TOTAL SYNTHESIS OF TAXOL .3. FORMATION OF TAXOLS ABC RING SKELETON

The synthesis of Taxol's ABC ring system has been achieved. The Shapir o coupling of an aldehydic C ring synthon (8) with an anionic A ring s ynthon derived from hydrazone 9 gave, diastereoselectively, A-B conjug ate 10. Functional group manipulations and McMurry ring closure produc ed the highly functionalized ABC ring system 17. Extensive attempts to optimize the McMurry reaction revealed a single predominant side reac tion leading to byproducts 19 and 20. Resolution of the CB,C10-diol (/-)-17 via its camphanyl esters provided the ABC ring system as its na tural isomer (+)17.