Metal‐Free Direct Oxidative C−N Bond Coupling of Quinoxalin‐2(1 H )‐ones with Azoles under Mild Conditions

Sunlight Induced and Recyclable g-C3N4 Catalyzed C-H Sulfenylation of Quinoxalin-2(1H)-Ones

A sunlight-promoted sulfenylation of quinoxalin-2(1H)-ones using recyclable graphitic carbon nitride (g-C₃N₄) as a heterogeneous photocatalyst was developed. Using the method, various 3-sulfenylated quinoxalin-2(1H)-ones were obtained in good to excellent yields under an ambient air atmosphere. Moreover, the heterogeneous catalyst can be recycled at least six times without significant loss of activity.

Updates on hypervalent-iodine reagents in metal-free organic synthesis

Hypervalent iodine (HVI) chemistry is a rapidly growing subdomain of contemporary organic chemistry because of its enormous synthetic applications. The high nucleofugality of the phenyliodonio group (I+Ph) and their radical...

Alkylation of quinoxalin-2(1H)-ones using phosphonium ylides as alkylating reagents

A practical and efficient methodology for the construction of 3-alkylquinoxalinones through base promoted direct alkylation of quinoxalin-2(1H)-ones with phosphonium ylides as alkylating reagents under metal- and oxidant-free conditions was developed. Various 3-alkylquinoxalin-2(1H)-ones were easily obtained in good to excellent yields. Tentative mechanistic studies suggest that this reaction is likely to involve a nucleophilic addition-elimination process.

Site-selective and metal-free C-H nitration of biologically relevant N-heterocycles

The site-selective and metal-free C-H nitration reaction of quinoxalinones and pyrazinones as biologically important N-heterocycles with t-butyl nitrite is described. A wide range of quinoxalinones were efficiently applied in this transformation, providing C7-nitrated quinoxalinones without undergoing C3-nitration. From the view of mechanistic point, the radical addition reaction exclusively occurred at the electron-rich aromatic region beyond electron-deficient N-heterocycle ring. This is a first report on the C7-H functionalization of quinoxalinones under metal-free conditions. In contrast, the nitration reaction readily takes place at the C3-position of pyrazinones. This transformation is characterized by the scale-up compatibility, mild reaction conditions, and excellent functional group tolerance. The applicability of the developed method is showcased by the selective reduction of NO₂ functionality on the C7-nitrated quinoxalinone product, providing aniline derivatives. Combined mechanistic investigations aided the elucidation of a plausible reaction mechanism.

Transition metal-free C-3 functionalization of quinoxalin-2(1H)-ones: recent advances and sanguine future

A gradual shift from metal-catalyzed to metal-free methods is occurring, as the latter are more environmentally benign. This review discusses sustainable protocols for the construction of C–C, C–N, C–P, C–S, and C–O bonds via C–H functionalization of quinoxalin-2(1H)-ones.