Stereoselective synthesis of all-cis boryl tetrahydroquinolines via copper-catalyzed regioselective addition/cyclization of o-aldiminyl cinnamate with B2Pin2.

A copper catalyzed intramolecular 1,2-carboboration of o-aldiminyl cinnamate has been realized in both regio- and stereoselective fashions. This reaction provides a convenient entry to highly valuable and otherwise challenging cis-2,3,4-trisubstituted tetrahydroquinolines carrying a 4-boryl group. An unusual non-Michael addition intermediate or alternatively, a cyclic enolate is proposed to account for the intriguing all-cis configuration in the final products.

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.