The reaction of ginkgolide C (3) with tert-butylchlorodiphenylsilane results exclusively in the formation of the 1-0-tertbutyldiphenylsilyl ether 5, which when treated with 0- phenylchlorothioformate leads to the 7-phenyloxythiocarbonyl derivative 6. The reduction of 6 with tributyltin hydride/AIBN yields the 1-0-tert-butyldiphenylsilyl ether 7 of ginkgolide B (2). Removal of the silyl protective group with tetrabutylammonium fluoride gives pure ...