Okumura S, Takeda Y, * Kiyokawa K, Minakata S. * Osaka University, Japan
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;
49: 9266-9268
Key words
annulation - hypervalent iodine - metal-free reaction - quinoxalines
Significance
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.
Comment
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.
