Ozone-Mediated Amine Oxidation and Beyond: A Solvent-Free, Flow-Chemistry Approach

Ozone is a powerful oxidant, most commonly used for oxidation of alkenes to carbonyls. The synthetic utility of other ozone-mediated reactions is hindered by its high reactivity and propensity to overoxidize organic molecules, including most solvents. This challenge can largely be mitigated by adsorbing both substrate and ozone onto silica gel, providing a solvent-free oxidation method. In this manuscript, a flow-based packed bed reactor approach is described that provides exceptional control of reaction temperature and time to achieve improved control and chemoselectivity over this challenging transformation. A powerful method to oxidize primary amines into nitroalkanes is achieved. Examples of pyridine, C-H bond, and arene oxidations are also demonstrated, confirming the system is generalizable to diverse ozone-mediated processes.