In connection with attempts to generate oxete (8) via anionically assisted retro-Diels–Alder reaction, the oxetanes (11) and (12) have been prepared together with their acyclic analogues (35) and (36). The X-ray crystal structure of compound (11) has been determined. Each of the substrates (11), (12), (35) and (36) was treated with potassium hydride in the presence of 18-crown-6, conditions known to promote retro-Diels–Alder reactions in other systems. However, the first three substrates failed to engage in any such reaction even at temperatures up to 100˚C. In contrast, at 18˚C compound (36) reacted to give anthrone (13) in quantitative yield. These results indicate, inter alia, that regioelectronic effects play a crucial role in determining the success, or otherwise, of anionically-assisted retro-Diels–Alder reactions leading to polarized alkenes.
为了尝试通过阴离子辅助的逆-Diels–Alder 反应生成氧杂环丁烷 (8),我们制备了氧杂环丁烷 (11) 和 (12),以及它们的无环类似物 (35) 和 (36)。化合物 (11) 的 X 射线晶体结构已经确定。每种底物 (11)、(12)、(35) 和 (36) 都是在有 18-crown-6 存在的情况下用氢化钾处理的,众所周知,在其他体系中,这种条件会促进逆-Diels–Alder 反应。然而,即使在高达 100˚C 的温度下,前三种底物也未能发生任何此类反应。相反,在 18˚C 时,化合物 (36) 发生反应,生成定量产率的蒽酮 (13)。这些结果特别表明,区域电子效应在决定阴离子辅助的逆-Diels–Alder 反应能否成功导致极化烯方面起着至关重要的作用。