Syngas reactions I. The catalytic carbonylation of conjugated dienes

3,8-Nonadienoate acid esters are prepared from 1,3-butadiene in 80 mol% yields and >90% selectivity when catalyzed by combinations of halide-free palladium salts and tertiary alkyl-phosphine ligands of pKa > 8, solubilized in N-heterocyclics and tertiary arylamines of moderate base strength (e.g., quinoline and N,N-diethylaniline). The related palladium(II) acetate-triphenylphosphine couple in isoquinoline/2-propanol allows continued improved activity upon recycle and turnover number exceeding 2 × 103. Concurrent C5 and C9 acid syntheses are possible with Pd(OAc)2-DIPHOS. The importance of counterion and Group VB donor ligand structure together with preferred solvent properties are discussed in relation to palladium carbonylation performance and inactivating side reactions.