Synthesis of quinoxalinones
Benzimidazoles and quinoxalin-2(1H)-ones were synthesized by treatment of 2-(N-Boc-amino)phenylisocyanide with carboxylic acids and glyoxylic acids, respectively via two-component coupling, deprotection, and intermolecular cyclization.
Z.-Z. Chen, Y. Tang, L. Zuo, D.-Y. Tang, J. Zhang, Z.-G. Xu, Synlett, 2014, 25, 2518-2520.
The combination of tert-butyl hypochlorite, tetrabutylammonium iodide and tetrabutylammonium chloride as oxidation system enables the transformation of ethyl 2-(N-arylcarbamoyl)-2-iminoacetates into the corresponding quinoxalinones in high yield. Oxygen exhibits a beneficial effect on the reaction.
D. Li, Y. Li, W. Yu, Synthesis, 2017, 49, 4283-4291.
Whereas the cyclocondensation of 2-aminothiophenols with 1,2-biselectrophiles such as ethyl glyoxalate and diethyl oxalate in aqueous medium leads to the formation of benzothiazole-2-carboxylates via a 5-endo-trig process contrary to Baldwin’s rule, the reaction of 2-aminophenols/anilines produced the corresponding benzazine-3-ones or benzazine-2,3-diones via a 6-exo-trig process in compliance with Baldwin’s rule.
T. M. Dhameliya, S. S. Chourasiya, E. Mishra, P. S: Hadhavar, P. V. Bharatam, A. K. Chakraborti, J. Org. Chem., 2017, 82, 10077-10091.
A tandem nitrosation/cyclization reaction of N-aryl cyanoacetamides with tert-butyl nitrite provides quinoxalin-2-ones in good yields with good functional group tolerance. The dehydrogenative N-incorporation is achieved through a sequence of nitrosation, tautomerization, and cyclization.
F. Wang, B.-L. Hu, L. Liu, H.-Y. Tu, X.-G. Zhang, J. Org. Chem., 2017, 82, 11247-11252.
An efficient visible-light-induced C(sp2)-H/N-H cross-dehydrogenative coupling (CDC)-amination with both primary and secondary aliphatic amines allows the direct formation of 3-aminoquinoxalin-2(1H)-ones. Preliminary mechanistic studies reveal that the reaction proceeds through a radical process.
W. Wei, L. Wang, P. Bao, Y. Shao, H. Yue, D. Yang, X. Yang, X. Zhao, H. Wang, Org. Lett., 2018, 20, 7125-7130.
A metal-free cross-dehydrogenative coupling between quinoxalinones and amines in the presence of catalytic iodine yields 3-aminoquinoxalinones in good yields under ambient conditions in dioxane as solvent and aqueous tert-butyl hydroperoxide as the terminal oxidant. The reaction is highly versatile and exhibits good functional group tolerance with a range of primary and secondary amines.
A. Gupta, M. S. Deshmuk, N. Jain, J. Org. Chem., 2017, 82, 4748-4792.