Two Faces of Styrylsulfonium Salts: Domino Michael Addition/Cyclopropanation of 2-(2-Acylvinyl)indoles for the Synthesis of Cyclopropa[3,4]pyrrolo[1,2-<i>a</i>]indoles

We report a domino reaction of 2-(2-acylvinyl)indoles as well as the corresponding pyrroles with styrylsulfonium salts under mild conditions, affording cyclopropamitosene analogues in high yields and complete diastereoselectivity. A wide range of (<i>E</i>)-β-hetaryl-α,β-unsaturated ketones were successfully employed for the synthesis of potentially bioactive cyclopropa[3,4]pyrrolo[1,2-<i>a</i>]indoles and related cyclopropa[<i>a</i>]pyrrolizines, demonstrating the versatility of the developed method. In contrast, (<i>Z</i>)-isomers of the substrates fail to give cyclopropamitosene derivatives but undergo cyclopropanation of the terminal methyl group.