the tripodal ligands 3a, b. In addition to their direct characterisation the tripod ligands 3a, b have been further structurally analysed by the syntheses and X‐ray analyses of specific cobalt (4a) and iron (4b) coordination compounds. An interesting side result from the X‐ray analysis of [(3b)Fe(NCCH3)3](BF4)2 (4b) is the organisation of its solid‐state structure by the hydrophobic 8‐nonenyl substituents in the ligand backbone.
Synthesen, Struktur und Eigenschaften von 1,2,5‐Phosphadiborolanen
Authors: Frankhauser Pascal , Drieß Matthias , Pritzkow Hans , Siebert Walter 
Published: July 2007

Syntheses, Structure and Properties of 1,2,5‐PhosphadiborolanesReactions of (Z)‐1,2‐bis[chloro(diisopropylamino)boryl]ethane with Li2PC6H5 and of 1,2‐bis[chloro(diisopropylamino)boryl]‐1,2‐diisopropylideneethane with [LiPh2·dme] yield the 1,2,5‐phosphadiborolanes 1 and 2, respectively. The compounds are characterized by 1H‐, 11B‐, 13C‐, and 31P‐NMR spectroscopy as well as an X‐ray structure analysis of 2. Low‐temperature 1H‐NMR studies show that the inversion barrier at P is distinctly lower than that of related unsaturated compounds. This might be the result of a favorable BP‐π interaction in the transition state of the inversion at the phosphorus atom. Reaction of 1 with S8 or CS2 leads to the 1,2,5‐thiadiborolane 3.
Stabilization of Triorganotin Cations — Competition between Intramolecular Coordinative O, S or NSn Bonds and Side‐on π Coordination to CC Bonds
Authors: Wrackmeyer Bernd , Kundler Sabine , Milius Wolfgang , Boese Roland 
Published: July 2007

AbstractDi‐1‐alkynyltin compounds 1 of the type Me2Sn(CCUL)2 [LU = 2‐pyridyl (a), Me2NCH2 (b), MeOCH2 (c), MeOCHCH (d), EtSCH2 (e)] were prepared and the 1,1‐organoboration of 1 with triethyl‐ (2a) and triisopropylborane (2b) has been studied. The first detectable intermediates were in all cases zwitterionic compounds 3 (from Et3B) and 4 (from iPr3B) with a cationic triorganotin fragment, stabilized by coordinative s̀ LSn bonds and by side‐on coordination to the CC bond of an alkynylborate moiety. The nature of this stabilization has been established by three X‐ray analyses (3b, 4b, and 4d) in the solid state and by multinuclear NMR (1H‐, 11B‐, 13C‐, 15N‐, 119Sn NMR) in solution. The comparison of the molecular structure of 3b, 4b, and 4d with that of intermediates without functional groups shows that the distance of the tin atom to the CC bond is elongated. However, the planar arrangement of all relevant atoms proves that the side‐on coordination of the tin atom to the CC bond is still present. These intermediates 3 and 4 rearrange to stannoles 5, 6 and/or to 1‐stanna‐4‐bora‐2,5‐cyclohexadienes 9, 10. In the case of 3b and 3e, 119Sn NMR indicates that dialkenyltin compounds 7b and 7e are also formed as minor products. In the case of 3e, the 3‐stannolene 8e is one of the final products. In the stannoles 5 and 6 a coordinative LB bond is evident, and there is NMR spectroscopic evidence of a weak coordinative L—Sn bond.
Elektrophile Additionen an das Bicyclo[1.1.0]butan‐System von Tricyclo[4.1.0.02,7]heptan‐Derivaten: Halogen‐Elektrophile
Authors: Gerstner Erwin , Kemmer Ralf , Christl Manfred 
Published: July 2007

Electrophilic Additions to the Bicyclo[1.1.0]butane System of Tricyclo[4.1.0.02,7]heptane Derivatives: Halogen ElectrophilesThe known reactions of 8,8‐dibromotetracyclo[5.1.0.02,4.03,5]octane (3a) and homobenzvalene (7) with pyridinium bromide perbromide and iodine, respectively, were carried out in the presence of tetra‐n‐butylammonium chloride. The formation of the chloro‐substituted norpinane derivatives 6a and 9 is evidence for cationic intermediates. The same mechanism is operative in the reaction of pyridinium bromide perbromide with the dichlorotetracyclooctane 3b, which was prepared from 7 and dichlorocarbene. On exposure of tricyclo[4.1.0.02,7]heptane (1) to N‐bromosuccinimide in acetone/water/triethylamine, the bromonorpinanol 22, the bromonorcaranols 23, and cyclohex‐1‐ene‐1‐carboxaldehyde (24) were obtained. On the basis of the steric course and thermodynamic considerations, the cationic intermediates generated in the above reactions by attack of the electrophiles at the bicyclobutane systems are assigned the halonium ion structure 38 and the nonclassical structures 34 and 35, respectively. Elemental bromine and iodine converted the phenyltricycloheptane 10 into the respective diastereomeric norpinanes 11 and 12, which were transformed smoothly into the diastereomeric methyl ethers 13 and 14 by treatment with sodium methoxide in methanol. The reactions of 10 with pyridinium bromide perbromide in pyridine, cyanogen bromide in the presence of aluminium trichloride, and N‐bromosuccinimide in acetone/water gave rise to norpinane derivatives, i.e. the pyridinium salt 15, the nitrile 16, and the alcohol 18, respectively. In the case of cyanogen iodide in acetonitrile, the solvent participated in the process to yield the 2‐(norpinylimino)propionitriles 17. Corresponding to the configurations of the products, the attack of a halogen electrophile at 10 leads to classical 6‐phenyl‐6‐norpinyl cations 41, which may be approached by nucleophiles from the two possible faces. As origin for the low tendency of the cations 33–35 and 41 to rearrange to norcaryl cations, the electronegativity of the halogen atoms is suggested. The reduced migratory aptitude of a CHHal relative to a CH2 group results from its electron deficiency and from the decreased stability of 7‐halo‐2‐norcaryl relative to the parent 2‐norcaryl cations. The chlorophenyltricycloheptane 25 was prepared from 10 and treated with aqueous sulfuric acid to give the norpinanol 27. Formed by protonation of the bicyclobutane system of 25, the cationic precursor of 27 shows a behaviour similar to that of cations 41.
Messung der Donorstärke substituierter 1‐Naphthole
Authors: Laatsch Hartmut , Sigel Christoph , Kral Andreas 
Published: July 2007

Measurement of the Donor Strength of Substituted 1‐NaphtholsThe oxidation potential of various substituted naphthols is available by cyclovoltammetry. The donor strength of substituents on the oxidation potential may be explained on the base of substituent increments. When correlating the oxidation potential with the transition energy of charge transfer complexes with TCNE, 1‐naphthols with 8‐alkoxy substituents and naphthols without oxygen in position 8 are giving different correlation curves. The experimental values correlate well with semiempirically calculated HOMO energies. Our measurements allow to predict the oxidation potentials of hitherto unknown substituted 1‐naphthols with high probality. Thus, it may be possible to synthesize 1‐naphthols with a defined oxidation potential.
Bis(benzo[4,5]thieno)[3,2‐c:2′,3′‐e][1,2]dithiin, ein Valenzisomer von „Dithioxo‐thioindigo”︁
Authors: Schroth Werner , Hintzsche Ekkehard , Viola Horst , Winkler Ralf , Klose Heike , Boese Roland , Kempe Rhett , Sieler Joachim 
Published: July 2007

Bis(benzo[4,5]thieno)[3,2‐c:2′,3′‐e][1,2]dithiin, ein Valenzisomer von „Dithioxo‐thioindigo”︁3‐Mercaptobenzo[b]thiophene (1) is transformed with assistance of bases, especially of amines, into the benzo[b]‐thieno‐annellated 1,2‐dithiine 6 and not into the originally claimed “Dithioxo‐thioindigo” trans‐3. Primarily, the formation of 6 from 1 involves oxidation to the disulfide 4 which may also be used separately. Conceivable rationalizations are discussed. The same compound is accessible (in lower yield)by thionation of thioindigo with the aid of the Lawesson reagent. X‐ray elucidation of 6 reveals a non‐planar structure of the cyclic disulfide with a dihedral CSSC‐angle of 53°. Despite of the absence of any established chromonphoric moiety, 6 is deeply red in the crystal and in solution, as it is representative for the “undisturbed” 1,2‐dithiine system. Contrary to the usual behaviour of the non‐annellated 1,2‐dithiines, 6 displays no spontaneous sulfur extrusion under mild conditions, but only at high temperatures and in the presence of sulfur‐binding agents, leading to the benzo[b]thieno‐annellated thiophene 22. Moreover, 6 may be reduced to the dithiol 14 (or 13, respectively) and regenerated exclusively from this by oxidation. Further characteristic reactions of 6 are described (e.g. to the sulfoxide 18, to the pyridazine 19, and to the thiphosphoric ester 21).
Komplexe mit makrocyclischen Liganden, I. Zweikernige Kupfer(II)‐Komplexe mit vollständig π‐konjugiertem Makrocyclus vom Schiff‐Basen‐Typ: Synthesen, Strukturen, elektro‐ und magnetochemische Eigenschaften
Authors: Brychcy Klaus , Dräger Klaus , Jens Klaus‐J. , Tilset Mats , Behrens Ullrich 
Published: July 2007

Complexes with Macrocyclic Ligands, I. ‐ Dinuclear Copper(II) Complexes with a Totally π‐Conjugated Macrocycle of Schiff Base Type: Syntheses, Structures, Electro‐, and Magnetochemical PropertiesThe dinuclear copper(II) complexes 6, 7, and 8 of three novel macrocyclic ligands were synthesized by the Schiff base condensation of 2 equiv. of 1,2‐phenylenediamine and 2,6‐diformylphenol in the presence of 2 equiv. of copper(II) perchlorate and were characterized by X‐ray structure analyses, electrochemical investigations (DCV), and variable‐temperature magnetic susceptibility measurements. Complex 6 exists in two different solvated crystalline forms. The Copper(II) ions in all three complexes are octahedrally coordinated with long axial distances to solvent molecules or perchlorate ions. The copper ions in 6 (in solvate a) are only five‐coordinate and square‐pyramidal. The CuIICuII complexes were reduced in successive, quasi‐reversible, one‐electron steps. The antiferromagnetic exchange interactions were determined. Upon dissolution in acetonitrile complex 8 decomposed to form [Cu(MeCN)4]+ClO−4 and the benzimidazolium percholorate 9 (X‐ray structure determination).
(2,4,6‐iPr3C6H2)(tBu)Si(AsH2)2: Das erste Diarsanylsilan und seine Umwandlung in ein 1,3‐Diarsa‐2‐sila‐4‐germacyclobutan und ein 1,3‐Diarsa‐2‐sila‐4‐germabicyclo[1.1.O]butan‐Derivat
Authors: Drieß Matthias , Pritzkow Hans 
Published: July 2007

(2,4,6‐iPr3C6H2)(tBu)Si(AsH2)2: The First Diarsanylsilane and Its Transformation into a 1,3‐Diarsa‐2‐sila‐4‐germabicyclobutane and a 1,3‐Diarsa‐2‐sila‐4‐germabicyclo[1.1.0]butane Derivative*The crowded diarsanylsilane (2,4,6‐iPr3C6H2)(tBu)Si(AsH2)2 (1) is synthesized by the reaction of (2,4,6‐iPr3C6H2)(tBu)‐SiCl2 with two equivalents of [LiAsH2(dme)] in 80% yield. Treatment of 1 with two equivalents of nBuLi yields the dilithio compound 7, which reacts with Mes(tBu)GeF2 to give the corresponding 1,3‐diarsa‐2‐sila‐4‐germacyclobutane 8. The X‐ray crystal structures of 1 and 8 were determined. The bond angles at silicon of 1 lie between 113.0(4) and 96.1(4)° indicating a distorted tetrahedral geometry. The four‐membered SiGeAs2 ring in 8 is puckered (As1‐Si1‐As2/As1‐Ge1‐As2 23.5°) with the two tBu groups being transoriented. Dilithiation of the AsH positions in 8 with nBuLi and subsequent reaction with tBuHgCl leads to the 1,3‐bis‐(tert‐butylmercurio) compound 9. The light‐induced elimination of the tBu groups in 9 gives the tBu/tBu‐exo,endo‐SiGeAs2‐bicyclo[1.1.0]butane 10 in 91% yield. 10 does not rearrange to the exo,exo isomer 11.
Halogen‐Kohlenstoff‐Schwefel‐Verbindungen: Zur Chemie von 1,1,1,4,4,4‐Hexafluor‐2‐buten‐2,3‐bissulfenylchlorid
Authors: Reimann‐Andersen Stefan , Pritzkow Hans , Sundermeyer Wolfgang 
Published: July 2007

Halogen‐Carbon‐Sulfur Compounds: Syntheses with 1,1,1,4,4,4‐Hexafluoro‐2‐butene‐2,3‐bissulfenyl ChlorideThe bifunctional bissulfenyl chloride 3 is obtained by chlorination of the dithiete 1 or tetrathiocine 2. By excessive chlorination the saturated bissulfenyl chloride 4 is formed. 3 reacts with primary amines to yield the 1,3,2‐dithiazoles 5a–e, whereas by reactions with active methylene compounds like ketones or β‐dicarbonyls the compounds 7–14 are obtained with HCl elimination. 13 as well as 14 are converted into the carboxylic acid 15 from which the 1,3‐dithiole 17 is obtained by decarboxylation. 3 reacts with disulfene to form tetrakis‐(trifluoromethyl)tetrathiafulvalene as well as 4,4′,5,5′‐tetrakis(trifluoromethyl)‐2,2′‐spirobi[1,3‐dithiole] (18), whose crystal structure has been determined.
In 2‐ und 3‐Stellung verzweigte, enantiomerenreine 4,4,4‐Trifluor‐3‐hydroxy‐buttersäure‐Derivate aus 6‐Trifluormethyl‐1,3‐dioxan‐und ‐dioxin‐4‐onen
Authors: Gautschi Markus , Schweizer W. Bernd , Seebach Dieter 
Published: July 2007

Preparation of Enantiomerically Pure 4,4,4‐Trifluoro‐3‐hydroxy‐butanoic Acid Derivatives, Branched in the 2‐ or 3‐Position, from 6‐Trifluoromethyl‐1,3‐dioxan‐ and ‐dioxin‐4‐onesEnantiomerically pure 3‐hydroxy‐3‐trifluoromethyl‐propionic acid and esters, substituted in the 2‐ or 3‐position, are prepared (13 examples) from (R)‐ or (S)‐4,4,4‐trifluoro‐3‐hydroxy‐butanoic acid. Key intermediates are the 2‐t‐butyl‐6‐trifluoromethyl‐1,3‐dioxan‐ and ‐dioxin‐4‐ones. The Li enolate of the cis‐dioxanone is generated with t‐BuLi and reacts with electrophiles (alkyl halides, aldehydes, imines, nitroolefins, Br2, I2) with predominant formation of trans,trans‐2,5,6‐trisubstituted dioxanones (9 examples). Elimination of HBr from the 5‐Br‐substituted dioxanone gives the (R)‐ or (S)‐dioxinone, a chiral derivative of 4,4,4‐trifluoro‐3‐oxo‐butanoic acid (trifluoro‐acetoacetate). Michael additions of cuprates or of CuCl‐doped Grignard reagents to the dioxinone produce 6,6‐disubstituted dioxanones (10 examples) bearing a CF3 group in the 6‐position. In most cases this addition is highly diastereoselective, with the new substituent winding up in the trans position. There are, however, surprising exceptions, such as the product formed with benzylmagnesium chloride which is an abnormal adduct with a p‐quinoid structure (26) and with the newly introduced group in the cis position with respect to the t‐Bu group. The structures of four trisubstituted dioxanones bearing CF3 groups are determined by X‐ray crystal structure analysis (Figure 1, Table 1), one of them including the absolute configuration (by anomalous diffraction). Besides the well‐known sofa, a twist‐boat conformation of dioxanones appears to be favorable. The solution conformations of the different types of CF3‐substituted dioxanones are derived from Nuclear Overhauser NMR measurements and compared with the crystal structures (Figure 3).