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.