Microwave-assisted synthesis of pyridylpyrroles from N-acylated amino acids

A small library of 3- and 4-pyridyl-substituted pyrroles was prepared from N-acylated amino acids. Nicotinoyl or isonicotinoyl chloride was used for the N-acylation of benzyl esters of amino acids. Debenzylation by palladium-catalyzed hydrogenation gave N-acylated amino acids. Dehydration of the acylated amino acids gave cyclic intermediates, münchnones or azlactones, which were treated in situ with alkynes in 1,3-dipolar cycloadditions. The starting materials were prepared in a parallel fashion, and microwave irradiation was used to facilitate the cycloaddition reactions. The regiochemistry of the cycloaddition was studied.