UBC Theses and Dissertations
Total synthesis of sesquiterpenoids (+)-eremophilenolide, (+)-Tetrahydroligularenolide,(+)-aristolochene,(-)-ylangocamphor,(-)- ylangoborneol,(-)-ylangoisoborneol Geraghty, M. Bert
The first part of this thesis is concerned with the successful development of a general synthetic approach to the eremophilane class of sesquiterpenoids, which culminated in the total synthesis of (+)-eremophilenolide 6, (+)-tetrahydroligularenolide 44 and (+)-aristolochene 34. The octalone 92 was converted via an efficient, regioselective route into the keto ester 105, which served as a common synthetic intermediate for the preparation of all three sesquiterpenoids. Successive subjection of 105 to alkylation, hydrolysis and decarboxylation afforded the keto acid 111. Hydrogenation of the latter provided both the cis-fused keto acid 113, which was readily converted into (+)-eremophilen-olide 6, and the trans-fused keto acid 112, which was similarly transformed into (+)-tetrahydroligularenolide 44. Conversion of 105 into the dithio-ketal 127, followed by desulfurization and treatment of the resultant olefinic ester 124 with excess methyllithium, provided the olefinic alcohol 130. Dehydration of the latter yielded (+)-aristolochene 34. In the second part of this thesis, a stereoselective total synthesis of the ylango-type sesquiterpenoids, (-)-ylangocamphor 7, (-)-ylango-borneol 23 and (-)-ylangoisoborneol 143, is described. The (+)-ketol 222, of known absolute stereochemistry, was converted by an efficient route into the keto ester 216. The latter was transformed into the bicyclo[3.2.l]octadione 203 by an intramolecular Claisen condensation. Homologation of 203 to the keto aldehyde 245 was achieved by an efficient three-step sequence of reactions. Reaction of keto aldehyde 245 with methoxymethylenetriphenylphosphorane afforded the (+)-keto olefin 204 which could hopefully be used as a common intermediate in the synthesis of the majority of known ylango sesquiterpenoids. Transformation of 204 into (-)-ylangocamphor 7 was achieved by successive hydroboration, mesylation and intramolecular alkylation. Ylangocamphor was converted in (-)-ylangoborneol 23 and (-)-ylangoisoborneol 143 by two completely stereoselective reductions.
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