Compounds with More than One Nitrogen Atom in the Same Ring

7 Compounds with More than One Nitrogen Atom in the Same Ring 

1 Pyrazoles, Imidazoles, and Related Compounds. Thoms and Schnupp hydrogenated pyrazole to 2-pyrazoline in ethanol-acetic acid over 5% Pd-BaSC 4 at 18°C. The hydrogenation of 1-phenyl- and 3-methyl-1-phenylpyrazoles at room temperature became very slow after the absorption of 1 mol of hydrogen and further uptake of hydrogen to give pyrazolidines occurred at 70-80°C with or without the addition of a new portion of the catalyst (eq. 12.69).130 

Generally, the N-N bond may be stabilized toward hydrogenolysis by acetylation or hydrogenation in acetic anhydride, as in eq. 12.72 in the Raney Ni-catalyzed hydrogenation of a pyrazoline derivative at a high temperature and pressure.133 In contrast, 5-methylpyrazoline was hydrogenolyzed to give butane-1,3-diamine in 67% yield under even milder conditions (eq. 12.73).134 

4-Aminomethylbenzimidazole dihydrochloride was hydrogenated to the 4,5,6,7-tetra-hydro derivative over 10% Rh-C in 3M hydrochloric acid in 72 h at ordinary conditions.143 9-Am inonaph11112,1 - i i midazole dihydrochloride (42) was hydrogenated to the 6,7,8,9-tetrahydro derivative under similar conditions and further to the octahy-dronathimidazole at 120°C and 12 MPa H2 in 48 h (eq. 12.76). 

In acetic anhydride as the solvent, however, imidazole was smoothly hydrogenated over platinum oxide at room temperature and atmospheric pressure to give 1,3-diace- 

---