TOTAL SYNTHESIS OF FORSKOLIN STUDIES .3. STUDIES RELATED TO AN ASYMMETRIC-SYNTHESIS

A modification of the Corey CBS methodology for the asymmetric reducti on of the dienone 3(A) affords the dienol 4(A) with an ee=98% (92% yie ld). The intramolecular Diels-Alder reaction of the derived tetrolate 7 yields the tricyclic lactone 8 (48-56%) with no significant loss of ee (less than 1%), thus demonstrating the feasibility of a total synth esis of forskolin in enantiomerically pure form according to our route . The present synthesis of the optically active lactone 8 (ee=98%) is the shortest and the most efficient.