TOTAL SYNTHESIS OF (-)-GRAMININ A BASED ON ASYMMETRIC CYCLIZATION CARBONYLATION OF PROPARGYL ACETATE

The first total synthesis of (-)-graminin A is described. Key features of our synthetic approach involve a palladium-catalyzed asymmetric cyclization carbonylation of prochiral propargylic acetate, conversion of the orthoester product into the methyl 4-oxo-3-furancarboxylate, and copper complex mediated aldol condensation of (+)-gregatin B bearing a diene moiety. A new synthesis of (+)-gregatin B and the first synthesis of (-)-graminin A were achieved.