Amberlyst-15-catalyzed intramolecular SN2′ oxaspirocyclization of secondary allylic alcohols. Application to the total synthesis of spirocyclic ethers theaspirane and theaspirone

A variety of substituted 1-oxaspiro[4.4]non-6-ene, 1-oxaspiro[4.5]dec-6-ene, 6-oxaspiro[4.5]dec-1-ene and 1-oxaspiro[5.5]undec-7-ene systems have been prepared by utilizing Amberlyst-15-catalyzed intramolecular SN2′ oxaspirocyclizations of secondary allylic alcohols under mild reaction conditions in quantitative yields. This oxaspirocyclization was applied to the total synthesis of theaspirane and theaspirone from β-ionone in five steps.