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Isoxazole Strategy for the Synthesis of α‑Aminopyrrole Derivatives

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posted on 19.08.2019, 21:45 by Ekaterina E. Galenko, Stanislav A. Linnik, Olesya V. Khoroshilova, Mikhail S. Novikov, Alexander F. Khlebnikov
The synthesis of methyl 5-aminopyrrole-3-carboxylates from 4-methyleneisoxazol-5-ones via “cyanide Michael addition/methylation/reductive isoxazole-pyrrole transformation” is developed. The last step occurs in a domino mode involving Mo­(CO)6-mediated reductive isoxazole ring-opening, Mo­(CO)6-catalyzed cistrans-isomerization of the enamine intermediate followed by 1,5-exo-dig cyclization. 5-Amino-1H-pyrrolo-3-carboxylates react with 1,3-diketones, affording pyrrolo­[1,2-a]­pyrimidine-7-carboxylates, and are easily converted into 2-diazo-2H-pyrrole-4-carboxylates. These compounds demonstrate the reactivity of both diazo compounds, giving pyrrole-containing products of intra/intermolecular azo coupling, and carbenes to give pyrrole-containing insertion products into CH and OH bonds under photolysis.