Role of Sterically Demanding Chiral Dirhodium Catalysts in Site-Selective C–H Functionalization of Activated Primary C–H Bonds

The influence of sterically demanding dirhodium tetracarboxylate catalysts on the site selectivity of C–H functionalization by means of rhodium carbene-induced C–H insertion is described. The established dirhodium tetraprolinate-catalyzed reactions of aryldiazoacetates cause preferential C–H functionalization of secondary C–H bonds as a result of competing steric and electronic effects. The sterically more demanding dirhodium tetrakis­(triarylcyclopropanecarboxylate) catalysts, exemplified by dirhodium tetrakis­[(R)-(1-(biphenyl)-2,2-diphenylcyclopropanecarboxylate)] [Rh2(R-BPCP)4], favor C–H functionalization of activated primary C–H bonds. Highly site-selective and enantioselective C–H functionalization of a variety of simple substrates containing primary benzylic, allylic, and methoxy C–H bonds was achieved with this catalyst. The utility of this approach has been demonstrated by the late-stage primary C–H functionalization of (−)-α-cedrene and a steroid.