Synthesis of new heterocycles: Part XXVIII. Syntheses of condensed imidazoles

Abstract

Reaction of imino ethers Ila, lib, VI, IX and methylmercapto compounds Xlla and XIIc with aminoacetal, followed by treatment with HC1 affords imidazo[2,l-c][l,4]thiazine (IVa), imidazo[2,l-d][l,4]thiazepine (IVb), imidazo[2,l-a]pyrazine (VIII), imidazo[l,2-a]azepine (X), imidazo[l,2-a]imidazole (XHIa) and imidazo[l,2-a]pyrimidine (Xlllb) respectively. IVa and IVb are oxidized by acetic acid-hydrogen peroxide to the sulphones Va and Vb respectively; while nitration of XHIa and Xlllb gives the mononitro derivatives XlVa and XlVb. Treatment of 2-mercaptoimidazole with ethylene dibromide affords imidazo[2,l-b]thiazole (XVa),'which is further nitrated to the nitro compound XVb and then oxidized to the sulphone XVI. Several alicylic ketones and N-substituted piperidones have been condensed with histamine to give 7-spirocyclic imidazo[4,5-c]pyridines (XVIIIa-j, XX and XXI). Histamine and histidine are converted to their 5-nitro derivatives XVIId and XXV respectively. Interaction of XVIId with aromatic aldehydes yields imidazo[l,5-c]pyrimidines (XXIIIa-g).