Treating azadiboriridines I (R = R1 = Me3C, R2 = Me3C, Me2CH) with BH3 in THF gave bicyclic adducts II (same R-R2). The structure of II (R = R1 = R2 = Me3C) was detd. by x-ray crystallog. Heats of formation of II (R = H, R1 = R2 = H, Me) were calcd. by ab initio methods.