Rhodium-Catalyzed Asymmetric Dearomative [4 + 3]-Cycloaddition of Vinylindoles with Vinyldiazoacetates: Access to Cyclohepta[b]indoles

A rhodium-catalyzed enantioselective formal [4 + 3]-cycloaddition of vinylindoles with vinyldiazoacetates has been developed, affording the dearomative cyclization products containing a newly formed seven-membered ring in up to 99% ee. Rh₂( S-DOSP)₄ has been proven to be the best catalyst for the cycloaddition of 3-vinylindoles with vinyldiazoacetates, whereas Rh₂( S-TCPTTL)₄ has enhanced the enantioselectivity for 2-vinylindoles.