Selective oxidation with lead tetra acetate

The synthesis has been modified to produce a series of porphyrin octaethanol derivatives (ethers) [162]. Pyrrole trimethyl ester (37) is selectively hydrolysed with sodium methoxide in methanol to give the diacid monoester (38), which is reduced (BH3/THF) and tosylated. The ditosylate was heated with the appropriate alcohol to afford the diether (with concommital transesterification of the pyrrolic a-ester). Oxidation with lead tetra-acetate gave compound 39, which was converted to the metal-free porphyrin in one pot by treatment with potassium hydroxide to hydrolyse the ester, hydrobromic acid to decarboxylate and cyclize, and chloranil to oxidize the macrocycle to the porphyrin (Scheme 44). 

A new method for selectively cleaving the D-glucuronidic linkages of saponins is based on oxidative decarboxylation of per-C>-methylated derivatives with lead tetra-acetate in benzene, followed by release of the aglycone with base (Scheme... 

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