Rh(III)-Catalyzed and Solvent-Controlled Chemoselective Synthesis of Chalcone and Benzofuran Frameworks via Synergistic Dual Directing Groups Enabled Regioselective C–H Functionalization: A Combined Experimental and Computational Study

Abstract

By virtue of a synergistically dual-directing-group (the O–NHAc part and the hydroxyl group)-assisted strategy, the efficient and practical Rh(III)-catalyzed regioselective redox-neutral C–H functionalization of diverse N-phenoxyacetamides with propargyl alcohols has been realized, which led to the divergent synthesis of privileged benzofuran and chalcone frameworks in a solvent-controlled chemoselective manner. Experimental and computational studies reveal that the formation of the hydrogen bonding between dual directing groups and the subsequent coordination interaction between the hydroxyl group and the Rh(III) catalyst play a decisive role in promoting the regioselective migratory insertion of the alkyne moiety. Thereafter, two solvent-controlled switchable reaction pathways, which respectively involve tandem β–H elimination/hydrogen transfer/oxidative addition/C–O bond reductive elimination/oxidation (for low-polar solvents: path I–Ia via a RhIII–RhI–RhIII pathway) and oxidative addition/β–H elimination/hydrogen transfer/protonolysis (for high-polar solvents: path II–IIb via a RhIII–RhV–RhIII pathway), are followed to deliver the corresponding products with excellent chemoselectivity. Taken together, our results presented here not only give an expansion in the area of O–NHAc-directed C–H activations but also provide a rational basis for future development of synergistic dual DGs-enabled C–H functionalization reactions.