BENZYNE FURAN CYCLOADDITION APPROACH TO THE ANGUCYCLINES - FIRST TOTAL SYNTHESIS OF ANTIBIOTIC C104

This paper describes the first total synthesis of an angucycline-class antibiotic, C104 (1), by exploiting regioselective benzyne-furan cycl oaddition. Angularly fused alpha-siloxyfuran 3, generated in situ by t reatment of butenolide 2 with NaH-TBDMSCl in THF, was directly subject ed to the reaction with alpha-alkoxybenzyne 5, which was generated als o in situ from alpha-iodo triflate 4. The high head-to-head selectivit y in the mode of the cycloaddition enabled the regiocontrolled constru ction of the characteristic benz[a]anthraquinone framework. The D-oliv osyl C-glycoside was introduced via the O --> C-glycoside rearrangemen t. This synthesis determined the absolute stereochemistry of this comp ound.