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Relevant academic research and scientific papers

A Short, Stereoselective Synthesis of the Eudesmane Sesquiterpene Selina-3,7(11)-diene

The intramolecular Diels-Alder reaction of the C15 tetraene (6) prepared by attachment of a long-chain alkyl group with a terminal double bond to 2,5-dihydro-3-methyl thiophene S,S-dioxide, followed by extrusion of SO2, has been employed in an efficient total synthesis of selina-3,7(11)-diene.

TOTAL SYNTHESIS OF RACEMIC SELINA-3,7(11)-DIENE, α-SELINENE AND α-EUDESMOL

Three natural products of the eudesmane family, selina-3,7(11)-diene, α-selinene and α-eudesmol, have been synthesized using a common strategy.The key steps involved in the strategy include the direct deprotonation/alkylation of isoprenyl sulfone and the intramolecular Diels-Alder reaction.

SYNTHETIC STUDIES ON TERPENOIDS. PART 8. TOTAL SYNTHESIS OF (+/-)-EUDESMA-3(4),7(11)-DIENE, (+/-)-EUDESMA-4(5),7(11)-DIENE AND (+/-)-EUDESMA-4(14),7(11)-DIEN-8-ONE.

The key intermediate in these synthetic studies, methyl (+/-)-6-oxo-4-epi-11,12,13-trinoreudesmane-4α-carboxylate (8) was prepared from the alcohol (4).Irradiation of the alcohol (4) with lead tetraacetate and iodine yielded the cyclic ether (5) which on oxidation with chromic acid followed by esterification with diazomethane afforded the ketoester (8).Treatment of the ketoester (8) with trimethylsilyl chloride in the presence of lithium diisopropylamide, epoxidation of the resulting enol ethers and acid hydrolysis yielded the keto alcohol (12) which on methoxylation produced the compound (13).The transformation of (13) to the keto-ester (15) was accomplished by Clemmensen reduction, demethoxylation and oxidation of the resulting material with Jones reagent.Hydrolysis of (15) followed by decarboxylation of the resulting acidic material (16) yielded the methylenedecalone (17) which on being treated with tetrabromomethane and triphenylphosphine followed by addition of an etheral solution of dimethylcopper lithium afforded the isopropylidenedecalone (20).The photooxidation of (20) produced a mixture of alcohols (21) and (22) whose tosyl derivatives on heating with sodium iodide and zinc afforded the naturally occurring diene (1) and (2).Keto-ester (15) on reduction with sodium borohydride yielded a mixture of alcohols (25) whose tosyl derivative on heating with lithium bromide in dimethylformamide yielded the olefin (26).The transformation sequence of the olefin (26) to the ester (28) involved the preparation of the bromohydrin derivative (27), oxidation with Jones reagent and heating the resulting compound with γ-collidine.Hydrolysis of (28) and oxidative decarboxylation of the resulting material produced the methylenedecalone (24) and this reacted with diethyl carbonate to produce the keto-ester (29).Addition of methyllithium to keto-ester (29) and dehydration of the resulting alcoholic material with thionyl chloride and pyridine yielded the diene (3).

NEUE SESQUITERPENLACTONE AUS ASTER UMBELLATUS

The investigation of Aster umbellatus afforded six new eudesmanolides and a new selina-triene and from Aster exilis a new tremetone derivative was isolated.The structures were elucidated by spectroscopic methods and by some chemical transformations.The chemotaxonomic situation is discussed briefly.Key Word Index - Aster umbellatus; A. exilis; Compositae; sesquiterpene lactones; new eudesmanolides; new selinene derivative; new tremetone derivative.