Stereochemistry and Some Kinetic Aspects of Fluorination of Phenyl-Substituted Alkenes with SelectfluorTM Reagent F-TEDA-BF4

Abstract

Abstract Reactions of phenyl-substituted alkenes with SelectfluorTM fluorinating reagent F-TEDA-BF4 in the presence of various alcohols resulted in the formation of vicinal fluoroalkoxy adducts with Markovnikov type of regioselectivity. The stereochemistry of the fluoro-methoxylation addition reaction was found to be slightly syn predominant in the case of (Z)-stilbene, indene, and dibenzosuberenone, while equal amounts of both diastereoisomers were formed in the case of (E)-1-phenyl-1-propene and acenaphthylene. In the phenyl-substituted benzocyclene series the stereochemistry of fluoro-alkoxylation was found to be dependent on ring size and on the structure of the alcohol. The resulting vicinal fluoroalkoxy adducts were transformed by heating in aqueous HBr to 2-fluoro-1-phenylbenzocyclenes. Correlation of the logarithms of relative rates of fluoro-methoxylation reactions in a series of ten α-phenyl and α,α-diphenyl acyclic and cyclic alkenes with the ionization potentials of these alkenes resulted in a linear relationship with a slope of −2.75. Correlation of log krel for the present reaction with those for the reaction of the same alkenes with CsSO4F or XeF2 yielded excellent linearity for the pair F-TEDA/CsSO4F and scarcely good one for the pair F-TEDA/XeF2. The Hammett correlation analysis of the reaction of substituted 1,1-diphenylethenes with F-TEDA in MeCN/MeOH solvent gave the reaction constant ρ+ of −1.42, so indicating a moderate electron deficiency on the reactive center in the rate-determining step of the reaction.