Synthesis of sulphoxides by intramolecular and intermolecular addition of sulphenic acids to olefins and dienes

Abstract

Alkene-ω-sulphenic acids generated by thermolysis of ω-(t-butylsulphinyl)alkenes at 140 °C cyclized regio- and stereo-specifically to cis-2-methylthiacycloalkane 1-oxides. Under these conditions cis-2-methylthietan 1-oxide equilibrated with its trans-isomer, and cis-2-methylthiepan 1-oxide underwent ring contraction to cis-2-ethylthian 1-oxide. The first examples are provided of the intermolecular addition of simple alkanesulphenic acids to unactivated olefins to gives ulphoxides; 2-methylpropane-2-sulphenic acid added regiospecifically and in high yield to terminal acyclic olefins, but in low yield to cyclic olefins. Addition of 2-methylpropane-2-sulphenic acid to cyclo-octa-1,5-diene occurred stereospecifically. Thermolysis of di-t-butyl sulphoxide in hexa-1,5-diene gave a mixture of cis-2,5-dimethylthiolan cis-1-oxide and trans-2,5-dimethylthiolan 1-oxide; thermolysis in cyclo-octa-1,5-diene gave 9-thiabicyclo[4.2.1]nonane endo-9-oxide. The constitutions and configurations of the cyclic sulphoxides were predicted from a consideration of the stereoelectronic requirements of the addition of sulphenic acids to olefins.