bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intramolecular Carbene Addition to a Triple Bond – Matrix Photochemistry of α‐Diazo‐2‐ethynylacetophenone
Authors: Komnick Peter , Sander Wolfram 
Published: June 2010

AbstractThe irradiation (λ =403 nm) of α‐diazo‐2‐ethynylacetophenone (1 a) in solid argon at 10 K leads to (2‐ethynylphenyl)ketene (11) as the major product. A minor product is benzo‐4‐oxo‐2,5‐cyclohexadienylidene (6) which on 475‐nm irradiation reversibly rearranges to cycloprop[a]inden‐6(6aH)‐one (5a). This demonstrates that the intramolecular addition of the carbene center to the double bond can compete with the Wolff rearrangement.
Synthesis of Enantiomerically Pure Hydroxyethylporphyrins and Their Transformation into Optically Active Chlorin Derivatives
Authors: Kusch Dirk , Montforts Franz‐Peter 
Published: June 2010

AbstractThe oxazaborolidine (9)‐catalyzed reduction of acetylporphyrins (4) led to enantiomerically pure hydroxyethylporphyrins (5), which were transformed into optically active chlorin derivatives (7 and 8) upon reaction by N,N‐dimethylacetamide dimethyl acetal followed by hydrogenation. The absolute configuration of the synthesized chlorins was elucidated by means of their CD spectra.
Ring‐Opening Reactions of 3,5‐Bis(methylthio)‐1,2‐dithiolium Salts with Cyclopentadienides
Authors: Hartke Klaus , Popp Xue‐Ping 
Published: June 2010

Abstract4‐Aryl‐substituted 3,5‐bis(methylthio)‐1,2‐dithiolium salts such as 1a react with metal cyclopentadienides 4 (M+ =Tl, Li) mainly by cleavage of the S–S bond. A subsequent intramolecular Diels‐Alder addition of the ring‐opened structures 5/6 gives the tricyclic compounds 7a and 8a, b. Intramolecular condensation of 5 or 6 yields the cyclopenta[b]thiopyran 11a. With the 4‐unsubstituted 3,5‐bis(methylthio)‐1,2‐dithiolium salt 1b the intramolecular Diels‐Alder adducts 8c, d and 9a, 10a were isolated. 4‐Alkyl‐substituted 1,3‐bis(methylthio)‐1,2‐dithiolium salts such as 1c react with thallium cyclopentadienides 4 mainly by substitution at C‐3 leading to the formation of the 2,3‐dithiafulvalenes 12a, b. The reaction of these salts with lithium cyclopentadienides leads to S–S bond cleavage followed by an intramolecular condensation affording the cyclopenta[b]thiopyran 11b.
Polycyclic Aromatic Alkaloids, XI A Convenient Formal Total Synthesis of the Cytotoxic Marine Alkaloid Amphimedine
Authors: Bracher Franz , Papke Thomas 
Published: June 2010

AbstractThe pyridylbenzo[c][2,7]naphthyridinone 2, a central intermediate for the total synthesis of amphimedine (1), was prepared in two steps from the readily available quinoline 3. Palladium‐catalyzed cross‐coupling of 3 with 4‐(trimethylstannyl)pyridine gave the biarene 4, which could be converted to the target compound 2 by using a one‐pot anellation method.
Enkastines: Amadori Products with a Specific Inhibiting Action against Endopeptidase – 24.11 – from Streptomyces albus and by Synthesis
Authors: Vértesy László , Fehlhaber Hans‐Wolfram , Kogler Herbert , Schindler Peter W. 
Published: June 2010

AbstractTarget‐oriented screening led to the detection of specific inhibitors of endopeptidase – EC 3.4.24.11 – (enkephalinase) in cultures of Streptomyces albus, ATCC 21 838. Isolation was performed by successive chromatographic methods and yielded enkastines in amounts of about 2 mg from 2000 kg of culture broth. Amino acid analysis, proton‐ and carbon‐NMR spectroscopy, mass spectrometry, and chemical degradation suggested the structure of the three most prominent enkastines to be N‐(1‐deoxyfructos‐1‐yl)‐isoleucyl‐aspartate (1), N‐(1‐deoxyfructos‐1‐yl)‐valyl‐aspartate (2), and N‐(1‐deoxyfructos‐1‐yl)‐valyl‐glutamate (3). This structural hypothesis was confirmed by chemical synthesis of the compounds according to the Amadori reaction of glucose with the corresponding dipeptides. The products turned out to be identical with the isolated material with respect to their NMR fingerprint (1H and 13C) and their biological properties. Enkastines are potent inhibitors of the endopeptidase 24.11. with IC50 of 1.8 × 10−9 M (1), 6.3 × 10−9 M (2) and 3 × 10−8 M (3). In contrast to phosphoramidon, a well‐known inhibitor of the enkephalinase, enkastines exhibit no activity against thermolysin. Kinetic studies characterize enkastine activity as competitively slow and tightly binding to endopeptidase – EC 3.4.24.11.
3‐Alkylidene‐2‐azetidinethiones: Useful Intermediates for the Synthesis of 3‐Substituted 2‐Azetidinethiones
Authors: Nieschalk Jens , Spanka Carsten , Schaumann Ernst 
Published: June 2010

Abstract3‐Lithiated 2‐azetidinethiones 1 were allowed to react with carbonyl compounds to give 3‐(1‐hydroxyalkyl)‐2‐azetidinethiones 3, 4 which were converted into α,β‐unsaturated β‐thiolactams 7, 8, 10 by elimination procedures. Alternatively, the title compounds were prepared by Peterson olefination of 3‐trimethylsilyl‐2‐azetidinethiones 9. Reactions of 7, 8, 10 with thiophenol or sodium diethyl malonate provided the Michael adducts 11. E/Z Photoisomerization of 7, 8 by visible light was observed. On deprotonation, 7a, 8a underwent allyl rearrangement to 13.
Sterically Congested Molecules, 16 A Convenient Synthesis of Di‐tert‐butyl Ketone via its Imine, 2,2,4,4‐tetramethyl‐3‐pentanimine
Authors: Knorr Rudolf , Donhärl Angelika , Hennig Karsten‐Olaf 
Published: June 2010

Abstract2,2,4,4‐Tetramethyl‐3‐pentanimine (3) is efficiently prepared by a Barbier‐type reaction of pivalonitrile (1) with an excess of tert‐butyl chloride (2) and metallic lithium in ether. Its purification by extraction into aqueous acid and slow hydrolysis permit an inexpensive and very simple production of di‐tert‐butyl ketone (4).
Chemoenzymatic Synthesis of (R)‐(+)‐Patulolide A, a Macrolide Antibiotic Isolated from Penicillium urticae
Authors: Kitamura Masaya , Nagaoka Hiroyuki , Naoshima Yoshinobu , Kamezawa Makoto , Tachibana Hojun , Ohtani Takehiko 
Published: June 2010

Abstract(R)‐(+)‐Patulolide A [(R)‐1] was synthesized with an enantiomeric purity of almost 100% e.e. by a two‐step lipase‐catalyzed enantioselective hydrolysis of racemic thioketal acetate (±)‐11.
Bimolecular Formation of Radicals by Hydrogen Transfer, 10. On the Mechanism of Quinone Dehydrogenations
Authors: Höfler Christoph , Rüchardt Christoph 
Published: June 2010

AbstractThe mechanistic alternatives in the literature for quinone dehydrogenations of hydroaromatic to aromatic hydrocarbons are reviewed. In a kinetic study of the reaction of DDQ 16 with 9,10‐dihydroanthracene (13) or xanthene (17) small solvent effects and small rate differences between 13 and 17 (Table 1) but large kinetic isotope effects kH/kD were observed. In addition, intermediate 9‐hydroanthryl radical 20b and 9‐xanthyl radicals 19b were trapped by the addition of nitrosobenzene to the dehydrogenation reaction mixtures as shown by the ESR spectra of the spin adducts 22 and 23. These results are better explained by an initial H atom transfer step (retrodisproportionation, RD) than by direct hydride transfer (DHT). Possible consequences for biochemical hydrogen transfer processes are addressed briefly.
Synthesis of a New Chiral Peptide Analogue of DNA Using Ornithine Subunits and Solid‐phase Peptide Synthesis Methodologies
Authors: Lioy Eduardo , Kessler Horst 
Published: June 2010

AbstractIn this paper we describe the synthesis of chiral peptide nucleic acids (PNAs) 1–3 using SPPS methodologies. Starting material for the monomer units was the commercially available amino acid ornithine. l‐ or D‐ornithine and the nucleobase thymine were linked by a carboxymethylene spacer giving the chiral monomers l‐7 and D‐7. The SPPS was performed according to the Fmoc strategy.
A Concise and Stereoselective Synthesis of threo‐γ‐Hydroxy‐l‐β‐lysine Lactone
Authors: Misiti Domenico , Zappia Giovanni , Monache Giuliano Delle 
Published: June 2010

AbstractA stereoselective synthesis of threo‐γ‐hydroxy‐β‐l‐lysine lactone is reported. The threo‐amino alcohol functionality is introduced by iodine‐mediated cyclocarbamation of the electron poor allylamine 6. The D‐phenylalanine was used as starting material as synthetic equivalent to D‐aspartic acid.
Preparation and Structure Proof of the Four Isomeric Dicyanocobyrinic Acid Hexamethyl Ester Monoamides Carrying the Amide Group on a Propionic Acid Side Chain
Authors: Ernst Ludger , Maag Hans 
Published: June 2010

AbstractSelective ammonolysis of dicyano‐cobalt(III)cobyrinic acid heptamethyl ester (cobester, 2) furnishes the four isomeric hexamethyl ester monoamides 2b, 2d, 2e, 2f carrying the amide function on one of the propionic acid side chains. The isomers were separated by liquid‐liquid chromatography and their structures determined by a comparison of their 13C‐NMR spectra with the spectrum of 2. Amide 2f served as the link between synthetic and authentic vitamin B12 derived material in the total synthesis of vitamin B12.
Organophosphorus Compounds, 111 Phospha Ene Reactions of a P‐Chlorophosphaalkene as a Versatile and Powerful Enophile Building Block
Authors: Mackewitz Thomas W. , Regitz Manfred 
Published: June 2010

Abstract[Bis(trimethylsilyl)methylene]chlorophosphane (1) has proved to act as an extremely reactive enophile in phospha ene reactions with all‐carbon enes of differing constitutions and so provides a general approach to β,γ‐unsaturated chlorophosphanes. Thus, for example, 1 reacts even at room temperature or slightly elevated temperatures with the terminal alkenes 6a–c, the methylenecycloalkanes 6d, e, h, and the cycloalkenes 6f, g to furnish the corresponding allyl‐substituted chlorophosphanes 7a–h. Dimethylallene (8) undergoes addition to 1 to yield the phosphanyl‐substituted buta‐1,3‐diene 9 whereas allene (10) itself reacts with 1 by way of a previously unknown phospha ene reaction to give the propynyl‐substituted chlorophosphane 11. By contrast, the (chlorophosphanyl)allene 13 results from the reaction of 1 with but‐2‐yne (12). All of these group transfer reactions proceed chemo‐ and regioselectively with P/C bond formation. The constitutions of all the phospha ene adducts, which were isolated in satisfactory to good yields after purification by distillation, were unequivocally confirmed by analytical and spectroscopic methods.
Synthesis and Stereoselective CC Bond‐forming Reactions of Peptide Aldehydes
Authors: Reetz Manfred T. , Griebenow Nils 
Published: June 2010

AbstractThe reaction of the activated form of N‐protected amino acids 6 and 10 or peptides 14 and 18 with chiral amino alcohols derived from the corresponding α‐amino acids affords peptide alcohols which can be oxidized under Swern conditions to produce the corresponding peptide aldehydes 9, 12, 16 and 20. The rational synthesis of diastereomeric di‐ and tripeptide aldehydes, e.g., (S,S)‐ or (R,S)‐dipeptides as well as (S,S,S)‐ or (R,S,S)‐tripeptides is possible by proper choice of the respective building blocks [(S)‐ versus (R)‐amino acids]. The compounds can be prepared without any undesired α‐epimerization. However, the long‐term configurational stability depends upon the configuration at the remote stereogenic center, e.g., (R,S)‐dipeptide aldehydes epimerize faster than the (S,S) diastereomers. Di‐ and tripeptide aldehydes 9, 12, 16 and 20 undergo chelation‐controlled Grignard‐type additions with Me2CuLi that involve little or no undesired α‐epimerization. The (S,S)‐ and (R,S)‐dipeptide aldehydes 9 and 12 undergo chelation‐controlled pinacol reactions induced by the low‐valent vanadium reagent [V2Cl3(THF)6]2[Zn2Cl6]. The major products in both cases are the corresponding C2‐symmetric diols 33 and 36, respectively, which are of interest as potential HIV‐protease inhibitors. The degree of stereoselectivity is significantly higher in the case of the (S,S)‐dipeptide aldehydes relative to the (R,S) analogs, an observation which can be explained on the basis of three‐point binding of the peptides to vanadium.
Influence of Substituents on the Rotational Energy Barrier of Axially Chiral Biphenyls, II
Authors: Wolf Christian , Hochmuth Detlev H. , A. König Wilfried , Roussel Christian 
Published: June 2010

AbstractThe influence of substituents on the rotational energy barrier of a series of 2,2′‐bis(trifluoromethyl)‐ and 2,2′‐diisopropylbiphenyl derivatives with various substitution patterns was investigated by dynamic gas chromatography (DGC) with selectively modified cyclodextrins and by high‐performance liquid chromatography (HPLC) on microcrystalline cellulose triacetate combined with polarimetry. Investigation of the steric effect of substituents was possible by gradually increasing the bulkiness of substituents in the ortho positions of 2,2′‐disubstituted biphenyls and determination of the corresponding energy barriers. The buttressing effect of alkyl groups adjacent to the ortho substituents is discussed. Comparison of the energy barriers of 2,2′‐bis(trifluoromethyl)biphenyl (1) with its derivatives possessing alkyl groups in positions 3 and 5, respectively, allows a discrimination between the electronic and steric contributions of the meta substituents and thus the determination of the influence on the energy barrier. The electronic effect on the rate of rotation, i.e. the rate of enantiomerization, of axially chiral biphenyls bearing substituents in the para positions depends on the aromatic system to which they are attached. Electron‐donating groups decrease the rotational energy barrier of 2,2′‐bis(trifluoromethyl)biphenyl derivatives but increase the barrier of 2,2′‐diisopropylbiphenyl derivatives. Electron‐accepting groups exhibit the opposite behavior. The unexpected effects in the case of para‐substituted 2,2′‐diisopropylbiphenyl derivatives are possibly related to C–H/π interactions.
Synthesis of Liposomal Phospholipid‐(N4‐palmitoyl‐1‐β‐D‐arabinofuranosylcytosine) Conjugates and Evaluation of Their Cytostatic Activity against l1210 Murine Leukemia
Authors: Schott Herbert , Schwendener Reto A. 
Published: June 2010

AbstractN4‐Palmitoyl‐araC, a prodrug of the cytostatic compound 1‐β‐D‐arabinofuranosylcytosine (araC), was linked by means of the triester method to the phospholipids (2‐chlorophenyl) (1,2‐di‐O‐palmitoylglyceryl) phosphate, (2‐chlorophenyl) (1,2‐di‐O‐octadecylglyceryl) phosphate and (2‐chlorophenyl) (1‐O‐octadecyl‐2‐O‐palmitoylglyceryl) phosphate. In the first step of these gram‐scale syntheses phospholipid‐(N4‐palmitoyl‐araC) conjugates were obtained the linkage of which was accomplished via a triester group. In the second step the final condensates were obtained through transformation of the triester into a diester linkage by removal of the 2‐chlorophenyl group. The cytostatic activity of these compounds which form stable liposomal preparations together with matrix lipids was evaluated according to the L1210 mouse leukemia model. The conjugates containing a triester linkage were shown to be ineffective, whereas those with a diester linkage display a significantly higher antitumor activity as compared to N4‐palmitoyl‐araC and araC. With the diester 6a–8a 80–100% of the treated animals were cured at a total dose of 200 μmol/kg, whereas with araC given at a fourfold higher concentration none of the treated mice survived.
Wechselwirkungen in Kristallen, 95 Formyl(2‐pyridyl)amin: Monomer in der Gasphase, dimer im Kristall
Authors: Bock Hans , Van Tran T. H. , Solouki Bahman , Schödel Holger , Artus Georg , Herdtweck Eberhardt , Herrmann Wolfgang A. 
Published: June 2010

Interactions in Crystals, 95. – Formyl(2‐pyridyl)amine: Monomeric in the Gasphase, Dimeric in the CrystalThe title molecule [HC]4NC–NH–CHO (2), an α‐aminopyridine derivative, forms a dimer via an hydrogen bridge pair (NH…N)2 in the crystal. In the gasphase, however, it remains a monomer as proven by the well‐resolved He(I) photoelectron spectrum and its Koopman's assignment, IEnv = ‐ϵJSCF, of the radical cation state pattern. The enthalpy difference for dimerization is approximated by AM1 calculations to be rather small. Nevertheless, on crystallization either from an aprotic solution or by sublimation through the gasphase, due to the cooperative effect and to the density‐dependent increase in lattice energy, a self‐organization to the dimer is observed.
Synthesis of 5‐/10‐Membered Ring Analogues of the Dienediyne Core of Neocarzinostatine Chromophore by Palladium(0)‐Mediated Ring‐Closure Reaction
Authors: Suffert Jean , Abraham Estelle , Raeppel Stéphane , Brückner Reinhard 
Published: June 2010

AbstractThe new dienediynes 5, 6, and 7 were synthesised from a monoprotected diyne and an already described bis(enol triflate) 4 derived from formylcyclopentanone. When 5 and 6 were subjected to nucleophilic attack by a thiol, cycloaromatisation occurred, and the phenanthrenes 23a and 23b were obtained in 30 and 42% yield, respectively.
Synthesis of 6‐/10‐Membered Ring Analogs of the Dienediyne Core of the Neocarzinostatin Chromophore by Palladium(0)‐Mediated Ring‐Closure Reactions
Authors: Brickmann Kay , Hambloch Frank , Suffert Jean , Brückner Reinhard 
Published: June 2010

AbstractA strategy for the synthesis of the benzo‐annulated bicyclic dienediyne analogs 46 and 48 of the DNA‐cleaving natural product neocarzinostatin chromophore was developed. 2‐Formylcyclohexanone (9) was converted stereoselectively first into the mono(enol triflate) Z‐11 and thereafter into the bis(enol triflate) Z‐2. The isomeric triflates E‐11 and E‐2 were prepared to facilitate correct E,Z assignments. The C≡C bonds of the target dienediynes 46 and 48 were introduced with the aid of the unsymmetrical bisalkynes 17 and 16, respectively. However, the latters furnished the formers not by reactions with the monotriflate Z‐11 (Schemes 4, 7, 10) but only by reactions with the bistriflate Z‐2. The success of this approach is due to a regioselective Csp2/Csp monocoupling which unites the reaction partners and to another Pd‐catalyzed Csp2/Csp coupling which furnished the 6‐/10‐membered ring dienediyne 46 (Scheme 13) and its isomer 48 (Scheme 14). Starting from ortho‐bromobenzaldehyde and cyclohexanone these syntheses required a total of 9 and 10 steps, respectively, the longest linear sequence comprising 6 steps.
Experimental and Theoretical Studies of the Internal Stereodifferentiation Occurring During the Lithiation of β‐Stereogenic Alkyl Carbamates. Kinetic Resolutions by (‐)‐Sparteine‐Mediated Deprotonation
Authors: Haller Jan , Hense Thomas , Hoppe Dieter 
Published: June 2010

AbstractThe deprotonation of β‐stereogenic alkyl carbamates 8 with sec‐butyllithium/TMEDA proceeds kinetically controlled with differentiation between the diastereotopic protons at the α‐methylene group. The lithium intermediates 9A and 9B are trapped by electrophiles to give carboxylic acid esters 10A/B and stannanes 11A/B, 13A/B. The diastereomeric ratio of A to B is independent of the electrophile. The highest efficiency is achieved with β‐aryl‐β‐alkyl‐substituted starting compounds 8d–f. The trends in the experimentally observed diastereoselectivities are reflected by the results of semiempirical PM3 calculations on the transition states of the deprotonation reaction. — As a result of double stereodifferentiation, application of the chiral base sec‐butyllithium/(‐)‐sparteine gives rise to efficient kinetic resolution of racemic alkyl carbamates.
Pheromone Synthesis, CLXXIV. Synthesis of (5R,11S)‐5,11‐Dimethylheptadecane and (S)‐2,5‐Dimethylheptadecane, the Major and the Minor Components of the Sex Pheromone of the Geometrid Moth, Lambdina fiscellaria lugubrosa
Authors: Mori Kenji , Horikiri Hiromasa 
Published: June 2010

Abstract(5R,11S)‐5,11‐Dimethylheptadecane (1), the major component of the female‐produced sex pheromone of the western hemlock looper (Lambdina fiscellaria lugubrosa), was synthesized by starting from the enantiomers of methyl 3‐hydroxy‐2‐methylpropanoate (3). (S)‐2,5‐Dimethylheptadecane (2), the minor and synergistic component of the pheromone, was also synthesized by starting from (S)‐citronellol (4).
Photoinduced Electron Transfer (PET) Cyclization and Photooxygenation of 2,6‐Diaryl‐1,6‐heptadienes and 2,7‐Diaryl‐1,7‐octadienes
Authors: Griesbeck Axel G. , Sadlek Oliver , Polborn Kurt 
Published: June 2010

AbstractThe 2,6‐diaryl‐substituted 1,6‐heptadienes 3a–c and the 2,7‐diaryl‐substituted 1,7‐octadienes 4a–b were cleanly converted into the corresponding anellated cyclobutanes 5 and 6, resp., when irradiated under photoelectron‐transfer conditions (9,10‐dicyanoanthracene in acetonitrile). Only for 4c did the rearranged compound 7c become the dominant photoproduct. Oxygen trapping experiments with formation of endoperoxides 8, 9 were successful in the case of the electron‐rich substrates 3b, c and 4c.
Novel Tetrathiafulvalenes Based on Macrocyclic Thioethers
Authors: Wagner Michael , Zeltner Stephan , Olk Ruth‐Maria 
Published: June 2010

AbstractMacrocyclic polythioethers (7–10, 17) and the oxothioether 21 were synthesized by starting with the key compound 4,5‐bis(benzoylthio)‐1,3‐dithiole‐2‐thione (1). Intramolecular phosphite coupling reactions yielded symmetrically and unsymmetrically substituted tetrathiafulvalenes 11–14 and 22, respectively.
Synthesis and Crystal Structure of a Bis[6.3.3]propellane
Authors: Jamrozik Janusz , Żeslawski Wojeciech , Grochowski Jacek , Serda Pawel , Dauter Zbigniew 
Published: June 2010

AbstractThe bis[6.3.3]propellane 6 derivative of 2,2′,6,6′‐tetramethylbiphenyl was, in the final stage, synthesized by dehydration, of octaalcohol 5. X‐ray structure analysis revealed the highly symmetric shape of the molecule and disordered oxygen atoms in the tetrahydrofuran rings. The dihedral angle between LSQ phenyl planes is 62.6(1)°.
Secondary Metabolites by Chemical Screening, 29.
Authors: Göhrt Axel , Grabley Susanne , Thiericke Ralf , Zeeck Axel 
Published: June 2010

AbstractNovel pyranacetals, named agistatines A, B, D, and E (1 to 4), were discovered by a chemical screening in the culture broth of the fungus FH‐A 6239. The structures were established by detailed spectroscopic investigations and confirmed by X‐ray analysis of agistatine B (2), 4‐O‐(2‐bromobenzoyl)dihydroagistatine A (6), 4‐O‐(2‐bromobenzoyl)agistatine B (7), and agistatine E (4) leading to the stereochemical information. The described secondary metabolites exhibit unusual bicyclic (1 and 3) and tricyclic (2 and 4) structures with a characteristic ketal moiety at C‐2 (except 3). The instability of the main fermentation product agistatine E (4) is caused by an additional hemiketal located at the adjacent C‐‐8a.
Pseudosugars, 37. Preparation of Versatile Intermediates for Ether‐Linked 5a‐Carba Oligosaccharides: Synthesis of 5a‐Carba‐β‐D‐GlcpNAc‐(1→4)‐D‐Manp
Authors: Ogawa Seiichiro , Hirai Keisuke , Ohno Masatsugu , Furuya Takashi , Sasaki Shin‐Ichi , Tsunoda Hidetoshi 
Published: June 2010

AbstractCoupling of 1,2‐anhydro‐3‐O‐benzyl‐4,6‐O‐benzylidene‐5a‐carba‐β‐D‐mannopyranose (3) with 1,6‐anhydro‐2,3‐O‐isopropylidene‐β‐D‐mannopyranose (4) afforded a 5a′‐carba disaccharide derivative linked by an ether bridge with α‐manno configuration. This compound 5 was transformed into three stereoisomers in regard to the configurations at C‐1′ and C‐2′. Thus, the free 2′‐hydroxyl group was oxidized, and the resulting ketone 8 was isomerized at C‐1′ to 11 by treatment with potassium tert‐butoxide. Reduction of the ketones 8 and 11 with l‐selectride afforded selectively the synthetic useful intermediate ether‐linked 5a′‐carba disaccharides 9, 12, and 14 with α‐gluco, β‐gluco, and β‐manno configurations, respectively. 5a‐Carba sugar analog 2 of biologically interesting disaccharide β‐D‐GlcpNAc‐(1→4)‐D‐Manp (1) was synthesized.
Synthesis of 1,4‐Oxathiocines and Thiopyrans by the Reaction of 2‐Amino‐4,5‐dihydro‐3‐thiophenecarbonitriles with Ethyl Diazoacetoacetate
Authors: Yamagata Kenji , Akizuki Keiko , Yamazaki Motoyoshi 
Published: June 2010

AbstractThe reaction of 4,5‐dihydro‐2‐(4‐morpholinyl)‐ or ‐2‐(1‐piperidinyl)‐ or ‐2‐(1‐pyrrolidinyl)‐3‐thiophenecarbonitriles 1a–i with ethyl diazoacetoacetate in the presence of rhodium (II) acetate dimer gave the corresponding ethyl 1,4‐oxathiocine‐3‐carboxylates 2a–f, h and acetyl(dihydro‐1‐thiophenylio)‐(ethoxycarbonyl)methanides 3a, b. Compounds 2a–f, h and 3a, b were heated at 140°C to give the corresponding ethyl thiopyran‐6‐carboxylates 4a–i in moderate to good yields.