Synthesis of 1,7-epoxycyclononanes and 1,8-epoxycyclodecanes by β-fragmentation reactions using LTA and I2

Abstract: The reaction of derivatives on C3 of 6-hydroxy-2,7-dimethyl-11-oxatricyclo[6.2.1.02,6]undecan-4-one with lead tetraacetate and iodine, gave, in a good yield, 1,7-epoxycyclononanes. These compounds are the result of a β-fragmentation at the level of C2–C6 respect to the tertiary hydroxyl group on C6, with an unexpected contraction from a ten to a nine-membered ring system, via a radical addition to the carbonyl group on C4. The treatment of precursors (non-functionalized on C3) with LTA and iodine produced again a β-fragmentation without any structural rearrangement, affording a typical 1,8-epoxycyclodecane system. The transformation of the carbonyl group on C4 into acetate avoided radical additions and rearrangements affording, in high yield, the corresponding cyclodecanes. By this methodology, either 1,7-epoxy-cyclononane or 1,8-epoxycyclodecane could be synthesized, in a good yield, from the same versatile precursor. [Copyright &y& Elsevier]