STEREOSELECTIVE SYNTHESIS OF 8,12-FURANOEUDESMANES FROM SANTONIN - ABSOLUTE STEREOCHEMISTRY OF NATURAL FURANOEUDESMA-1,3-DIENE AND TUBIPOFURANE

Ketobutenolide 3, easily obtained from santonin (1), has been transfor med into two natural furanoeudesmanes 4 and 5, isolated from Commiphor a molmol and Tubipora musica, respectively. trans- And cis-decalin sys tems were obtained by stereoselective reduction of the C-4-C-5 double bond in 3 in the following way: hydrogenation of 3 over Pd/C followed by acidic treatment gave the cis isomer 10 as the major product; selec tive hydrogenation of the C-1-C-2 double bond with the Wilkinson's cat alyst followed by reduction with NaTeH yielded mainly the trans isomer 9. Compounds 9 and 10 were transformed into 4 and 5 in parallel seque nces. Optical rotation and CD measurements of the synthetic products r evealed that the stereochemistry of both natural products should be re vised to their enantiomeric form.