1,3-Dipolar Cycloaddition of Diazoalkanes to (S)-(+)-3-[(4-Methylphenyl)sulfinyl]-5,6-dihydropyran-2-one. Synthesis of Optically Pure Cyclopropanes by Denitrogenation of Sulfinyl and Sulfonyl Pyrazolines

The addition of diazomethane and diazoethane to enantiopure (S)-(+)-3-[(4-methylphenyl)sulfinyl]-5,6-dihydropyran-2-one (3) afforded the corresponding pyrazolines 4 and 6-exo in good yields and with almost complete pi-facial selectivity. When the reaction is effected in the presence of Yb(OTf)(3), the facial selectivity is inverted to give the pyrazolines 5 and 7-exo. The denitrogenation of optically pure sulfinyl pyrazolines 4-7-exo into the corresponding cyclopropanes with Yb(OTf)(3) occurred with complete retention of configuration but moderate chemoselectivity and yields. These results were significantly improved starting from sulfonyl pyrazolines, which afforded optically pure 3-oxabicyclo[4.1.0]heptan-2-ones with yields ranging between 65% (17 and ent-17) and >= 95% (16 and ent-16)

A formal synthesis of (+)-(S)-kurasoin B

A new diastereoselective synthesis of (S)-1-[(S)-oxiran-2-yl]-2-phenylethanone (10), a key intermediate in the synthesis of kurasoin B (2), has been accomplished in seven steps in an overall yield of 32%. The key synthetic step in the process is the diastereoselective reduction of the beta-keto sulfoxide 6 derived from (S)-phenyllactic acid

High stereocontrol in aldol reactions with ketones: enantioselective synthesis of beta-hydroxy gamma-ketoesters by ester enolate reactions with 2-acyl-2-alkyl-1,3-dithiane 1-oxides

The asymmetric aldol reaction of 1,2-diketones, masked as nonracemic 2-acyl dithiane oxides, with lithium enolates derived from several esters and lactones, proceeds with a high degree of stereocontrol at both carbonyl and enolate prochiral centers, the stereocontrol mainly determined by the configuration of the sulfoxide sulfur atom. The sense of induced stereochemistry observed for ester enolates is different from that seen for lactone enolates. Hydrolysis of the dithiane oxide units of the major diastereoisomerically pure aldol products affords enantiomerically pure tertiary alpha-substituted beta-hydroxy-gamma-ketoesters.</p

A stereodivergent approach to syn- and anti-beta-hydroxy-gamma-amino acids. Enantioselective synthesis of N-Boc-statine and N-Boc-3-epistatine mediated by sulfoxides

Asymmetric syntheses of the syn- and anti-stereoisomers of N-Boc statine, based on the stereodivergent reduction of a single sulfoxide 5, derived from N-Boc-L-leucine, are reported. (C) 2003 Elsevier Science Ltd. All rights reserved

Enantioselective synthesis of alpha-hydroxy-beta-amino acids from alpha-amino acids mediated by sulfoxides

The synthesis of the optically pure (2S, 3S)- and (2R, 3S)-3-amino-2-hydroxybutanoic acids from commercially available ( S)alanine derivatives is reported. The key step of the synthetic sequence is the conversion of gamma-amino sulfoxides into gamma-amino alcohols by treatment with TFAA and sym-collidine. The efficiency of this non-oxidative Pummerer reaction (NOPR) is dependent on the stereochemistry of the starting sulfoxide. (c) 2007 Elsevier Ltd. All rights reserved