EDWARD PIERS, M. BERT GERAGHTY, R. DEAN SMILLIE, and MARCEL SOUCY. Can. J. Chem. 53,2849 (1975).Stereoselective total syntheses of the tricyclic sesquiterpenoids (-)-copacamphene (1) and (+)-sativene (3) and of the related tetracyclic compounds (-)-cyclocopacamphene (2) and (+)-cyclosativene (4) are described. An efficient four-step synthetic sequence was employed to convert the bicyclic dione 5 into the olefinic ketone 8. The latter compound was converted in four steps into the olefinic alcohol 23. Eliminative cyclization of the corresponding tosylate 25 gave (-)-copacamphene (1) in high yield. In similar fashion, (+)-sativene (3) was obtained by cyclization of the olefinic tosylate 42, which in turn was derived via a four-step synthetic sequence from the olefinic ketone 9. Oxidation of the olefinic alcohol 23 afforded the aldehyde 34. Conversion of the latter compound into the p-tosylhydrazone 35, followed by pyrolysis of the corresponding lithium salt 36, gave the pyrazoline 37. Photolysis of 37 afforded, in high yield, (-)-cyclocopacamphene (2). Similarly, (+)-cyclosativene (4) On decrit des syntheses totales et stCreos6lectives des sesquiterpenoides tricycliques (-) copacamphene (1)et (+) sativene (3)et des composCs t6tracycliques (-) cyclocopacamphene (2) et (+) cyclosativtne (4) qui leur sont relies. On a utilise une sequence de synthtse efficace impliquant 4 Btapes pour transformer la dione 5 en cetone non-saturee 8. On a converti ce dernier compose en alcool olefinique 23 en quatre etapes. L'elimination cyclisante du tosylate correspondant 25 donne le (-) copacamphtne (1) avec un bon rendement. D e la mCme maniere, on obtient le (+) sativene (3) par cyclisation du tosylate non-sature 42, qui derive de la cetone non-saturk 9 par I'intermediaire d'une sequence de synthese en 4 etapes. L'oxydation de I'alcool insature 23 fournit l'aldehyde 34 qui est transforme en p-tosylhydrazone 35. La pyrolyse du sel de lithium de cette derniere (36) donne la pyrazoline 37 qui par photolyse conduit, avec un bon rendement, au (-) cyclocopacamphtne (2). On obtient le (+) cyclosativene (4) de la mCme maniere a partir de I'alcool 41 par I'intermediaire de la pyrazoline 46.
The total synthesis of the racemic forms of the eremophilane-type sesquiterpenoids eremophilenolide (21, tetrahydroligularenolide (3). and aristolochene (4) is described. The octalone 7 was converted via an efficient, regioselective route into the keto ester 12, which served as a common synthetic intermediate for the preparation of the three sesquiterpenoids. Successive subjection of 12 t o alkylation, hydrolysis, and decarboxylation afforded the keto acid 14. Hydrogenation of the latter provided both the cis-fused keto acid 20, which was readily converted into (i)-eremophilenolide (2), and the trnr~s-fused keto acid 15, which was similarly transformed into (i)-tetrahydroligularenolide (3). Conversion of 12 into the dithioketal 23, followed by desulfurization and treatment of the resultant olefinic ester 2 5 with excess mcthyllithium, provided the olefinic alcohol 27. Dehydration of the latter yielded (i)-aristolochene (4).La synthese totale des formes rackmiques des sesquiterpCnoi'des erCmophilenolide (2) du type eremophilane, tCtrahydroligularenolide (3) et I'aristolochtne (4) est dCcrite. L'octalone 7 a CtC converti en passant par un chemin regiosklectif efficace en &to-ester 12, qui sert d'intermkdiaire synthktique commun pour la prCparation de trois sesquiterpenoi'des. Lorsque I'on soumet 12 successivement a une alcoylation,
Efficient, stereoselective syntheses of the tricyclic sesquiterpenoids (+)-copacamphor (3), (+)-copaborneol (4), (+)-copaisoborneol (5), (−)-ylangocamphor (6), (−)-ylangoborneol (7), and (−)-ylangoisoborneol (8) are described. Conversion of the keto acetate 9 (previously synthesized from the dione 1) into the keto tosylate 17 was accomplished via an eight-step sequence. Intramolecular alkylation of 17 afforded, in high yield, (+)-copacamphor (3), which had previously been converted into the corresponding alcohols 4 and 5 by Kolbe-Haugwitz and Westfelt. Alkylation of the enolate anion of the bicyclic dione 2 with 2-bromopropane in hexamethylphosphoramide gave mainly the O-alkylation product 19. Conversion of 19 into the keto mesylate 29 was carried out in 5 synthetic steps. Intramolecular alkylation of 29 afforded (−)-ylangocamphor (6). Reduction of the latter with calcium in liquid ammonia gave (−)-ylangoborneol (7), while reduction with lithium aluminum hydride yielded (−)-ylangoisoborneol (8).
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