| Abstract
| - Several 4-substituted dihydropyridones or 2-pyridones have been prepared by nucleophilic additionof α-(methylsulfanyl)ester enolates to N-alkyl-2-fluoropyridinium salts, followed by acid hydrolysisor oxidation with concomitant hydrolysis, of the intermediate 2-fluoro-1,4-dihydropyridine adducts,respectively. Addition of the enolate derived from isopropyl α-(methylsulfanyl)butyrate to N-(quinolylmethyl)-2-fluoropyridinium triflate 21 followed by DDQ treatment gave pyridone 29, from which(±)-20-deoxycamptothecin (31), a known precursor of camptothecin, was synthesized by a radicalcyclization−desulfurization, with subsequent elaboration of the lactone E ring by chemoselectivereduction. A similar sequence starting from the enolate of a chiral 2-hydroxybutyric acid derivative(33) provides access to natural (+)-camptothecin (37).
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