Highly diastereoselective alkylation onto 4-acetoxy-2-azetidinones employing tin(II) enolates of 3-acyl C-4-chiral 1,3-thiazolidine-2-thiones

Syntheses of chiral intermediates of 1-β-methylcarbapenems: (3S,4R)-3-[1(R)-tert-butyldimethylsilyloxyethyl]-4-chloroazetidin-2-one and (3S,4S)-3-[1(R)-tert-butyldimethylsilyloxyethyl]-4-[1(R)-tert-butylthiocarbonylethyl]azetidin-2-one

“…Fuentes et al (13) reported that Evans type enolates 14a (14) undergo stereoselective aldol type condensation with 4-acetoxyazetidinone 4 in the presence of Lewis acid to afford 16a in good yields with predominantly the p-isomer. Similar results on 16b, using tin(I1) enolates of thiazolidine-2-thiones and oxazolidine-2-thiones, have been reported by other groups (15,16). As well, Iimori and Shibasaki (17) reported a stereoselective introduction of the P-methyl group by reducing an olefinic ester 15a with L-Selectride ( P / a 8:1, 77% yield).…”

Lasonolide A: Synthesis of A and B Rings via a Cycloetherification Strategy

“…Thiazolidinethione 27 was converted to the corresponding Sn(II) enolate and reacted with E,E-5-(4-methoxyphenyl)penta-2,4-dienal to provide aldol product 28 in 79% yield. 20, 21 The diastereomeric ratio in this reaction was 95:5 (based on integration of the 1 H NMR signals due to the C 2 methyl doublets), and the absolute stereochemistry was assigned by analogy with the many examples of this process reported by Nagao and others. 21 Treatment of 28 with the aluminum amide derived from N,O-dimethylhydroxylamine gave Weinreb amide 29 in 93% yield along with greater than 80% recovery of the chiral auxiliary.…”

“…20, 21 The diastereomeric ratio in this reaction was 95:5 (based on integration of the 1 H NMR signals due to the C 2 methyl doublets), and the absolute stereochemistry was assigned by analogy with the many examples of this process reported by Nagao and others. 21 Treatment of 28 with the aluminum amide derived from N,O-dimethylhydroxylamine gave Weinreb amide 29 in 93% yield along with greater than 80% recovery of the chiral auxiliary. 22 Protection of the secondary alcohol as TES-ether 30 was then accomplished in 94% yield.…”

α-Amino acid synthesis via a Cu(II) chiral Lewis acid mediated addition of soft carbon nucleophiles to glycine cation equivalents

“…[1][2][3][4][5][6][7] However there have only been a few reported chiral Lewis acid catalysed variants of this Mannich-type reaction. [8][9][10][11][12] The use of a-imino esters as substrates in Mannich-type reactions leads to the formation of a-amino acids.…”