Reactions of 1-trifluoromethyl-prop-2-yne1-iminium salts with 2- and 3-aminopyridines

Abstract

Abstract 4-CF3-pyrido[1,2-a]pyrimidin-5-ium triflates could be prepared in fair to high yields from acetylenic iminium salts R-C≡C–C(CF3)=N+Me2·CF3SO3 − and 2-aminopyridinium triflate under thermal conditions. Their reactions with protic heteronucleophiles, leading to 4-CF3, 4-XR-substituted 1,4-dihydropyrido[1,2-a]pyrimidin-5-ium salts, have been studied and reversible addition as well as subsequent opening of the pyrimidine ring have been observed. The cyclocondensation of a 3-phenyl-propyniminium triflate and 3-aminoyridinium triflate required strong thermal activation and yielded a 4-CF3-and a 4-CF3,5-CH3-[1,7]naphthyridine. A 1-CF3-benzo[f][1,7]naphthyridine was obtained from the same propyniminium salt and 3-aminoquinolinium triflate.