Rhodium-catalyzed C–H functionalization of cyclohexadiene
derivatives with diaryldiazomethanes followed by oxidation with DDQ
provides ready access to triarylmethanes. Two chiral dirhodium tetracarboxylates,
Rh2(S-PTAD)4and Rh2(S-TPPTTL)4, were found to be the optimum
chiral catalysts for these transformations. This method showcases
the ability of diaryldiazomethanes to perform intermolecular C–H
insertion with high enantioselectivity and good yields. The method
has a broad substrate scope, leading to triarylmethane products with
a variety of aryl and heteroaryl substituents, including benzofuran
and pyridine heterocycles.