Rate-determining nitrogen inversion in the isomerisation of isoimides to imides and azides to tetrazoles: direct observation of intermediates stabilized by trifluoroethyl groups
Rate-determining nitrogen inversion in the isomerisation of isoimides to imides and azides to tetrazoles: direct observation of intermediates stabilized by trifluoroethyl groups
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DOI：
10.1039/b202005j
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发表时间：
2002-01-01
期刊：
影响因子：
--
通讯作者：
Fergus, S
中科院分区：
文献类型：
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作者：
Hegarty, AF;Tynan, NM;Fergus, S
N-烷基和N-三氟烷基苯并亚胺基氯化物在乙酸盐或叠氮离子存在下反应，首先生成相应的异亚胺4(Z)和亚胺基叠氮化物8(Z)(这两种产物都可以用光谱观察到)。它们是通过亲核捕获氮离子3在有机水溶液中形成的。随后，这些亚胺基乙酸酯和叠氮化合物重排成更稳定的酰亚胺5或四唑9。这些重排的特点是对溶剂极性的依赖性低，对添加的盐不敏感，这表明速度决定步骤是亚胺最初形成的Z-异构体异构化为E-异构体(亚胺氮反转)，而不是随后的N-&O酰基转移或环化。亚胺基叠氮化物重排为四唑的Hammett Rho值(-0.4)与其他速率决定步骤(氮气反转)相似的体系相比很好。因此，在三氟乙基存在的情况下，这些亚胺体系中的氮转化速度明显较慢(约为乙基的10倍)。
Reaction of N-alkyl-andN-trifluoroalkylbenzimidoyl chlorides 2 in the presence of either acetate or azide ion leads initially to the formation of the corresponding isoimides 4(Z) and imidoyl azides 8(Z) (both of which could be observed spectroscopically). These are formed via nucleophilic trapping of the nitrilium cations 3 in aqueous organic solutions. Subsequently these imidoyl acetates and azides rearrange to the more stable imides 5 or tetrazoles 9. These rearrangements are characterised by a low dependence on solvent polarity and insensitivity to added salts, indicating that the rate-determining step is the isomerisation of the initially formed Z-isomer of the imine to the E-isomer (imine nitrogen inversion) rather than the subsequent N-->O acyl group transfer or cyclisation. The Hammett rho value (-0.4), obtained for the rearrangement of the imidoyl azides to the tetrazoles, compares well to other systems where the rate-determining step (nitrogen inversion) was similar. Nitrogen inversion in these imine systems is therefore significantly slower (ca. 10-fold relative to an ethyl group) in the presence of the trifluoroethyl group on nitrogen.