Polycyclic arene episulfides. Attempted synthesis, molecular orbital calculations and comparison with arene oxides

Article abstract of DOI:10.1016/S0040-4020(98)00884-9

In pursuit of the elusive polycyclic arene episulfides, the synthesis of phenanthrene-9,10-episulfide (5b) was attempted. However, the reactions of phenanthrene-9,10-oxide and of phenanthrene with sulfur transfer agents and of 5,7-dihydrodibenzo[c,e]thiepine (9) with butyllithium did not afford 5b, although its intermediacy could be detected by NMR and inferred from the products isolated. Quantum-mechanical ab initio and density functional methods were used to calculate the thermodynamic stability of representative arene episulfides and arene oxides. The arene episulfides were found to be thermodynamically significantly less stable than the corresponding oxides, towards elimination of sulfur and oxygen respectively. K-region arene episulfides are found to be thermodynamically more stable towards sulfur extrusion than their bay-region isomers. The thermodynamic stabilities of analogous arene oxides and arene episulfides parallel each other, and the relative thermodynamic stabilities of arene oxides and episulfides can be deduced from the degree of the aromatic character of the rings which do not carry the heteroatom.