Synthesis of alkenyl sulphoxides by intramolecular and intermolecular addition of sulphenic acids to alkynes

Abstract

Alkyne-ω-sulphenic acids formed by thermolysis of ω-(t-butylsulphinyl)alkynes at 140 °C cyclized regiospecifically to 2-methylenethiacycloalkane 1-oxides; 2-methylenethietan 1-oxide was not formed in this way. 2-Methylpropane-2-sulphenic acid, obtained by heating di-t-butyl sulphoxide, added regioselectively to oct-1-yne to give predominantly 2-t-butylsulphinyloct-1-ene, which itself decomposed thermally to a mixture of dioctenyl sulphoxides by way of alkenesulphenic acid–dialkyl sulphine interconversions. Benzenesulphenic acid, methanesulphenic acid, and ethoxycarbonylmethanesulphenic acid, conveniently generated by thermolysis of 1-cyano-2-alkyl(or aryl)sulphinylethanes, underwent intermolecular addition to unactivated and activated alkynes regioselectively to give alkenyl sulphoxides in good yields.