Direct Magnesiation Reactions

Magnesium amides, known as the Hauser bases [26], are able to magnesiate arenes and heteroarenes [27]. However, their low solubility in most organic solvents makes them difficult to handle. Furthermore, in noncoordinating solvents, these species behave as reducing agents for various functional groups such as keto, nitro, nitroso, and azoxy derivatives [28]. 

Not only magnesium amides but also magnesiate bases can be used for the preparation of organomagnesium derivatives or even dimagnesiated species via alkali-metal-mediated metaUations [35]. 

---

The excellent direct magnesiating properties of Turbo-Hauser reagent A extends beyond the confines of aromatic substrates (though these are by far the most frequently encountered substrates in such transformations). For example, the ether-functionalised ester, ethyl 2-ethoxyacrylate, can be selectively magnesiated in a reaction favoured by the stabilising effect of the adjacent carbonyl group, with work-up of the reaction mixture affording a non-aromatic cyclic lactone in an excellent yield (Fig. 16) [39]. 

Deprotonative zincation and magnesiation have been developed as alternatives for the lithiation of thiophenes. The drawbacks associated with lithiation are that it usually requires the reactions to be performed at —78°C, and the lithium derivatives so formed cannot he directly used for cross-coupling reactions. 

---