Synthesis and properties of 3-chloro- and 3,7-dichloro-3,4-dihydro-1-hydroxycarbostyrils and related heterocyclic compounds

3-Chloro- and 3,7-dichloro-3,4-dihydro-1-hydroxycarbostyrils were synthesized by the catalytic hydrogenation of the α-chloro- and α,4-dichloro-β-(o-nitrophenyl)propionic acids in strong acidic solution over platinum-on-carbon sulfided catalyst. However, the catalytic hydrogenation of α-bromo-β-(o-nitrophenyl)propionic acid yielded 3,4-dihydro-1-hydroxycarbostyril under the same experimental conditions. The 3-chloro-3,4-dihydro-1-hydroxycarbostyril and the α-chloro-β-(o-nitrophenyl)propionic acid underwent facile dehydrochlorination in mild alkaline solution to give 1-hydroxycarbostyril and o-nitrocinnamic acid, respectively. Selective reduction of 3-chloro-3,4-dihydro-1-hydroxycarbostyril and 1-hydroxycarbostyril to the corresponding lactams, 3-chloro-3,4-dihydrocarbostyril and carbostyril, was effected by catalytic hydrogenation in hydrochloric acid over platinum black catalyst. The structures of the substituted carbostyril derivatives were correlated with their proton nmr spectra.