First Isolation of Eclipsed <i>v</i><i>ic</i>-Disulfoxide: 7,8-Dithiabicyclo[4.2.1]nona-2,4-diene 7-<i>e</i><i>xo</i>,8-<i>e</i><i>xo</i>-Dioxide

The oxidation of 7,8-dithiabicyclo[4.2.1]nona-2,4-diene 7-exo-oxide with dimethyldioxirane (DMD) provided the 7-exo-8-exo-dioxide, the structure of which was determined by X-ray crystallography [S−S 2.341(2) Å and ∠O−S−S−O 4.1(3)°]. The exo attack of DMD to give the exo,exo-dioxide was kinetically more favorable than the endo attack to give the endo,exo-dioxide. DFT calculations showed that the exo,exo-dioxide is thermodynamically more stable than the other stereoisomers.