Alternative to Ozonolysis for the Oxidative Cleavage of Olefins

Key words

ozonolysis - photoexcitation - alkenes - selectivity - nitroarenes

Significance

Ozonolysis is widely utilized as a method to transform feedstock olefins into value-added oxygenated building blocks (alcohols, aldehydes, ketones, or carboxylic acids depending on work-up conditions), though practically the reaction presents significant challenges based on the toxicity of ozone as well as safety concerns around the high-energy intermediates formed. The current report presents an alternative reactive paradigm that accomplishes the same overall transformation as classic ozonolysis though proceeds through an ‘N-doped’ ozonide (formally a 1,3,2-dioxazolidine) that is formed through photo-mediated stepwise radical [3+2] cycloaddition of a nitroarene to the olefin with controlled hydrolytic cleavage leading to the desired carbonyl compounds.

Comment

Kinetic studies on the nature of the ­nitroarene employed in the photocycloaddition highlighted that tuning of the reagents could be achieved through judicious placement of EWGs on the aromatic core, whilst increased steric hindrance through ortho-substitution hindered reactivity. Furthermore, it was demonstrated that it was possible that in contrast to the explosive nature of 1,2,3-ozonides, it was possible to accumulate the ‘N-doped’ ozonides (4) in solution and even isolate them as stable solids. A broad range of simple and complex olefins were successful substrates with broad functional group tolerance being observed, while ‘tuning’ of the nitroarene enabled highly ­selective alkene-cleavage (16–20) to be achieved based on electronic, steric, and mediated polar effects in a diverse array of simple/complex systems presenting multiple potential reactive sites.