Synthesis of a 2,9-Dioxabicyclo[3.3.1]nonane via Double Intramolecular Hetero-Michael Addition: Entry to teh F-G Ring System of the Azaspiracids

摘要

An effective approach to form a 1,3-disubstituted 2,9-dioxabicyclo[3.3.1]nonane system repressenting the core of the F and G rings (C28-C34) of the azaspiracid natural products has been eveloped.The double intramolecular hetero-Michael additon (DIHMA) of a diol upon an ynone generated the bicyclic ketal in a highly diastereoselective fashion.