Remarkable Improvement Achieved by Imidazole Derivatives in Ruthenium-Catalyzed Hydroesterification of Alkenes Using Formates

Abstract

Imidazole derivatives are revealed to be effective ligands in the Ru-catalyzed hydroesterification of alkenes using formates, affording one-carbon-elongated esters in high yields. Further, intramolecular hydroesterification was successfully performed to give lactones for the first time. Imidazole derivatives can contribute to promote the reaction as well as to suppress the undesired decarbonylation of formate. Toxic CO gas, a directing group, and large excess alkenes are not required.

Ruthenium-catalysed alkoxycarbonylation of alkenes with carbon dioxide

“…For example, aldehydes 13 and higher alcohols like cinnamyl alcohol 14 or polyols 15 were used as carbon monoxide source especially in hydroformylation and Pauson-Khand-type reactions. For alkoxycarbonylation reactions, formates are known to be a CO substitute 16 . Apart from above-mentioned CO sources, stoichiometric amounts of metal carbonyls such as Mo(CO) 6 and W(CO) 6 are also applied to deliver carbon monoxide 17 .…”

Creation of Novel Toxic Gas Surrogates and the Development of Safe and Facile Catalytic Reactions

“…The substrate scope (both alkene and formate) was then examined under the optimal conditions, showing that the Ru-imidazole catalyst system greatly improved the scope of the reaction, from the perspectives of both the alkene and formate, compared to the previously reported conditions 36,39) (Table 2). Alkyl and aryl formates could be used, with the former affording products in higher yields than the latter (entries 1, 2).…”

“…The exploration of the use of additives during the hydroesterification of 4-methoxystyrene (5) and benzyl formate (6) in the presence of the Ru 3 (CO) 12 catalyst identified effective additives, such as imidazoles 9 and 10. Because 10 cannot undergo ester exchange due to the absence of a hydroxy group, these effective additives might act as ligands to Ru metal, rather than through the initially assumed reaction mechanism [36][37][38] (Chart 1C). After extensive screening of over 50 ligand candidates, imidazole-type ligands were revealed to be effective, with 13 exhibiting the best performance on the basis of high yields of the desired products 36,39) (Table 1).…”

“…Because 10 cannot undergo ester exchange due to the absence of a hydroxy group, these effective additives might act as ligands to Ru metal, rather than through the initially assumed reaction mechanism [36][37][38] (Chart 1C). After extensive screening of over 50 ligand candidates, imidazole-type ligands were revealed to be effective, with 13 exhibiting the best performance on the basis of high yields of the desired products 36,39) (Table 1). It was noted that only 13 showed a reversal in regioselectivity, although the reasons remain unclear.…”

Transition-metal Catalyzed Synthesis of Carbonyl Compounds Using Formates or Formamides as Carbonyl Sources

“…In 2002, Chang and co-workers reported the Ru-catalyzed hydroesterification of alkenes with chelating formates under mild reaction conditions (Scheme 1(c)) 19) . Manabe and co-workers also found the Ru-catalyzed hydroesterification of alkenes with formates, in which the use of a hydroxymethyl imidazole ligand was effective and a mixture of the corresponding esters was obtained (Scheme 1(d)) 20) . The ligand-controlled regiodivergent esterification of alkenes with phenyl formate proceeded under Pd catalysis (Scheme 1(e)) 21) .…”