A Spontaneous Fragmentation: From the Criegee Zwitterion to Coarctate Möbius Aromaticity

The extremely fast fragmentation of the spiroozonides prepared from formaldehyde O-oxide and three-membered ring ketones proceeds via the coarctate transition state 1. The ozonides decompose at temperatures as low as −90°C to form carbon dioxide, alkene/alkyne, and formaldehyde (the topology of the structure of 1 is depicted on the right). The mechanism is in accordance with the rules for the stereochemical course of coarctate reactions.