Alkoxycarbonylation of 3,3,3-trifluoropropyne: an intriguing reaction to prepare trifluoromethyl-substituted unsaturated acid derivatives

The addition of CO and methanol to 3,3,3-trifluoropropyne is catalysed by Pd(OAc)(2) in the presence of (6-methylpyrid-2-yl)diphenylphosphine and CH3SO3H. The main products of the reaction are the methyl esters of 2-(trifluoromethyl)propenoic acid 1 and of 3-(trifluoromethyl)propenoic acid 2 (4,4,4-trifluorobut-2-enoic acid). ne regioselectivity of the reaction can be controlled to a great extent by a suitable choice of the composition of the catalytic system and the reaction conditions. Thus, 1 can be obtained in 93% yield by using P(CO) = 20 atm and high ligand/Pd and acid/Pd ratios. On the other hand, selectivity up to 85% in 2 can be achieved using P(CO) = 80 atm and a low ligand/Pd ratio together with a high acid/Pd ratio. The reaction mechanism is also discussed.