Highly enantioselective synthesis of γ-substituted butenolides via the vinylogous Mukaiyama-Michael reaction catalyzed by a chiral scandium(III)-N,N'-dioxide complex.

A highly efficient catalytic asymmetric vinylogous Mukaiyama-Michael reaction of the 2-silyloxyfuran with chalcone derivatives, catalyzed by a chiral N,N'-dioxide-scandium(III) complex, has been accomplished which tolerates a wide range of substrates. The reaction proceeds with complete regioselectivities, excellent diastereoselectivities (up to >99 : 1 dr) and good to excellent enantioselectivities (up to 94% ee) under mild conditions, delivering highly functionalized enantiomerically enriched anti-γ-substituted butenolides. The process is air-tolerant and easily manipulated with available reagents. In order to illustrate the synthetic potential of this reaction, the gram-scale synthesis and the elaboration of the butenolides have been explored. On the basis of the experimental results, a possible catalytic cycle and favorable stereorecognition model have been proposed.