Unveiling Hetero‐Enyne Reactivity of Aryliminoboranes: Dearomative Hetero‐Diels–Alder‐Like Reactions.

Being isoelectronic with alkynes, iminoboranes with a polar B≡N triple bond have been exclusively investigated as a potent 1,2‐dipole in synthetic chemistry. Herein, we disclose the unprecedented reactivity of aryliminoboranes via the BNCC π conjugation, namely hetero‐enyne behavior. This allows for facile dearomative Diels–Alder‐like reactions of aryliminoboranes with aldehydes. This cycloaddition features mild conditions, is catalyst‐free, and has a broad substrate scope and good functional group tolerance. Kinetic and computational studies reveal its second‐order reaction and concerted cyclization mechanism. This report unveils new synthetic application of iminoboranes beyond their classical reaction patterns. [ABSTRACT FROM AUTHOR]