Dissociation or Cyclization: Options for a Triad of Radicals Released from Oxime

ABSTRACT: A set of oxime carbamates having N-alkyl and N,N-dialkyl substituents were prepared via carbonyldiimidazole intermedi-ates. It was shown by EPR spectroscopy that they underwent clean homolysis of their N−O bonds upon UV photolysis. During photolysis of acetophenone O-allylcarbamoyl oxime, the correspond-ing oxazolidin-2-onylmethyl radical was detected by EPR spectrosco-py, providing the first evidence that N-monosubstituted carbamoyloxyl radicals can hold their structural integrity. N,N-Disubstituted carbamoyloxyl radicals dissociated rapidly at the lowest accessible temperatures. Above room temperature, both types of oxime carbamate acted as selective new precursors for aminyl and iminyl radicals. Rate parameters were measured for 5-exo cyclization of N-benzyl-N-pent-4-enylaminyl radicals; the rate constant was smaller than for C-centered and O-centered analogues. Oxime carbamates derived from the volatile diethylamine afforded aryliminyl radicals that proved convenient for phenanthridine preparations