Reactions of 2-fluorotropone with Grignard reagents

Abstract

On the addition of ethylmagnesium bromide to 2-fluorotropone in tetrahydrofuran, direct substitution of fluorine occurs to give 2-ethyltropone which, under the reaction conditions, undergoes, to some extent, Grignard addition at C-7 to give an intermediate enolate. The latter either acts as an O- andC-nucleophile, competing in the replacement of fluorine from unchanged 2-fluorotropone, or undergoes C-protonation during work-up to give a mixture of cis- and trans-2,7-diethylcyclohepta-3,5-dien-1 -one. All the products have been separated by chromatography. A similar reaction scheme applies to other alkyl and aryl Grignard reagents.