Cycloadditions of anionic N-heterocyclic carbenes of sydnone imines |
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Authors: | Tyll Freese Martin Nieger Jan C Namyslo Andreas Schmidt |
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Institution: | 1. Clausthal University of Technology, Institute of Organic Chemistry, Leibnizstrasse 6, D-38678 Clausthal-Zellerfeld, Germany;2. University of Helsinki, Department of Chemistry, P.O. Box 55, FIN-00014 Helsinki, Finland |
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Abstract: | 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. |
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Keywords: | Mesoionic compounds 1 3-Dipoles Tautomerism Pyrazole Bisiminonitrile |
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