Overturning Established Chemoselectivities: Selective Reduction of Arenes over Malonates and Cyanoacetates by Photoactivated Organic Electron Donors

The prevalence of metal-based reducing reagents, including metals, metal complexes, and metal salts, has produced an empirical order of reactivity that governs our approach to chemical synthesis. However, this reactivity may be influenced by stabilization of transition states, intermediates, and products through substrate–metal bonding. This article reports that in the absence of such stabilizing interactions, established chemoselectivities can be overthrown. Thus, photoactivation of the recently developed neutral organic superelectron donor <b>5</b> selectively reduces alkyl-substituted benzene rings in the presence of activated esters and nitriles, in direct contrast to metal-based reductions, opening a new perspective on reactivity. The altered outcomes arising from the organic electron donors are attributed to selective interactions between the neutral organic donors and the arene rings of the substrates

KO<i>t</i>Bu: A Privileged Reagent for Electron Transfer Reactions?

Many recent studies have used KO<i>t</i>Bu in organic reactions that involve single electron transfer; in the literature, the electron transfer is proposed to occur either directly from the metal alkoxide or indirectly, following reaction of the alkoxide with a solvent or additive. These reaction classes include coupling reactions of halobenzenes and arenes, reductive cleavages of dithianes, and S_RN1 reactions. Direct electron transfer would imply that alkali metal alkoxides are willing partners in these electron transfer reactions, but the literature reports provide little or no experimental evidence for this. This paper examines each of these classes of reaction in turn, and contests the roles proposed for KO<i>t</i>Bu; instead, it provides new mechanistic information that in each case supports the <i>in situ</i> formation of organic electron donors. We go on to show that direct electron transfer from KO<i>t</i>Bu can however occur in appropriate cases, where the electron acceptor has a reduction potential near the oxidation potential of KO<i>t</i>Bu, and the example that we use is CBr₄. In this case, computational results support electrochemical data in backing a direct electron transfer reaction