Cycloadditions of anionic N-heterocyclic carbenes of sydnone imines

TETRAHEDRON LETTERS

卷:60

Article

Freese, Tyll¹  Nieger, Martin²  Namyslo, Jan C.¹  Schmidt, Andreas¹ 

[1] Tech Univ Clausthal, Inst Organ Chem, Leibnizstr 6, D-38678 Clausthal Zellerfeld, Germany

[2] Univ Helsinki, Dept Chem, POB 55, FIN-00014 Helsinki, Finland

关键词: Mesoionic compounds;    1,3-Dipoles;    Tautomerism;    Pyrazole;    Bisiminonitrile;   

DOI  :  10.1016/j.tetlet.2019.04.006

来源: Elsevier

【 摘 要 】

Sydnone imines were deprotonated with lithium bis(trimethylsilyl)amide at the C4 position to give the corresponding sydnone imine anions as lithium adducts. These can be represented as lithium stabilized anionic N-heterocyclic carbenes. Treatment with diisopropyl azodicarboxylate (DIAD) gave the corresponding C4 adducts, i.e. 4-hydrazinyl-sydnone imines, which form tautomers in solution. Reductive 1,3-dipolar cycloadditions of the sydnone imine anions with tetracyanoethylene (TCNE) resulted in the formation of pyrazoles, the mechanism of formation of which differs from known reactions. Reaction of the anion derived from the 2-methoxyphenyl sydnone imine with N,N-diisopropylcarbodiimide gave a ring-cleaved bisiminonitrile. Structure elucidations were accomplished by NMR spectroscopy and by four single crystal X-ray analyses. (C) 2019 Elsevier Ltd. All rights reserved.

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