Stereochemical aspects of base-promoted reactions of o-alkenyl substituted arylhydrazonoyl chlorides with triphenylphosphine

The title arylhydrazonoyl chlorides treated with Et₃N and PPh₃ give arylazomethyl-enetriphenylphosphoranes and, in some cases, products of intramolecular cyclization (cyclopropacinnolines and benzodiazepines). A high concentration of base and a polar solvent accelerate all the observed reactions. In the presence of PPh₃ a low reaction temperature and a non polar solvent favour the formation of the phosphoranes over the cyclization reaction. The steric configuration of phosphoranes and cyclopropacinnolines is determined by the relative stability of the two isomers.