RELATIVE AND ABSOLUTE-CONFIGURATION OF ALLOHEDYCARYOL - ENANTIOSPECIFIC TOTAL SYNTHESIS OF ITS ENANTIOMER

The enantiomer of (+)-allohedycaryol, a germacrane alcohol isolated fr om giant fennel (Ferula communis L.), has been synthesized, thereby el ucidating the relative and absolute stereochemistry of the natural pro duct. The synthesis of (-)-allohedycaryol started from (+)-alpha-cyper one (5) which was available in relatively large quantities via alkylat ion of imine 7 derived from (+)-dihydrocarvone and (R)-(+)-1-phenyleth ylamine. In a number of steps 5 was converted into the mesylate 4 with a regio- and stereoselective epoxidation as the key step. A Marshall fragmentation of 4 was used to prepare the trans,trans-cyclodeca-1,6-d iene ring present in allohedycaryol. The conformation of synthetic (-) -allohedycaryol was elucidated via photochemical conversion into a bou rbonane system. The synthesis of (-)-allohedycaryol also showed that n atural (+)-allohedycaryol has the opposite absolute stereochemistry to that normally found in higher plants.