The peculiar behaviour of the trifluoromethyl substituent in SRN1 processes

Abstract

Reaction of the enolate of 3,3-dimethylbutan-2-one with α,α,α-trifluoro-o-iodotoluene in a S_RN1 process does not yield the expected substitution product, but a more complex molecule deriving from It. An accurate n.m.r. analysis of the products, along with other evidence, indicates a mechanism for this rearrangement, where an interaction of the trifluoromethyl group with the adjacent enolate moiety occurs, once the ‘normal’S_RN1 substitution product has formed. The peculiar effect of the CF₃ substituent is not only confined to the ortho position. Even α,α,α-trifluoro-p-iodotoluene shows unusual behaviour and affords a rearranged product. A mechanistic explanation is offered, where some of the key steps are similar to those involved in the case of the ortho isomer.