Photoelectrochemical oxidative C(sp3)−H borylation of unactivated hydrocarbons

Abstract

Organoboron compounds are of high significance in organic synthesis due to the unique versatility of boryl substituents to access further modifications. The high demand for the incorporation of boryl moieties into molecular structures has witnessed significant progress, particularly in the C(sp3)−H borylation of hydrocarbons. Taking advantage of special characteristics of photo/electrochemistry, we herein describe the development of an oxidative C(sp3)−H borylation reaction under metal- and oxidant-free conditions, enabled by photoelectrochemical strategy. The reaction exhibits broad substrate scope (>57 examples), and includes the use of simple alkanes, halides, silanes, ketones, esters and nitriles as viable substrates. Notably, unconventional regioselectivity of C(sp3)−H borylation is achieved, with the coupling site of C(sp3)−H borylation selectively located in the distal methyl group. Our method is operationally simple and easily scalable, and offers a feasible approach for the one-step synthesis of high-value organoboron building blocks from simple hydrocarbons, which would provide ample opportunities for drug discovery.

Organoboron-Promoted Electrochemical Chlorosulfonylation of Alkenes with Sulfonyl Chlorides

“…To investigate the presence of chlorine radical, N,Ndiallyl-4-methylbenzenesulfonamide was employed to trap it. 33 However, the chlorinated ring-closing product 48 was not detected. Nevertheless, the chlorine-substituted borane 49 was detected by HRMS after electrolyzing for 45 min (Scheme 3A.c).…”

“…The development of a transition-metal-free paired electrolytic additive represents a promising approach. Organoboron reagents are known to facilitate chemical transformation by serving as Lewis acids due to their possession of a vacant p-orbital. − For instance, boronic esters were able to react with a chlorine radical, or CuCl 2 under the photoelectrochemical conditions, forming Cl–boron complexes.…”

“… The adducts 46 and 47 formed by the tosyl radical and the benzyl radical intermediate with DMPO, respectively, were detected by HRMS (Scheme A.b) These results revealed that a radical process was probably involved in this chlorosulfonylation reaction. To investigate the presence of chlorine radical, N , N -diallyl-4-methylbenzenesulfonamide was employed to trap it . However, the chlorinated ring-closing product 48 was not detected.…”

2-Aminophenanthroline Ligands Enable Mild, Undirected, Iridium-Catalyzed Borylation of Alkyl C–H Bonds

“…In contrast, the borylation of unactivated alkyl C–H bonds with iridium catalysts is under development. Such reactions have required higher temperatures and superstoichiometric quantities of substrate, − except for reactions of activated alkyl C–H bonds in cyclopropanes, in methylarenes, or nearby a directing group. − The photochemical and electrochemical borylations of alkyl C–H bonds occur at mild temperatures but have required high loadings of the substrate or metal. − These limitations have prevented the widespread adoption of alkyl C–H borylation by synthetic chemists.…”

Accelerated Electrophotocatalytic C(sp3)−H Heteroarylation Enabled by an Efficient Continuous‐Flow Reactor**

“…[10] Despite known attempts at employing f-EPC, it is noteworthy that the photochemical and electrochemical steps have not been operated simultaneously in practices to date. [11] Conventionally, starting materials traverse through a photochemical and an electrochemical reactor connected in series, likely attributed to a blend of technological and chemical challenges in balancing the rates of the two concurrent transformations. [6,12] However, from a chemical perspective, the transient nature of species formed in electrophotocatalysis necessitates the simultaneous execution of both the photochemical and electrochemical steps for effective outcomes.…”