Synthesis of Cyclopentadienols by Rhodium-Catalyzed C–H Activation of 8-Formylquinolines and [2+2+1] Carbocyclization with Alkynes

An efficient Rh(III)-catalyzed redox-neutral [2+2+1] coupling between 8-formylquinolines and alkynes has been realized for the synthesis of cyclopentadienols with broad substrate scope and functional group tolerance. The reaction occurs via C (acyl)–H activation with double insertion of the alkyne in high atom-economy. Instead of simply undergoing a [2+2+1] cyclization, a subsequent formal intermolecular 1,5-shift of the hydroxyl group is involved, which affords a thermodynamically more stable, conjugated cyclopentadienol.