Beyond HAT: harnessing TBADT for photocatalyzed Giese-type C(sp3)–C(sp3) bond formation through reductive decarboxylation

Abstract

The decatungstate anion as a tetrabutylammonium salt (TBADT) facilitates a variety of chemical transformations under mild conditions, primarily through hydrogen atom transfer (HAT) and marginally through single electron transfer (SET) mechanisms. This study explores the dual ability of TBADT to cleave C–H bonds and initiate SET processes, leading to efficient C(sp³)–C(sp³) coupling reactions. We address the main limitations of direct HAT by leveraging the doubly-reduced form of TBADT [W₁₀O₃₂]⁶⁻ to activate redox-active esters (RAEs), enabling the formation of alkyl radicals for Giese-type additions. An extensive screening of various hydrogen donors showed their pivotal role in the selective generation of the reduced form of TBADT and in suppressing any undesired C–H activation. Our optimized conditions, using γ-terpinene as the hydrogen donor, gave high yields in alkylations of various olefins, demonstrating the versatility and robustness of the proposed strategy. This methodology extends the application of TBADT in sustainable organic synthesis and in late-stage functionalization of complex molecules for the synthesis of pharmaceutical building blocks.