Combined Effect of Palladium Catalyst and the Alcohol to Promote the Uncommon Bis-Alkoxycarbonylation of Allylic Substrates

A chemoselective method for the carbonylation of allylic substrates CH2=CHCH2X (X=OAc, OC(O)CH2CN, OPh, OEt, OC(O)OPh, OC(O)OiBu, N(H)C(O)Ph, N(Ph)C(O)Ph, N(H)Boc, N(Ph)Boc, Ph, CO2Bn, CN), leading to alkyl succinates with preservation of the X group, under Pd(II)-catalyzed oxidative carbonylation conditions, has been developed. Our method shows a completely different inverse chemoselectivity with respect to the “classical” substitutive carbonylation of the allyl compounds, which is known to provide β,γ-unsaturated carbonyl derivatives through the formation of a π-allylpalladium intermediate. An accurate study, carried out using allyl acetate as model substrate, allowed to maximize the selectivity in the envisioned 2-CH2X substituted succinates. The best catalyst is generated in situ by mixing Pd(TFA)2 (TFA=trifluoroacetate) and the N,N′-di(anthracen-9-yl)butane-2,3-diimine ligand. p-Benzoquinone was used as oxidant in presence of benzyl alcohol, which acts as a nucleophile and as a solvent, under 4 bar of CO at 20 °C. A combined effect of the ligand and the nucleophile, rationalized through DFT calculations, has been observed both in promoting the bis-alkoxycarbonylation process and in preventing π-allylpalladium-mediated side reactions, allowing the attainment of succinate derivatives with moderate to good yields.