Synthetic Studies on Cephalotaxus Alkaloids. A synthesis of (.+-.)-Cephalotaxine.

Abstract

A stereoselective total synthesis of (±)-cephalotaxine (1) has been achieved. Palladium-catalyzed [3+2] cycloaddition of 2-(trimethylsilylmethyl)-2-propenyl acetate to the nitrostyrene 7 gave the methylenecyclopentane 6, which was converted into the α-sulfinylacetamide 19. Treatment of 19 either with trifluoroacetic anhydride in dichloromethane at room temperature or with p-toluenesulfonic acid in boiling 1, 2-dichloroethane gave the benzazepinone 20 in good yield, and this was transformed to (±)-1 via Hanaoka's key intermediate 4.