Author :
Dabbagh, Hossein A.,Ghaelee, Saied
Descriptors :
Nitrenes,Imidoyl azides,Cycloaddition,Electrophilic armatic stubstititution,Linear free energy,Relation ship,Unclei vs. therodynamic
Abstract :
The thermal decomposition of Nʹ-[(cyanoaryl)oxy]imidoyl azides with various substituted benzenes (OCH3 NHCOCH3, C(CH3)3,p-xylene, CH3,H,CI,CO2,CH3,NO2)has been studied in detail.With electron-rich aromatic nuclei,the addition of a nitrene yields a benzenonium ion (3) intermediate.Banzaziridine (1) and/or 3 intermediate is formed from benzene. Electron-poor aromatic nuclei generated only intermediate 1,in which no benzenonium diradical is formed. Intermediate 3 is stabilized by extended conjugation through an extra resonance structure. For electron-rich aromatic compounds at 65-120 c,the thermodynamically-controlled products, N-arylisoureas ((Z)-NH=Ar),were produced in very high yield. Azepenes (the kinetically-controlled products)were detected by neither 1H-NMR nor a trapping experiment using tetracyanoethylene (TCNE). In the case of banzene 95,azepene was produced,which at 80 C converted to isourea (k=7.0*10-5 s-1). The ortho/para ratio resembles that of electrophilic aromatic substitution reactions. The Hammett plot of log KX/KH or log fp versus 0+-values showed excellent correlation ,with p+-values of-2,.80 and-3.10, respectively (poor correlation resulted with 0-values). The Hammett p+-or p-values are inconsistent with a radical mechanism for these reactions.
