Abstract
The mechanism is investigated for Rh(III)-catalyzed C-H alkenylation of enamide with enone and Rh(I)-catalyzed decarbonylative version of 1,2,3,4-tetrahydroquinoline with anhydride. The former contains β-C(sp2)−H activation of enamide, 1,2-migratory insertion of enone, β-hydride elimination or protodemetalation with additional HCl. The diastereoselectivity is kinetically controlled favoring alkenylation N-(2Z,4E)-butadiene while the regio-divergence is switchable to alkylation. The latter is composed of rate-limiting oxidative addition of anhydride to Rh(I), C8-selective C–H activation after ligand exchange producing tBuCO2H and six-membered rhodacycle, decarbonylation releasing CO as new carboxylate ligand and reductive elimination of Rh-alkenyl precursor leading to C8-alkenylated product. The whole process with huge heat release is favorable thermodynamically and all barriers capable to overcome under microwave assistance. The positive solvation effect is suggested by decreased absolute and activation energies in solution compared with in gas. These results are supported by Multiwfn analysis on FMO composition of specific TSs, and MBO value of vital bonding, breaking.
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