Synthesis of Pyrazolo[1,5‐a]quinolines from 1‐Aryl‐5‐styrylpyrazoles via Intramolecular Friedel‐Crafts Reaction/Aerobic Oxidation

Abstract

Various pyrazolo[1,5‐a]quinolines were synthesized via the intramolecular Friedel‐Crafts reaction of 1‐aryl‐5‐styrylpyrazoles and the following base‐catalyzed aerobic oxidation process. The required 1‐aryl‐5‐styrylpyrazoles were readily prepared from the corresponding conjugated dienones and arylhydrazines in a one‐pot process.

An Expedient Synthesis of Pyrrolo[3,2,1‐ij]quinoline‐1,2‐diones via Intramolecular Friedel–Crafts Cyclization Protocol

“…During our recent interest in IMFC reactions and the chemical transformations of isatin derivatives, we reasoned out that pyrrolo[3,2,1‐ ij ]quinoline‐1,2‐diones could be prepared via an IMFC approach as shown in Scheme (Eq. (3)).…”

Styrylpyrazoles: Properties, Synthesis and Transformations

“…The base-catalyzed aerobic oxidation of dihydropyrazolo[1,5-a]quinolines 126 afforded the corresponding pyrazolo[1,5-a]quinolines 127 (Scheme 38, ii). However, the reaction only occurred when R 5 = Ph and R 6 = H [87]. In 2015, Moon et al reported the acid-catalyzed intramolecular Friedel-Crafts (IMFC) reaction of several 1-aryl-5-styrylpyrazoles 125 in the presence of PPA to produce dihydropyrazolo[1,5a]quinolines 126 (Scheme 38, i) [87].…”

“…However, the reaction only occurred when R 5 = Ph and R 6 = H [87]. In 2015, Moon et al reported the acid-catalyzed intramolecular Friedel-Crafts (IMFC) reaction of several 1-aryl-5-styrylpyrazoles 125 in the presence of PPA to produce dihydropyrazolo[1,5a]quinolines 126 (Scheme 38, i) [87]. It is worth mentioning that the corresponding five-membered ring product was not obtained.…”

“…No expected dihydropyrazole was obtained in the reaction of 1,5-diphenylpenta-2,4-dien-1-one with phenyl hydrazine due to fast oxidation by atmospheric oxygen affording the corresponding pyrazole [ 34 ]. Furthermore, 1-aryl-5-styrylpyrazoles 98 were synthetized by the one-pot reaction of conjugated dienones 96 with aryl hydrazine hydrochlorides in 1,2-dichlorobenzene at 130 °C, under O 2 atmosphere ( Scheme 30 , ii) [ 86 , 87 ]. Similar conditions for the reaction of Baylis–Hillman adduct 99 with phenyl hydrazine afforded the styrylpyrazole 100 ( Scheme 30 ) [ 87 ].…”

“…Furthermore, 1-aryl-5-styrylpyrazoles 98 were synthetized by the one-pot reaction of conjugated dienones 96 with aryl hydrazine hydrochlorides in 1,2-dichlorobenzene at 130 °C, under O 2 atmosphere ( Scheme 30 , ii) [ 86 , 87 ]. Similar conditions for the reaction of Baylis–Hillman adduct 99 with phenyl hydrazine afforded the styrylpyrazole 100 ( Scheme 30 ) [ 87 ].…”