Depending on the conditions and the acid employed, 18β,19β-epoxy-28-hydroxy- 21-oxolupan-3β-yl acetate (2a) and 18β,19β-epoxy-21-oxolupane-3β,28-diyl diacetate (2b) on treatment with acid gave three types of products: (i) 28-nor derivatives: 21-oxo-28-norlupa-16,18-dien-3β-yl acetate (6), 19β-hydroxy-21-oxo-28-norlup-17-en-3β-yl acetate (7) and 17ξ-hydroxy-21-oxo-28-norlup-18-en-3β-yl acetate (8), (ii) lupa-12,18-dien-21-ones 4a and 4b, and (iii) 22β-substituted lup-18-en-21-one derivatives of the type 5. The formation of 22β-substituted derivatives of the type 5 probably proceeds in the enol form of epoxy ketone 2. Opening of the epoxide ring with shift of the double bond to position 19(21) and attack by nucleophilic species at C-22 followed by elimination of water and re-formation of the 22-oxo group leads to derivatives of the type 5.
根据条件和使用的酸,18β,19β-环氧-28-羟基-21-氧代鲁珀烷-3β-
乙酸酯(
2a)和18β,19β-环氧-21-氧代鲁珀烷-3β,28-二
乙酸酯(
2b)在酸的处理下分别产生三种类型的产物:(i)28-去衍
生物:21-氧代-28-去鲁珀-16,18-二烯-3β-
乙酸酯(
6),19β-羟基-21-氧代-28-去鲁珀-17-烯-3β-
乙酸酯(
7)和17ξ-羟基-21-氧代-28-去鲁珀-18-烯-3β-
乙酸酯(
8),(ii)鲁珀-12,18-二烯-21-酮
4a和
4b,以及(iii)22β-取代的鲁珀-18-烯-21-酮衍
生物5型。类型
5的22β-取代衍
生物的形成可能是在环氧酮
2的烯醇形式中进行的。环氧环的开放,双键移位至19(21)位,核ophilic物种攻击C-22,随后消除
水并重新形成22-氧基团,导致
5型衍
生物的形成。