The preparation of functionalized 2-substituted allyl bromides and chlorides from carboxylic esters is reported. The carboxylic esters were transformed first to 1-substituted cyclopropanols by treating with ethylmagnesium bromide in the presence of titanium alkoxide. Mesylation of the cyclopropanols followed by halide displacement of the sulfonate group to halogen, accompanied by cyclopropyl-allyl rearrangement, affords the required allyl bromides and chlorides.
cyclopropanation - titanium alkoxides - cyclopropanols - cyclopropyl-allyl rearrangement - allyl halides