Iron-Catalyzed Oxidation of Triols Containing Vicinal Diols into Hydroxylactones: A DFT Study

A combined experimental and theoretical study on the iron-catalyzed oxidation of unprotected triols incorporating vicinal diols into hydroxylactones is presented using the Knölker catalyst. Focused on triols as mimics for complex polyols derived from sugars, this report rationalizes the difference in reactivity and selectivity observed between vicinal and nonvicinal primary alcohols in transfer hydrogenation. Moreover, DFT calculations performed on a model substrate allowed us to elucidate the key steps of the sequence, highlighting that the final oxidation step determines the selectivity of the whole process. Interestingly, the final product distribution was unexpectedly governed by an entropic contribution instead of electronics or steric effects.