NEIGHBORING GROUP PARTICIPATION IN LEWIS ACID-PROMOTED [3+4] AND [3+5] ANNULATIONS - THE SYNTHESIS OF OXABICYCLO[3.N.1]ALKAN-3-ONES

Lewis acids are employed as catalysts in the annulation of 1,4- and 1,5-dicarbonyl dielectrophiles with bis(trimethylsilyl) enol ethers of beta-diketones and beta-keto esters. A variety of 2-(alkoxycarbonyl)-m-oxabicyclo[3.n.1]alkan-3-ones can be constructed by this process in which two new carbon-carbon bonds are generated Unusually high regiocontrol is observed, and good to excellent stereochemical control can be achieved at virtually every position on the new carbocycles. Intramolecular neighboring group participation is proposed to explain the unusually high selectivities attained in the annulation reaction.