Grignard group-transfer reactions

Many organoarsenic compounds are prepared by reactions of AsC13 with alkyl group transfer agents such as Grignard reagents, lithium alkyls, or aluminum alkyls. Typical reactions include... 

Chiral sulfoxides are conveniently synthesised by Andersen s method (1962), in which a chiral sulfinate (4) is treated with a Grignard reagent. The reaction involves a sulfinyl group transfer and occurs with complete stereochemical inversion at the sulfur atom... 

Thus, the Grignard reagent can add to the less accessible 4 -position of the quinoline moiety rather than the 2 -position, and single diastereomers were isolated from all reactions (e.g., 14 and 15). Both observations were explained by assuming a group transfer within a metal chelate (Scheme 12.7). The choice of toluene as solvent for not breaking up those metal clusters is a key factor for obtaining satisfactory... 

Suppose, for example, that you wanted to add methylmagnesium chloride (CHsMgCl) to the carbonyl group of 5-hydroxy-2-pentanone to form a diol. Nucleophilic addition will not occur with this substrate. Instead, because Grignard reagents are strong bases and proton transfer reactions are fast, CH3MgCI removes the O-H proton before nucleophilic addition takes place. 

Addition to Carbonyl Compounds. Unlike Grignard and alkykitliium compounds, trialkylboranes are inert to carbonyl compounds. The air-catalyzed addition to formaldehyde is exceptional (373). Alkylborates are more reactive and can transfer alkyl groups to acyl halides. The reaction provides a highly chemoselective method for the synthesis of ketones (374). 

Grignard reagents that contain a /3-hydrogen—e.g. 15—can reduce a carbonyl substrate by transfer of that hydrogen as a side-reaction. The so-called Grignard reduction is likely to proceed via a six-membered cyclic transition state 16 the alkyl group of alkylmagnesium compound 15 is thereby converted into an alkene 17. 

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