Synthesis of macrocyclic ketoesters by an n + 1 strategy based on free-radical carbonylation

The synthesis of 10-17 membered 4-oxolactones 2 from alkyl iodides 1 having an acryloxy moiety at the termini, carbon monoxide, and TTMSS (or tin hydride) was achieved under free radical reaction conditions. The allyltin mediated reaction of 1 also proceeded successfully to furnish 2-allyl-substituted 4-oxolactones 3 in moderate to good yields. In this n + 1 type macrocyclization, high dilution conditions ([1] = 0.005-0.01 M) are beneficial for both the intermolecular trapping of CO and the intramolecular acyl radical addition to the C-C double bond.