Click the structures and reaction arrows in sequence to view the 3D models and animations respectively
Cheleotropic reactions are a subclass of cycloadditions where two new bonds are formed to one molecule. In this example, the sulfur dioxide molecule donates two electrons to form the ring whilst being simultaneously attacked. The stereochemistry of the product is determined by the geometry of the starting diene. The reactions can also be reversed by heating.
Animations based on Suarez, D.; Sordo, T. L.; Sordo, J. A. J. Org. Chem. 1995, 60, 2848-2852