Regioselective Bromine/Magnesium Exchange for the Selective Functionalization of Polyhalogenated Arenes and Heterocycles

Using the bimetallic combination sBu(2)Mg⋅2 LiOR (R=2‐ethylhexyl) in toluene enables efficient and regioselective Br/Mg exchanges with various dibromo‐arenes and ‐heteroarenes under mild reaction conditions and provides bromo‐substituted magnesium reagents. Assessing the role of Lewis donor additives in these reactions revealed that N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDTA) finely tunes the regioselectivity of the Br/Mg exchange on dibromo‐pyridines and quinolines. Combining spectroscopic with X‐ray crystallographic studies, light has been shed on the mixed Li/Mg constitution of the organometallic intermediates accomplishing these transformations. These systems reacted effectively with a broad range of electrophiles, including allyl bromides, ketones, aldehydes, and Weinreb amides in good yields.