Electrochemically Driven Deoxygenative Borylation of Alcohols and Carbonyl Compounds

Abstract

We present a new, unified approach for the transformation of benzylic and allylic alcohols, aldehydes, and ketones into boronic esters under electroreductive conditions. Key to our strategy is the use of readily available pinacolborane, which serves both as an activator and an electrophile by first generating a redox-active trialkylborate species and then delivering the desired deoxygenatively borylated product. This strategy is applicable to a variety of substrates and can be employed for the late-stage functionalization of complex molecules.

Electroreductive Deoxygenative C−H and C−C Bond Formation from Non‐Derivatized Alcohols Fueled by Anodic Borohydride Oxidation

“…However, when a selection of boron compounds were added to the reaction mixture (Figure 4A), none of the additives except the benchmark borohydride reagent improved the yield of 2 a compared to the additive‐free reaction, thus providing little support for this hypothesis. Recently, formation of borate esters intermediates between pinacolborane and alcohols was proposed in electrochemically driven deoxygenative borylation by Lin and co‐workers [96] . Such borate ester intermediates may be envisioned to form also in the present system from electrooxidatively formed borane and alcohols or in situ formed aldehydes.…”

“…Recently, formation of borate esters intermediates between pinacolborane and alcohols was proposed in electrochemically driven deoxygenative borylation by Lin and co-workers. [96] Such borate ester intermediates may be envisioned to form also in the present system from electrooxidatively formed borane and alcohols or in situ formed aldehydes. Indeed, trialkylborate esters were found to furnish the desired alkane products upon electroreduction as indicated by DFT as well as electrolysis of pre-formed 5 a (Figure 4B and ESI, Sections 7 and 12).…”

Enabling Al sacrificial anodes in tetrahydrofuran electrolytes for reductive electrosynthesis

“…We first focus on an electrochemically driven deoxygenative borylation reaction in THF (Scheme 1), where Al was tested in a previous effort of reaction optimization but gave 0% yield of the desired product. 43 As shown in entry 1, in TBABF 4 /THF electrolyte, the overall cell potential rapidly reaches 30 V, the upper limit of the ElectraSyn capability, and merely 0.03 F mol −1 of the charges was passed even after prolonged reaction time. The observation aligns with the high potential at the Al anode shown in Fig.…”

“…Currently, the use of an Al sacrificial anode in THF-based electrolytes is commonly accompanied with extremely high overall cell potentials (>30 V) that inhibit electrolysis of the organic substrates. 15,42–44 The escalation in voltage is frequently attributed to the formation of an oxide layer on the Al surface. Thus, to realize a wide application of Al sacrificial anodes in THF-based electrolytes, the ability to control the Al interface is essential.…”

Electroreductive Radical Addition–Polar Cyclization Cascade to Access Cycloalkanes

“…In this regard, we recently demonstrated deep electroreductive chemistry as a general and versatile approach for a diverse range of cross-coupling and alkene functionalization reactions to construct C–C, C–Si, C–B, and Si–Si bonds . Closely related to the objectives of this work, we developed eXEC of alkyl halides and dialkylation of alkenes by taking advantage of the distinct redox and steric properties of alkyl halides.…”