Hydroesterification of alkenes

Directed ruthenium-catalyzed hydroesterifications of alkenes, employing 2-pyridylmethyl formate, leads to esters (Equation (136)). With vinyl ethers a-adducts are obtained (Equation (137)). 

So far, very little work has been carried out on asymmetric carbonylation. Existing studies all concern the hydroesterification of alkenes (equation 145). Depending on the structure of the alkene and the regioselectivity of the reaction, one or two asymmetric carbon atoms may be present in the product (equation 145).S74... 

High enantiomeric excesses in the hydroesterification of alkenes have not been achieved. The reaction carried out with unbranched 1-alkenes or internal alkenes gives products in less than 20% enantiomeric excess (equation 59). The low enantiomeric excesses are due, in part, to the relatively high temperatures necessary to effect the reaction. 

The presence of catalytic amounts of halide salts (e.g. BU4NI) was found to enhance dramatically the efficiency of hydroesterification of alkenes (e.g. cyclohexenone) and alkynes catalysed by [(CO)i2Ru3] in the presence of the chelating 2-pyridylmethyl formate (2-C5H4NCH2OCHO). On the basis of IR and NMR studies, the halide effect... 

The hydroesterification of alkenes is a versatile method for obtaining carboxylic esters from alkene, CO, and alcohol (Eq. 11.13) [45, 46]. 

In a manner similar manner, the hydrocarbalkoxylation (commonly called hydroesterification) of alkenes in the presence of alcohols can be effected by the nickel, cobalt, platinum, and palladium catalysts described above (Eq. 

Homologation. The hydroesterification of alkenes using Pd(OAc)2, CO, Ph,P, and an alcohol under pressure also works when the clay-supported catalyst is used. ... 

Two mechanisms for the hydroesterification of alkenes have been considered. One pathway—the "alkoxide cycle"— begins with the insertion of CO into a metal alkoxide (Scheme 17.18) and the other—"the hydride cycle"— begins with the insertion of an alkene into a metal hydride (Scheme 17.19). The relative importance of the different pathways depends on the identity of the dative ligand. However, hydroesterification of ethylene with the bis(di-ferf-butylphosphinomethyl)benzene ligand is now generally accepted to occur through a palladium hydride. The mechanism of the hydroesterification of alkynes is less established, but is likely to occur by a sequence that shares some steps with the mechanism for the hydroesterifcation of alkenes. 

Hydroesterification of alkenes with alcohols under a CO atmosphere gave a mixture of regioisomeric alkanoic acid esters (eq 123)7 ... 

Oxo or Hydroformylation and Hydroesterification. Reactions of alkenes with hydrogen and formyl groups are cataly2ed by HCo(CO)4... 

Similar 0—4 generations silica-supported Pd-PAMAM dendrimers with various spacer lengths were used by Alper et al. as recyclable catalysts for the hydroesterification reaction of alkenes (55) and the oxidation of terminal alkenes to methyl ketones (56). The hydroesterification experiments (Scheme 16) showed that (PPh3)2Pd-PPh2-PAMAM-Si02 complexes were highly active catalysts for styrene derivatives and linear long-chain alkenes (numbers of turnovers up to 1200). 

Palladium salts can bring about oxidative carbonylation of alkenes in the presence of copper(II) salts which can reoxidize Pd° to Pd . Oxidative carbonylation is favored over simple hydroesterification by the presence of bases and by low temperatures (25 C) and low pressures (3-15 bar). The products can be a, -unsaturated esters, dicarboxylic acid esters or -alkoxy esters. By careful optimization of the conditions (25 °C, 4 bar CO, methanol solvent, CuCh reoxidant and sodium butyrate buffer) high yields of diesters can be obtained (equation 35). ... 

Asymmetric induction in the palladium-catalyzed hydroesterification of z-methylstyrene, styrene and other alkenes in the presence of ligands with rigid 5//-dibenzophospholyl units linked to chiral cyclobutane, dioxolane or cyclohexane skeletons (CBDBP, DIPHOL, CHDBP) is compared with the effect of the analogous diphenylphosphane ligands18 23. 

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