FRIEDEL-CRAFTS CYCLISATIONS .2. FURTHER STUDIES OF POLYPHOSPHORIC ACID-CATALYSED CYCLISATIONS OF N-CINNAMOYL DERIVATIVES OF AROMATIC AMINES

Further studies of the effects of substituents in the N‐phenyl nucleus on the polyphosphoric acid‐catalysed cyclisation of cinnamanilide to 4‐phenyl‐3,4‐dihydrocarbostyril have confirmed that the isomerisation is prevented by a nitro group and retarded by other substituents in the ortho position to the NH‐ group. Although a methyl group ortho to the only position at which cyclisation can occur was also shown to retard the reaction, N‐cinnamoyl‐2,4,5‐trichloroaniline was cyclised in moderate yield after prolonged heating, but the 2,4‐dibromo and 2,5‐dimethoxy analogues were not isomerised. Isomerisation of 2‐cinnamamidobiphenyl to 4,8‐diphenyl‐3,4‐dihydrocarbostyril was accompanied by cyclodehydration to 6‐styrylphenanthridine. Five new derivatives of cinnamanilide and eight new derivatives of 4‐phenyl‐3,4‐dihydrocarbostyril are described. Copyright © 1969 Journal of Heterocyclic Chemistry