Quinolines, Isoquinolines, and Related Compounds

Over copper-chromium oxide, quinoline is quantitatively hydrogenated to tetrahydroquinoline, and further hydrogenation to decahydroquinoline does not proceed even at 190°C and 10-15 MPa H2 (eq. 12.45).71 Over reduced copper catalyst quinoline was hydrogenated to tetrahydroquinoline at 130°C and 14 MPa H2. Hydrogenation of the tetrahydroquinoline produced took place only very slowly at 260°C and 16 MPa H2 to give /ra/i.v-dccahydroqu incline.20 

Over ruthenium dioxide quinoline was hydrogenated to tetrahydroquinoline in 97.5% yield at 80°C and 8.2 MPa H2 and to decahydroquinoline in 98% yield at 120°C and 9.3 MPa H2.3 Quinoline was also hydrogenated to tetrahydroquinoline over colloidal platinum in neutral solution or as the hydrochloride over platinum oxide in absolute ethanol.30 Hydrogenation to decahydroquinoline was performed with platinum black (Willstatter) or colloidal platinum (Skita) in acetic acid.73,74 Hiickel and Stepf hydrogenated quinoline under almost the same conditions as used by Skita and Meyer, and obtained the decahydroquinoline consisting of approximately 80% of trans and 20% of cis isomers (eq. 12.46). 

Formation of the cis isomer increased to 65% when quinoline was hydrogenated in acetic acid added by a large quantity of hydrochloric acid.72 Booth and Bostock obtained practically pure cw-decahydroquinoline by hydrogenation of quinoline in concentrated hydrochloric acid over platinum black (eq. 12.47).75 Vierhapper and Eliel showed that the hydrogenation in the strongly acidic medium proceeds mostly via 5,6,7,8-tetrahydroquinoline as intermediate, which probably is related to the high stereoselectivity in the formation of the cis isomer.37 

3 Selectivity to Tetrahydro Derivatives. As already described, the hydrogenation of quinoline and isoquinoline usually occurs at the nitrogen ring to give the corresponding 1,2,3,4-tetrahydro derivatives, unless bulky substituents in the 2,3, 

Shaw and Stapp studied the selectivity of various transition metal catalysts in the hydrogenation of methyl-substituted quinolines in hexadecane mostly at 100-160°C and an initial hydrogen pressure of 5.17 MPa (at room temperature).15 As seen from the results shown in Table 12.4, with 2-methylquinoline the selectivity to 1,2,3,4- 

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