Kinetic control in the formation of meso-dithia[3.3]-paracyclophane S,S′-dioxide

meso-(R,S)-Dithia3.3]-paracyclophane S,S′-dioxide is formed with complete stereoselection by the thermolysis of 3,3′-1,4-phenylene-bis(methylenesulfinyl)]-dipropanoate—that generates in situ two transient sulfenic acid functions—in the presence of p-diethynylbenzene. By employing an improved procedure that we have recently optimized, the title compound has been prepared in a 70% yield as a single diastereoisomer. A density functional B3LYP/6-311+G(d,p) study demonstrates that the final syn-addition cyclization step takes place under kinetic control, through a five-membered transition state that defines the stereochemistry of the resulting cyclophane.