A novel C–N cleavage in isoquinolines allowing the first direct transformation of 1-benzylisoquinolines into benzo[c]phenanthridines and a new route to 2-phenyl-1,4-naphthoquinones

Treatment of N-carbethoxy-1-benzylideneisoquinolines with LDA gives N-ethoxycarbonyl-1-amino-1-(2-vinylphenyl)-2-phenylethylenes, which can easily be transformed into N-carbethoxy-1-amino-2-phenylnaphthalenes. Bichler–Napieralski reaction of these latter compounds affords the corresponding benzo[c]phenanthridines, while their hydrolysis and subsequent oxidation constitutes a route to 2-phenyl-1,4-naphthoquinones.