Stereoselective synthesis of flavonoids part 6 - The novel flavan-3-ol, (2R,3S)-guibourtinidol and its diastereomers

The novel (2R,3S)-guibourtinidol, representing the first flavan-3-ol with 4 ',7-dihydroxy phenolic substitution pattern, was identified in the heartwoo d of Cassia abbreviata. Asymmetric dihydroxylation of (E)-1-(4'-O-methoxyme thylphenyl)-3-(2 ",4 " di- O-methoxymethylphenyl)-propene with AD-mix-alpha or AD-mix-beta and subsequent acid-catalyzed cyclization afforded the four free phenolic guibourtinidol diastereomers, essentially enantiopure and in good yield. (C) 1999 Elsevier Science Ltd. All rights reserved.