Photochemical Synthesis of Octahydro‐ and 3a,4,5,6,7,7a‐Hexahydro‐benzo[b]thiophenes from Methyl (E)‐4‐Mercapto‐2,6‐heptadienoate and Alkenes or Alkynes via Consecutive Radical Ring Closure. Preliminary Communication

Abstract

AbstractOn irradiation (λ = 300 nm) in MeOH 5‐(2‐propenyl)‐2(5H)‐thiophenone (1c) affords methyl (E)‐4‐mercapto‐2,6‐heptadienoate (2c) which undergoes light‐induced homolysis of the S–H bond to give the alkylthio radical 3c. This species can be trapped by 2,3‐dimethyl‐2‐butene or 2‐butyne to afford octahydrobenzo‐[b]thiophene 9 or 3a,4,5,6,7,7a‐hexahydrobenzo[b]thiophene 13, respectively, as main products via consecutive radical ring closure. In the absence of unsaturated hydrocarbons, 3c cyclizes to give methyl (E)‐3(thiolan‐2‐yl)‐2‐propenoate (8).