Dienes, sugar-derived, osmylation

The C-glycoside 178 was used by Boyd and Sulikowski [87] in the total synthesis of enantiomerically pure urdamycinone B (182) and 104-2 (183) making use of the diene 107 derived from shikimic acid (Scheme 29) and the NMO oxidation to generate the C-5 phenols (Scheme 40). Thus, the bromonaphthoquinone 179 (prepared by treatment of phenol 178 with NBS) formed the tetracycle 180 through a Diels-Alder reaction with the diene 107 in analogy to sugar-free reactants. Osmylation to a cis-diol, deprotection, oxidation, and acetalization gave the acetonide 181. The decisive step in the aromatization to 182 and 183 was the reaction with NMO (Scheme 46). Aromatization was also effected by direct periodane oxidation of adduct 180 to derive 182 after deprotection. 

The diastereoselective synthesis of higher sugars was accomplished by bZi-osmylation of sugar derived dienes using OsO4-NMO4°. As shown in equation 23, osmylation of diene 26 afforded diastereomeric sugars 27, 28, and 29 in 90% overall yield in a 6.6 1.2 1.0 ratio, respectively. 

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