Boron trifluoride-catalyzed reaction of β-4(20)-epoxy-5-O-triethylsilyltaxinine A (1) gave the 3,5-diene (3) and the 3,8-cyclopropane (4) derivatives, while the similar reaction of the corresponding α-4(20)-epoxide (2) afforded the ring contracted derivative (5) and its hemiacetal dimer (6). Plausible mechanisms of these reactions containing 1,2-hydride shift (3 and 4 from 1) or pinacol-type rearrangement
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
taxinine(环氧化1),taxinine A(2),和taxinine衍生物7与米,得到氯过苯甲酸的α-4(20) -环氧化物选择性(α:β = 99:1),而taxinine衍生物的环氧化7和8与二甲基二,得到β-4(20) -环氧化物主要(α:β = 1:4〜5)。发现环氧化物的取向可通过1 H NMR光谱中双环环氧质子之间的化学位移差异的大小来确定。1β-羟基浆果赤霉素I的相对立体化学(9通过X射线分析确定具有β-4(20)-环氧部分的),以提供环氧方向的有效分配。
Further unexpected boron trifluoride-catalyzed reactions of taxoids with α- and β-4,20-epoxides
Three unusual taxinine derivatives, the cyclobutane 3, the dioxane 4, and the orthoester 5, were obtained by borontrifluoride-catalyzed reactions of β- and α-4,20-epoxy-5-O-triethylsilyltaxinine A (1 and 2, respectively) (3 and 4 from 1; 5 from 2).