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Paper | Regular issue | Vol 89, No. 1, 2014, pp.83-101
Published online, 14th November, 2013
DOI: 10.3987/COM-13-12863
■ Radical Cyclization and 1,5-Hydrogen Transfer in Selected Aromatic Diazonium Salts

Benedetta Maggio, Gianfranco Fontana, Demetrio Raffa, Francesco Ferrante, and Giuseppe Daidone*

*STEBICEF, University of Palermo, Via Archirafi 32, 90123 Palermo, Italy

Abstract

2-(Methyl-(3-methyl-1-phenyl-1H-pyrazol-5-yl)carbamoyl)thiophene- 3-diazonium hydrogen sulfate 20, 2-(methyl-(3-methylisoxazol-5-yl)carbamoyl)benzenediazonium hydrogen sulfate 21 and 2-(methyl(phenyl)carbamoyl)benzenediazonium hydrogen sulphate 22 were synthesized and reacted with a CuSO4/NaCl/ascorbic acid combination to give complex mixtures. The structures of the reaction products were elucidated, depending upon the pathways followed. Compound 20 almost exclusively afforded an Ar-5 cyclization product and trace amounts of the product derived from a competing Ar-6 Pschorr closure. In the case of compound 21, the Ar-6 cyclization was not observed, while the Ar-5 cyclization and 1,5-hydrogen radical transfer processes equally occurred. Finally, the Ar-6 cyclization was observed as the main process for compound 22, accompanied by the Ar-5 cyclization and, in a much lesser extent, by an 1,5-hydrogen radical transfer process.