Synthetic Studies on Spiroketal Natural Products. II. An Enantioselective Synthesis of (R)- and (S)-1, 7-Dioxaspiro[5.5]undecane

Abstract

Both enantiomers of 1, 7-dioxaspiro[5.5]undecane, a chiral compound with C₂ symmetry, were stereoselectively synthesized from an (R)-sulfoxide compound 8. The reaction of menthyl (S)-p-toluenesulfinate with a Grignard reagent gave the chiral sulfoxide (8), which was derived to a dihydropyran (12) by a several-step sequence. The base-catalyzed intramolecular Michael reaction of 12 exclusively afforded a dioxaspiro product (13) as a single stereoisomer. An acidic treatment of 13 resulted in isomerization of the spiro center to give 14. Desulfurization of 13 and 14 over Raney nickel in the presence of sodium hydroxide gave (R) -and (S)-1, 7-dioxaspiro[5.5]undecane (R-1 and S-1), respectively.