Silver Ion-mediated Desulfurization-Condensation of Thiocarbonyl Compounds

The title reaction of N-hydroxybenzamide with aryl isothiocyanates at ambient temperature gave 5-(arylimino)-3-phenyl-1,4,2-dioxazoles (1, 2) with elimination of Ag 2 S. The structure of 1 was determined by X-Ray crystal structure analysis.N-Hydroxybenzamide also reacted with diaryl thioketones to afford condensation products, 5,5-diaryl-3-phenyl-1,4,2-dioxazoles(3, 4).Desulfurizations of diaryl thioketones with α-hydroxy acids and with salicylic acid gave in the same way 2,2-diaryl-5-phenyl-1,3-dioxolan-4-ones (5-8) and 2,2-diaryl-1,3-benzodioxan-4ones (9-11), respectively.N-Phenylglycine and N-methylanthranilic acid gave similar types of condensation products (12, 13).We previously reported that C=C, C=N or acetal bond formation can be readily achieved under mild conditions through silver ion-mediated desulfurization-condensation of some thiocarbonyl compounds with reagents, such as active methylenes and amines, 1-3 Such bond formation occurs only to a small extent when mixtures of these reagents and aldehydes or ketones are subjected to heating in the presence of a strong acid or base.To extend our previous studies, we investigated the desulfurization of aryl isothiocyanates and diaryl thioketones with less reactive reagents such as N-hydroxybenzamide and hydroxy acids, which give no condensation products by dehydration with aldehydes or ketones.