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Solid-phase Synthesis of [4.4] Spirocyclic Oximes
Published on: February 6, 2019
[2 + 2] Cycloaddition/Retro-Electrocyclization/Decarboxylation Reaction Sequence: Access to 4-Aminopyridines from
Ekaterina E Galenko1, Mikhail S Novikov1, Alexander F Khlebnikov1
1Institute of Chemistry, St. Petersburg State University, 7/9 Universitetskaya nab., St. Petersburg 199034, Russia.
Abstract:
4-(1-Aminoallylidene)isoxazol-5-ones were synthesized in good yields by the [2 + 2]cycloaddition-retro-electrocyclization reaction of 4-methylideneisoxazol-5(4H)-ones with ynamines. The reaction mechanism and the absence of hetero-Diels-Alder cycloadducts were investigated by DFT calculations. 4-(1-Aminoallylidene)isoxazol-5-ones were found to be convenient substrates for the preparation of 4-aminopyridines under thermal metal-free conditions. The process proceeds via decarboxylative isomerization with cyclic amino groups and accompanied by partial dealkylation of acyclic amino groups. 4-Aminopyridines can also be prepared directly from 4-methylideneisoxazol-5(4H)-ones and ynamines by the one-pot protocol.
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