Seminar

Seminar

Efficient Synthetic Methods of N-Heterocyclic Compounds using Pyridinium Zwitterion

  • POSTED DATE : 2016-06-03
  • WRITER : 관리자
  • HIT : 3498
  • DATE : 2016-06-09
  • PLACE : 화학관 330118호

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제  목 : Efficient Synthetic Methods of N-Heterocyclic Compounds using Pyridinium Zwitterion


연  사 : 유은정 교수(강원대학교)


일  시 : 2016년 6월 9일(목) 오후 4시 30분


장  소 : 화학관 세미나실 (330118호실)

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Efficient Synthetic Methods of N-Heterocyclic Compounds using Pyridinium Zwitterion


Eun Jeong Yoo

Department of Chemistry, Kangwon National University, Chuncheon 200-701, Korea

E-mail:ejyoo@kangwon.ac.kr


[m+n]-Dipolar cycloaddition is a powerful and widely used strategy for synthesizing heterocyclic compounds in a single operation without giving rise to byproducts. Among the known dipoles, azomethine ylide, consisting of an iminium ion adjacent to a carbanion, is an allyl anionic type 1,3-dipole that can be applied to construct N-heterocyclic compounds. However, most studies have mainly focused on [3+2]-dipolar cycloaddition using well-known 1,3-dipoles and 2p-dipolarophiles, while scarce attention has been focused on the development of new types of dipoles, such as 1,2-dipole, 1,4-dipole, and 1,5-dipole, for the formation of non-five-memberted heterocycles. In this presentation, [5+n]-dipolar cycloaddition, which is an extraordinary tool for formation of medium-sized N-heterocyclic compound, will be present.


Air-stable pyridinium zwitterion is efficiently prepared via the rhodium-catalyzed reaction between pyridines and 1-sulfonyl-1,2,3-triazoles. This unprecedented pyridinium zwitterion are quite stable and exhibits different pattern of charge distribution in comparison with that of typical azomethine ylides. In addition, isolated zwitterions could be used as a 1,5-dipole for forming medium-sized heterocyclic compounds. Thermal [5+2]-dipolar cycloaddition of pyridinium zwitterions and dimethyl acetylenedicarboxylate (DMAD) successfully occurs to afford the seven-membered heterocycles with excellent yields. This breakthrough spurred the development of rhodium(II)-catalyzed three-component [5+2] cycloaddition reactions of pyridines, 1-sulfonyl-1,2,3-triazoles, and activated alkynes via the in situ generated 1,5-dipole; thus, a user-friendly and operationally simple strategy for systematic generation of the core structure of 1,4-diazepines was afforded.


We will also discuss a new type of intermolecular rhodium(II)-catalyzed [5+3]-dipolar cycloaddition of pyridinum zwitterions and enol diazoacetates. This higher-order cycloaddition allows for the formation of an eight-membered heterocyclic skeleton, which is otherwise difficult to construct. The optimized dipolar cycloaddition occurs efficiently under mild conditions over a wide range of pyridinium zwitterions with high functional group tolerance.


References

  1. Lee, D. J.; Ko, D.; Yoo, E. J.* “A Class of Rh(II)-Catalyzed Cycloaddition Reaction of Non-classical 1,5-Dipoles for Formation of Eight-Membered Heterocycles” Angew. Chem., Int. Ed. 2015, 54, 13715.

  2. Yoo, E. J.* “Azomethine Ylide: an Isolable 1,5-Dipole for Affecting [5+2] Cycloaddition Reaction” Synlett 2015, 26, 2189 (SYNPACTS, invited article).

  3. Lee, D. J.; Han, H. S.; Shin, J.; Yoo, E. J.* “Multicomponent [5+2] Cycloaddition Reaction for the Synthesis of 1,4-Diazepines: Isolation and Reactivity of Azomethine Ylides” J. Am. Chem. Soc. 2014, 136, 11606