Enantioselective Synthesis of Flavan-3-ols Using a Mitsunobu Cyclization

Abstract

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.