Trityl compounds, hydrogenolysis

Carbonylat ion of 13 4-nitrophenyloxycarbonyl chloride (J 6) in pyridine] gave a good yield of the trityl ether-carbonate 14 which was de-tritylated by hydrogenolysis (2 4) to afford the 7,8-diol-4,5-carbonate 15 in practically quantitative yield. Compound 15.. by way of its 7,8-0 -dibutylstannylidene derivative (25> 26) was regioselectively 8-0-benzylated (dibutyltin oxide, benzene, reflux then benzyl bromide, dimethyl formamide, 95 ), in fair yield (J ). Finally, the aglycon U3 was obtained in high yield by sequential 7-Q-tert.-butyldimethylsilylation (27) (compound 17) and Zemplen saponification. 

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