Synthesis of cyclic bis(trimethysilyl) enol ethers and their [3+4] and [3+5] annulation reactions with dicarbonyl electrophiles. Access to highly functionalized tricyclic ethers possessing trans intrabridgehead stereochemistry

The synthesis of cyclic bis(trimethylsilyl) enol ethers from cycloalkanone carboxylates is described. The [3 + 4] and [3 + 5] annulation reactions of these bis(dinucleophilic), synthons with various 1,4- and 1,5-dicarbonyl el ectrophiles leads to the formation of tricyclic keto ethers with good regio - and stereochemical control. An interesting trans intrabridgehead stereoch emistry is observed when using bis(trimethylsilyl) enol ethers derived from nine- to 12-membered ring beta-keto esters.