Pd(II)-catalyzed ligand controlled synthesis of pyrazole-4-carboxylates and benzo[b]thiophene-3-carboxylates

Cyclization–carbonylation of α,β-alkynic hydrazones and (o-alkynylphenyl) (methoxymethyl) sulfides with Pd(tfa)2 in DMSO/MeOH afforded methyl pyrazole-4-carboxylates and benzo[b]thiophene-3-carboxylates, respectively, in good yields. A simple change of the ligand (solvent) allowed controlled, effective switching between cyclization–carbonylation–cyclization-coupling (CCC-coupling) reactions and cyclization–carbonylation reactions.