Synthesis of peri-fused indolizines and azaindolizines by intramolecular 1,3-dipolar cycloaddition of 3-(phenylpropynoyloxyalkyl)pyridine N-ylides

Abstract

Treatment of 3-(phenylpropynoyloxymethyl)-N-aminopyridinium salt with potassium carbonate in methanol gave unexpectedly 4-methyl-2-phenylpyrazolo [1,5-a]pyridine and methyl 6- and 4-hydroxy-methyl-2-phenylpyrazolo[1,5-a]pyridine-3-carboxylates. Similar treatment of N-methoxycarbonyl-methyl-3-(phenylpropynoyloxymethyl)pyridinium salt again failed to give the intramolecular cycloaddition product. In contrast, the 3-[2-(phenylpropynoyloxy)ethyl], 3-[3-(phenylpropynoyloxy)propyl], and 3-[4(phenylpropynoyloxy)butyl] analogues underwent smooth intramolecular 1,3-dipolar cycloaddition to yield the tricyclic pyrazolo[1,5-a]pyridine and indolizine derivatives containing seven-, eight-, and nine-membered lactone rings.