Generation of Aryl and Heteroaryl Magnesium Reagents in Toluene by Br/Mg or Cl/Mg Exchange.

The alkylmagnesium alkoxide sBuMgOR⋅LiOR (R=2-ethylhexyl), which was prepared as a 1.5 m solution in toluene, undergoes very fast Br/Mg exchange with aryl and heteroaryl bromides, producing aryl and heteroaryl magnesium alkoxides (ArMgOR⋅LiOR) in toluene. These Grignard reagents react with a broad range of electrophiles, including aldehydes, ketones, allyl bromides, acyl chlorides, epoxides, and aziridines, in good yields. Remarkably, the related reagent sBu2 Mg⋅2 LiOR (R=2-ethylhexyl) undergoes Cl/Mg exchange with various electron-rich aryl chlorides in toluene, producing diorganomagnesium species of type Ar2 Mg⋅2 LiOR, which react well with aldehydes and allyl bromides.