Palladium-Catalyzed Dual C(sp²)–H Functionalization of Indole-2-carboxamides Involving a 1,2-Acyl Migration: A Synthesis of Indolo[3,2-c]quinolinones

Abstract

A novel Pd/Cu catalytic system to construct indolo[3,2- c]quinolinones has been developed starting from indole-2-carboxamides. Substrates were transformed into indolo[3,2- c]quinolinones through dual C(sp)-H functionalization of the indole moiety and arene, in which a carbonyl 1,2-migration was involved. The corresponding products were obtained in moderate to excellent yields with a wide substrate scope.

Pd-Catalyzed de Novo Assembly of Diversely Substituted Indole-Fused Polyheterocycles

“…Recently, Lingkai and his colleagues developed an efficient method to construct indolo[3,2- c ]quinolinones starting from indole-2-carboxamides in the presence of a Pd-catalyst. 8 From our point of view, the methodology is ideally suitable for a multicomponent reaction. Therefore, our aim is to use easily accessible starting materials in a Ugi four-component reaction followed by a tandem/sequential Pd(OAc) 2 -catalyzed dual C(sp 2 )–H functionalization of the Ugi products toward indolo[3,2- c ]quinolinone analogues, involving a 1,2-acyl migration.…”

“…A plausible mechanism of the cyclization path was explained based on the previous report as shown in Scheme 5. 8 After obtaining the Ugi adduct 5a , Pd(OAc) 2 attacks the indole to give the iminium intermediate A , which undergoes a nucleophilic attack of the N -aryl to the iminium moiety which forms the intermediate B . Then B is further converted to the intermediate C via a nucleophilic addition process.…”

“…Surprisingly, N-methyl substituted indole-2carboxylic acid (3r) also formed the polyheterocycle in 65% yield, which was not the case with the substrate of N,1dimethyl-N-phenyl-1H-indole-2-carboxamide. 8 Scheme 2 clearly indicates that there are no electronic or steric effects on the outcome of the reaction.…”

Application of Polyphosphoric Acid‐Mediated Acyl Migration for Regiospecific Synthesis of Diverse 2‐Acylpyrroles from Chalcones

“…Base-promoted C → N acyl migration was used by Vicario and co-workers for the synthesis of nonproteinogenic tertiary and quaternary N-alkyl α-amino acids [13]. In a recent work by Kong et al,indolo[3,quinolinones were synthesized via a Pd/Cu catalyzed 1,2-acyl migration, starting from indole-2-carboxamides [14]. The methods reported thus clearly demonstrate the applicability of acyl rearrangement in diverse synthetic routes.…”

1,2-Acyl migration with α-imino rhodium carbenoids leading to substituted 1-naphthols

“…6 Recently, the group of Li reported that 1-sulfonyl-4-(2-acetoxyethyl)-1,2,3-triazoles underwent 1,3-acetoxy migration to give substituted cyclopropanes (Scheme 1c). 7,8 During our ongoing investigation on the synthetic transformations triggered by α-imino metal carbenoids, we found that ring expansions of 2-triazolyl-1-indanone derivatives proceeded via 1,2-acyl migration, 9 which was hardly seen in carbene-induced reactions. We report here that these reactions provide a unique method for the synthesis of substituted 1-naphthols, which constitute an important class of bicyclic compounds widely found in many natural and synthetic products.…”