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

meso-(R,S)-Dithia[3.3]-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 diasteroisomer. 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.