Lewis base catalyzed aerobic oxidative intermolecular azide-zwitterion cycloaddition

Abstract

The discovery of a novel aerobic oxidative intermolecular azide-zwitterion reaction catalyzed by an organocatalyst is presented. It is demonstrated that the merger of the Lewis base 1,8-diazabicyclo[5.4.0]undec-7-ene and electron-deficient olefins generates reactive zwitterion intermediates, which readily participate in cycloaddition reactions with an array of azides, thus providing facile entry to fully or highly substituted 1,2,3-triazole frameworks. The reaction features an excellent substrate scope, and the products are obtained with high yields and excellent regioselectivities. It is demonstrated that some of these products can be transformed into pharmaceutically important agents. In addition to the experimental results, a detailed mechanistic survey is also provided, including MS studies rationalizing the origin of regioselective control.

Keywords: Lewis base; azides; cycloadditions; organocatalysis; zwitterions.