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)2C6H3 (7), 3,4-(MeO)2C6H3 (8), 3,5-(MeO)2C6H3 (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 (1 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.