CHEMISTRY OF AMIDYL RADICALS PRODUCED FROM N-HYDROXYPYRIDINE-2-THIONEIMIDATE ESTERS

The title radical precursors were prepared from secondary amides by re action of the amide with phosgene to give an imidoyl chloride followed by reaction with the sodium salt of N-hydroxypyridine-2-thione. Visib le light initiated reactions of these precursors gave amidyl radicals 2 which could react with their precursors to give N-(2-pyridylthio) am ides or with t-BuSH to give the parent amide. Radicals 2 containing de lta,epsilon-unsaturation on the acyl or alkyl chain cyclized in a 5-ex o fashion to give ultimately gamma-lactams and N-acylpyrrolidines, res pectively. Tandem 5-exo cyclizations of the N-allyl-4-pentenamidyl rad ical 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 synt hetic planning.