Quinoline heteroaromatic compounds

Several heteroaromatic compounds can be hydrogenated by [Rh(COD) (PPh3)2]+ species. Thus, this cationic complex has been reported to be a catalyst precursor for the homogeneous hydrogenation of heteroaromatic compounds such as quinoline [32] or benzothiophene [33]. Detailed mechanistic cycles have been proposed by Sanchez-Delgado and coworkers. The mechanism of hydrogenation of benzothiophene by the cationic rhodium(III) complex, [Rh(C5Me5) (MeCN)3]2+, has been elucidated by Fish and coworkers [34]. 

DMAD get thermally converted to quinolones (66), through a Cope rearrangement. These quinolones give rise to tricyclic heteroaromatic compounds, namely, pyrano[3,4-6]quinoline-l,5-diones (67) and furo-[3,2-c]quinolines (68), depending on the reaction conditions (Scheme... 

The enantioselective hydrogenation of olefins, ketones and imines still represents an important topic and various highly enantioselective processes based on chiral Rh, Ru or Ir complexes have been reported. However, most of these catalysts failed to give satisfactory results in the asymmetric hydrogenation of aromatic and heteroaromatic compounds and examples of efficient catalysts are rare. This is especially the case for the partial reduction of quinoline derivatives which provide 1,2,3,4-tetrahydroquinolines, important synthetic intermediates in the preparation of pharmaceutical and agrochemical products. Additionally, many alkaloid natural products consist of this stmctural key element. 

The Brpnsted acid catalyzed hydrogenation of quinolines with Hantzsch dihydropyridine as reducing agent provides a direct access to a variety of substituted tetrahydroquinolines (Table 4.2). The mild reaction conditions of this metal-free reduction of heteroaromatic compounds, high yields, operational simplicity and practicability, broad scope, functional group tolerance and remarkably low catalyst loading render this environment-friendly process an attractive approach to optically active tetrahydroquinolines and their derivatives (Table 4.3) (see page 176). ... 

The six-membered nitrogen heteroaromatic compound is pyridine (70) the benzo analogues are quinoline (71) and isoquinoline (72). 

Pyridines and Quinolines 22.83 Heteroaromatic Compounds containing more than Two Heteroatoms... 

Heteroaromatic compounds such as pyridine and quinoline derivatives give complexes with five-membered rings ... 

Udenfriend et al. observed that aromatic compounds are hydroxyl-ated by a system consisting of ferrous ion, EDTA, ascorbic acid, and oxygen.122 Aromatic and heteroaromatic compounds are hydroxylated at the positions which are normally most reactive in electrophilic substitutions. For example, acetanilide gives rise exclusively to the o-and p-hydroxy isomers whereas quinoline gives the 3-hydroxy product.12211 The products of the reaction of this system with heterocyclic compounds are shown in Table XIII. 

TO Enantioselective Reduction of Nitrogen Based Heteroaromatic Compounds Table 10.3 Asymmetric hydrogenation of quinolines by Lam, Fan, and Chan. (S,S)-Cp lr(OTf)(CF3TsDPEN)... 

Certain heteroaromatic compounds that have acidic methyl groups are effective in the Knoevenagel condensation. 6-Methyl-1,3,5-triazine (156), 2-methylpyridine V-oxides (157), quinolines and pyrimidines all condense with aromatic aldehydes in the presence of the usual catalysts. An example of a doubly activated methylene compound in which one activation group is a heterocycle is the 2-oxopro-pylthiazole (158), which condenses with a number of aldehydes. " ... 

Trifluoromethylation reactions of heteroaromatic compounds represent a majority of reported nucleophihc perfluoroalkylations. For example, trifluoromethylation of halogenated quinolines, isoquinolines, or pyridines carried out under pressure using CF3X/CU powder system (X = 1 or Br) in DMF or (Me0)3P=0 solvent affords the corresponding trifluoromethylated heterocycles in 22-60% yield (Fig. 7.21). ... 

---