Bifunctional phosphine-catalyzed domino reaction: highly stereoselective synthesis of cis-2,3-dihydrobenzofurans from salicyl N-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.