Divergent Synthesis of 1<i>H</i>-Indazoles and 1<i>H</i>-Pyrazoles from Hydrazones<i>via</i>Iodine-Mediated Intramolecular Aryl and<i>sp</i><sup>3</sup>C-H Amination
by condensation of hydrazines with the corresponding ketones. In the presence of potassium iodide, I2-mediated oxidative cyclization of diaryl and tert-butyl aryl ketone hydrazones produced 1H-indazoles via direct aryl C–H amination. Under similar reaction conditions, primary and secondary alkyl ketone hydrazones were transformed into 1H-pyrazole products in a reaction involving sp3 C–H amination. This
New Synthesis of 1-Substituted-1<i>H</i>-indazoles via 1,3-Dipolar Cycloaddition of <i>in situ</i> Generated Nitrile Imines and Benzyne
作者:Christian Spiteri、Steve Keeling、John E. Moses
DOI:10.1021/ol101150t
日期:2010.8.6
A new synthesis of 1-substitued-1H-indazoles via 1,3-dipolar cycloaddition of nitrile imines to benzyne is described. The reaction is completed within 5 min, affording the corresponding N(1)−C(3) disubstituted indazoles in moderate to excellent yields.
Synthesis of Substituted 1<i>H</i>-Indazoles from Arynes and Hydrazones
作者:Pan Li、Chunrui Wu、Jingjing Zhao、Donald C. Rogness、Feng Shi
DOI:10.1021/jo202598e
日期:2012.4.6
The 1H-indazole skeleton can be constructed by a [3 + 2] annulation approach from arynes and hydrazones. Under different reaction conditions, both N-tosylhydrazones and N-aryl/alkylhydrazones can be used to afford a variety of indazoles. The former reaction affords 3-substituted indazoles either via in situ generated diazo compounds or through an annulation/elimination process. The latter reaction leads to 1,3-disubstituted indazoles likely through an annulation/oxidation process. The reactions operate under mild conditions and can accommodate aryl, vinyl, and less satisfactorily, alkyl groups.
Facile Access to 1<i>H</i>-Indazoles through Iodobenzene-Catalyzed C-H Amination under Mild, Transition-Metal-Free Conditions
1H-indazole and derivatives was accomplished on the basis of the iodobenzene-catalyzed intramolecular C–Hamination of hydrazones undermildconditions. Reactions of hydrazones derived from ketones and hydrazines with a catalytic amount of iodobenzene in the presence of Oxone as an oxidant in trifluoroacetic acid took place to afford 1H-indazoles in moderate to good yields. A plausible reaction mechanism