Spin trapping of alkoxyl radicals generated from 5-methyl and 5-aryl-3-alkoxy-4-methylthiazole-2(3H)-thiones in photochemically induced and microwave-initiated reactions

Abstract Methoxyl and isopropoxyl radicals were generated from N -alkoxy-4,5-dimethylthiazole-2(3 H )-thiones ( λ max ∼320 nm) and 5-aryl derivatives (aryl= p -XC 6 H 4 ; X=MeO, H, AcNH, Cl) ( λ max ∼335 nm) in photochemically and microwave-induced reactions. Alkoxyl radicals were trapped with dimethylpyrrolidine N -oxide and characterized as spin adducts via EPR. Cumyloxyl radicals were liberated in a similar manner from N -cumyloxy-5-(4-methoxyphenyl)-4-methylthiazole-2(3 H )-thione. A noteworthy bathochromic shift was found for the lowest energy transition of N -(hydroxy)indeno[2,1- d ]thiazole-2(3 H )-thione ( λ max =376 nm), if compared to the UV–vis absorption of N -hydroxy-4-methyl-5-phenylthiazole-2(3 H )-thione ( λ max =338 nm). Syntheses of alkoxyl radical precursors and procedures for conducting N,O-homolysis are described in a full account.