Synthesis of novel cage oxaheterocycles.

m-CPBA-promoted Baeyer-Villiger oxidation of pentacyclo[6.3.0.0(2,6).0(3,10).0(5,9)]undecan-4-one (1) afforded the corresponding lactone 2 in 93% yield. Lithium aluminum hydride promoted reduction of lactones 2, 6, and 9, performed in the presence of BF(3).OEt(2) reagent, afforded the corresponding cage ethers, i.e., 4, 7, and 10, respectively. Two methods that can be used to replace a cage C=O group by ether oxygen without concomitant rearrangement are delineated. A key step in the first of these methods employs m-CPBA promoted "double Criegee rearrangement", which was used to convert pentacyclo[6.3.0.0(2,6).0(3,10).0(5,9)]undecan-4-one diethyl acetal (11) into 7,9-dioxapentacyclo-[8.3.0.0(2,6).0(3,12).0(5,11)]tridecan-8-one (12). Subsequently, 12 was converted into 4-oxapentacyclo[6.3.0.0(2,6).0(3,10).0(5,9)]undecane (14) via a two-step reduction-dehydration reaction sequence. The second method utilized PhI(OAc)(2)-I(2) reagent to convert cage lactols 15 and 17 into the corresponding cage ethers, i.e., 14 and 2-oxaadamantane (18), respectively.