We have studied the reaction of allenylboronic acid pinacol ester with cyclopentadiene with experimental and computational methods. The reaction occurred efficiently with complete Diels–Alder periselectivity and regioselectivity at the proximal double bond. The concerted mechanism for the observed transformation was computed to be favored over competitive addition to the distal double bond, [3,3]-sigmatropic rearrangements, and stepwise radical mechanism. This unprecedented Diels–Alder reaction enables the construction of synthetically versatile boron-substituted cycloadducts.

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Attempts to improve the organocatalytic Diels‐Alder reactions of vinylboronic compounds are described. Further experiments, theoretical calculations and NMR studies were performed to optimize the existing procedure and analyze the reactivity of the reactive intermediate and the ligand‐exchange process. In particular, the relationship between the structure and the performance of the organocatalysts was studied theoretically and experimentally. Although the catalytic activity of the α‐hydroxy acids could not be improved much, a deeper insight has been gained, which might be useful for the development of other organocatalytic reactions of organoboron compounds.