Application of Electrochemical Cross-Dehydrogenative Couplings in the Syntheses of Heterocycles

Abstract

Heterocycles are becoming ubiquitous in the modern chemistry nowadays. However, the synthesis of heterocycles remains challenging. Issues like simplicity, selectivity, environmental friendliness, and availability of starting materials are still key factors to be considered before planning for a synthesis. In the past three decades, the transition-metal-catalyzed cross-coupling and direct oxidative cross-coupling reactions have been commonly utilized for the construction of heterocycles. Although these strategies are efficient, the use of organic halides and organometallic reagents resulted in generating undesirable chemical wastes. Recently, cross-dehydrogenative coupling (CDC) or cross-coupling with hydrogen evolution has been recognized as a powerful tool for the synthesis and functionalization of heterocycles. The benefits of using electrochemical cross-dehydrogenative coupling method over conventional cross-couplings are the avoidance of reagent waste and the mild reaction conditions. The method maximizes atom efficiency by replacing stoichiometric redox reagents with electrical current. Majority of the electrochemical cross-dehydrogenative coupling reactions can be carried out at an ambient temperature. It is chemoselective and tolerates with many functional groups. In this chapter, an overview of the electrochemical CDC strategies for carrying out carbon–carbon (C–C), carbon–nitrogen (C–N), carbon–oxygen (C–O) bond formations as well as carbon–hydrogen (C–H) functionalization is presented with examples of reaction and mechanistic insight. This chapter is organized based on the aforementioned reaction types, and majority of information retrieved between those of 2000 and 2018 will hopefully serve as a useful reference to readers.