Magnesiation of pyridine N-oxides via iodine or bromine-magnesium exchange: a useful tool for functionalizing pyridine N-oxides.

Iodo- or 2-bromopyridine N-oxides were readily magnesiated with i-PrMgCl x LiCl via the iodine or bromine-magnesium exchange. The bromine adjacent to pyridine N-oxide (at the 2- or 6-position) can be regioselectively magnesiated in the presence of other position substituted halogens. This method was tested in various substituted pyridine N-oxide systems, and has been successfully applied to the total synthesis of caerulomycins E and A.