Palladium-catalyzed formation of 3,5-diaryl-1,2,4-selenadiazoles from arylselenocarboxamide

A number of new and known arylselenocarboxamides (i.e. Ar-C(=Se)NH2; Ar = C6H5 (1), 4-BrC6H4 (2), 2-MeOC6H4 (3), 4-MeOC6H4 (4), 4-MeSC6H4 (5), 4-EtOC6H4 (6), 2,3-(MeO)(2)C6H3 (7), 3,4-(MeO)(2)C6H3 (8), 3,5-(MeO)(2)C6H3 (9), 4-PhC6H4 (10), 6-MeOC10H6 (11), 4-MeOC10H6 (12)) have been prepared in high yields by the reaction of arylnitrile with NaHSe. Treatment of arylselenocarboxamides (4 mmol) with aqueous Na2PdCl4 0 mmol) in acetone at room temperature resulted in the formation of 3,5-diaryl-1,2,4-selenadiazoles as unexpected products together with palladium(II) complexes containing 3,5-diaryl-1,2,4-selenadiazoles. Treatment of arylselenocarboxamides (4 mmol) with catalytic amounts of Na2PdCl4 (10(-3) mmol) gave only 3,5-diaryl-1,2,4-selenadiazoles in good yields. 3,5-Diaryl-1,2,4-selenodiazoles were also prepared by oxidation of arylselenocarboxamides with iodine for comparison. (C) 2002 Elsevier Science B.V. All rights reserved.