Mechanistic Insights into Selective Indium-Catalyzed Coupling of Epoxides and Lactones

Spiro-orthoesters, produced from the coupling of lactones
and epoxides,
are presequenced monomers capable of generating alternating poly(ether-alt-esters) after ring-opening polymerization. Recently,
we reported the selective synthesis of spiro-orthoesters through the
coupling of epoxides and lactones catalyzed by a cationic alkyl indium
catalyst. Herein, we investigate the mechanism of this reaction using
structure–function relationships and computational studies.
We show that this reaction is governed by Michaelis–Menten-type
saturation kinetics, which, along with the low Lewis acidity of these
indium catalysts, explains their selectivity.