Diazoesters conversion

Some examples of transformations involving carbonyl ylides are listed in Table 4.20. Entry 1 illustrates the conversion of P-acyloxy-a-diazoesters into a-acyloxyacrylates by ring fission of a cyclic carbonyl ylide [978]. This reaction has been used for the synthesis of the natural aldonic acid KDO (3-deoxy-Z)-manno-2-octulosonic acid), which is an essential component of the cell wall lipopolysaccharide of gram-negative bacteria (Figure 4.15). 

Although the present procedure illustrates the formation of the diazoacetic ester without isolation of the intermediate ester of glyoxylic acid />-toluenesulfonylhydrazone, the two geometric isomers of this hydrazone can be isolated if only one molar equivalent of triethylamine is used in the reaction of the acid chloride with the alcohol. The extremely mild conditions required for the further conversion of these hydrazones to the diazo esters should be noted. Other methods for decomposing arylsulfonyl-hydrazones to form diazocarbonyl compounds have included aqueous sodium hydroxide, sodium hydride in dimethoxyethane at 60°, and aluminum oxide in methylene chloride or ethyl acetate." Although the latter method competes in mildness and convenience with the procedure described here, it was found not to be applicable to the preparation of aliphatic diazoesters such as ethyl 2-diazopropionate. Hence the conditions used in the present procedure may offer a useful complement to the last-mentioned method when the appropriate arylsulfonylhydrazone is available. 

Rhodium-catalysed carbenoid insertion has been used to make fused y-lac-tones, as in the conversion of diazoesters of type 93 into products 94 (R = H, COMe, C02Me), in which the indicated exo-isomer strongly predominated. When the readily-accessible uridine derivative 95 is treated as indicated in Scheme 5, the lactone 96 is obtained, and this can be used to make nucleosides 97 containing other bases, either purines or pyrimidines. ... 

Enantioselective conversion of a-alkyl diazoesters to a-alkyl-/ -ketoesters has been catalysed by an oxazaborolidium ion," °° and the H" -catalysed reaction of methyl-diazoacetate with benzaldehyde to form ketoesters and 3-hydroxy acrylates has been studied theoretically by DFT." ° ... 

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