Mechanism of the rearrangement of vinyl allene oxide to 2-cyclopenten-1-one
Mechanism of the rearrangement of vinyl allene oxide to 2-cyclopenten-1-one
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DOI：
10.1021/ja990728j
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发表时间：
1999-06-16
影响因子：
15
通讯作者：
Cha, JK
中科院分区：
文献类型：
--
作者：
Hess, BA;Smentek, L;Cha, JK
前列腺素(PG)和结构上相关的环戊烷类化合物在植物界和动物界都有发现。在哺乳动物中，PGs是环氧合酶催化不饱和脂肪酸代谢的结果。另一方面，海洋生物中环戊烷生物合成的机制细节仍未解决。在植物和海洋生物中，丙二烯氧化物是PGs和相关的环戊烷类化合物的潜在前体，它是由脂氧合酶衍生的不饱和脂肪酸氢过氧化氢在酶作用下脱水产生的。1，2乙烯基丙二烯氧化物被认为首先开放为乙烯氧基烯丙基(即2-氧基戊二烯基阳离子)，然后经历旋转环闭合得到环戊烯酮产品。关于环戊酮环化的仿生研究也是已知的。3然而，在以前的任何工作中都没有讨论乙烯基环氧丙烯协同重排为环戊酮的可能性。在这里，我们首次详细地报道了乙烯基烯氧化物重排为2-环戊烯-1-酮的理论研究，并讨论了它对天然生成的烯丙烯氧化物中双键的未知几何构型的影响。4我们最近报道了一项关于母体环氧丙烷通过氧烯丙基中间体重排为环丙酮的从头算研究，其中密度泛函方法(DFT)被证明是处理两性离子(或双自由基)的合适方法。因此，所有的计算都是用密度泛函方法进行的，采用6-31G*基组7和Becke的三参数泛函(U)B3LYP。8，9我们发现环氧烯丙烷可以以两种能量相似的构象存在，S-反式(1)，具有平面碳骨架，S-顺式(3)，具有非平面碳骨架，由过渡结构2连接，1比3更稳定(见图1)。10，11 S-顺式构象与S-反式构象处于平衡状态，可协同重排为2-环戊烯-1-酮(5)。实际上，确定了协同重排的过渡结构4，IRC计算9表明它连接了3和5。过渡结构4具有SN2特征，通过双键π电子的攻击从背面辅助CO键的断裂。
Prostaglandins (PGs) and structurally related cyclopentanoids have been found in both the plant and animal kingdoms. In mammals, PGs result from cyclooxygenase-catalyzed metabolism of unsaturated fatty acids. On the other hand, the mechanistic details of cyclopentanoid biosynthesis in marine organisms remain unresolved. Implicated as potential precursors to PGs and related cyclopentanoids in plants and marine organisms are allene oxides, which are produced by the enzymatic dehydration of a lipoxygenase-derived unsaturated fatty acid hydroperoxide. 1, 2 Vinyl allene oxide is thought to first open to vinyl oxyallyl (ie, 2-oxidopentadienyl cation), which then undergoes a conrotatory ring closure to give the cyclopentenone product. Biomimetic studies on the cyclopentenone annulation are also known. 3 However, the possibility of a concerted rearrangement of vinyl allene oxide to cyclopentenone has not been addressed in any previous work. Herein we report the first detailed theoretical study on the rearrangement of vinyl allene oxide to 2-cyclopenten-1-one and discuss its implication in the hitherto unknown geometry of the double bond in naturally occurring allene oxides. 4 We have recently reported an ab initio study on the rearrangement of the parent allene oxide (methyleneoxirane) to cyclopropanone via the oxyallyl intermediate, 5 in which the density functional method (DFT) was demonstrated to be appropriate for treating zwitterions (or diradicals). Hence, all calculations6 were done with the DFT method using the 6-31G* basis set7 with Becke’s three-parameter functional,(U) B3LYP. 8, 9We found that vinyl allene oxide can exist in two energetically similar conformations, s-trans (1), with a planar carbon skeleton, and s-cis (3), with a nonplanar carbon skeleton, linked by a transition structure 2, with 1 more stable than 3 (see Figure 1). 10, 11 A concerted rearrangement to 2-cyclopenten-1-one (5) could occur from the s-cis conformer, which is in equilibrium with the s-trans conformer. Indeed, a transition structure 4 for the concerted rearrangement was located, and IRC calculations9 showed it linked 3 with 5. The transition structure 4 has SN2 characteristics, with the CO bond breakage assisted from the back side by attack of the double bond π electrons.