Ring Expansion of Alkylidenecarbenes Derived from Lactams, Lactones, and Thiolactones into Strained Heterocyclic Alkynes: A Theoretical Study
Ring Expansion of Alkylidenecarbenes Derived from Lactams, Lactones, and Thiolactones into Strained Heterocyclic Alkynes: A Theoretical Study
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DOI：
10.3390/molecules24030593
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发表时间：
2019-02
期刊：
影响因子：
4.6
通讯作者：
Nguyen Nhat Thu Le;Josefine Just;Jonathan M. Pankauski;P. Rablen;D. Thamattoor
中科院分区：
文献类型：
--
作者：
Nguyen Nhat Thu Le;Josefine Just;Jonathan M. Pankauski;P. Rablen;D. Thamattoor
张力环炔化合物是理论和实验工作者十分感兴趣的一类化合物，也具有很高的合成价值。本文在CCSD（T）/cc-pVTZ//B3 LYP/6-311+G** 和CCSD（T）/cc-pVTZ//CCSD/6- 311 +G** 理论水平上模拟了一系列环状亚烷基卡宾（形式上通过用二价碳取代四元、五元和六元内酰胺、内酯和硫代内酯的羰基氧获得）。发现单重态卡宾比三重态卡宾更稳定。这些单重态卡宾的扩环形成的应变杂环炔也被建模。有趣的是，从β-内酰胺和β-内酯衍生的亚烷基卡宾的重排获得的五元杂环中的C → C键显示出介于形式双键和三键之间的长度。此外，发现2-（1-氮杂环亚丁基）卡宾与其扩环异构体几乎是等能的，并且1-氧杂环戊二烯-2-炔的能量明显高于其前体卡宾。在所有其他情况下，环炔的能量低于相应的卡宾。扩环的过渡态对于1，2-碳位移总是低于1，2-氮或氧位移，但高于1，2-硫位移。这些预测应该可以用带有适当同位素标记的卡宾来验证。计算的振动光谱的卡宾，和它们的扩环异构体，提出和可能是有价值的矩阵隔离实验。
Strained cycloalkynes are of considerable interest to theoreticians and experimentalists, and possess much synthetic value as well. Herein, a series of cyclic alkylidenecarbenes—formally obtained by replacing the carbonyl oxygen of four-, five-, and six-membered lactams, lactones, and thiolactones with a divalent carbon—were modeled at the CCSD(T)/cc-pVTZ//B3LYP/6-311+G** and CCSD(T)/cc-pVTZ//CCSD/6-311+G** levels of theory. The singlet carbenes were found to be more stable than the triplets. The strained heterocyclic alkynes formed by ring expansion of these singlet carbenes were also modeled. Interestingly, the C≡C bonds in the five-membered heterocycles, obtained from the rearrangement of β-lactam- and β-lactone-derived alkylidenecarbenes, displayed lengths intermediate between formal double and triple bonds. Furthermore, 2-(1-azacyclobutylidene)carbene was found to be nearly isoenergetic with its ring-expanded isomer, and 1-oxacyclopent-2-yne was notably higher in energy than its precursor carbene. In all other cases, the cycloalkynes were lower in energy than the corresponding carbenes. The transition states for ring-expansion were always lower for the 1,2-carbon shifts than for 1,2-nitrogen or oxygen shifts, but higher than for the 1,2-sulfur shifts. These predictions should be verifiable using carbenes bearing appropriate isotopic labels. Computed vibrational spectra for the carbenes, and their ring-expanded isomers, are presented and could be of value to matrix isolation experiments.