Mechanism study of the intramolecular anti-Michael addition of N-alkylfurylacrylacetamides.

The mechanism of the intramolecular nucleophilic addition of N-alkylfurylacrylacetamides is investigated by density functional theory calculations. Three possible reaction pathways have been considered based on possible conformations of the same reactant, which undergoes three stages, including hydrogen elimination by the base NaH, followed by the nucleophilic addition of N(-) on C(α) (C(β)) via an anti-Michael (Michael) mechanism, and then proton transfer affords the final product Pr-5 (Pr-6). The pathway corresponding to the reactant with the most stable conformation is found to be the most favorable one. The rate-determining step of the intramolecular nucleophilic addition is the nucleophilic addition of N(-) on C(α) (C(β)) featuring a cyclic ring transition state. Solvent effects are considered at the B3LYP/6-31G(d,p) level in solvent DMSO, and the results suggest that the relative reaction trends are consistent with the gas-phase reaction. Furthermore, the difference of the energy barriers explains the origin of the regioselectivity of the experiment. Finally, the effects of the substituent on N1 and C(β) to the regioselectivity have been discussed.

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