Lower Temperature Condensations to Ketones

Enantioselective additions are facilitated with chiral Lewis acids or L-proline  

Tridentate BINOL catalysts can be derived from titanium tetra(isopropoxide), BINOL ligands, and hindered amine bases. These catalysts have also been shown to provide good yields and ee s for the aldol reactions at low temperatures of 2-methoxypropene with several aldehydes to the P-hydroxyketones, but an acid workup of the products is required. 

The use of L-proline as an aldolase mimic has produced extraordinary results in cross-aldol reactions of acetone and aldehydes and of dissimilar aldehydes, giving p-hydroxyketones with ee s 80%. From limited results it appears that L-proline is as active or more active than the catalysts mentioned above (below ambient temperatures, with good yields in 24 h), and exhibits consider- 

An oxidative decarboxylation at ambient temperature is that of the a-hy-droxy, a-trifluoromethyl acids or esters to the corresponding trifluoromethyl-ketones, using bidentate Co-amide catalysts, with yields 80%. Again, these are slow reactions requiring relatively low reactant/catalyst ( 25/1) ratios, and an aldehyde promoter which is partly oxidized itself. 

The impetus for low temperature aldol processes in the absence or minimization of organic solvent has resulted in several new approaches. For example, Dewa et al. describe an aldehyde-ketone condensation catalyst that can be suspended in water, prepared by reacting lanthanum tris(isopropoxide) with anthracenebisresorcinol (ABR). A polymeric aquo complex with several 1,2-linked ABRs and two (LaOH) + groups is formed, coordinating 30 water molecules and relatively stable to decomposition. The base strength of this complex approached that of aqueous NaaCOs. 

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