Successive construction of polycyclic molecules: Ethyl 1,2,3,5,6,7-hexahydroimidazo[1,2-a]pyridine-8-carboxylate for the synthesis of imidazonaphthyridines, -azocines, tri- and tetraazaacenaphthylenes and triazacyclooct[cd]indenes

Article abstract of DOI:10.1055/s-1993-25811

The imidazo[1,2-a]pyridine 1 gives with acetylenic esters the (imidazo[1,2-a]pyridin-8-yl)maleates 2a,b, the 4-oxoimidazo[1,2,3-ij][1,8]naphthyridines 3a-c, and imidazo[1,2-a]azocine-8,9,10-tricarboxylates 7a,b, respectively, depending on the conditions applied. Compound 1 affords with dimethyl allene-1,3-dicarboxylate analogously methyl 2-(1,2,4,7,8,9-hexahydro-4-oxoimidazo[1,2,3-ij][1,8]naphthyridin-6- yl)acetate (3d). Treatment of 1 and 7b with isocyanates affords the heterocondensed 3,5-dioxo-2a,4,8a-triazaacenaphthylenes 9a-d and 3,5-dioxo-2a,4,10a-triazacyclooct[cd]indenes 10a,b. Analogously, 1,2,3,4,5,6,7,8-octahydro-3,5,6,8-tetraoxo-4,7-diphenyl-2a,4,7,8a- tetraazaacenaphthylene (12) results from dimethyl (imidazolidin-2-ylidene)malonate (11). 2,5-Dihydro-4H-1,2,4-triazole-3,5-dione 13 inserts in the 5-C-H bond of 3a,b d to give 5-(1,2,4-triazolidin-1-yl)imidazo[1,2,3-ij][1,8]naphthyridines 14a,b,d.