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Fe(II)-Catalyzed Isomerization of 5‑Chloroisoxazoles to 2H‑Azirine-2-carbonyl Chlorides as a Key Stage in the Synthesis of Pyrazole–Nitrogen Heterocycle Dyads
journal contribution
posted on 2018-02-15, 00:00 authored by Kirill
I. Mikhailov, Ekaterina E. Galenko, Alexey V. Galenko, Mikhail S. Novikov, Alexander Yu. Ivanov, Galina L. Starova, Alexander F. Khlebnikov2-(1H-Pyrazol-1-ylcarbonyl)-2H-azirines were synthesized by in situ trapping of 2H-azirine-2-carbonyl chlorides, generated by Fe(II)-catalyzed
isomerization
of 5-chloroisoxazoles, with pyrazoles. According to DFT calculations,
the selectivity of nucleophilic substitution at the carbonyl group
of 2H-azirine-2-carbonyl chloride by a pyrazole nucleophile,
which is a mixture of two tautomers, is controlled by thermodynamic
factors. 2-(1H-Pyrazol-1-ylcarbonyl)-2H-azirines are excellent precursors for the preparation of two other
pyrazole–nitrogen heterocycle dyads: 5-(1H-pyrazol-1-yl)oxazoles by photolysis and 1-(1H-pyrrol-2-ylcarbonyl)-1H-pyrazoles by a Ni(II)-catalyzed reaction with 1,3-dicarbonyl
compounds. 5-(1H-Pyrazol-1-yl)oxazoles show strong
emission in acetonitrile at 360–410 nm with high quantum yields.