Ring enlargement of 1-cyclopropyl and 1-(trans-2′-phenyl cyclopropyl)tetrahydroisoquinoline N-oxide derivatives

Thermolysis of the 1-(2′-phenylcyclopropyl)tetrahydroisoquinoline N-oxide derivative 3b in butyronitrile/mesitylene gave the 1,3,4,5-tetrahydro-2,3-benzoxazepine derivative 4b and the 2,3,5,6-tetrahydro-10,11-dimethoxy-3-methyl-5-phenyl-1H-4,3-benzoxazecine 5b, the first representative of the 4,3-benzoxazecine system, in low yield. The structure of 5b was confirmed by X-ray crystallography. Thermolysis of the 1-cyclopropyltetrahydroisoquinoline N-oxide derivative 3a gave only the 2,3-benzoxazepine derivative 4a.