Synthesis of 2-alkynylquinolines from 2-chloro and 2,4-dichloroquinoline via Pd/C-catalyzed coupling reaction in water

Recent Advances of Pd/C-Catalyzed Reactions

The Pd/C-catalyzed reactions, including reduction reactions and cross-coupling reactions, play an irreplaceable role in modern organic synthesis. Compared to the homogeneous palladium catalyst system, the heterogeneous Pd/C catalyst system offers an alternative protocol that has particular advantages and applications. Herein, a review on Pd/C-catalyzed reactions is presented. Both the advances in Pd/C-catalyzed methodologies and the application of Pd/C-catalysis in total synthesis are covered in this review.

Benzoquinoline amines - Key intermediates for the synthesis of angular and linear dinaphthonaphthyridines

A systematic study on the condensation reaction of 2,4-dichlorobenzo[h]quinoline and naphth-1-ylamine in the presence of CuI as catalyst to functionalised mono- and di-substituted (naphthalen-1-yl)benzo[h]quinoline amines was described. Subsequently these mono- and di-substituted amines on polyphosphoric acid catalysed cyclisation reaction with aromatic/heteroaromatic carboxylic acids led to the construction of angular and linear aromatic/heteroaromatic substituted dinaphthonaphthyridines in good yields.

One-Pot Site-Selective Sonogashira Cross-Coupling–Heteroannulation of the 2-Aryl-6,8-Dibromoquinolin-4(1H)-Ones: Synthesis of Novel 6-H-Pyrrolo[3,2,1-ij]Quinolin-6-Ones

The 2-aryl-6,8-dibromoquinolin-4(1 H)-ones were subjected to site-selective Sonogashira cross-coupling with terminal acetylenes as models for C sp2-C sp bond formation in the presence of Pd/C–PPh3 and CuI as catalysts and K2CO3 as a base in dioxane to afford the 2-substituted 4-aryl-8-bromo-4 H-pyrrolo[3,2,1- ij]quinolin-6-ones. These were, in turn, subjected to Suzuki–Miyaura cross-coupling with 4-fluorophenylboronic acid as coupling partner to afford the 2-substituted 4,8-diaryl-4 H-pyrrolo[3,2,1- ij]quinolin-6-ones.

Pd/C-catalyzed, copper-free Sonogashira coupling: one-pot synthesis of 1-aryl-4-(2-phenylethynyl)[1,2,4]triazolo[4,3-a]quinoxalines in water

Abstract

Copper-free, Pd/C-catalyzed, one-pot reaction of 2,3-dichloroquinoxaline with hydrazine hydrate, bromine, phenylacetylene, and a variety of aldehydes provides an efficient and direct method for the preparation of 1-aryl-4-(2-phenylethynyl)[1,2,4]triazolo[4,3-a]quinoxalines in water at 70 °C. This methodology involves the use of inexpensive reagents or catalysts, and thus permits a new and practical access to triazolo[4,3-a]quinoxalines.

Graphical abstract

Studies of one-pot double couplings on dibromoquinolines

In a series of studies, the regioselectivity of Suzuki couplings of dibromoquinolines has been investigated. In general, it is much harder to achieve high levels of regioselectivity in these systems compared to many of the other dibromoheteroaromatics that have been studied. Useful levels of selectivity could be achieved for both a 5,7-dibromoquinoline as well as 3,4-dibromoquinoline. Double Suzuki couplings could also be achieved on these two compounds.

Sonogashira reaction of aryl and heteroaryl halides with terminal alkynes catalyzed by a highly efficient and recyclable nanosized MCM-41 anchored palladium bipyridyl complex

A heterogeneous catalyst, nanosized MCM-41-Pd, was used to catalyze the Sonogashira coupling of aryl and heteroaryl halides with terminal alkynes in the presence of CuI and triphenylphosphine. The coupling products were obtained in high yields using low Pd loadings to 0.01 mol%, and the nanosized MCM-41-Pd catalyst was recovered by centrifugation of the reaction solution and re-used in further runs without significant loss of reactivity.

Regioselective alkynylation followed by Suzuki coupling of 2,4-dichloroquinoline: synthesis of 2-alkynyl-4-arylquinolines

A two step synthesis of 2-alkynyl-4-arylquinolines has been accomplished via Pd/C-mediated regioselective C-2 alkynylation of 2,4-dichloroquinoline in water followed by Suzuki coupling at C-4 of the resulting 4-chloro derivative.