Phosphine-catalysed asymmetric dearomative formal [4+2] cycloadditions of 3-benzofuranyl vinyl ketones

Abstract

In contrast to the catalytic asymmetric dearomative reactions of indole substrates, those of the analogous benzofuran derivatives have been less explored. Here we report that the stereoselective domino Rauhut–Currier/Michael addition process of 3-benzofuranyl vinyl ketones and 3-olefinic (7-aza)oxindoles can be realised via catalysis by a chiral bifunctional phosphine, furnishing the previously unreported direct asymmetric dearomative reaction of benzofuran substrates tethered to a carbonyl group in a formal [4+2] cycloaddition manner. An array of hydrodibenzofuran derivatives with dense substitutions is generally constructed with excellent diastereoselectivity and enantioselectivity (up to >19 : 1 dr, >99% ee).