Relative and Absolute Configuration of Allohedycaryol. Enantiospecific Total Synthesis of Its Enantiomer.
The enantiomer of (+)-allohedycaryol, a germacrane alcohol isolated from giant fennel (Ferula communis L.), has been synthesized, thereby elucidating the relative and absolute stereochemistry of the natural product. The synthesis of (-)-allohedycaryol started from (+)-alpha-cyperone (5) which was available in relatively large quantities via alkylation of imine 7 derived from (+)-dihydrocarvone and (R)-(+)-1-phenylethylamine. In a number of steps 5 was converted into the mesylate 4with a regio- and stereoselective epoxidation as the key step. A Marshall fragmentation of 4 was used to prepare the trans,trans-cyclodeca-1,6-diene ring present in allohedycaryol. The conformation of synthetic (-)-allohedycaryol was elucidated via photochemical conversion into a bourbonane system. The synthesis of (-)-allohedycaryol also showed that natural (+)-allohedycaryol has the opposite absolute stereochemistry to that normally found in higher plants.
Zhabinskii
Vladimir N.
VN
Laboratory of Organic Chemistry, Agricultural University, Dreijenplein 8, 6703 HB Wageningen, The Netherlands.
Minnaard
Adriaan J.
AJ
Wijnberg
Joannes B. P. A.
JB
de Groot
Aede
A