Copper-Catalyzed Borylative Cyclization of Substituted N-(2-Vinylaryl)benzaldimines.

A t-BuOCu-initiated reaction sequence of styrene borometalation and intramolecular imine addition has been achieved using a Cu(OTf)2/dppf combination as catalyst. The product of this reaction cascade is a useful 2,3-disubstituted indoline bearing a versatile boryl moiety and is formed with sole cis-selectivity. To account for the observation of the exclusive formation of cis-stereoisomers, a transition state featuring copper-imine coordination is suggested. The application to the synthesis of antioxidant tetrahydroindenoindoles is described.