Divergent Reactivity in Amine- and Phosphine-Catalyzed C–C Bond-Forming Reactions of Allenoates with 2,2,2-Trifluoroacetophenones

Abstract

A divergent reactivity pattern of allenoates with 2,2,2-trifluoroacetophenones under Lewis base catalysis is reported. Whereas phosphine catalysis leads to a [3 + 2]-cycloaddition to form dihydrofurans, an alternative pathway was discovered in which 1,4-diazabicyclo-[2.2.2]-octane catalyzes a formal [2 + 2]-cycloaddition to form oxetanes. This unusual mode of reactivity leads to structurally complex products in moderate to excellent yields (32–86%) and adds to the repertoire of Lewis base-catalyzed allenoate transformations.