Abstract
Hydroalkoxycarbonylation of dienes offers a straightforward and atom-economic route to valuable esters derived from simple unsaturated feedstocks and carbon monoxide. In this work, we investigated the regioselective hydroalkoxycarbonylation of three representative substrates: 1.3-butadiene, 1.5-hexadiene, and 1.7-octadiene, using palladium-phosphine catalysts in ethanol at 120°C under 2.5 MPa CO. Two catalysts, [PdCl2(PPh3)2] and [Pd(PPh3)4], were tested in combination with additional PPh3 and p-toluenesulfonic acid. Across all three dienes, the reactions consistently favored formation of the linear ester, with yields increasing as the diene chain length grew and conjugation decreased: from 2.31% for ethyl 4-pentenoate (from 1,3-butadiene) up to 32.08% for ethyl 8-nonenoate (from 1,7-octadiene). The superior performance of Pd(PPh3)4 compared with PdCl2(PPh3)2 highlights the importance of electron-rich Pd(0) species in stabilizing acyl intermediates and sustaining catalytic turnover. These findings not only clarify how catalyst structure and substrate features influence reactivity in diene hydroalkoxycarbonylation but also provide practical guidance for tailoring conditions to enhance linear selectivity. Such insights expand the synthetic potential of this methodology for producing C5-C10 esters relevant to polymer, plasticizer, fragrance, and fine-chemical applications.