The probability of existence of a stepwise route which is in parallel with the well-known concerted pathway for the mechanism of 1,3-dipolar cycloaddition is debated by many researchers. As the route is stepwise, it would lead to emergence of at least a metastable intermediate which would produce some stereoisomers such as enantiomers and diastereomers. In 1986 the first clear stepwise example for a 1,3-dipolar cycloaddition was reported by Huisgen where an electron-poor alkene was reacted with a thiocarbonyl ylide. Since then, researchers have focused on the thiocarbonyl ylide 1,3-dipolar group in finding more stepwise examples. It was found that some reactions of a thiocarbonyl ylide with some dipolarophiles proceeded by a stepwise route, while others did not. This situation led us to investigate the probability of existence a stepwise route in parallel with the concerted path for the reaction of methyl thiocarbonyl S-oxide and C20 fullerene as a chemically active and nano-dimension electronegative alkene. To give more reliable data, Born–Oppenheimer ab initio QM/MM molecular dynamics was used.
