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

Cyclization-carbonylation of α,ß-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.