Electrochemical production and examination of redox conversions of 2,4-diphenyl-6H-cyclopenta[b]thiopyran and 2,4-diphenylcyclopenta[b]thiopyrilium perchlorate

The mechanism governing the formation of 2,4-diphenyl-6H-cyclopenta[b]thiopyran and corresponding thiopyrilium perchlorate from 1,3-diphenyl-3-(2-oxocyclopentyl)-1-propanon in conditions of oxidative activation of hydrogen sulfide is considered. The process of oxidation of 2,4-diphenyl-6H-cyclopenta[b]thiopyran in a nonaqueous environment is shown to proceed stepwise through the intermediate formation of a radical cation, radical, and anhydrobase, to aromatic system 2,4-diphenylcyclopentadieno[b]thiopyranilidene. A similar product is obtained when oxidizing the 2,4-diphenylcyclopenta[b]thiopyrilium cation. Reduction of thiopyrilium perchlorate was observed to lead to the formation of a 2,4-diphenylcyclopenta[b]thiopyranyl radical, which is confirmed by an ESR method. The mechanism of redox conversions of thiopyran and thiopyrilium salt is substantiated by a quantum-chemical calculation.