A Nitrilium-Type N-Heterocyclic Aryne

The first solution-phase synthesis and reactivity of a nitrilium-type N-hetaryne are described. The 1,2-azaborine-derived 1,6-BN-aryne 2 exhibits [4+2], [3+2], and [2+2] cycloadditions and electrophilic aromatic substitution (EAS) reactivity. The observed regio- and diastereoselectivity of the cycloaddition and EAS products are consistent with a polarized aryne/nitrilium species. A Lewis structure description where the 1,6-BN-aryne 2 resonates between two limiting forms (ketenimine vs. nitrilium) is consistent with DFT calculations. New 1,2-azaborine structures that are functionalized at the C6- and N-positions, including highly strained derivatives that are previously not accessible, can now be accessed using 1,6-BN-aryne 2 as a versatile synthetic building block.