Mechanistic Investigation of Copper-Catalyzed Three-Component Synthesis of Quinazoline Derivative: A DFT Study

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Quinazoline derivatives are a biologically significant class of nitrogen heterocycles with wide-ranging pharmacological relevance, motivating continued interest in efficient, mild, and modular synthetic routes. In this study, density functional theory (DFT) calculations were used to clarify the mechanism of the CuI/L-proline–catalyzed three-component reaction of 2-bromobenzaldehyde, benzylamine, and sodium azide reported to afford quinazoline derivatives under aerobic conditions. Free-energy profiles computed with an M06-based protocol in implicit DMSO were used to evaluate two competing sequences: (A) initial azide nucleophilic aromatic substitution (SNAr) on the o-bromobenzaldehyde followed by amine addition/imine formation, and (B) initial hemiaminal/imine formation followed by azide substitution and cyclization. Pathway A is favored both kinetically and thermodynamically, with the turnover-limiting SNAr step requiring ΔGsp ≈ 23.8 kcal/mol. Subsequent benzylamine addition is facilitated by an amine-assisted proton shuttle (ΔGsp ≈ 15.0 kcal/mol), while copper/oxygen participation lowers the barriers for dehydration and benzylic hydride abstraction (each ΔGsp ≈ 19.7 kcal/mol) and enables rapid intramolecular ring closure (ΔGsp ≈ 5.2 kcal/mol), followed by product release (ΔGsp ≈ 18.3 kcal/mol). In contrast, Pathway B is disfavored due to a high dehydration barrier (ΔGsp ≈ 34.3 kcal/mol) and energetically inaccessible alternatives, including the previously proposed Cu–C bonded intermediate (ΔGsp ≈ 44.8 kcal/mol). Overall, the calculations support an azide-first mechanism and rationalize the essential roles of CuI/L-proline and O₂ in stabilizing charged intermediates and enabling efficient quinazoline assembly. These findings provide mechanistic clarity on copper’s catalytic role and offer guidance for the rational design of improved synthetic routes toward quinazoline derivatives.

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Related topics: Quinazolinone synthesis and applications · Asymmetric Hydrogenation and Catalysis · Click Chemistry and Applications