Formation of 2,3‐Dihydrothiophene‐3‐carboxylates from 2(5<i>H</i>)‐Thiophenones <i>via</i> Sequential Cyclization and Ring‐Opening Reactions of 3‐Thiahexa‐1,5‐dienyl Radicals. Preliminary Communication

Abstract

Abstract Methyl 4‐mercapto‐2‐alkenoates 1 , obtained by irradiation of 2(5 H )‐thiophenones 2 in MeOH, undergo light‐induced S–H bond homolysis to give thio radicals 3 which can be trapped with 2‐butyne to afford 3‐thiahexa‐1,5‐dienyl radicals 12 . Intermediates 12 undergo selective 1,5‐ring closure to allylcarbinyl radicals 18 , which cyclize to cyclopropylcarbinyl radicals 19 . A novel rearrangement of 19 to 23 , the direct precursors of title compounds 15 and 17 , occurs via two additional ring‐opening and one 1,5‐ring‐closure step.