Catalyst-free conjugate addition of 1-alkenylboronic acids to enones: a self-mediated sustainable protocol

Abstract

Catalyst-free 1,4-addition of 1-alkenylboronic acids to enones is reported. Contrary to conventional methodologies requiring Lewis acids or transition metals, we discovered that 1-alkenylboronic acids intrinsically mediate efficient conjugate additions (up to 95 % yield) without external catalysts. This reactivity stems from a dual activation mode: the boronic acid simultaneously acts as a nucleophile and a Lewis acidic activator, enhancing the electrophilicity of the enone carbonyl group. While brominated chalcones exhibited moderately reduced reactivity, the reaction proceeds cleanly with broad substrate tolerance and no observable byproducts. This method eliminates the need for metal catalysts—exemplified by the superior performance over cationic iron complexes (78 % vs. 95 % yield)—aligning with green chemistry principles through reduced resource consumption and waste generation. Our findings unveil an unprecedented role for boronic acids as self-sufficient mediators, offering a sustainable paradigm for ketone synthesis.