Electrophotochemical Ring-Opening Bromination of tert-Cycloalkanols

Abstract

An electrophotochemical ring-opening bromination of unstrained tert-cycloalkanols has been developed. This electrophotochemical method enables the oxidative transformation of cycloalkanols with 5-to 7membered rings into synthetically useful ω-bromoketones without the use of chemical oxidants or transition-metal catalysts. Alkoxy radical species would be key intermediates in the present transformation, which generate through homolysis of the O−Br bond in hypobromite intermediates under visible light irradiation.

Electrophotochemical Ce-Catalyzed Ring-Opening Functionalization of Cycloalkanols under Redox-Neutral Conditions: Scope and Mechanism

“…Onomura and co-workers realized ring-opening bromination of unstrained tert -cycloalkanols via electrophotocatalysis by using MgBr 2 as the mediator . In this work, by applying earth-abundant simple Ce chloride as a catalyst, , we report an EPC LMCT process to enable β-scission of cycloalkanols with different ring sizes and formation of C–CN, C–C, C–S, C–oxime, etc., bonds without the formation of C-halides, which was inevitable in previous electrochemical synthetic methods (Scheme c). , …”

“…44 Onomura and co-workers realized ring-opening bromination of unstrained tert-cycloalkanols via electrophotocatalysis by using MgBr 2 as the mediator. 45 In this work, by applying earth-abundant simple Ce chloride as a catalyst, 46,47 we report an EPC LMCT process to enable βscission of cycloalkanols with different ring sizes and formation of C−CN, C−C, C−S, C−oxime, etc., bonds without the formation of C-halides, which was inevitable in previous electrochemical synthetic methods (Scheme 2c). 45,48 ■ RESULTS AND DISCUSSION Reaction Optimization.…”

Electrochemical Synthesis of β-Functionalized Ketones via Ring-Opening of Cycloalkanols

“…Driven by the prevalence of β-functionalized ketone moiety in a myriad of natural products and biologically relevant molecules, we envisioned that the exploration of a new and sustainable synthetic approach to β-functionalized ketones from cycloalkanols under electrolysis and transition metal-free conditions would be highly rewarding. To date, the development of electrochemical methods for the generation of alkoxy radicals directly from alkanols has received little attention, and remains largely restricted to the generation of alkoxy radicals that require a Mn catalyst or halogen as a mediator, or relies on special anode material . We reported herein a sustainable electrochemical system that allows an oxidative ring-opening of cycloalkanols to proceed (Scheme d).…”

Electrochemical Deconstructive Functionalization of Cycloalkanols via Alkoxy Radicals Enabled by Proton-Coupled Electron Transfer

“…During the latter stages of this investigation, Onomura and co-workers reported an electrophotochemical deconstructive bromination of cycloalkanols, which involves the electrochemical generation of hypobromite intermediates via anodic bromide oxidation followed by visible light-promoted homolysis of the weak O–Br bond to generate an alkoxy radical. 24 …”

“…To develop a more general electrochemical method to access and utilize alkoxy radicals, we envisaged an electrochemically driven PCET approach, and herein we report the successful realization of this strategy. During the latter stages of this investigation, Onomura and co-workers reported an electrophotochemical deconstructive bromination of cycloalkanols, which involves the electrochemical generation of hypobromite intermediates via anodic bromide oxidation followed by visible light-promoted homolysis of the weak O–Br bond to generate an alkoxy radical …”