Ru(ii)-Catalyzed, Cu(ii)-mediated carbene migratory insertion in the synthesis of trisubstituted pyrroles from isoxazoles

Abstract

A convenient, “one-pot” synthesis of trisubstituted pyrroles via a Ru(II)-catalyzed and Cu(II)-mediated reaction of substituted isoxazoles with sulfonylhydrazones has been developed. A series of highly functionalized pyrroles are obtained via...

Transition Metal‐Mediated Functionalization of Isoxazoles: A Review

“…The desired pyrrole product could be generated by subsequent oxidation by Cu (II)/Cu(I). The ring opened intermediate IV, was detected by ESI-HRMS thus supporting the proposed mechanism [100].…”

“…[99] Recently, Kapur and co-workers developed an one-pot synthetic protocol for the synthesis of trisubstituted pyrrole by a Ru(II)-catalyzed, Cu(II)-mediated carbene migratory insertion reaction with 3,5-disubstituted isoxazoles and sulfonylhydrazones (Scheme 72). [100] The copper carbene intermediate formed…”

“…Recently, Kapur and co‐workers developed an one‐pot synthetic protocol for the synthesis of trisubstituted pyrrole by a Ru(II)‐catalyzed, Cu(II)‐mediated carbene migratory insertion reaction with 3,5‐disubstituted isoxazoles and sulfonylhydrazones (Scheme 72). [100] The copper carbene intermediate formed by the reaction of Cu(II) with p ‐toluenesulfonyl hydrazone derived diazo compound, reacts with the Ru‐activated isoxazole to form intermediate III via a carbene migratory insertion reaction. Subsequent Ru‐assisted N−O bond cleavage of isoxazole leads to intermediate IV and its tautomer V which undergoes radical initiated cyclization to form intermediate VIII via intermediate VI .…”

Ruthenium‐Catalyzed Decarboxylative Rearrangement of 4‐Alkenyl‐isoxazol‐5‐ones to Pyrrole Derivatives

“…[8] In the second-one, the treatment of isoxazoles with sulfonylhydrazones in rutheniumcatalyzed copper-mediated conditions was proven to be a convenient procedure to the synthesis of trisubstituted pyrroles (Scheme 1, reaction 5). [9] Exploitation of isoxazol-5-ones as building blocks in organic synthesis has attracted considerable attention not only due to their easy availability, but also to the versatile reactivity of the generated nitrenoid active species arising from the NÀ O bond cleavage, depending on their substituents. [10] Also in this field, transition metal catalysis by palladium, [11] ruthenium, [12] iron, [13] iridium [14] and rhodium [15] complexes has proved a powerful tool for widening processes to obtain various types of heterocycles, mainly through decarboxylative reactions.…”

“…The former, reported by Makarov, is a rearrangement of furyl‐tethered O ‐acetyl oximes, which undergoes 5‐ exo‐trig cyclization to generate spiro‐intermediates susceptible of aromatization by dihydrofuran ring‐opening (Scheme 1, reaction 4) [8] . In the second‐one, the treatment of isoxazoles with sulfonylhydrazones in ruthenium‐catalyzed copper‐mediated conditions was proven to be a convenient procedure to the synthesis of trisubstituted pyrroles (Scheme 1, reaction 5) [9] …”