Resolution of an Iridoid Synthon, Gastrolactol, by Means of Dynamic Acetylation and Lipase-Catalyzed Alcoholysis

A short synthetic route to asymmetric iridoids was developed. The three key steps were an intramolecular [4 + 2] cycloaddition reaction of an enamine derivative of 8-oxocitral (<b>2</b>), a dynamic acetylation, and an enzymatic resolution of the gastrolactyl acetates <b>5a </b>and<b> 5b</b>, iridoids with three stereocenters. Some regio- and stereoselective heterogeneous catalytic hydrogenations of double bonds in iridoid aglucones were discussed.