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‐2Н‐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‐4Н‐naphtho[2,1‐b]azepin‐4‐ones, 5‐aryl‐1,3,4,5‐tetrahydro‐2Н‐naphtho[2,3‐b]azepin‐2‐ones, and 5‐aryl‐1‐(2‐naphthyl)pyrrolidin‐2‐ones.