Tandem 1,3-dipolar cycloaddition of mesoionic 2,4-diphenyl-1,3-oxathiolium-5-olate with cycloocta-1,5-diene. A new synthesis of the tetracyclo[6.2.0.04,10.05,9]decane ring system

The mesoionic heterocycle 2,4-diphenyl-1,3-oxathiolium-5-olate (5) undergoes a tandem 1,3-dipolar cycloaddition reaction with cycloocta-1,5-diene (6) to give cycloadduct sulfide 7 in modest yield. Oxidation to sulfone 8 and photochemical extrusion of SO2 affords 9,10-diphenyltetracyclo[6.2.0.04,10.05,9]decane (9) in high yield.