Expedient stereoselective synthesis of coronafacic acid through intramolecular Diels-Alder cyclization.

A stereoselective synthesis of coronafacic acid, a natural component of the phytotoxin coronatin, was achieved using an intramolecular Diels-Alder reaction as the key step. The triene precursor bearing a substituted diene and a vinylketone as dienophile was synthesized and then tested in the thermal intramolecular cyclization. We have devised a new strategy to assemble the E,Z-diene through the stereoselective aldol reaction of an ester enolate followed by a stereoselective dehydration. Following the thermal cyclization, the corresponding hydrindanone thereby obtained with the desired relative stereochemistry could easily be converted into the natural product. The synthesis of the coronafacic acid was accomplished in six steps in 29% overall yield.