Nucleophilic reactions of fluoroolefins.IV. Regioselectivity in the reactions of 1-phenylpentafluoropropenes with alkyllithium reagents

Reactions of 1-phenylpentafluoropropenes $\text{1a}$–$\text{c}$ with a number of alkyllithium reagents were investigated in detail. In all cases mixtures of 1-alkly-1-phenyltetrafluoropropenes $\text{2}$ and 2-alkyl-1-phenyltetrafluoropropenes $\text{3}$ were obtained. The ratio of products $\text{2}$ and $\text{3}$ is strongly influenced by both the electronegativity of the benzene ring substituents and the bulk of the alkyl group of the alkyllithium reagents. The increase of both of these factors favours formation of 2-alkyl-substituted alkenes $\text{3}$ with a reduced yield of 1-alkyl-substituted alkenes $\text{2}$. The influence of the benzene ring substituents in alkenes $\text{1}$ obeys the Hammett type correlation, while the influence of the bulk of the alkyllithium reagents exhibits good relationships with the Fellous and Luft scale of steric substituent constants E^x_s ; no linear correlation with other scales of steric constants was found. Overall regioselectivity, in the reaction of 1-phenylpentafluoropropenes $\text{1}$ with alkyllithium reagents, considering both the influence of the benzene ring substituents and steric factors, is expressed by the Pavelich-Taft type equation. Observed direction of the influence of the bulk of the alkyllithium reagents on the ratio of products $\text{2}$ and $\text{3}$ is interpreted in terms of steric strains influencing the geometry and free energy of the supposed intermediates involved in these reactions.