A Novel Synthesis of N-Styryl Heterocycles

Abstract

Reaction of the anions of a variety of 2-carboethoxy N-heterocycles with styrene oxide yields directly the N-(trans-2-styryl)-2-carboxylic acids. The reaction has been shown to proceed through a lactone intermediate which undergoes rapid elimination to form the unsaturated acid. The reaction has been used to alkylate 2-carboethoxy pyrrole, diethyl pyrazole-3,5-dicarboxylate, ethyl indole-2-carboxylate, ethyl benzimidazole-2-carboxylate, and ethyl 2-pyrrolidone-5-carboxylate. Yields were 82, 88, 93.5, 57, and 5% respectively.1-(trans-2-Styryl)benzirnidazole-2-carboxylic acid of m.p. 75–77 °C undergoes an interesting, reversible solid-state transformation to a high melting (255–260 °C), presumably zwitterionic, form.