Total Synthesis of C-Glycosylangucycline, Urdamycinone B, Using an Unprotected Sugar

The total synthesis of urdamycinone B ( 1 ), a prototypical member of the C -glycosylangucycline antibiotics, was achieved by a novel and effective strategy without any protecting group in the sugar moiety. The unprotected C -glycosyljuglone 6 was effectively synthesized by the aryl C -glycosidation of 1,5-naphthalenediol ( 16 ) with the totally unprotected d -olivose ( 8 ) and the subsequent regioselective photooxygenation of the resultant C -glycosylnaphthalenediol 17 . On the other hand, the diene 7 was prepared from 3-methyl-2-cyclohexen-1-one ( 9 ) in a short step via the cross-coupling of the vinyl triflate 20 and vinylbutyltin ( 21 ) and the Wittig reaction of the aldehyde 24 and the phosphine 25 . Finally, the regioselective Diels−Alder reaction of the unprotected C -glycosyljuglone 6 and the diene 7, followed by the regioselecitive introduction of the ketone function at the C1 position, led to the total synthesis of 1 .