Organometallic aldol condensation

One of the several mechanisms for decarboxylation is the reverse of the familiar carboxylation reaction of organometallic compounds or carbanions. Many of the acids RCOOH that are readily decarboxylated in basic media are compounds for which the corresponding R( ) is a comparatively stable carbanion.405 The postulated intermediate has actually been trapped or diverted in a few cases as the product of an aldol condensation.406... 

Cp 2La CH(SiMe3)2 reacts with 3-pentanone to form the solvated enolate, Cp 2La —O—C(Et)=CHMe Et2CO (equation 9a), while with acetone it forms a chelate (equation 9b) after intramolecular aldol condensation. The reaction of the precursor bistrimethylsi-lyhnethyl organometallic with hydroxyketone, preformed from the pentanone, yields the enolate ketone solvate. This difference between acetone and 3-pentanone presumably reflects the difference in strain in the condensation product because the ethyl groups in 3-pentanone are rather much bigger than the methyl groups in acetone. 

This Schiff base is metallated with an appropriate lithium compound to XII and subsequently reacted with benzophenone or acetone. Since the protective group can be removed following the aldol addition, this method is a means of bringing about organometallic directed aldol condensations ... 

The ethyl derivatives of aluminum, cadmium, magnesium, and zinc yield highly crystalline polymers. Organometallic eomplexes such as magnesium diethyl cobalt chloride, which coordinate strongly with the polymer anion and the monomer, produce white crystalline PMVK. PMVK obtained by alkoxides, sodium naphthalene, and -butyllithium are intensively colored because of a partially occurring aldol condensation [292]. The mechanism of these reactions has been studied intensively. It is assumed that... 

General reviews include the direct aldol/" aldoi and related processes,the Zimmerman-Traxler TS model used to explain the stereochemistry of the aldoi condensation,catalysis of direct asymmetric aldols by prolinamides versus prolinef/zioamides, " " the catalytic asymmetric aldoi reaction in aqueous media (considering both organometallic and organocatalytic approaches), " the use of BINAP oxide in enantioselective direct aldols,and the use of metal enolates as synthons. " ... 

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