Computational studies on the reactivity of substituted 1,2-dihydro-1,2-azaborines.

We have investigated important intermediates of electrophilic aromatic substitution reactions and one-electron oxidation of substituted 1,2-dihydro-1,2-azaborines with density-functional theory. The results show that electrophilic substitution reactions and one-electron oxidation of substituted 1,2-azaborines are generally much more favorable than those of the corresponding benzene derivatives. Both chlorination and nitration of several boron-unsubstituted 1,2-azaborines are expected to break the boron-hydrogen bond, yielding boron-chlorinated 1,2-azaborines and a novel class of boron-bound 1,2-azaborinyl nitrites, respectively. Comparison between the relative stabilities of C(3)-bound and C(5)-bound Wheland intermediates of different electrophilic substitution reactions of 1,2-azaborines further suggests that the preference of the C(3)- over C(5)-substitution decreases with decreasing electrophilicity of the attacking group.