Unveiling the Significance of tert-Butoxides in Transition Metal-Free Cross-Coupling Reactions

Abstract

The astounding reactivity of tert-butoxides in transition metal-free coupling reactions is driving the scientific community towards a new era of environmental friendly, as well as cost-effective, transformation strategies. Transition metal-catalyzed coupling reactions generate hazardous wastes and require harsh reaction conditions, mostly at elevated temperature, which increases not only costs but also environmental concerns regarding the methodology. Tert-butoxide-catalyzed/mediated coupling reactions have several advantages and potential applications. They can form carbon–carbon, carbon–heteroatom, and heteroatom–heteroatom bonds under mild reaction conditions. Mechanistic insights into these reactions include both ionic and radical pathways, with the fate of the intermediates depending on the reaction conditions and/or additives used in the reactions. Among all of the known tert-butoxides, potassium tert-butoxide has pronounced applications in transition metal-free coupling reactions as compared to other tert-butoxides, such as sodium and lithium tert-butoxides, because of the higher electropositivity of potassium compared to sodium and lithium. Moreover, potassium tert-butoxide can act as a source of base, nucleophile and single electron donors in various important transformations. In this review, we provide an extensive overview and complete compilation of transition metal-free cross-coupling reactions catalyzed/promoted by tert-butoxides during the past 10 years.

Graphical Abstract

Tert-butoxide-mediated/activated cross-coupling reactions under the transition metal-free condition for benign organic transformation using a greener approach.