Bifunctional Phosphine-Catalyzed Domino Reaction: Highly Stereoselective Synthesis of <i>cis</i>-2,3-Dihydrobenzofurans from Salicyl <i>N</i>-Thiophosphinyl Imines and Allenes

A new bifunctional phosphine catalyst, (2′-hydroxy-biphenyl-2-yl)-diethylphosphane (LBBA-1), was developed for the highly stereoselective synthesis of cis-2,3-dihydrobenzofurans via an aza-Morita−Baylis−Hillman/umpolung addition domino reaction of salicyl N-thiophosphinyl imines with electron-deficient allenes. Dual activation of both nucleophile and electrophile by the bifunctional catalyst accounts for the observed high reactivity and stereoselectivity.