To a stirred solution of 4 (220 mg, 0.5 mmol, 1.0 equiv) in dry toluene (20 mL) was added a solution of PhSH (76 µL, 0.75 mmol, 1.5 equiv) and AIBN (24.6 mg, 0.15 mmol, 0.3 equiv) in dry toluene (10 mL) at temperature ranging from 60°C-120°C (entries 1-4) under argon atmosphere in a dropwise manner by a syringe pump over 3h. Another solution of PhSH (76 µL, 0.75 mmol, 1.5 equiv) and AIBN (24.6 mg, 0.15 mmol, 0.3 equiv) in dry toluene (10 mL) was added to the solution at the same temperature in a dropwise manner over an additional 3h. After completion, the mixture was cooled to ambient temperature and the solvent was removed under vacuum and the residue was purified by a flash column chromatography on silica gel (hexane/EtOAc = 10:1) to give product 3 as a colorless oil at a 35% yield.
     To identify reaction parameters including thiyl radical precursor, radical initiator, solvent, and temperature, further experiments with variable parameters were carried out. Because of the thermal instability of the vinylcyclopropane moiety in 4, in a separate procedure, the resultant reaction mixture containing 4, PhSH, and AIBN was stirred at room temperature under UV irradiation for 5h. Purification process remained the same as in the general procedure to yield 32%. Then, AlMe3 was used as a Lewis Acid in a separate synthesis of 3 from 4, increasing the yield to 40-48%. To test the key annulation reaction in the presence of transition-metal catalysis under visible light, the solvent toluene was replaced with MeCN (5 mL) and several commercially available catalysts were added to reaction. The use of catalyst Ir(dF(CF3)ppy)2(dtbbpy)PF6 provided 3 at the highest yield of 50% under irradiation with low-energy blue light-emitting diodes (LEDs).