Acta Chimica Sinica ›› 2020, Vol. 78 ›› Issue (8): 758-762.DOI: 10.6023/A20050191 Previous Articles     Next Articles

Communication

三氟乙酸酐(TFAA)促进的Stieglitz重排反应制备苯胺

罗潇, 焦宁   

  1. 北京大学药学院 天然药物及仿生药物国家重点实验室 北京 100191
  • 投稿日期:2020-05-28 出版日期:2020-08-15 发布日期:2020-07-10
  • 通讯作者: 焦宁 E-mail:jiaoning@pku.edu.cn
  • 基金资助:
    项目受国家自然科学基金(Nos.21632001 and 21772002)资助.

From Hydroxylamines to Anilines via Trifluoroacetic Anhydride (TFAA) Assisted Stieglitz Rearrangement

Luo Xiao, Jiao Ning   

  1. State Key Laboratory of Natural and Biomimetic Drugs, School of Pharmaceutical Sciences, Peking University, Beijing 100191
  • Received:2020-05-28 Online:2020-08-15 Published:2020-07-10
  • Supported by:
    Project supported by the National Natural Science Foundation of China (Nos. 21632001 and 21772002).

Hydroxylamines have a wide range of biological properties and have been used as a useful synthon in organic synthesis. In the past decades, many transformations of hydroxylamines have been developed and widely applied. In contrast, one of the interesting reactions of hydroxylamines through C—C bond cleavage, named Stieglitz rearrangement, was less developed. Due to the poor leaving ability of the hydroxyl groups, the reported Stieglitz rearrangement reactions suffered from the harsh conditions and the very limited substrate scope with triarylmethyl hydroxylamine substrates. Since an interesting C—C bond cleavage is involved which will extend the synthetic application of hydroxylamine, the practical method under mild conditions with broad substrate scope for Stieglitz rearrangement is very desired. However, there are three potential problems which need to be addressed. First, the activator must selectively react with the hydroxyl group but not the N-nucleophile of the hydroxylamine substrates. Secondary, a suitable leaving group must be generated to weaken the N—O bond. In addition, the employed activator must be inactive to the formed imine intermediates and the subsequent amine products. Herein, we developed an efficient Stieglitz rearrangement reaction of hydroxylamines under mild conditions for the preparation of corresponding primary aryl amines. This chemistry using simple trifluoroacetic anhydride (TFAA) as an activator resolves the issues mentioned above and therefore provides a practical protocol for the further transformation and application of hydroxylamines. Mechanistic studies demonstrate that the in situ generation of an active trifluoroacetate leaving group derived the aryl migration process via both of the C—C and N—O bond cleavage. A general procedure for the TFAA assisted stieglitz rearrangement is as follows: BF3·Et2O (28.4 mg, 0.2 mmol), TFAA (46.2 mg, 0.22 mmol) were added to the solution of hydroxylamine (0.2 mmol) in 2 mL hexafluoroisopropanol (HFIP). The reaction mixture was stirred at room temperature for 1 h. After that, the reaction was quenched by 4 mL 2 mol/L NaOH (aq.) and extracted by the mixture of petroleum ether and ethyl acetate (1∶1, VV). The combined organic phase was concentrated, and purified by flash chromatography on a short silica gel to afford the desired product (eluent: petroleum ether/ethyl acetate).

Key words: C—C bond cleavage, Stieglitz rearrangement, hydroxylamine, aniline, aryl migration