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Lignans chiral

Lignans by Chiral Auxiliary-Based Biaryl Coupling. 187... [Pg.185]

Keywords a-Hydroxylated lignans Natural product synthesis Enantioselective hydrogenation Chiral building blocks Malic acid... [Pg.185]

Two classes of a-hydroxylated lignans have been enantioselectively prepared a) wikstromol (3) [10, 38] and related natural products [39] and b) gomisin A (1) and congeners [40, 41]. In both cases, chiral, non-racemic ita-conic acid derivatives have been synthesized as key compounds for the preparation of -benzyl-y-butyrolactones (either by resolution (g [32]) or by asymmetric hydrogenation (h [25])). [Pg.193]

The stereoselective introduction of both benzyl groups simultaneously in one step seemed to be particularly attractive for a short synthesis of a- hy-droxylated lactone lignans from malic acid (99). Such a simultaneous double alkylation requires the formation of a chiral l,3-diene-l,4-diolate, which was not known. On the other hand, achiral 1,3-diene-1,4-diolates (di-enolates) have been previously prepared by Garrett et al. [58] and subsequently employed for the synthesis of racemic lignans by Snieckus [59] and Pohmakotr [60]. With knowledge of the synthesis and reactivity of di-enolates, we planned to prepare chiral di-enolates from dioxolanones and to alkylate these di-enolates in a stereocontrolled manner (Scheme 22). For the development of the described double deprotonation/alkylation strategy, tert-hutyl... [Pg.209]

LT048 Moinuddin, S. G., S. Hishiyama, M. H. Cho, L. B. Davin, and N. G. Lewis. Synthesis and chiral HPLC analysis of the dibenzyltetrahydrofuran lignans, larreatricins, 8 -epi-larreatricins, 3,3 -didemethoxyverrucosins and meso-3,3 -didemethoxynectandrin B in the creosote bush (Larrea tridentata) evidence for regiospecific control of coupling. Org Biomol Chem 2003 1(13) 2307-2313. [Pg.270]

The chiral lactone (178) has been used for the synthesis of a variety of natural products, such as sugars, lignans, terpenes, alkaloids, and P-lactams as a chiral building block 182c,184). The use of (178) as a powerful inductor of asymmetry was mainly established by Takano et al. 181, 84> one can expect more highly interesting reports from this group. [Pg.215]

Honda T, Kimura N et al (1994) Chiral synthesis of lignan lactones, (—)-hinokinin, (—)-deoxypodorhizone, (—)-isohibalactone and (—)-savinin by means of enantioselective deprotonation strategy. J Chem Soc Perkin Trans 1 1043-1046... [Pg.42]

A short and highly stereoselective route to lignan natural products ( )-dihydrosesamin and ( )-lariciresinol using radical methods has been reported [95JCS(P1)927]. These cyclizations proceed in good yields and the stereochemistry at two contiguous chiral centers are established. [Pg.25]

Although structural elucidation of lignans is not a difficult task, the similarities between the structures can create problems. In particular, the determination of stereochemistry at the chiral center requires NOE/ NOESY NMR experiments and/or X-ray analyses. The enantiomeric excesses of the known lignans (+)-lariciresinol, (-)-secoisolariciresinol and (+)-taxiresinol, isolated from Japanese yew T. cuspidata roots, were determined by chiral high-performance liquid chromatographic analyses [78] except for (+)-pinoresinol (77% enantiomeric excess), they were found to be optically pure by Kawamura et al. In an earlier study, the presence of taxiresinol in Taxus species was reported by Mujumdar et al. [69] after they had isolated it from the heartwood of T. baccata, although they did not study its stereochemistry. [Pg.124]

Modified chiral biphosphinic dioxolane ligands and their use in the asymmetric synthesis of natural lignans 92H(33)435. [Pg.327]

The (S)-(+)-y-butyrolactone-Y-carboxylic acid is a useful Intermediate for the synthesis of pheromones,4 natural lignans,5 and other derivatives.6 In the same manner, but starting with D-glutamic acid, the (R)-(-)-lactone acid may be prepared. Lactonization occurs with full retention of configuration at the chiral center.8 9 Recently, authors have described an efficient method which allows the formation of derivatives of the (R)-(-)-lactone from the more available (S)-(+) counterpart.10... [Pg.124]

Dianion aldol condensation reactions with Evans oxazolidinones or Oppolzer sultams as chiral auxiliaries have been demonstrated to be a useful method to generate the core skeleton of furofurans with diastereoselectivities of 5 1-20 1. Stereoselective total syntheses of the furofuran lignans (-l-)-eudesmin, (+)-yangambin, (—)-eudesmin, and (-)-yangambin according to this procedure have been reported (Equation 102) <2006TL6433>. [Pg.542]

A wide series of oxidants, spanning from TiCLj to iodine, has been used in the oxidative homocoupling of chiral 3-arylpropionic acid derivatives aimed at the preparation of lignans. The /f,/f-selectivity in the reactivity of 34 has been explained by a radical coupling mechanism (equation 20). The initially formed lithium (Z)-enolate may transform into the titanium enolate 35, which undergoes oxidation to the radical intermediate 36 via a single electron transfer process. The iyw-Z-type radicals 36 couple each other at the less hindered S-side si face) to give the R,/f-isomers 37 stereoselectively. [Pg.474]

A measure of the interest in the biological activity of these dibenzyl-butyrolactone lignans is evinced in the recent spate of publications dealing with the total synthesis of the natural optically active products. Again, the Stobbe condensation pathway (Scheme 9) has been usefully exploited for this purpose. In a series of papers, resolution of the intermediate hemisuccinate esters (433 by chiral bases has been described (54), as has asymmetric hydrogenation (55), and the optically active lignan products synthesized in the usual way (42 - 44 45). [Pg.323]

Other methods of preparation and diastereoselective alkylation of chiral butyrolactones (44) are summarized in the recent review of asymmetric synthesis of lignans (16). [Pg.324]

This is the smallest group of lignan tetrahydrofurans with fewer than ten members. All of reasonably well defined constitution are 3,4-trarw-disubstituted. Of these, most attention has been directed towards burseran, a constituent of Bursera microphylla with tumour-inhibiting properties (82). Optically pure (-)-/ra/w-burseran (82) and (-f-)-cw-burseran (83) were stereoselectively synthesized from chiral butyrolactones and gas chromatographic comparison indicated that the natural... [Pg.330]

Cp—Cp coupling occurs, probably via the first-formed palladium phenolate (315) to give the bisquinone methide (316), and the latter spontaneously undergoes intramolecular Diels-Alder reaction to the natural lignan carpanone (317) in 46% yield, with stereocontrol at five chiral centers. High yields, up to 94%, have been recorded using oxygen as oxidant with a metal(II)-salen complex as catalyst, e.g. cobalt(II) salen. A low yield of carpanone was also obtained in electrooxidation. 8... [Pg.698]

A large number of chiral a,a -orz/zo-disubstituted diphenyldiselenides with hydroxy and amino functions (e.g., 244 and 245) have been prepared by Wirth and co-workers. They were used as electrophiles for a number of asymmetric addition and cyclization reactions including the total synthesis of the lignan derivatives (-l-)-samin and (-l-)-membrine as well as catalysts in the asymmetric diethylzinc addition to aldehydes. [Pg.147]


See other pages where Lignans chiral is mentioned: [Pg.71]    [Pg.183]    [Pg.196]    [Pg.185]    [Pg.186]    [Pg.191]    [Pg.194]    [Pg.197]    [Pg.205]    [Pg.206]    [Pg.330]    [Pg.576]    [Pg.206]    [Pg.211]    [Pg.119]    [Pg.34]    [Pg.112]    [Pg.360]    [Pg.143]    [Pg.134]    [Pg.71]    [Pg.30]    [Pg.566]    [Pg.315]    [Pg.566]    [Pg.360]    [Pg.621]    [Pg.336]    [Pg.543]    [Pg.549]    [Pg.553]    [Pg.563]   
See also in sourсe #XX -- [ Pg.4 ]




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Lignan

Lignans

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