Bm. Sykes et al., RADIOLYTIC STUDIES OF THE REDUCTIVE CYCLIZATION OF 2-NITROARYLAMIDES - CYCLIZATION VIA HYDROXYLAMINE INTERMEDIATES, Journal of physical organic chemistry, 8(9), 1995, pp. 587-596
The reductive cyclization of several 2-nitroarylamides was studied by
radiolytic reduction, examining the effects of substituents on the nit
rophenyl ring and on the leaving aniline and variations in the nature
of the link between the nitrophenyl ring and the leaving aniline, The
stoichiometry of the reduction and the identification of N-hydroxylact
am and aniline products suggest that the major initial products of suc
h a reduction of the nitroamides are the corresponding hydroxylamines.
Under anaerobic conditions, cyclization via the hydroxylamines was co
nsiderably faster (up to 160-fold) than via the corresponding amines u
nder comparable conditions, but was similarly influenced by changes in
geometry, Unlike cyclization via the amines, rates of cyclization via
the hydroxylamines were sensitive to substitution on the leaving anil
ine, being accelerated by electron-withdrawing groups. The rate-determ
ining step in the cyclization of the hydroxylamines is proposed to be
breakdown of the tetrahedral intermediate.