N-methyl-B-mesityldibenzo-1,4-azaborinine: the first experimental structure of a 1,4-azaborinine derivative

The structure of the 1,4-azaborinine ring in the title compound, a representative of a novel class of potentially aromatic compounds that are isoelectronic with arenes, confirms conclusions of earlier ab initio calculations that cyclic conjugation in 1,4-azaborinines is interrupted by the boron atom.