Isoprene hydrocarboxylation

Palladium catalysts that are free of halide ions effect the dimerization and carboxylation of butadiene to yield 3,8-nonadienoate esters. Palladium acetate, solubilized by a tertiary amine or an aromatic amine, gives the best yields and selectivities (equation 57).87 Palladium chloride catalyzes the hydrocarboxylation to yield primarily 3-pentenoates.88 The hydrocarboxylation of isoprene and chloroprene is regio-selective, placing the carboxy function at the least-hindered carbon (82% and 71% selectively) minor amounts of other products are obtained (equation 58). Cyclic dienes such as 1,3-cyclohexadiene and 1,3-cyclooctadiene are similarly hydrocarboxylated. 

Di- and trisubstituted 1,3-dienes were converted to y-S-unsaturated acids by using the previously described catalytic system involving formic acid, carbon monoxide, and Pd-C/PPhj/dppb in 1,2-dimethoxyethane (DME). The hydrocarboxylation of isoprene, for example, occurs under 6.2 atm of CO and at 110 °C to form the corresponding jS-y-unsat-urated acid in 52% yield (Eq. 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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