Structural and Synthetic Studies on Maleic Anhydride and Related Diacid Natural Products.

A concise approach has been developed for the total syntheses of tricladic acids A, B and C previously isolated from Tricladium castaneicola confirming the structures of these fungal natural products. The required (E)-1,3-diene scaffolds were generated with complete stereocontrol via coupling of the appropriate nitronate with an unsaturated bromo-diester which was prepared in 2 steps from citraconic anhydride. The reported structures of the anhydride waquafranone B and the parent diacid were synthesised leading to revision of the originally proposed structure of the natural product and, in accord with Sutherland, confirming that anhydrides with exo-dienes are unstable. Biomimetic dimerisations of the proposed monomers of the nonadride scytalidin were investigated.