Gold catalysis in quinoline synthesis

Quinolines are biologically and pharmaceutically important N-heterocyclic aromatic compounds, which have broad applications in medicinal chemistry. Thus, their efficient synthesis has attracted extensive attention, and a broad range of synthetic strategies have been established. Of note, gold-catalyzed methodologies for the synthesis of quinolines have greatly advanced this field. Various gold-catalyzed intermolecular annulation reactions, such as annulations of aniline derivatives with carbonyl compounds or alkynes, annulations of anthranils with alkynes, and annulations based on A3-coupling reactions, as well as intramolecular cyclization reactions of azide-tethered alkynes, 1,2-diphenylethynes, and 2-ethynyl N-aryl indoles, have been developed. This review provides an overview of this exciting research area. Typical achievements in reaction methodologies and plausible reaction mechanisms are summarized.

Gold-Catalyzed Oxidation Reactions of Thioalkynes with Quinoline N-Oxides: A DFT Study

Mechanistic investigation of the gold-catalyzed oxidative reactions of thioalkynes with quinoline N-oxides was performed using density functional theory (DFT) calculations. For the oxidative rearrangement of thioalkynes with quinoline N-oxide to yield the same products, the Cβ-oxidation of thioalkynes was predicted to be competitive with Cα-oxidation, with the Cβ-oxidative process slightly more favorable. However, for the oxidative alkenylation of propargyl aryl thioethers with quinoline N-oxides, the Cβ-oxidation of thioether by quinoline N-oxide generated the product 3-hydroxy-1-alkylidene phenylthiopropan-2-one. Moreover, the ring opening of the four-membered sulfonium intermediate was achieved by the nucleophilic attack of quinoline N-oxide rather than a water molecule.

Access to 3-Sulfonamidoquinolines by Gold-Catalyzed Cyclization of 1-(2'-Azidoaryl)propargylsulfonamides through 1,2-N Migration

We describe a gold-catalyzed cyclization of 1-(2'-azidoaryl)propargylsulfonamides for the synthesis of 3-sulfonamidoquinolines, featuring a rare and highly selective 1,2-N migration. The key α-imino gold carbene intermediate is generated through an intramolecular nucleophilic attack of the azide group to the Au-activated triple bonds in a 6-endo-dig manner.

NHC-Cu(I)-Catalyzed Friedländer-Type Annulation of Fluorinated o-Aminophenones with Alkynes on Water: Competitive Base-Catalyzed Dibenzo[b,f][1,5]diazocine Formation

An efficient, easily scalable synthesis of 4-trifluoromethylquinolines and naphthydrines (as well as their difluoro- and perfluoro-analogues) as a result of tandem direct catalytic alkynylation/dehydrative condensation of o-aminofluoromethylketones (o-FMKs), for the first time catalyzed by NHC-copper(I) complexes on water, is reported. A wide range of terminal alkynes is tolerated under the reaction conditions, including β-lactam-, steroid-, and sugar-derived ones, leading to desired quinolines and naphthydrines with good yields. Further investigations proved that o-FMKs could be efficiently transformed into a rare class of heterocyclic compounds-dibenzo[b,f][1,5]diazocines-by a base-catalyzed condensation, also on water. The developed method was applied for gram-scale synthesis of a fluorinated analogue of G protein-coupled receptor antagonist (GPR91).

Novel routes to quinoline derivatives from N-propargylamines

A walk around the new avenue to the synthesis of quinoline derivatives from N-propargylamines.

Synthesis of polysubstituted quinolines via transition-metal-free oxidative cycloisomerization of o-cinnamylanilines

An efficient synthesis of 2-aryl 4-substituted quinolines from stable and readily available o-cinnamylanilines, prepared from anilines and cinnamylalcohols, has been developed. The reaction occurred via a regioselective 6-endo-trig intramolecular oxidative cyclization using KO(t)Bu as a mediator and DMSO as an oxidant at rt. The reaction showed a broad substrate scope with good to excellent yields.

Enantioselective cooperative catalysis

This review focuses on enantioselective cooperative catalytic reactions, wherein two catalysts work simultaneously to form products which cannot be obtained by the use of a single catalyst alone, which have attracted considerable attention in recent years.

Palladium(ii)-catalysed regioselective synthesis of 3,4-disubstituted quinolines and 2,3,5-trisubstituted pyrroles from alkenes via anti-Markovnikov selectivity

A novel strategy has been identified for the regioselective synthesis of 3,4-disubstituted quinolines and 2,3,5-trisubstituted pyrroles through anti-Markovnikov selectivity.

Exploiting the higher alkynophilicity of Au-species: development of a highly selective fluorescent probe for gold ions

A new approach, involving the anchoring-unanchoring of a fluorophore, has been developed for the detection of Au-species. The fluorescent probe was found to be highly selective for sensing gold species in the presence of several other metal ions. A successful application to bioimaging has also been demonstrated with A549 lung cancer cells.