1,2,3,4-Tetrahydroquinoline, hydrogenation of quinoline to

TABLE 12.5 Selective Hydrogenation of Methyl-Substituted Quinolines to 1,2,3,4-Tetrahydroquinolines in the Presence of Sulfur Compounds or Carbon Monoxide ... 

Acidic media in the hydrogenation of quinolines may be avoided by the use of Rh/Al2C>3 as catalyst. Selective reduction may then be effected in hexafluoroisopropanol or methanol <2004SL2827>. Use of methanol leads to the isolation of the corresponding 1,2,3,4-tetrahydroquinoline while performing the hydrogenation in hexafluoroisopropanol results in total reduction to the decahydro product. 

Table I gives the results from the experiments with [M(PC)] supported on Si02 The conversion of quinoline is almost exclusively to 1,2,3,4-tetrahydroquinoline with only traces of other products (<1%). No propylaniline, propylbenzene, propyl-cyclohexane, 5,6,7,8-tetrahydroquinoline or decahydroquinoline were noted. No change is noted in the conversions when the SiC>2 is activated in vacuo at 400°C prior to supporting the complex. When the hydrogenations are run at 200°C only low conversions are...

Hydrogenation of Quinolines Under Water Gas Shift Conditions and Oxidation of 1,2,3,4-Tetrahydro-quinolines to Hydroxamic Acids 6-Methoxy-1,2,3,4-tetrahydroquinoline and 1-Hydroxy-6-methoxy-3,4-dihydroquinolin-2(1 H)-one. 

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. 

Hydrogenation of 2-phenylpyridine or quinoline over the hydrogen storage alloy could be carried out at an elevated temperature to give 2-cyclohexylpyridine or 1,2,3,4-tetrahydroquinoline, respectively. In the case of 2-phenylpyridine, the product distribution was observed to be different from the hydrogenation over nickel or platinum catalysts. 

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