Aldol diazoacetates

The group of Arai and Nishida investigated the catalytic asymmetric aldol reaction between tert-butyl diazoacetate and various aldehydes under phase-transfer conditions with chiral quaternary ammonium chloride 4c as a catalyst. The reactions were found to proceed smoothly in toluene, even at —40°C, when using 50% RbOH aqueous solution as a base, giving rise to the desired aldol adducts 23 with good enantioselectivities. The resulting 23 can be stereoselectively transformed into the corresponding syn- or anti-P-hydroxy-a-amino acid derivatives (Scheme 2.20) [42],... 

Direct aldol-type condensations of aldehydes with ethyl diazoacetate to give /S-hydroxy-a-diazocarbonyl compounds, R-CH(0H)-C(=N2)-C02Et, are catalysed by tetrabutylammonium hydroxide.155... 

Acetylphosphonate diesters undergo an aldol-type condensation with diazoacetic ester to give (102). Another novel substituted phosphonate ester... 

Scheme 3.25 Aldol reaction of ethyl diazoacetate with aldehydes.

Dialkylzincs promote direct aldol-type reaction of ethyl diazoacetate with trilluoro-methyl ketones to give highly functionalized products, R-C(0H)(CF3)-C(=N2)-C02Et, in good to excellent yield. Preliminary screening of chiral catalysts gives some good ccs. ... 

Recently, the direct aldol reaction between commercially available ethyl diazoacetate (EDA) and an aldehyde represents an attractive process in synthetic chemistry. In this context, Trost and co-workers (141) surveyed a series of metal and the magnesium/prophenol ligand 88-derived catalyst system was found to give the highest enantioselectivity. Evaluation of the reaction revealed that high levels of enantioselectivities (87-98% ee) could be achieved for a wide range of aldehydes (Scheme 28). 

Scandium trifiate was found to be an effective catalyst for the aldol reactions of silyl enol ethers with aldehydes in aqueous solvent/micellar systems (205). While the reactions proceeded sluggishly in water, remarkable enhancement of the reactivity was observed in the presence of a small amount of a surfactant (206). In related asymmetric version, scandium trifiate (Sc(OTf)3) catalyzed asymmetric aldol of formaldehyde (hydroxymethylation) could be conducted with highly enantioselectively in the presence of chiral bipyridine based ligand (Scheme 53) (207). A significant progress was also made by Feng and co-workers recently a C-2-symmetric iV,iV -dioxide-Sc(III) complex has been developed to asymmetric catalytic aldol reaction of a-ketoesters and diazoacetate... 

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