Quantum Chemical Study of the Cycloaddition Reaction of Tropone with 1,1-Diethoxyethene Catalyzed by B(C(6)F(5))(3) or BPh(3)

[Image: see text] Cycloaddition reaction of tropone with 1,1-diethoxyethene catalyzed by Lewis acid (LA), B(C(6)F(5))(3) or BPh(3), was examined by using ωB97X-D-level density functional theory (DFT) calculations. In the absence of LA, the reaction proceeds in a stepwise fashion to form two chemical bonds, first between the C(2) atom in tropone and the C(2) atom in ethene and then between the C(5) atom in the former and the C(1) atom in the latter. When B(C(6)F(5))(3) is attached to the O atom in tropone, the C(5) atom in tropone is attacked preferentially by the C(1) atom in ethene in the second stage. The attack of the O atom in tropone is shown to be less likely; thus, the [4 + 2] addition is favored in the B(C(6)F(5))(3)-catalyzed reaction. In contrast, the attack of the O atom in the BPh(3)-attached tropone to the C(1) atom in ethene is preferred over the attack of the C(5) atom, indicating that the [8 + 2] cycloaddition instead of the [4 + 2] cycloaddition proceeds in the BPh(3)-catalyzed reaction. Whether the C(1) atom in ethene is attacked by C(5) or by O in the second bond formation step is shown in this study to be governed mainly by the nucleophilicity of σ-lone pair electrons of the carbonyl O atom of tropone in the presence of LA. These results are consistent with the experiments reported by Li and Yamamoto.