A regioselective protocol for the
synthesis of substituted allylic chlorides, bromides, and fluorides
has been established. Remarkably, the method can be applied to the
enantioselective synthesis of challenging chiral allylic chlorides.
When the allylic halides are treated with the base triazabicyclodecene
as the catalyst, a [1,3]-proton shift takes place, giving the corresponding
vinyl halides in excellent yields with excellent
Z
:
E
ratios. Furthermore, the [1,3]-proton shift takes
place with an outstanding level of chirality transfer from chiral
allylic alcohols (≤98%) to give chiral trifluoromethylated
vinyl chlorides.