The lead tetraacetate oxidation of Δ6-unsaturated tertiary alcohols. Eight-membered cyclic ether formation

In the lead tetraacetate oxidation of the unsaturated tertiary cyclic alcohols 1a and 1b, and the acyclic alcohol 15a, all possessing a Δ⁶-olefinic bond (with respect to the hydroxyl group), the α-acetoxylated eight-membered cyclic ethers 6a, 6b and 16a, respectively, were obtained. With these substrates lead tetraaeetate reacts at the double bond and, if at all, only by weak association with the hydroxyl group, so that fragmentation products derived from alkoxy radical intermediates (such as 2) were not formed. The mechanism of this cyclisation reaction is discussed.