CuBr-Catalyzed Aerobic Decarboxylative Cycloaddition for the Synthesis of Indolizines under Solvent-Free Conditions

An
efficient synthesis of diversified indolizine derivatives was
developed via CuBr-catalyzed reaction of pyridines, methyl ketones
and alkenoic acids under solvent-free conditions in oxygen atmosphere.
This synthesis involves cascade processes of copper-catalyzed bromination
of the methyl ketone, 1,3-dipolar cycloaddition of the pyridinium
ylide with the alkenoic acid, followed by oxidative decarboxylation
and dehydrogenative aromatization of the primary cycloadduct. By this
protocol, a wide range of indoliznes with different substitution patterns
were selectively prepared in one pot from simple substrates in good
to excellent yields.