1-Methyl-1-azacyclohexa-2,3-diene(N−B)borane − Generation and Interception of an Unsymmetrical Isodihydropyridine

3-Bromo-1-methyl-1,2,5,6-tetrahydropyridine(N−B)borane (7) was prepared from 3-bromopyridine by conversion to 3-bromo-1-methylpyridinium iodide, hydrogenation of the latter with sodium tetrahydroborate and treatment of the resulting 3-bromo-1-methyl-1,2,5,6-tetrahydropyridine (6) with borane−dimethyl sulfide. Whereas no trapping product of the possible intermediate 1-methyl-1-azacyclohexa-2,3-diene (4) could be observed on treatment of 6 with potassium tert-butoxide in the presence of furan, the subjection of 7 to the same conditions produced the hexahydroepoxyquinoline derivatives 8a−c. Treatment of 7, dissolved in styrene, with sodium bis(trimethylsilyl)amide furnished the hexahydrocyclobutapyridine derivatives 9a−c. The six-membered cycloallene 1-methyl-1-azacyclohexa-2,3-diene(N−B)borane (10) must be regarded as the key intermediate en route to 8 and 9.