PCET beyond Simple pKa-Related Base Effects: Unlocking Inaccessible Substrates for Direct Intermolecular Photocatalytic Ring-Opening Remote Alkylative C-C Functionalization of Cycloalkanols

Oxidative multisite proton-coupled electron transfer (MS-PCET) reactions, particularly those occurring under metal-free pho¬to¬catalytic conditions using visible light, have emerged as a promising tool for the activation of strong O-H bonds in (cyclo)alkanols. However, these methods generally require the use of e-rich arene-containing derivatives (para-methoxyphenyl (PMP), etc.) – a factor that greatly restricts their broader applicability. Herein, we report the successful implementation of targeted modulation of the base partner in photocatalytic cascade reactions of cyclic alcohols, unlocking previously inaccessible, non-activated substrates. This approach successfully circumvents the prevalent limitations of ring-opening transformations of cycloalkanols by deliberately promoting base-alcohol interactions. As a result, we here demonstrate a general, operationally simple and widely applicable protocol for the redox-neutral transformations of cycloalkanols into terminally C(sp3)-C(sp3)-coupled, functionalized open-chain products. NMR-based mechanistic studies, comprising in-depth H-bond analysis and DOSY experiments, have elucidated the crucial role of the (pyridine) base in this multisite PCET, which surpasses typical pKa-related and/or steric effects. Ultimately, our gained insights into the key importance of additional weak interactions in promoting a pivotal productive alcohol-base pre-organization were directly put into practice to successfully pioneer remote alkylative Giese-type C-C-bond formations of previously challenging alkyl-substituted cycloalkanols.