Visible Light-Induced Pd-Catalyzed Alkyl-Heck Reaction of Oximes

Abstract

A visible light-induced palladium-catalyzed oxidative C–H alkylation of oximes has been developed. This mild protocol allows for an efficient atom economical C–C bond construction of alkyl-substituted oximes. A broad range of primary, secondary, and tertiary alkyl bromides and iodides, as well as a range of different formaldoximes, can efficiently undergo this transformation. The method features visible light-induced generation of nucleophilic hybrid alkyl Pd radical intermediates, which upon radical addition at the imine moiety and a subsequent β-hydrogen elimination deliver substituted imines.

Visible Light Induced Brønsted Acid Assisted Pd‐Catalyzed Alkyl Heck Reaction of Diazo Compounds and N‐Tosylhydrazones

“…We hypothesized that the formation of traces amount of acetic acid from palladium acetate is crucial for the reaction to occur, which was later validated using Pd(PPh 3 ) 4 as catalyst with and without exogenous acetic acid (entries 4, 5). The addition of triphenylphosphine as monodentate ligand [10] further improved reaction efficiency (entry 3). Encouraged by these results, we began optimizing this novel visible light-induced Brønsted acid-assisted alkyl Heck reaction of diazo compounds by screening different additives.…”

“…Among them, more soluble and inexpensive 4chloro-piperidine hydrochloride produced the desired coupling product 3 a in 80 % yield (entry 7). Control experiments demonstrated both Pd catalyst and Xantphos ligand are essential for this transformation (entries [8][9][10][11], and thermal reaction under dark gave only traces of product (entry 12).…”

Light-Driven Palladium-Radical Hybrid Species: Mechanistic Aspects and Recent Examples

“…Recently, the same group described the use of oximes in Heck-type alkylations induced by visible light in a straightforward protocol to achieve a wide range of E / Z mixtures of substituted imines (Scheme 4 C). 22 In this approach, the authors explored a system composed of two types of phosphine ligand (PPh 3 and Xantphos) and In(OAc) 3 as a Lewis acid additive. A broad scope of products was constructed by employing different types of alkyl halides, giving the desired substituted oximes in excellent yields.…”

Boron Chelates Derived from N-Acylhydrazones as Radical Acceptors: Photocatalyzed Coupling of Hydrazones with Carboxylic Acids

“…Radical addition at the CN bond is an important process, serving as a key step in many synthetic methods. , These reactions have become even more popular due to the advent of photoredox catalysis, which provided convenient ways for the generation of free radicals. − Indeed, photocatalytic reactions of azomethines with alkyl halides, − redox active esters, − sulfinates and sulfides, the C–H bond, − borates, and siliconates have been described . Herein we report that difluoroboryl complexes 2 can serve as efficient acceptors of alkyl radicals (Scheme ).…”