Yves Castanet

Palladium-catalyzed carbonylative coupling of pyridine halides with aryl boronic acids

Abstract The carbonylative Suzuki cross-coupling of a variety of mono-iodopyridines and bromopyridines ( 1a,b , 3a–c , 5 ) catalyzed by palladium-phosphane systems has been studied to prepare benzoylpyridine derivatives ( 2 , 4 , 6 ). The selectivity and the rate of the reaction are highly dependent on the reaction conditions, i.e. nature of the palladium catalyst precursor, solvent, temperature and CO pressure. The main side-products arise from direct, non-carbonylative cross-coupling. Under optimized conditions, benzoylpyridines are recovered in high yields (80–95%). The order of reactivity decreases from iodo- to bromopyridines and from 2-, 4- to 3-substituted halopyridines. The reactivity of dihalopyridines has been investigated; 2,6-dibromopyridine ( 7 ) and 3,5-dibromopyridine ( 11 ) are selectively transformed into either the corresponding benzoyl-phenylpyridine ( 8 , 12 ) or the corresponding dibenzoylpyridine ( 9 , 13 ). Dissymmetric 2,5-dihalopyridines ( 15a,b ) are transformed into 2-benzoyl-5-bromopyridine ( 16 ) or 2,5-dibenzoylpyridine ( 17 ) in high yields.

Palladium-catalyzed carbonylative cross-coupling reactions of pyridine halides and aryl boronic acids: a convenient access to α-pyridyl ketones

Abstract The proper choice of solvent, catalyst precursor and CO pressure enables the easy and selective transformation of mono- and dihalopyridines into phenyl pyridyl ketones in 81–95% yields.

A novel and convenient method for palladium-catalysed alkoxycarbonylation of aryl and vinyl halides using HCO2R/NaOR system

Abstract Aryl iodides, vinyl bromides and tricarbonyl(chloroarene)chromium complexes react under mild conditions with sodium alkoxides and alkyl formates as source of carbon monoxide in the presence of dichlorobis(triphenylphosphine)-palladium as catalyst to give the corresponding carboxylic esters in high yields.

Palladium-catalysed alkoxycarbonylation of tricarbonyl(η6-mono and dichloroarene)chromium complexes under mild conditions using HCO2R/MOR system

Alkoxycarbonylation competes with nucleophilic aromatic substitution and palladium-catalysed reduction during treatment of Cr(CO)3-complexed chloroarenes with HCO2R / MOR / PdCl2(PPh3)2. The influence of the nature of the HCO2R / MOR system and of stereoelectronic factors in dichlorobenzene complexes are discussed.

Selective palladium-catalysed carbonylations of dichloroquinoline and simple dichloropyridines

Dichloroquinoline and some dichloropyridines undergo selective alkoxycarbonylation in the presence of carbon monoxide, an alcohol and PdCl2(PPh3)2 as a catalyst, affording chloro-monoester and/or diesters in good yields under selected reaction conditions.

Synthesis of pyridylglyoxylic acid derivatives via a palladium-catalysed double carbonylation of iodopyridines

Abstract 4-Iodopyridiens react with CO and HNEt2 or 2- BuOH NEt 3 in the presence of a catalytic amount of PdCl2(PPh3)2 to give the corresponding α-keto amides and esters in fair to high yields.

Epoxide–tertiary amine combinations as efficient catalysts for methanol carbonylation into methyl formate in the presence of carbon dioxide

Abstract The influence of CO2 on the carbonylation of methanol into methyl formate was investigated with two classes of catalytic systems: MeO− and epoxide–amine combinations. In the absence of CO2, NaOMe is the more active, but its efficiency is rapidly destroyed by CO2. On the other hand, the epoxide–amine system is much less sensitive to the presence of CO2. Different classes of amines and epoxides have been tested. Tertiary alkyl amines and terminal epoxides are the most efficient. Phosphines associated with an epoxide have also been found to be able to catalyse this reaction. On the basis of 31 P NMR studies, a plausible mechanism which can also be applied to amines is proposed for the reaction.

Kinetic resolution of racemic tricarbonyl(2-chloroanisole)chromium via palladium-catalysed asymmetric alkoxycarbonylation

Abstract Tricarbonyl(o-chloroanisole)chromium was treated with an alcohol and carbon monoxide in the presence of triethylamine and a chiral palladium catalyst to give (o-methoxybenzoate ester)Cr(CO) 3 complexes in high selectivity with up to 30% ee. Starting tricarbonyl(o-chloroanisole)chromium was recovered in up to 39% ee. The Pd/PPFA catalytic system exhibited high reactivity and selectivity for the carbonylation reaction.

CO pressure as a key factor for the palladium-catalyzed methoxycarbonylation of benzyl chloride under mild conditions

Palladium-catalyzed methoxycarbonylation of benzyl chloride was investigated at low temperature and low carbon monoxide pressure. The presence of benzylpalladium moiety at the beginning of the reaction (before CO addition), a low CO pressure and a moderate stirring rate are needed to achieve the reaction with high efficiency. Increasing the CO pressure or the stirring rate leads to the deactivation of the catalyst by formation of palladium carbonyl species.

Mechanistic investigations of palladium-catalysed single and double carbonylation of aryl and vinyl halides by methyl formate

Abstract The palladium-catalysed methoxycarbonylation of PhCHCHBr in the presence of HCO 2 CH 3 , NEt 3 and CO has been investigated and compared to that of PhI. Methyl cinnamate was the only product observed. Model reaction studies were conducted on the possible intermediates [(PhCHCH)Pd(PPh 3 ) 2 Br] ( 1 ), [(PhCHCHCO)Pd(PPh 3 ) 2 Br] ( 2a ), and (PhCO)Pd(PPh 3) 2 I] ( 3 ). The results suggest that the high alcoholysis rate of complex 2a is responsible for the lack of double carbonylation product from PhCHCHBr. NMR studies of the catalytic systems in the presence of HCO 2 CH 3 revealed the presence of the suggested aroylpalladium complexes ( 2a and 3 ) in conjunction with [PdCl(PPh 3 ) 2 (CO 2 CH 3 )] ( 4 ). Both stoichiometric and catalytic experiments indicated that complex 4 is a possible intermediate in the formation of both simple esters and α-keto esters, but that the latter arise mainly from classical aroylpalladium (II) complexes. The activation pathway of HCO 2 CH 3 has been studied and a dramatic influence of CH 3 OH concentration in the reaction medium has been found. These results suggest that CH 3 OH arising from smooth decarbonylation of HCO 2 CH 3 under the reaction conditions is the main alkoxy-transfer agent.