ADDITION-ELIMINATION REACTION IN THE TRIFLUOROACETYLATION OF ELECTRON-RICH OLEFINS

Reactions of electron-rich olefins such as vinyl ether 1 and vinyl sulfide 2 with trifluoroacetic anhydride in carbon tetrachloride at room temperature proceeded by the formation of addition products 7 and 8, respectively, which were identified as stable intermediates by H-1 NMR and IR spectra, eventually giving the, corresponding trifluoroacetylated olefins 5 and 6 as substitution products. These reactions were also observed in chloroform and dichloromethane in the absence. of base, such as pyridine. These results supported the addition-elimination mechanism. The processes of the addition and elimination were confirmed by the H-1 NMR spectrum and kinetic study which led to the following results: The addition products 7 and 8 were formed through a stepwise trans addition, and the trifluoroacetylated olefins 5 and 6 were self-catalytically formed from the addition products 7 and 8 through Ei, E2, or E1, depending on the stability of the cationic intermediates 3 and 4.