Phosphine-Catalyzed Internal Redox [4 + 2] Annulation between 1,4-Enynoates and Electron-Deficient Alkenes

Herein we describe a phosphine-catalyzed internal redox [4 + 2] annulation of 1,4-enynoates with electron-deficient alkenes, in which the γ- and φ-C(sp3)-H of the enynoates are formally oxidized for the annulation while the alkynyl moiety is converted to an alkene. The reaction offers an efficient synthesis of highly functionalized cyclohexenes in moderate to good yields with exclusive regioselectivity and high diastereoselectivity under mild conditions.