Perkin communications. Heterocyclic [4++ 2] cycloadditions: the reactivity of pyridinium salts with electron-rich olefins

Abstract

The N-(2,4-dinitrophenyl) salts of N,N-diethylnicotinamide and ethyl nicotinate undergo [4++ 2] cycloaddition with enol ethers at room temperature, providing the first examples of Bradsher cyclization by monocyclic quaternary aza-aromatics; other derivatives and salts of pyridine are inert under these conditions.