Direct, regioselective synthesis of 2,2-dimethyl-2H-chromenes. Total syntheses of octandrenolone and precocenes I and II

Herein is reported an efficient method for the synthesis of 2,2-dimethyl-2H-chromenes in a single step front the corresponding phenol and 3-methyl-2-butenal via microwave irradiation in CDCl(3). This protocol features a mild reaction environment (neutral, no added catalyst) which yields regioselective formation of the chromene and displays tolerance toward acid- and base-sensitive protecting groups. (C)c 2009 Elsevier Ltd. All rights reserved.