Unexpected pyrazolo[4,3-d][2,3]benzodiazepine synthesis from 1-(N,N-diaroyl)amino-4-phenyl-[1,2,3]triazol-5-yl-methyltriphenylphosp honium bromide via tandem phosphorylide formation and subsequent Dimroth-like rearrangement of the triazole ring

Article abstract of DOI:10.1016/0040-4039(95)01034-f

1-(N,N-diaroyl)amino-4-phenyl-1,2,3-triazol-5-yl-methyltriphenylphosph onium bromide 2 reacted with potassium t-butoxide or triethylamine in dry toluene giving the very stable phosphorus ylide 5. Refluxing of 5 in xylene gave the unexpected 3-aroyl-6-aryl-pyrazolo[4,3-d][2,3]benzodiazepines 6 by a Dimroth-like rearrangement of the triazole ring and a 1,7-electrocyclization of the nitrilimine intermediate 11. When the xylene solution was not rigorously refluxed the 3(5)-aroyl-5(3)-phenyl pyrazole 7 was isolated. The x-ray crystal structures of compounds 5d and 6b are also given.