Synthesis of isoquinolines by electrophilic ring closure of iminoalkynes

Abstract

A variety of substituted isoquinolines have been synthesized in good to excellent yields by the electrophilic ring closure of iminoalkynes in the presence of various external electrophiles. The best results were obtained with •an excess of the electrophile, plus 3 equiv of sodium bicarbonate as a base when needed, at room temperature with either acetonitrile or methylene chloride as the solvent. This electrophilic ring closure is highly effective when an aryl-or alkenyl-substituted alkyne is utilized. Other acetylenes fail to undergo this ring closure. Mono-substituted isoquinolines have been prepared in good to• excellent yields by the silver-catalyzed cyclization of various iminoalkynes. The best results were obtained using 5 mol % silver nitrate at 50 °C in chloroform. Aryl-, vinylic-, and alkyl-substituted iminoalkynes undergo this. silver-catalyzed cyclization in excellent yields.