Etude de l'influence des groupements F-alkyles sur la reactivite des alkyl- (F-alkyl) -cetones R-CO-R F vis-a-vis des organometalliques

Abstract

The present paper deals with a systematic study of the reaction of organometallic compounds, especially Grignard and lithium reagents, upon hemifluorinated ketones R-CO-R F. Whereas organolithium reagents lead, as in hydrocarbon series, to the exclusive formation of tertiary alcohols, by addition, Grignard reagents give a very high percentage of secondary alcohols by reduction. These results are initially explained by the differences in the reaction mechanisms of the organometallics : an ionic reaction for the lithium derivatives, and a cyclic concerted mechanism, involving reactions sensitive to substituent effects, for Grignard reagents. In these latter cases, the reduction alcohol percentage, which is already high for the short R F derivatives, increases with increasing length of the F-alkyl chain. A discussion is presented in order to explain this result, by considering the influence of both electronic and steric effects of F-alkyl groups. The results we obtained, compared to those of the literature, lead us to confirm the particular role of perfluorinated groups C nF 2n+1 on the behaviour of the molecules in which they are substituted.