- A general approach to the asymmetric synthesis of lignans: (-)-methyl piperitol, (-)-sesamin, (-)-aschantin, (+)-yatein, (+)-dihydroclusin, (+)-burseran, and (-)-isostegane
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A highly efficient, diastereo- and enantioselective route was developed to access a great variety of lignans. The asymmetric synthesis of the 2,3-disubstituted γ-butyrolactones 9a-c could be improved in the case of aldol reactions by employing 2.2 equivalents of LiCl as an additive to provide, after purification, highly diastereo- and enantioenriched starting materials for the synthesis of the furofuran lignans (-)-methyl piperitol, (-)-sesamin, and (-)-aschantin. Furthermore, the γ-butyrolactone 15 was converted into dibenzylbutyrolactone lignan (+)-yatein, the dibenzylbutandiol type (+)-dihydroclusin, the tetrahydrofuran type (+)-burseran, and the dibenzocyclooctadiene type (-)-isostegane.
- Enders, Dieter,Lausberg, Vivien,Del Signore, Giuseppe,Berner, Otto Mathias
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p. 515 - 522
(2007/10/03)
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- Enantiocontrolled Synthesis of Burseran, Brassilignan, Dehydroxycubebin, and Other Tetrahydrofuran Lignans in Both Enantiomeric Forms. Application of Intermolecular Nitrile Oxide Cycloadditions and Lipase Mediated Kinetic Resolutions
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Several natural and unnatural tetrahydrofuran lignans have been synthesized by a convergent approach.Our methodology utilizes a nitrile oxide cycloaddition to dihydrofuran 8 and an enzymatic resolution of alcohols 11 by lipase PS.The lipase-mediated kinetic resolution of alcohols 11 furnished both enantiomers of the lignan precursors 12 and 14 in high optical purity (>99percent ee).This is followed by a SN2 displacement of tosylates 15 and 18 by α-lithiobenzyl phenyl sulfides.In this manner, both enantiomers of 3,4-dibenzyltetrahydrofuran (17a, 20a), 3,4-bis(3-methoxybenzyl)tetrahydrofuran (17b, 20b), brassilignan (17c, 20c), dehydroxy cubebin (17d, 20d), and burseran (17e, 20e) were synthesized in overall yields of 6-16percent.
- Gaboury, Janet A.,Sibi, Mukund P.
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p. 2173 - 2180
(2007/10/02)
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- General Conjugate-Addition Method for the Synthesis of Enantiomerically Pure Lignans. Total Synthesis of (-)- and (+)-Burseran, (-)-Dehydroxycubebin, (-)-Trichostin, (-)-Cubebin, (-)-5''-Methoxyhinokinin, and (-)-Hinokinin
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Conjugate addition of benzylic diphenyldithioacetal anions to enantiomerically pure (-)-(2R)-and (+)-(2S)-(benzyloxy)-2,5-dihydro-4-furan (2 r and 2 s) gave complete lignan skeletons of the dibenzylbutane class.Desulfurization followed by hydrogenolysis and, when appropriate, oxidation gave the title enantiomerically pure > 99 percent ee) lignans 45 - 50 in 24 - 35 percent overall yields from 2 r and 2 s.
- Rehnberg, Nicola,Magnusson, Goeran
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p. 4340 - 4349
(2007/10/02)
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