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

Abstract

1-(N,N-Diaroyl)amino-4-phenyl-1,2,3-triazol-5-yl-methyltriphenylphosphonium 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-arylpyrazolo[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. Phosphonium bromides 2 on treatment with a base in dry toluene gave the stable phosphorylides 5 , which upon refluxing in xylene gave in good yields the pyrazolo[4,3-d][2,3]benzodiazepines 6 .