Synthesis of α-enamino esters via Cu(ii)-promoted dehydrogenation of α-amino acid esters: application to the synthesis of polysubstituted pyrroles

Abstract

α-Enamino esters are synthesized from α-amino acid esters using Cu(ii)-promoted dehydrogenation. Application of the α-enamino esters to the synthesis of polysubstituted pyrroles is achieved through oxidative coupling with alkynes under Cu(ii)-promoted conditions.

α,β-Dehydroamino Acid Synthesis through Proline-Catalyzed Aldol Condensation with a Glycine Schiff Base

“…tert -Butyl ester 3ca could be converted into the corresponding N-unprotected α,β-dehydroamino ester 10 in higher yield on a gram scale, presumably due to suppression of the hydrazide formation. These results demonstrated that the present method is a complementary approach for the synthesis of N-unprotected α,β-dehydroamino ester. − …”

Recent Advances on Pyrrole Synthesis through Different Annulation Modes

“…After developing a method on the synthesis of α-enamino esters from α-amino acid esters, Xie and co-workers [72] presented a oxidative coupling reaction between α-enamino esters and activated alkynes under Cu(II)-promoted conditions to form polysubstituted pyrroles in high yields (Scheme 42). In this methodology, α-enamino esters were used for the first time as the substrates for the synthesis of In 2016, Zhang and co-workers [73] reported a regioselective cobalt-catalyzed synthesis of pyrroles from enamides and alkynes in the present of AgOTf and CuO (Scheme 43).…”

BF3-promoted reactions of α-amino acetals with alkynes to 2,5-disubstituted pyrroles

“…Since the report of the Hantzsch reaction for the synthesis of substituted pyrroles from the condensation of a β-keto ester with an α-amino ketone in situ formed from α-chloro ketone and ammonia, 8 a variety of novel cyclization approaches leading to substituted pyrroles have been successfully developed. 9 Among them, some typical examples involve transition metal-catalyzed cycloadditions of alkynes to access pyrroles, 10 which include C sp 2 –H bond cycloaddition of N -acetylenamides 11 and enaminones, 12 cycloaddition of enamines 13 and imine derivatives 14 via C sp 3 –H bond activation, [3 + 2] annulation of 2 H -azirines by ruthenium catalysis, 15 and the gold-catalyzed cascade reaction of acetals and terminal acetylenes 16 (Fig. 2a).…”