Methoxide Promoted Anionic Cyclization of 2-Alkynylbenzonitrile:A New Synthesis of 3-Substituted Isoqunolin-1-one

The treatment of 2-(2-alkylethynyl)benzonitrile with sodium methoxide in methanol gave 3-alkyl-l(2H)-isoquinolinone in modest yield. Under the same reaction conditions methanolysis of 2-(2-arylethynyl)benzonitrile lead to the formation of 3-alkylidene isoindol-1-one. Partially hydrolysis of 2-(l-hexynyl)benzonitrile to the corresponding benzamide,followed by the treatment of the benzamide with sodium methoxide gave 3-pentylidene isoindol-1-one in 11% yield. This result suggests that benzamide is not the intermediate of the formation of isoquinolinone. The more plausible mechanism of this methanolysis process is involving the iminium anion cycloaromatization to form 2-methoxyisoquinoline and subsequent hydrolyze to isoquinolinone. In one case,2-methoxyisoquinoline product was isolated.