Divergent synthesis of 5- and 4-(2,1-azaborine) substituted isoxazoles via regioselective [3 + 2] cycloadditions of nitrile oxides and B-ethynyl-1,2-azaborines

Abstract

Herein we report the highly regioselective synthesis of 5- and 4-(2,1-azaborine) substituted isoxazoles via [3 + 2] cycloaddition reactions between nitrile oxides and B-ethynyl-1,2-azaborines. 5-(2,1-Azaborine) substituted isoxazoles are favored in the absence of a catalyst, while 4-(2,1-azaborine) substituted isoxazoles are favored in the presence of a ruthenium catalyst. The reaction exhibits excellent regioselectivity, mild reaction conditions, high functional group tolerance and a broad substrate scope.