The synthesis and synthetic utilization of the dimethyleneketene acetal 3 are described in this report. Thermal rearrangement of the methylenecyclopropanone acetal 1 at 150°C gives the dimethyleneketene acetal 3, which serves as a reactive surrogate of the enolate of alkyl cyclopropanecarboxylate, which has thus far been difficult to prepare. The ketene acetal 3 not only gives the corresponding alkyl cyclopropanecarboxylate 4 upon hydrolysis but also undergoes smooth [2+2] cycloaddition to electron-deficient olefins including C60. The cycloadduct undergoes facile ring cleavage upon aqueous workup to give the Michael addition product 6 in high yield. While the cycloadduct 8 due to the reaction between 3 and C60 is thermally unstable to generate C60 upon thermolysis, it undergoes quantitative hydrolytic cleavage to give the ester 10 upon attempted hydrolysis of the acetal moiety under acidic conditions. The cycloaddition of 3 with dialkyl azodicarboxylate also proceeds smoothly to afford cyclopropyl amino acid derivative in excellent yield.
本报告描述了二亚甲基烯
丙酸酯 3 的合成及其合成应用。将亚甲基环
丙酮酯 1 在 150°C 下进行热重排,可得到二亚甲基烯
丙酸酯 3,后者作为烷基
环丙烷羧酸酯的烯醇盐的反应性替代物,而烷基
环丙烷羧酸酯迄今为止难以制备。烯
丙酸酯 3 不仅在
水解后生成相应的烷基
环丙烷羧酸酯 4,还能顺利与电子缺乏的烯烃(包括 C60)发生平滑的 [2+2] 环加成反应。环加成产物在
水相处理后容易发生环裂解,生成迈克尔加成产物 6,产率高。由于 3 和 C60 的反应生成的环加成产物 8 在热解时不稳定,会生成 C60,但在酸性条件下尝试
水解醇酯基时,会量化
水解裂解生成酯 10。3 与双烷基偶氮二
羧酸酯的环加成也顺利进行,生成了优秀产率的环丙基
氨基酸衍
生物。