Isoxazole Strategy for the Synthesis of α‑Aminopyrrole Derivatives

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 cis–trans-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.