Grignard reagents solvent effects

The solvent, magnesium, and RX can have a deleterious effect on the preparation of the Grignard reagent. Some of the problems are a homocoupled product, formation of RMg02X, and noniaitiated reaction of RX with Mg. Therefore, proper preparation and handling of each component must be carried out. 

Cesium forms simple alkyl and aryl compounds that are similar to those of the other alkah metals (6). They are colorless, sohd, amorphous, nonvolatile, and insoluble, except by decomposition, in most solvents except diethylzinc. As a result of exceptional reactivity, cesium aryls should be effective in alkylations wherever other alkaline alkyls or Grignard reagents have failed (see Grignard reactions). Cesium reacts with hydrocarbons in which the activity of a C—H link is increased by attachment to the carbon atom of doubly linked or aromatic radicals. A brown, sohd addition product is formed when cesium reacts with ethylene, and a very reactive dark red powder, triphenylmethylcesium [76-83-5] (C H )2CCs, is formed by the reaction of cesium amalgam and a solution of triphenylmethyl chloride in anhydrous ether. 

Whereas THF and DME were suitable solvents, Lewis basic additives such as HMPA, DMSO or TMEDA hampered the reaction.82 These results point towards an intramolecular assistance of the zinc coordinated by the nitrogen atom. A related effect was evidenced in the additions of Grignard reagents to allylic alcohols83-87. Two mechanisms were proposed for the allylzincation of homoallylic amines involving formation of a complex with the... 

Furthermore, such a C3 -> C4 ring expansion could even be induced by lithium chloride. Thus, the cyclopropylcarbinol 228, prepared by addition of acetylenic Grignard reagents to the cyclopropanecarboxaldehyde 171a in 80-90% yield1101, was transformed into the tosylate 229 upon successive treatment with one equivalent of methyllithium in ether at 0 °C and with one equivalent of tosyl chloride at —40 °C, lithium chloride being formed as by-product. The formation of tosylate 229 appeared, however, to be strongly dependent upon the nature of the solvent effectively, the same... 

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