Reactivity of 2-Halo-2H-azirines. Part II. [1] Thermal Ring Expansion Reactions: Synthesis of 4-Haloisoxazoles

Abstract

The thermolysis of haloazidoalkenes and 2-halo-2H-azirines is described. 2-Benzoyl-2-halo-2H-azirine-3-carboxylates (2a and 2b) underwent ring expansion leading to the synthesis of new 4-haloisoxazoles in high yield. The same isoxazoles were also obtained in high yield directly from haloazidoalkenes (1a and 1b). The thermolysis of the β-azido-α,β-unsaturated ketone 1e led to complete conversion to form the corresponding isoxazole 4e. An isoxazole derivative 4c could also be obtained, in moderate yield, from 2-bromo-3-phenyl-2H-azirine-2-carboxylate (1c). From the thermolysis of azidoalkene 1d the only product that could be isolated was pyrazine-2,3,5,6-tetracarboxylate (5).

Key words

ring expansion - phosphorus ylides - haloazidoalkenes - 2-halo-2H-azirines - 4-haloisoxazoles

References

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Chrystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with Cambridge Crystallographic Data Centre as supplementary publication No. CCDC 181125. Copies of the data can be obtained free of charge on application to The Director, CCDC, 12 Union Road, Cambridge CB2 IEZ, UK (fax: [phone], email: [e-mail]).