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Quinoxalines Directly from Electron-Deficient Alkynes
Hypervalent Iodine(III)-Induced Oxidative [4+2] Annulation of o-Phenylenediamines and Electron-Deficient Alkynes: Direct Synthesis of Quinoxalines from Alkyne Substrates under Metal-Free Conditions.
Chem. Commun. 2013;
13 December 2013 (online)
The authors report the metal-free oxidative [4+2] annulation of electron-deficient alkynes and ortho-phenylenediamines to synthesize quinoxalines, which are most commonly prepared by condensing diamines with α-diketones. The reactions with electron-rich, -neutral, and -poor substrates all proceed with high yield. The synthesis of anhydride 4 demonstrates the utility of this method, as such electron-deficient quinoxalines are challenging to prepare by traditional methods.
Initial results with tert-butyl hypoiodite predominately yielded the dearomatized cis,cis-mucononitrile. Phenyliodine diacetate (PIDA) proved to be crucial, despite attempts with several other hypervalent iodine reagents. The reaction is also highly solvent-dependent, proceeding more effectively with increasing solvent polarity.