Synthesis of the Tetrahydropyran Subunit (C8-C20 Fragment) of (-)-Dactylolide and (-)-Zampanolide

The asymmetric synthesis of the tetrahydropyran containing C8-C20 fragment, a common key subunit of both (-)-dactylolide and (-)-zampanolide, is described. The salient feature of this synthesis is the extension of carbon chains using alkynols followed by the use of an alkyne system to generate the desired functionalities, in particular formation of the embedded pyran via an intramolecular oxa-Michael addition of a beta-hydroxyynone.