An Efficient Synthesis of 1,2-Dithiolanes and 1,2,4-Trithiolanes by the Reaction of Phosphorus Ylides with Elemental Sulfur

Abstract

Reaction of diarylmethylenetriphenylphosphoranes with elemental sulfur followed by the addition of maleic anhydride afforded 1,2-dithiolanes in good yields.When the reaction was carried out in the presence of adamantane-2-thione, two types of 1,2,4-trithiolane were formed.Thiation of thiobenzophenones with elemental sulfur also afforded the corresponding 1,2dithiolanes.The chemistry of cyclic polysulfides is of current interest. 11,2-Dithiolanes (1) and 1,2,4-trithiolanes (2) are an important class of compounds because of their biological activity and structural interest. 2The synthesis of 1 includes the oxidation of 1,3-dithiols, 3 and the intramolecular cyclization of thiosulfine with double bond. 41,2,4-Trithiolanes 2 were prepared by the reaction of thiobenzophenone with ochloranil, 5 the reaction of thiobenzophenones with 1,1-diphenylethylene sulfide, 6 the reaction of thiones with Lowesson reagents, 7 the reaction of dialkyl ketones with hydrogen sulfide, elemental sulfur, and amines, 8 and the fragmentation of 1,2,3-thiadiazoles. 9Recently, Senning and coworkers reported that reaction of α-chlorosulfenyl disulfides with morpholine afforded the corresponding dispirotrithiolanes. 10 Previously, we have reported the synthesis of 1,2-dithiolanes 1 from Wittig reagents (3), elemental sulfur, and maleic anhydride. 11Recently, we have reported that the reaction of pivalophenones with tetraphosphorus decasulfide afforded cis-and trans-3,5-di-tert-butyl-3,5-diaryl-1,2,4-trithiolanes, which equilibrated to give other isomers in refluxing toluene via thiopivalophenones and thiopivalophenone Ssulfides. 12We report a synthesis of 1 and 2 from diarylmethylenetriphenylphosphoranes (3) and elemental sulfur. Results and DiscussionTreatment of diphenylmethylenetriphenylphosphorane (3a) with excess sulfur in the presence of maleic anhydride resulted in the formation of 5,5-diphenyl-1,2-dithiolane-3,4-dicarboxylic acid anhydride (1a) in good yield.Reactions of other phosphoranes (3b-d) with elemental sulfur and maleic anhydride were carried out in a similar manner (Scheme 1, Table 1).The reaction required relatively elevated temperature for completion.When the reaction was carried out in refluxing benzene, 50% of thiobenzophenone (4a) was remained unreacted.