The site-selective incorporation of a trifluoromethyl group into biologically active molecules and pharmaceuticals has emerged as a central topic in medicinal chemistry and drug discovery. Herein, we demonstrate the rhodium(III)-catalyzed conjugate addition of β-trifluoromethylated enones with quinoline N-oxides, which result in the generation of β-trifluoromethyl-β′quinolinated ketones. The reaction proceeds under mild conditions with complete functional group tolerance. The synthetic applicability was showcased by successful gram-scale experiments and valuable synthetic transformations of coupling products.
The ruthenium(II)-catalyzed tandem C−H allylation and intramolecular dipolar cycloaddition between azomethine imines and 2-methylidenetrimethylene carbonate is described herein. The initially formed β-substituted allyl fragment could trigger the exotype [3 + 2] cycloaddition with the polar azomethine group, resulting in the formation of bridged tetracycles bearing a hydroxymethylene group at a bridgehead carbon center. A wide substrate scope and broad functional group compatibility were observed. The gram-scale synthesis and synthetic transformations demonstrate the synthetic utility of this process.
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.
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