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

Add time:08/20/2019    Source:sciencedirect.com

Epoxidation of taxinine (1), taxinine A (2), and taxinine derivative 7 with m-chloroperbenzoic acid afforded the α-4(20)-epoxides selectively (α : β = 99 : 1), while epoxidation of taxinine derivatives 7 and 8 with dimethyldioxirane gave the β-4(20)-epoxides predominantly (α : β = 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 1β-hydroxybaccatin I (9) possessing β-4(20)-epoxide moiety was established by X-ray analysis to provide valid assignment of the epoxide orientation.

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