Nonplanar Structures of Thioamides Derived from 7-Azabicyclo[2.2.1]heptane. Electronically Tunable Planarity of Thioamides
Nonplanar Structures of Thioamides Derived from 7-Azabicyclo[2.2.1]heptane. Electronically Tunable Planarity of Thioamides
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DOI：
10.1021/jo801996b
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发表时间：
2008-11-21
影响因子：
3.6
通讯作者：
Ohwada, Tomohiko
中科院分区：
文献类型：
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作者：
Hori, Tetsuharu;Otani, Yuko;Ohwada, Tomohiko
X-射线晶体学分析表明，与相应的单环吡咯烷硫代酰胺（2a，α = 174.7度和竖线τ竖线= 3.9度）相比，N-硫代苯甲酰基-7-氮杂双环[2.2.1]庚烷显示出硫代酰胺的显著非平面性（1a，α = 167.1度和竖线τ竖线= 11.2度）。在一系列对位取代或未取代的硫代芳酰基-7-氮杂双环[2.2.1]庚烷（1a-1h）中，硫代酰胺的平面性明显取决于取代基的电子性质;例如，在对硝基取代的化合物中，平面性基本恢复（1h，α = 175.2度，垂直条τ垂直条= 0.1度）。在溶液中，增加吸电子字符的芳香族取代基与一个较大的旋转障碍的双环硫代酰胺，通过变温H-1 NMR光谱和线形分析确定。与硝基苯-d（5）中的2a相比，la的降低的转动势垒，即硫代酰胺转动的降低的活化焓（Δ H双匕首）与la在溶液中呈现非平面硫代酰胺结构的假设一致。这些结果表明，基于7-氮杂双环[2.2.1]庚烷的硫代酰胺的平面性由固相和溶液中的电子因素控制。
X-ray crystallographic analysis showed that N-thiobenzoyl-7-azabicyclo[2.2.1]heptane displays marked nonplanarity of the thioamide (1a, alpha = 167.1 degrees and vertical bar tau vertical bar = 11.2 degrees) as compared with the corresponding monocyclic pyrrolidine thioamide (2a, alpha = 174.7 degrees and vertical bar tau vertical bar = 3.9 degrees). In a series of para-substituted or unsubstituted thioaroyl-7-azabicyclo[2.2.1]heptanes (1a-1h), the planarity of the thioamide depended significantly on the electronic nature of the substituent; for example, in the p-nitro-substituted compound, planarity was substantially restored (1h, alpha = 175.2 degrees and vertical bar tau vertical bar = 0.1 degrees). In solution, increasing electron-withdrawing character of the aromatic substituent was associated with a larger rotational barrier of the bicyclic thioamides, as determined by means of variable-temperature H-1 NMR spectroscopy and line shape analysis. The reduced rotational barrier, that is, reduced enthalpy of activation (Delta H double dagger) for thioamide rotation, of la as compared with that of 2a in nitrobenzene-d(5) is consistent with the postulate that la assumes a nonplanar thioamide structure in solution. These results indicate that the planarity of thioamides based on 7-azabicyclo[2.2.1]heptane is controlled by electronic factors in the solid phase and in solution.