Reactions of Acetylenecarboxylic Esters with Nitrogen-Containing Heterocycles

This chapter describes the reactions of acetylenecarboxylic esters with nitrogen-containing heterocycles. Some reactions of dimethyl acetylenedicarboxylate (DMAD), the corresponding diethyl ester (DEAD), methyl (MP) and ethyl propiolates (EP), and ethyl phenylpropiolate (EPP) take place with reasonable certainty through each of radical, ionic, and concerted pathways. Reactions between nitrogen-containing heterocycles and acetylenic esters often lead to complex mixtures, which may require chromatography and great experimental skill for successful resolution. The products sometimes depend on the precise conditions employed, and on the purity of the reactants or solvents. The choice of solvent can be important. Thus, ether and tetrahydrofuran give different results for the combination of DMAD with 1-methylbenzotriazole. The products obtainable from indoles and quinazolines are particularly dependent on the reaction conditions and purity of the solvent. The chapter discusses compounds from six-membered ring heterocycles containing only nitrogen as heteroatom, five-membered rings containing only nitrogen as heteroatom, four-membered ring nitrogen-containing heterocycles, and three-membered ring nitrogen-containing heterocycles.