First example of hydro-thiophosphorylation of 3-thiolene 1,1-dioxide

Abstract

Keywords: bis(2-phenylethyl)phosphine sulfide, 3-[di(2-phenylethyl)thiophosphoryl]tetrahydro-1H-thiophene-1,1-dione, 3-thiolene 1,1-dioxide, nucleophilic addition.Functionalized derivatives of 3-thiolene 1,1-dioxide (1) continue to attract attention as building blocks for organic synthesis, intermediates for obtaining biologically active substances, complexing solvents, and models for studying substituent effects in dihydrothiophenes [1][2][3][4].Synthesis of phosphorus-containing sulfolanes based on thiolene 1 opens up new prospects for constructing functionalized extraction and complexing agents as well as special solvents and ligands for metal complex catalysts. Information about reactions of thiolene 1 with PH acids includes data on nucleophilic and radical addition of dialkylphosphites [5,6], and also addition of primary and secondary phosphines and phosphine oxides [7].With the aim of further extending our knowledge about the reactivity of 3-thiolene 1,1-dioxide with respect to PH-acids and also in order to obtain new representatives of phosphorus-containing tetrahydrothiophenes, we have studied for the first time the reaction of thiolene 1 with secondary phosphine sulfides, using as an example bis(2-phenylethyl)phosphine sulfide (2) which can be readily obtained from the accessible bis(2-phenylethyl)phosphine [[8] and sulfur. Since phosphine sulfides are ambident compounds [9] and prototropism is possible in thiolene 1, the direction and outcome of the reaction under study were not predictable.We found that under mild conditions (45-50°C, 1 h, KOH, DMSO), phosphine sulfide 2 can add to thiolene 1 chemospecifically and regiospecifically, forming 3-[di(2-phenylethyl)thiophosphoryl]tetrahydro-1H-thiophene-1,1-dione (3) in 72% yield. We did not observe the SH tautomer of phosphine sulfide 2a in the reaction mixture among the products of hydrothiophosphorylation of thiolene 1. Without KOH and also under radical initiation conditions (65°C, 6 h, AIBN [azoisobutyronitrile]) and with all other conditions the same, hydrothiophosphorylation of thiolene 1 does not occur. This is support for the nucleophilic nature of this reaction, probably occurring through the electrophilic isomer 1a formed as a result of a prototropic shift of the double bond in the dihydrothiophene ring [7]. __________________________________________________________________________________________