Benzazole-N(SINGLE BOND)BH3 adducts. Reductive transposition of 2-benzimidazole, 2-benzothiazole, and 2-benzoxazole N(SINGLE BOND)BH3 adducts to 1,3,2-benzimidazaborole, 1,3,2-benzoxaborole, and 1,3,2-benzothiazaborole

1,3,2-Benzimidazaborole, 1,3,2-benzoxaborole, and 1,3,2-benzothiazaborole were synthesized from the corresponding 2-benzazole N(SINGLE BOND)BH3 and 2-benzazole S(SINGLE BOND)BH3 adducts through a reductive transposition from the isolobal fragment X(SINGLE BOND)C(sp2) (DOUBLE BOND) N(sp2) (SINGLE BOND) B(sp3) (X (DOUBLE BOND) N, O, S) to the fragment X(SINGLE BOND)B(sp2) (DOUBLE BOND) N(sp2) (SINGLE BOND) C(sp3). N(SINGLE BOND)BH3 substitution shifts to lower frequencies 4-H, C-3a, and C-7a resonances. The X-ray diffraction analysis of 2-(o-methoxyphenyl)benzothiazole N(SINGLE BOND)BH3 adduct is reported. Two new tetracyclic boron-bridged compounds were observed as by-products (6,9-(ethyl)-diaza-2-oxa-1-bora[3,4,7,8]-dibenzobycyclo[4.3.0]-nona-3,7-diene, 6d, and 8-aza-9-oxa-2-thia-1-bora-[3,4,7,8]dibenzobycyclo[3.4.0]nona-3,7-diene, 15d, when 2-(o-methoxyphenyl)-1-ethylbenzimidazole-BH36b and 2-(o-methoxyphenyl)-benzothiazole-BH315b adducts were heated