The synthesis of four flavan-3-ols with different substitution
patterns and electron densities has been achieved in high stereo-
and regioselectivity by a one-step Mitsunobu reaction from the corresponding
diols, which were prepared by enantioselective Sharpless dihydroxylation
of suitable olefins. The six-membered flavan-3-ols were the only
cyclization products and the theoretically possible formation of
five-membered rings during the Mitsunobu cyclization was not observed.
The flavanols are important starting materials for the synthesis
of dimers such as the procyanidins or other coupling products such
as the flavan part of the potent DNA polymerase β inhibitor
myristinin A. The enantioselectivities of both the Sharpless dihydroxylation
and the Mitsunobu cyclization steps were monitored by chiral HPLC.
myristinin A - Sharpless dihydroxylation - flavanol
synthesis - Mitsunobu reaction
