TOTAL SYNTHESIS OF NEOHEDYCARYOL - ITS POSSIBLE ROLE IN THE BIOSYNTHESIS OF EUDESMANE SESQUITERPENES

The total synthesis of neohedycaryol (4), the C(9)-C(10) double bond r egioisomer of the germacrane sesquiterpene hedycaryol, was accomplishe d in 10 steps from the known dione 6. A Marshall fragmentation of the intermediate mesylate 14 was used to prepare the trans,trans-cyclodeca -1,6-diene ping present in neohedycaryol. During the synthesis of 14, a pronounced example of through-bond interactions (TBI) was observed, The preferred elongated chair conformation of neohedycaryol was demons trated spectroscopically and by chemical conversion into alpha-, beta- , and gamma-eudesmol. These findings indicate that the occurrence of n eohedycaryol as a precursor in the biosynthesis of epi-eudesmanes as p roposed in the literature is unlikely. The preference of neohedycaryol for the elongated chair conformation further shows that the compound occupies the meso form. This implies that neohedycaryol may act as a p recursor in the biosynthesis of both ent- and usual eudesmanes.