Functional fluorocarbon derivatives via free radical reactions

Abstract

Gamma-ray and benzoyl peroxide initiated addition of the functional hydrocarbons, methanol, acetaldehyde, and dimethyl ether to perfluorocyoloalkenes generally resulted in mixtures of geometric isomers. The exception was the addition of aoetaldehyde to perfluorocyolohexene which gave stereospecific cis addition with the acyl group positioned equatorial and the hydrogen axial. The assignment of structures to the geometric isomers was based on a simple correllation with the 19(_F) nuclear magnetic resonance chemical shifts of the fluorine atoms geminal to the substituents. Additions to tetra-F-alkyl ethenes gave adducts, one of which underwent a remarkable cyclization: pyrolysis of the dihydrofuran product provided a novel furan synthesis. Further, reaction with dimethyl ether favoured a two-to-one rather than a one-to-one adduct and an intramolecular rearrangement is proposed to account for this process. A preliminary study of the effect of substituents on carbon-hydrogen bond reactivity has shown that an aromatic nucleus causes deactivation. Otherwise, a methoxy group tends to react readily under free-radical conditions but the reactivity of a methylene is more dependent on the nature of the substituents. Many of the reactions of the functional fluorocarbon derivatives were found to be influenced by the fluorine-containing substituent. The main effects were steric and electron-withdrawing inductive effects. Ghlorination of a methyl ether derivative resulted mainly in substitution at the least expected carbon-hydrogen bond.