Spin trapping of alkoxyl radicals generated from 5-methyl and 5-aryl-3-alkoxy-4-methylthiazole-2(3 H)-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 6H 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.