“Trading” a CC moiety for four C–O bonds and a peroxide: combining ozone and <i>O</i> -nucleophiles for peroxidative ring expansion of cycloalkenes into medium-sized 1,2-dioxacycloalkanes

Despite the long and rich history of C[double bond, length as m-dash]C double bond ozonolysis, ozonolysis of cyclic alkenes has generally been limited to the formation of ring-opening products and fragmentary evidence of unstable ozonide formation. We present a non-orthodox cycloalkene ring expansion reaction involving ozone and <i>O</i>-nucleophiles, which results in the formation of medium-sized peroxycycles. The mechanism is governed by a delicate balance: the cyclic structure of the substrate dictates conformational restrictions in the generated carbonyl oxide intermediate that kinetically retard the rapid [3 + 2] cycloaddition between the carbonyl and carbonyl oxide groups, enabling competitive trapping of the carbonyl oxide intermediate by an external <i>O</i>-nucleophile. Some of the synthesized peroxides exhibit ring-chain tautomerism, existing in either a hydroperoxide or a cyclic peroxy hemiacetal form. The use of hydroperoxides as <i>O</i>-nucleophiles leads to compounds containing both cyclic and exocyclic peroxide fragments. Additionally, these unique bisperoxides demonstrate intriguing reactivity, undergoing a highly selective rearrangement under basic conditions, which affects only one of the peroxide fragments. The developed peroxidative ring expansion of cycloalkenes <i>via</i> ozonolysis broadens the synthetic potential of classical ozonolysis and provides new pathways for constructing structurally diverse peroxides and polyfunctionalized products of their transformation.