Selective C-C Bond Scission of Ketones via Visible-Light-Mediated Cerium Catalysis

Abstract

Here, we report a general catalytic manifold for the selective C-C bond scission of ketones via the exploitation of the ligand-to-metal charge transfer (LMCT) excitation mode. Through a cooperative utilization of Lewis acid catalysis and LMCT catalysis, the C-C bond of ketones could be selectively and effectively cleaved, enabling the installation of different functionalities at each carbon of the cleaved C-C bond through a sequential and orthogonal manner. This reaction manifold serves as a photocatalytic alternative to the Norrish type I reaction with the combination of visible light and inexpensive cerium salts. Under operationally simple conditions, a wide range of acyclic and cyclic ketones, from simple strained cyclobutanones to complex androsterone with less strained cyclopentanone moiety, could be successfully transformed into versatile chemical building blocks.

Deacylative Carbon‐Carbon Bond Cleavage of Ketone Equivalents: Applications to Radical Carbon‐Carbon Bond Formation Reactions

“…However, most reactions were restricted to the use of strained cyclobutanones, while the use of unstrained cyclic and acyclic ketones remains underdeveloped. Recently, Zuo and co‐workers have developed an efficient method for the selective cleavage of C−C bonds of both cyclic and acyclic ketones via the cooperative use of Lewis acid catalysis and ligand‐to‐metal charge transfer catalysis, although the application of the resulting alkyl radicals is limited to cyanation or amination (Scheme 1b) [8] . Herein, we describe a new approach for the deacylative C−C bond cleavage of ketone equivalents to generate various alkyl radicals, which can be applied to C−C bond formation reactions.…”

Catalytic generation of alkoxy radicals from unfunctionalized alcohols

“…Recently, the Zuo lab merged LMCT-mediated alkoxy radical generation with Lewis acid catalysis to achieve a one-step protocol for the C-C bond cleavage of ketones. 71 In 2018, Zuo and coworkers extended this method of alkoxy radical generation to the synthesis of bridged lactones by leveraging cerium-catalyzed b-scission and ring expansion of cycloalkanols. 72 Given the redox potential of their Ce(III) catalyst (E 1/2 (Ce IV /Ce III ) ¼ 0.40 V vs. SCE in MeCN), regeneration of photoactive Ce(IV) to turn over the catalytic cycle requires a sufficiently oxidizing radical intermediate, such as the Ncentered radical employed in the authors' earlier alkoxy radical-mediated amination work.…”

“…Recently, the Zuo lab merged LMCT-mediated alkoxy radical generation with Lewis acid catalysis to achieve a one-step protocol for the C–C bond cleavage of ketones. 71 …”

Synthetic Approaches to Acyl Hydrazides and Their Use as Synthons in Organic Synthesis

“…Recently, Zuo and co-workers developed a method that aims at ring expansion of four-and five-membered-ring ketones 113, to six-and seven-membered lactams 115, respectively via the acyl hydrazide intermediate 114 (Scheme 30). 40 This methodology is based on the photochemical cleavage of a C-C bond, leading to the formation of an open structure intermediate. The keto group of 113 was transformed to acyl hydrazide 114, while the -carbon was substituted with a cyanο group.…”