Generation and cyclization of acyl radicals from thiol esters under nonreducing, tin-free conditions

The preparation of 2-(2-((tert-butyloxycarbonyl)amino)phenyl)ethyl mercaptan from 2-(2-amino-phenyl)ethanol is described. This thiol is condensed with a series of suitably unsaturated carboxylic acids to give a series of thiol esters. The Boc group is removed and the amine reacted with isoamyl nitrite to give a series of diazonium salts. Exposure to iodide in acetone solution then generates the aryl radical, which undergoes intramolecular homolytic substitution at sulfur with liberation of the acylradical. Following acyl radical cyclization, quenching by iodine and then elimination of HI leads to the isolation of alpha-methylene cycloalkanones in good yield.