Carbon Monoxide

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

“…We also tested a dimeric Pd complex. When the reaction of 1-iodooctane (1 a), CO, and EtOH was carried out in the presence of a catalytic amount of 6 ] 2 under photoirradiation conditions, the corresponding carboxylic acid ester (2 a) was obtained in 87 % yield (Table 1, entry 3). Pd/light-induced acceleration was also observed when cyclopropylcarbinyl iodide (1 b) was used as a substrate (Table 1, entries 4 and 5), which gave butyl 4-butenoate (2 b) through the ring-opening of a cyclopropylcarbinyl radical.…”

“…This procedure provides a general synthetic approach for the synthesis of various carboxylic-acid derivatives through useful cascade sequences that are tolerant of a variety of alkyl iodides as starting materials. In many cases, Pd dimer [Pd 2 A C H T U N G T R E N N U N G (CNMe) 6 ]A C H T U N G T R E N N U N G [PF 6 ] 2 worked equally as well as Pd 0 catalysts for these photoinduced carbonylation reactions. To affect the somewhat-inefficient oxidative addition of sp 3 -carbon-halogen bonds to Pd 0 complexes, electron-rich ligands are used [33,34] that can suppress the b-hydride elimi-nation of the rather labile alkylpalladium intermediates.…”

“…[5] The synthesis of acetic acid by transition-metal-catalyzed carbonylation from MeOH and carbon monoxide represents one of the most successful examples of an industrial carbonylation process for which the transition-metal-catalyzed carbonylation of iodomethane is key. [6,7] However, the extension of Monsanto acetic acid synthesis to C3 and larger alcohols is known to give isomeric mixtures of carboxylic acids owing to the isomerization of rhodium-alkyl intermediates through b-hydride elimination. [7a] To circumvent a longstanding problem surrounding the carbonylation of alkyl halides thereby leading to aliphatic carboxylic-acid derivatives, we have developed a conceptually different approach involving radical carbonylation and iodine-atom transfer, which we call atom-transfer carbonylation (ATC).…”

“…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 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.…”

“…[16] Herein, we report the full scope of the Pd/hn-induced ATC reaction for primary, secondary, and tertiary alkyl iodides, which can provide useful synthetic methods to prepare a variety of carboxylic acid derivatives. Interestingly, more than two decades ago, Kubiak and co-workers reported that [ 6 ] 2 is an isolable Pd dimer that, under photoirradiation, is likely to produce a pair of Pd radicals. [17] With great interest in this basic phenomena, we tested this dimeric Pd I complex in our three-component coupling reactions and found that it also worked well.…”