N-N bond and ring contraction. 4-Methylphthalazinone thus reduced to

A ring contraction occurs during the reduction of7-chloro-2-methylamino-5-phenyl3H-4,5-dihydro-l ,4-benzodiazepine to 6-ch\oro-2-methyl-4-phenyl-3,4-dihydroquinazo-\ine [157). It has been suggested (51) that the cleavage occurs between C-3 and N-4, although another interpretation has also been offered [157].