Transition-Metal-Free Synthesis of Heterobiaryls through 1,2-Migration of Boronate Complex

Abstract

The synthesis of a diverse range of heterobiaryls has been achieved by a transition-metal-free sp² -sp² cross-coupling strategy using lithiated heterocycle, aryl or heteroaryl boronic ester and an electrophilic halogen source. The construction of heterobiaryls was carried out through electrophilic activation of the aryl-heteroaryl boronate complex, which triggered 1,2-migration from boron to the carbon atom. Subsequent oxidation of the intermediate boronic ester afforded heterobiaryls in good yield. A comprehensive ¹¹ B NMR study has been conducted to support the mechanism. The cross coupling between two nucleophilic cross coupling partners without transition metals reveals a reliable manifold to procure heterobiaryls in good yields. Various heterocycles like furan, thiophene, benzofuran, benzothiophene, and indole are well tolerated. Finally, we have successfully demonstrated the gram scale synthesis of the intermediates for an anticancer drug and OLED material using our methodology.

Keywords: 1,2-migration; boronate esters; electrophiles; heteroaryls; heterobiaryls.