Stereoselective epoxidation of 4(20)-exomethylene in taxinine derivatives and assignment of the epoxide orientation by NMR

✍ Scribed by Hirokazu Hosoyama; Hideyuki Shigemori; Yasuko In; Toshimasa Ishida; Jun'ichi Kobayashi

• Publisher: Elsevier Science
• Year: 1998
• Tongue: French
• Weight: 591 KB
• Volume: 54
• Category: Article
• ISSN: 0040-4020
• DOI: 10.1016/s0040-4020(98)00018-0

✦ Synopsis

Epoxidation of taxinine (1), taxinine A (2), and taxinine derivative 7 with m-chloroperbenzoic acid afforded the a-4(20)-epoxides selectively (ct : 13 = 99 : 1), while epoxidation of taxinine derivatives 7 and 8 with dimethyldioxirane gave the 13-4(20)-epoxides predominantly (ct : I 3 = 1 : 4-5). The epoxide orientation was found to be assignable by magnitude of chemical shift differences between the geminal epoxide protons in the 1H NMR spectra. Relative stereochemistry of 113-hydroxybaccatin I (9) possessing 13-4(20)-epoxide moiety was established by X-ray analysis to provide valid assignment of the epoxide orientation.