Regioselective Bromine/Magnesium Exchange for the Selective Functionalization of Polyhalogenated Arenes and Heterocycles. Issue 3 (19th November 2020)

• Record Type: Journal Article
• Authors: Desaintjean, Alexandre; Haupt, Tobias; Bole, Leonie J.; Judge, Neil R.; Hevia, Eva; Knochel, Paul
• Is Part Of: Angewandte Chemie international edition. Volume 60:Issue 3(2021)
• Page Start: 1513
• Page End: 1518
• Publication Date: 2020-11-19
• Subjects: alkoxides -- bromine/magnesium exchange -- lewis bases -- lithium -- magnesiates; Chemistry -- Periodicals; 540
• DOI: 10.1002/anie.202012496
• Languages: English
• ISSNs: 1433-7851

Abstract

Abstract: Using the bimetallic combination sBu2 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. Abstract : Using the bimetallic combination s Bu2 Mg⋅2 LiOR (R=2‐ethylhexyl) in toluene enables a very fast regioselective Br/Mg exchange of dibromo(hetero)arenes in toluene. The regioselectivity of the exchange can be finely tuned by the coordination preference of lithium, which can be switched, in some cases, by the addition of Lewis donors such as PMDTA.