monoacetate 5.2. It is noteworthy that this reaction was exclusive for the allylic alcohol, and the adjacent hydroxyl group was not acetylated. Alcohol 5.2 was oxidized with tetrapropylammonium perruthenate and N-methylmorpholine N-oxide to give ketone 5.3. Alkene 5.3 underwent hydroboration in tetrahydrofuran. Oxidation with basic hydrogen peroxide and sodium bicarbonate gave alcohol 5.4 in 35% yield, with 15% yield of a regioisomer. The acetonide was removed, giving triol 5.5. This alcohol was monoacetylated, to give acetate 5.6. The benzyl group was removed and replaced with a triethylsilyl group. Diol 5.7 was selectively activated using methanesulfonyl chloride and 4-(dimethylamino)pyridine to give mesylate 5.8, in 78% yield. The acetyl group in 6.1 (Scheme 6) was removed to give primary alcohol 6.2. The Taxol ring (D) was added by an intramolecular nucleophilic substitution involving this hydroxyl group to give oxetane 6.3. After acetylation, phenyllithium was used to open the carbonate ester ring to give alcohol 6.5. Allylic oxidation with pyridinium chlorochromate, sodium acetate, and celite gave ketone 6.6, which was subsequently reduced using sodium borohydride to give secondary alcohol 6.7. This was the last compound before the addition of the amide tail. Tail addition As shown in Scheme 7, Ojima lactam 7.1 reacted with alcohol 7.2 with sodium bis(trimethylsilyl)amide as a base. This alcohol is the triethylsilyl ether of the naturally occurring compound baccatin III. The related compound, 10-deacetylbaccatin III, is found in Taxus baccata, also known as the European Yew, in concentrations of 1 gram per kilogram leaves. Removal of the triethylsilyl protecting group gave Taxol. Precursor synthesis Synthesis of the Diels-Alder dienophile for Ring C The ethyl ester of propionic acid (1) was brominated and then converted to the Wittig reagent using triphenylphosphine. Aldehyde 6 was obtained from allyl alcohol (4) by protection as the tert-butyldiphenylsilyl ether (5) followed by ozonolysis. Wittig reagent 3 and aldehyde 6 reacted in a Wittig reaction to give unsaturated ester 7, which was deprotected to give dienophile 8 (Scheme 1, compound 1). Synthesis of the Diels-Alder diene for Ring A Aldol condensation of acetone and ethyl acetoacetate gave β-keto-ester 3. A Grignard reaction involving methylmagnesium bromide provided alcohol 4, which was subjected to acid catalyzed elimination to give diene 5. Reduction and acetylation gave diene 7 (Scheme 3, compound 1). Protecting groups Ac (acetyl) Protection: Acetic anhydride, pyridine, 4-(dimethylamino)pyridine, and dichloromethane Deprotection: Potassium carbonate in methanol and water solvent Protection prevented mesylation of the primary