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71.
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Mariusz Majchrzak Yujiro Itami Bogdan Marciniec Piotr Pawluc 《Tetrahedron letters》2000,41(52):10303-10307
[RuCl2(CO)3]2 catalyzed cross-coupling polycondensation of 1,4-bis(vinyldimethylsilyl)benzene (A) appears to be a new, very efficient, method for highly stereo- and regioselective synthesis of phenylene–silylene–vinylene polymers (B). 相似文献
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Computational study on the reaction mechanism of the key thermal [4 + 4] cycloaddition reaction in the biosynthesis of epoxytwinol A 总被引:1,自引:0,他引:1
[reaction: see text] The key [4 + 4] cycloaddition in the biosynthesis of epoxytwinol A has been established by theoretical calculations to comprise of three processes. The first step is formation of the C8-C8' bond generating a biradical intermediate. Next, rotation about the C8-C8' bond occurs, and finally the C1-C1' bond is formed. Biradicals stabilized by conjugation and two hydrogen bonds are essential for realization of this rare thermal [4 + 4] cycloaddition. 相似文献
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Tubiferal A, a novel rearranged triterpenoid lactone, has been isolated from field-collected fruit bodies of the myxomycete, Tubifera dimorphotheca, and its structure elucidated by spectral data. Tubiferal A (1) possesses a 9,10-secocycloartan-16,21-olide skeleton, and this new compound exhibited a reversal effect of vincristine (VCR) resistance (more than 4-fold) against VCR-resistant KB cell lines. Tubiferal B (2), corresponding to the seco acid of 1 was also isolated, but showed no comparable activity. 相似文献
78.
Mitsuru ShojiSatoshi Kishida Yusuke KoderaIsamu Shiina Hideaki KakeyaHiroyuki Osada Yujiro Hayashi 《Tetrahedron letters》2003,44(38):7205-7207
Of the 16 possible modes of the oxidation-6π-electrocylization-Diels-Alder reaction cascade for an epoxyquinone, and eight for a 2-alkenyl-3-hydroxymethyl-2-cyclohexen-1-one, only the endo-anti(epoxide)-anti(Me)-hetero and endo-anti(Me)-hetero are respectively observed, while both the endo-anti(epoxide)-anti(Me)-hetero and exo-anti(epoxide)-anti(Me)-homo reaction modes occur with epoxy-4-hydroxycyclohexenones owing to a hydrogen-bonding interaction. 相似文献
79.
A general method for the asymmetric synthesis of α-substituted β-amino secondary alcohols is described, which comprises the four-reaction sequence (1) the proline-mediated, asymmetric, three-component Mannich reaction of two different aldehydes, (2) nucleophilic carbon addition to aldehyde, (3) oxidation of the resulting alcohol to the corresponding ketone, and (4) diastereoselective reduction with LiAlH(O-t-Bu)3 or catecholborane. The former reductant afforded the 1,2-syn isomer, while the latter gave the 1,2-anti isomer stereoselectively. The present method was successfully applied to the efficient asymmetric synthesis of the N-terminal amino acid moiety of nikkomycin B and BX. 相似文献
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A stereocontrolled total synthesis of both the (+)- and (-)-epolactaene ((+)- and (-)-1) enantiomers from tetrahydropyran-2-ol is described. The following reactions in this synthesis are particularly noteworthy: (1) the stereoselective construction of the conjugated (E,E,E)-triene by a combination of kinetic deprotonation and thermodynamic equilibration, (2) the E-selective Knoevenagel condensation of beta-ketonitrile 33 with a chiral 2-alkoxyaldehyde, (3) a diastereoselective epoxidation achieved using a bulky nucleophile (TrOOLi) and an appropriate protecting group, (4) the mild hydrolysis of an alpha-epoxy nitrile by silica gel on TLC facilitated by hydroxyl-mediated, intramolecular assistance. 相似文献