Magnesium metal activated

The reaction might be initiated by one-electron transfer from magnesium metal, activated by TMSCl, to -arylacrylates 137 to give the corresponding anion radicals 139 (Scheme 3.143), which might be then subject to electrophilic attack by aldehydes 140, activated by TMSCl, generating anionic radical species 141, followed by the fast second electron transfer. Subsequently, the formed anionic cross-coupling intermediates 142 (possibly coordinated with Mg ion or stabilized by TMSCl) can be transformed to the product, y-lactones 138, by intramolecular cych-zation. 

We may use the activity series to predict certain types of redox reactions. For example, suppose you wanted to write the equation between magnesium metal and hydrochloric acid ... 

Alcohols, (a) Monohydric The common impurities in alcohols are aldehydes or ketones, and water. [Ethanol in Chapter 3 is typical.] Aldehydes and ketones can be removed by adding a small amount of sodium metal and refluxing for 2 hours, followed by distillation. Water can be removed in a similar way but it is preferable to use magnesium metal instead of sodium because it forms a more insoluble hydroxide, thereby shifting the equilibrium more completely from metal alkoxide to metal hydroxide. The magnesium should be activated with iodine (or a small amount of methyl iodide), and the water content should be low, otherwise the magnesium will be deactivated. 

Selective reduction of only one C-F bond in hexafluoroacetone (1) to give enol 2 is accomplished using activated aluminum as a reducing agent.89 90 It has been found in the reduction of hexafluoroacetone by magnesium metal in tetrahydrofuran that the intermediate penta-fluoropropen-2-olate subsequently reacts with a molecule of hexafluoroacetone to yield per-... 

Activation of magnesium. Numerous procedures have been used, whereby the surface of magnesium is activated [A, D] in many cases the procedures are empirical — it is not known whether they work merely by cleaning or etching the metal surface, or whether the formation of some intermediate reactive magnesium compound is involved. A selection of better-known procedures follows examples are described or listed in Section 3.1.1. 

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