Effects of remote unsaturated bonds at C-2 on nucleophilic aromatic substitution of fluorine in 6,7-difluoro-1,2,3,4-tetrahydro-3,3-dimethyl-1,4-methanonaphthalenes

Abstract

Approximate values of the second-order rate constant for fluorine replacement by isopropoxide ion in propan-2-ol–dimethyl sulphoxide (1 : 1 v/v) have been determined for a series of 6,7-difluoro-1,2,3,4-tetrahydro-3,3-dimethyl-1,4-methanonaphthalenes containing unsaturated groups at C-2. A factor of 13 separates the most reactive system [the 2-oxo compound (10)] from the least reactive [the 2-methylene compound (13)] but the lack of product regiospecificity excludes homoconjugation as a possible effect in stabilising the transition state for attack at C-6; the (E)-2-benzylidene compound (14) gave identical product ratios at 100 and at 150° in propan-2-ol.