Pd/Light‐Accelerated Atom‐Transfer Carbonylation of Alkyl Iodides: Applications in Multicomponent Coupling Processes Leading to Functionalized Carboxylic Acid Derivatives

Abstract

The atom-transfer carbonylation reaction of various alkyl iodides thereby leading to carboxylic acid esters was effectively accelerated by the addition of transition-metal catalysts under photoirradiation conditions. By using a combined Pd/hν reaction system, vicinal C-functionalization of alkenes was attained in which α-substituted iodoalkanes, alkenes, carbon monoxide, and alcohols were coupled to give functionalized esters. When alkenyl alcohols were used as acceptor alkenes, three-component coupling reactions, which were accompanied by intramolecular esterification, proceeded to give lactones. Pd-dimer complex [Pd(2)(CNMe)(6)][PF(6)](2), which is known to undergo homolysis under photoirradiation conditions, worked quite well as a catalyst in these three- or four-component coupling reactions. In this metal/radical hybrid system, both Pd radicals and acyl radicals are key players and a stereochemical study confirmed the carbonylation step proceeded through a radical carbonylation mechanism.

Catalytic Radical Domino Reactions in Organic Synthesis

“…22 When irradiated with light, this radical/radical/reduction process begins with the abstraction of an iodine atom from 30 to form radical 33 . This primary radical then adds to olefin 31 to form 34 , which can add to an equivalent of CO to form keto-radical 35 .…”

Free‐Radical Multicomponent Processes

“…The discovery that transition metals such as Pd 0 in the presence of light could significantly accelerate this transformation has stimulated much effort recently to extend the scope of application of ATC [65]. Extensive mechanistic studies showed that photoexcited Pd 0 species may promote the formation of the Ccentered radical through SET with the formation of a Pd I I species, which is later trapped by the acyl radical to produce an acyl palladium complex, reacting in the last step with the nucleophile [66]. This mechanism was preferred to the putative migratory insertion of CO into an alkyl-palladium bond formed through oxidative addition of Pd 0 onto R-I.…”

Cobalt-Catalyzed Silylcarbonylation of Unactivated Secondary Alkyl Tosylates at Low Pressure

“…1 Recent studies have developed carbonylations 2 and carboxylations 3 of alkyl electrophiles, which have been much less studied than aryl or vinyl substrates. These catalytic transformations are proposed to involve radical intermediates produced from the activation of alkyl halide substrates.…”