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