Palladium-Catalyzed 1,4-Acetoxy-Trifluoroacetoxylation and 1,4-Alkoxy-Trifluoroacetoxylation of Cyclic 1,3-Dienes. Scope and Mechanism

Palladium-catalyzed unsymmetrical 1,4-functionalizations of cyclic 1,3-dienes are described. Trifluoroacetate in combination with acetate or alcohols is utilized to obtain 1-acetoxy-4-(trifluoroacetoxy)-2-cycloalkenes and 1-alkoxy-4-(trifluoroacetoxy)-2-cycloalkenes, respectively, with good regio- and stereoselectivities. The chemoselectivity of these reactions relies on the different kinetic stability of the intermediate 4-(trifluoroacetoxy)-, 4-acetoxy-, and 4-methoxy-[eta(3)-(1,2,3)-cycloalkenyl]palladium complexes. Under the acidic reaction conditions employed, the 4-trifluoroacetoxy pi-allyl intermediate is the least stable of the three. Certain mechanistic aspects of the reactions are discussed in the light of DFT calculations.