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The synthesis of the AB spiroketal fragment of spongistatin 1 (altohyrtin A) has been accomplished utilizing the addition of a metalated pyrone to an aldehyde followed by acid catalyzed spirocyclization. A stereoselective copper ( I ) promoted conjugate addition of vinylmagnesium bromide was used to establish the C11 stereogenic center.

Addition of lithiated γ-pyrones to β-alkoxy aldehydes followed by acid catalyzed spiroketalization provides a rapid efficient entry to functionalized hydroxylated spiroketals. The efficiency of the spiroketalization step is dependent on the substituents, particularly unprotected hydroxyls, on the chain which becomes the second ring of the spiroketal.