Enantioselctive Syntheses of Sulfur Analogues of Flavan-3-Ols

Abstract

The first enantioselective syntheses of sulfur flavan-3-ol analogues 1–8 have been accomplished, whereby the oxygen atom of the pyran ring has been replaced by a sulfur atom. The key steps were: (a) Pd(0) catalyzed introduction of –S t-butyl group, (b) Sharpless enantioselective dihydroxylation of the alkene, (c) acid catalyzed ring closure to produce the thiopyran ring, and (d) removal of benzyl groups using N,N-dimethylaniline and AlCl3. The compounds were isolated in high chemical and optical purity.

Keywords

• flavan-3-ols
• 5,7-dideoxythiocatechin
• 5,7-dideoxythioepicatechin
• thiocatechin
• thioepicatechin
• asymmetric dihydroxylation