Isoxazole Strategy for the Synthesis of α-Aminopyrrole Derivatives.

ABSTRACT

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.