Reaction pathways for arylcarbamoyl radicals and the cyclization of o-substituted phenylcarbamoyl radicals

Abstract

N-Arylcarbamoyl radicals generated from N-arylformamides with di-t-butyl peroxide (Bu^tOOBu^t) in chlorobenzene at 110 °C give rise to a series of reactions depending on the nature and the position of the substituent in the aromatic ring. When the aryl group is phenyl or p-chlorophenyl the following reactions on carbamoyl radicals occur: (i) loss of hydrogen with formation of aryl isocyanates, whereas the loss of carbon monoxide leads to arylamines via arylaminyl radicals; (ii) dimerization to NN′-diaryloxamides; (iii) aromatic substitution on chlorbenzene leading to N-arylbenzamides (ipso-substitution) and N-arylchlorobenzamides. The isocyanates trapped by t-butyl alcohol and arylamines give t-butyl N-arylcarbamates and NN′-diarylureas. With o-substituted N-phenylformamides intramolecular cyclization is observed as well; in fact, the N-(o-cyanophenyl)formamide affords isatin via addition of the carbamoyl radical to the cyano-group while the N-[(o-phenylthio) phenyl]formamide gives 2-benzothiazolone and phenyl radicals through an S_Hi reaction on the sulphur atom; finally 2-formamidobiphenyls furnish phenanthridones in very high yields.