Studies on Flavans. 1. Facile Synthesis of (±)-7-Hydroxy-3‘,4‘-methylenedioxyflavan and (±)-4‘-Hydroxy-7-methoxyflavan by a BF3·Et2O-Mediated Pyran Cyclization
摘要:
A facile approach for the synthesis of flavans was developed by employing a BF3. Et2O-catalyzed pyran cyclization in an aprotic polar solvent as a key step, by which concise total syntheses of(+/-)-7-hydroxy-3',4'-methylenedioxyflavan (1) and (+/-)-4'-hydroxy-7-methoxyflavan (2), two naturally occurring flavans, were achieved.