γ-Substituted Allenic Amides in the Phosphine-Catalyzed Enantioselective Higher Order Cycloaddition with Azaheptafulvenes

Abstract

Racemic γ-substituted allenes undergo enantioselective higher order [8 + 2]-cycloaddition with azaheptafulvenes using a chiral amino acid derived amidophosphine as catalyst, providing the corresponding azaazulenoid cycloadducts with excellent levels of regio-, diastereo-, and enantioselectivities. In this reaction, the activated allylic phosphonium ylide intermediate participates as the C2-component of the reaction, in contrast to the conventional reactivity of this type of zwitterionic intermediates as C3-components in cycloaddition reactions.