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

Abstract

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.

Cyclic (Alkyl)(Amino)Carbene-Iminoboryl Compounds with Three Formal Oxidation States

“…Iminoboranes, as the triply bonded B�N analogues of alkynes, can be isolated as persistent compounds in neutral, cationic, and anionic forms. 7−11 These species exhibit diverse reactivity, such as coordination, 8 1,2-dipolar addition, 9 cycloaddition, 10 and iminoborane−transfer reaction, 11 enabling them excellent synthons for constructing unusual organoboron compounds. However, iminoboranes are usually not redox-active for electron−transfer reactions, probably because of the relatively strong B�N triple bond, with both B and N atoms obeying the octet rule.…”