Divergent Phosphine-Catalyzed [2+4] or [3+2] Cycloaddition Reactions of γ-Substituted Allenoates with Oxadienes

A strategy was developed to construct dihydropyran and multifunctional cyclopentene derivatives from the same starting materials by using different phosphine catalysts. By exploiting the different nucleophilicities of the phosphine catalysts, the gamma-substituted allenoates selectively acted as C-3 or C-2 synthons. Under the catalysis of different organophosphine catalysts, the domino reaction proceeded smoothly with broad substrate tolerance and excellent total yields. The results suggest that the ethyl group of the gamma-substituted allenoates played a key role in the domino reaction.