Phosphine-catalyzed β′-umpolung addition of nucleophiles to activated α-alkyl allenes

Highly functionalized alkenes can be prepared through phosphine-catalyzed β′-umpolung additions of nucleophiles (carbon-, oxygen-, nitrogen-, and sulfur-centered) to activated α-disubstituted allenes, providing many potentially useful synthetic intermediates in good to excellent yields, often with high levels of stereoselectivity for the product olefin geometry. Various substitution patterns around the allene are compatible with the process, showcasing the synthetic utility of allenes under the conditions of nucleophilic phosphine catalysis.