The reaction of peroxyformate CF3OOC(O)F with fluoroolefins (CF2=CFCl and CF2=CF2) leads to the formation of new acylfluorides (CF3OCF2CFROC(O)F, R=Cl and F) as major products. The peroxyformate can be prepared by the reaction CsOCF3 with CF2(OF)2 and COF2 in the presence of CsF. The CF2(OF)2 is prepared by the reaction between CO2 and F2 in CsF. To get the new acylfluorides, the reaction should be carried out at high temperature (more than 100°C). The pure products can be obtained by passing through different temperature traps.