Methylene magnesium halides

Bertini, F., Grasselli, P., Zubiani, G., Cainelli, G. Geminal dimetallic compounds. Reactivity of methylene magnesium halides and related compounds. General carbonyl olefination reaction. Tetrahedron 9 0, 26,1281-1290. 

The yields indicated refer to the in situ procedure. With the use of preformed methylene magnesium halide the yields are generally better and the reaction is cleaner. This latter procedure is, however, less practical if a large scale reaction is performed... 

As in the Grignard reaction we may use any aliphatic aldehyde, ketone, ester or acid chloride, or an aryl compound of the same type and also, we may use either alkyl magnesium halides or aryl magnesium halides the synthesis makes possible the preparation of practically any desired secondary or tertiary alcohol either aliphatic or aromatic. Also if formaldehyde, in the form of its polymer, tri-oxy methylene, is used in the second reaction we will obtain primary alcohols. In the third reaction formic acid esters yield secondary instead of tertiary alcohols. These syntheses of alcohols by the Grignard reaction give us an idea of its importance in synthetic work. 

Methylene chloride has high solvent power for magnesium halide etherates, even those derived from terminal acetylenes, which are sparingly soluble in ether, and is recommended for use in Grignard reactions (comparable to the more expensive tetrahydrofurane).- Thus a reagent is prepared in ether as usual but the solvent is replaced by methylene chloride prior to subsequent Grignard reaction. 

More recently Rathke and coworkers have described a procedure involving the carboxylation of a ketone in the presence of magnesium halide and triethylamine in acetonitrile with an optimal ratio of amine halide ketone of 4 2 1. Advantages included a lower reaction temperature and a solvent more readily removed (equation 40). The reaction showed little regioselectivity, as 2-butanone was carboxy-lated on the methyl and methylene groups in a ratio of SS 4S. The same group reacted a magnesium enol-ate with butenone in the initial Michael step of a Robinson annelation. 

It is, therefore, to be expected that a compound such as trimethyl-methylene stiborane, (CHs SbCtE, should be relatively unstable and attempts to synthesize this species would have to be carried out at low temperature. Another difficulty arises from the experimental fact (104) that all conventional methods of synthesis for stibonium ylides lead to pentaalkylstiboranes instead of ylides (see Introduction). Thus mcthyl-ation of (CH3)4SbX or (CHY) sHbX2 halides by organometallic reagents of lithium, magnesium, aluminum, or zinc invariably yield (CHY) 5Sb as the sole product. 

Methylenemagnesium bromide (iodide), CH2(MgX)2 [1, 678, before Methylene-triphenylphosphorane]. Prepared1 by reaction of magnesium amalgam with one of the following halides methylene bromide, CH2Br2, mol. wt. 173.86, b.p. 98.2° methylene iodide, CH2I2, mol. wt. 267.85,b.p. 180°. Supplier of both Eastman. 

The bisacylation of methylene-active compounds mentioned above can be avoided by using acylimidazoles in place of acyl halides (acylimidazoles are obtained from the carboxylic acid and sulfinyldiimidazole) for example, reaction of the magnesium enolate of ethyl hydrogen malonate and an acylimid-azole, with concomitant decarboxylation, gives the corresponding / -oxo ester 430... 

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