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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syntheses of sulfur flavan-3-ol analogues 1-8 have been accomplished, whereby the oxygen atom of the pyran ring has been replaced by a sulfur atom.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 AlCl(3). The compounds were isolated in high chemical and optical purity.
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Sharma et al. (2010) studied this question.
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