Periselectivity and ambimodal transition states in cycloadditions of tetrachloro-o-benzoquinone with 6,6-dimethylfulvene.

The reaction mechanism of cycloadditions of tetrachloro-o-benzoquinone with 6,6-dimethylfulvene were systematically investigated with density functional theory calculations. It was found that conditional primary interactions stabilize the ambimodal transition states in the endo pathways. Ambimodal transition states lead to [6 + 4]/[4 + 2] adducts or [4 + 2]/[2 + 4] adducts, which interconvert through 3,3-sigmatropic shift reactions. The substituent effects on periselectivity were also investigated.