CHEMISTRY OF AMIDYL RADICALS PRODUCED FROM N-HYDROXYPYRIDINE-2-THIONE IMIDATE ESTERS

The title radical precursors were prepared from secondary amides by reaction of the amide with phosgene to give an imidoyl chloride followed by reaction with the sodium salt of N-hydroxypyridine-2-thione. Visible light initiated reactions of these precursors gave amidyl radicals 2 which could react with their precursors to give N-(2-pyridylthio) amides or with t-BuSH to give the parent amide. Radicals 2 containing delta,epsilon-unsaturation on the acyl or alkyl chain cyclized in a 5-exo fashion to give ultimately gamma-lactams and N-acylpyrrolidines, respectively. Tandem 5-exo cyclizations of the N-allyl-4-pentenamidyl radical gave pyrrolizidinone products, and a tandem 5-exo/6-endo reaction sequence of the N-(4-pentenyl)benzamidyl radical gave, ultimately, 3,4-benzoindolizidinone. Several relative rate constants for cyclization and trapping of the amidyl radicals and for intramolecular reactions and trapping of the carbon-centered radicals formed by amidyl radical cyclizations were determined, and these values can be employed in synthetic planning.