Synthesis of naphtho[1,2‐ b ]‐, naphtho[2,1‐ b ]‐, and naphtho[2,3‐ b ]azepinones via proton‐induced cyclization of N ‐1(2)‐naphthyl styrylacetamides

On heating in polyphosphoric acid, N ‐1‐naphthyl styrylacetamides undergo proton‐induced intramolecular cyclization at position 2 of the naphthyl ring to provide 5‐aryl‐1,3,4,5‐tetrahydro‐2 Н ‐naphtho[1,2‐ b ]azepin‐2‐ones, while their N ‐2‐naphthyl analogues, when similarly reacted, are cyclized at positions 1 and 3 of the naphthyl ring and at the amide nitrogen atom leading, respectively, to 1‐aryl‐1,2,3,5‐tetrahydro‐4 Н ‐naphtho[2,1‐ b ]azepin‐4‐ones, 5‐aryl‐1,3,4,5‐tetrahydro‐2 Н ‐naphtho[2,3‐ b ]azepin‐2‐ones, and 5‐aryl‐1‐(2‐naphthyl)pyrrolidin‐2‐ones.