At this stage, the formal syntheses of ginkgolide A (1) and B (2) were attempted using anomer 23 (Scheme 1B). The sequence was initiated by converting 23 into the corresponding enone 24 via a one-pot double oxidation with SeO2 and Dess-Martin periodinane (78% yield, rr = 6.4:1)). The stage was set for the stereoselective conjugate addition of the tBu group which required a carefully planned sequence using tBuLi, CuCN followed by the addition of TMSI. The resulting TMS enol ether was then exposed to TBAF yielding ketone 25 (81%) as a single diastereomer. Gratifyingly, a stereoselective reduction with LiBH4 provided the corresponding alcohol which after the addition of NaOH (1M) underwent a 5-exo-dig cyclization forming the D-ring of 26 in 92% yield. Under these basic conditions the acetate group was hydrolysed liberating the alcohol at C3. Ozonolysis of enol ether 26 yielded the hydroxylactone 27 in 91% yield which was directly oxidized with IBX and 4-methoxypyridine N-oxide (MPO) leading to enone 28 in 41% yield. This Although the formal syntheses of 1 and 2 were accomplished, we turned our attention to the preparation of the "pièce de résistance" ginkgolide C (3) (Scheme 2). Starting with anomer 22 and using similar allylic oxidation conditions as for 24 (vide supra), the corresponding enone 29 was obtained in 85% yield. Although the conjugate addition of the tert-butyl group afforded the desired enol ether or ketone, it was not possible to achieve the α-oxygenation as originally planned despite considerable experimentation. Further examination of 29 suggests that the phenylacetylene overhangs the enone portion of ring E, thus preventing electrophilic addition to the enol ether or enolate. We imagined that freeing the B ring from the acetylene group would allow the desired oxygenation reaction to occur. For this purpose, a one-pot reaction was conducted. After the addition of the tert-butyl cuprate reagent, an aqueous solution of NaOH (1M) was then added to the reaction mixture, hydrolyzing the acetate group and at the same time inducing a 5-endo-dig cyclization of the C3 alcohol onto the proximal alkyne to generate the ketone 30 in 80% yield (in one step).