Synthesis
Combination of HBr and AlBr3 would be expected to give a super-acid
(H+ AIBq-) and we might anticipate that this would provide a very powerful brominating
agent. Indeed it has been shown that tetrafluoropyrazine (which is less basic than
pentafluoropyridine) gives tetrabromopyrazine on treatment with H+ AlBr4-, therefore,
we expected that H+ AIBq- would react well with (3). This proved to be the case and
reaction of pentafluoropyridine with H+ AIBq- gave 2,4,6-tribromo-3,5-difluoropyridine
as a single product in high yield.
