Solvolysis of 3-keto-23-tosyloxy (A) and 3-keto-24-tosyloxy (B) derivatives of triterpenoid with t-butoxide proceeded in stereospecific manner to yield rearranged bicyclo [3, 2, 0] heptanones (C) and (D), being antipodal to one another with respect to the ketonic chromophor, whose structures were respectively established by spectral and chemical means. Reinvestigation of solvolysis for the simplest keto-tosylate (13) confirmed the formation of two bicyclo [3, 1, 1]- (14) and bicyclo [3, 2, 0]-(15) heptanones. The former rearranged by acid to a new bicyclo [3, 2, 0] heptanone (20), while the latter was stable to acid. Based on these evidences a plausible mechanism (Chart 4) of the homo-Favorskii rearrangement (13→15) was proposed. A new method of selectively converting a cyclobutanone to a γ-lactone in high yield was described.
三
萜类化合物3-酮-23-对
甲苯磺酰氧基(A)和3-酮-24-对
甲苯磺酰氧基(B)衍
生物与
叔丁醇的溶剂化反应以立体特异性方式进行,生成重排的双环[3,2,0]
庚酮(C)和(D),二者在酮基发色团方面互为对立,其结构分别通过光谱和
化学手段确定。对最简单的酮
对甲苯磺酸盐(13)的溶剂化反应进行重新研究,证实了两种双环[3,1,1](14)和双环[3,2,0](15)
庚酮的形成。前者通过酸重排为新的双环[3,2,0]
庚酮(20),而后者对酸稳定。根据这些证据,提出了同型Favorskii重排(13→15)的合理机制(图4)。描述了一种选择性地将
环丁酮转化为γ-内酯的新方法