Preparation of Magnesiated Nitrogen-Heterocycles

Direct access to pyridylmagnesium hahdes by use of melallic magnesium is diffi- 

Queguiner has examined the exchange reactions of bromopyridines, which are cheaper than iodopyridines and often commercially available [101, 102]. The exchange reactions occur with PrMgCl in THF at room temperature. Tab. 3.5 shows the results of exchange reactions and subsequent trapping by electrophiles. 

The exchange reaction of 2-, 3-, and 4-bromopyridine with PrMgCl proceeds smoothly to provide the corresponding magnesium species. The reaction of dibro-rnopyridines affords mono-magnesium species, with complete regioselectivity for 2,3- and 2,5-dibromopyridine. 

Examples of the preparation of other heterocyclic magnesium compounds are shown in Tab. 3.6. The preparation of Grignard reagents derived from bromofuran, bromothiophene, and bromoselenophene has been reported, but no synthetic application has been attempted [106]. 

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