Copper-catalyzed decarboxylative propargylation/hydroamination reactions: access to C3 β-ketoester-functionalized indoles

Abstract

A copper-catalyzed reaction of ethynyl benzoxazinanones with readily accessible β-ketoesters via a decarboxylative propargylation/hydroamination sequence has been developed. This protocol furnished a diverse range of C3 β-ketoester-functionalized indoles in good to excellent yields.

Formal [3+2] Annulation of Copper‐Allenylidenes with 3‐Oxo‐3‐Arylpropanenitriles: Synthesis of Tetrasubstituted Furans

“…In addition, the use of the ester (for example, ethyl 3‐oxo‐3‐phenylpropanoate) instead of the nitrile as the bisnucleophile for the present reaction was performed under standard reaction conditions. However, no corresponding product was detected, and a decarboxylative propargylation/hydroamination reaction was observed, which had been reported by Zhai's group in 2018 [22] …”

“…Gong [15] and Jiang [16] accomplished catalytic asymmetric [4+3] cycloaddition of copper allenylidenes with isatin‐derived enals or C,N‐cyclic azomethine imines. Besides intermolecular cycloadditions, Cu‐allenylidene generated by ethynyl benzoxazinanones was also a useful intermediate for intramolecular annulation [17–22] . Various tandem reactions were achieved by Xiao and Lu, [17–20] Song, [21] and Zhai [22] to synthesize heterocyclic compounds.…”

“…Besides intermolecular cycloadditions, Cu-allenylidene generated by ethynyl benzoxazinanones was also a useful intermediate for intramolecular annulation. [17][18][19][20][21][22] Various tandem reactions were achieved by Xiao and Lu, [17][18][19][20] Song, [21] and Zhai [22] to synthesize heterocyclic compounds.…”

“…However, no corresponding product was detected, and a decarboxylative propargylation/hydroamination reaction was observed, which had been reported by Zhai's group in 2018. [22] Next, the generality of the reaction for substituted ethynyl benzoxazinanones was explored (Table 3). It was obvious that the benzoxazinanones with electron-Scheme 1.…”

Base‐Mediated Decarboxylative [3+2] Annulation of Ethynyl Benzoxazinanones and Benzimidamides: Synthesis of Imidazole Derivatives

“…Most recently, we revealed the use of copper‐allenylidenes as two‐membered synthon in a [3+2] annulation of ethynyl benzoxazinanones with 3‐oxo‐3‐arylpropanenitriles [13] . Besides intermolecular annualtion reactions, copper‐allenylidene was also a useful intermediate for intramolecular annulation (Scheme 1a) [14–16] . Interestingly, the manganese‐catalyzed sequential C−H activation/decarboxylative intramolecular annulation worked well to afford the diheteroarylmethanes [17] .…”