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1.
Reaction of tricrotylborane with 1-pyrroline proceeds stereoselectively to give (1R
*
,1′S
*
)-2-(1-methylallyl)pyrrolidine. The latter was converted to the pyrrolizidine alkaloid (±)-pseudoheliotridane through hydroboration-oxidation-intramolecular
cyclization.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1450–1452, July, 1998. 相似文献
2.
《Tetrahedron letters》2004,45(40):7499-7501
A stereoselective synthesis of the C14-C26 fragment of the naturally occurring, cytotoxic macrolide FD-891, is described. Asymmetric Evans aldol reactions and aldehyde Brown allylations are key steps of the synthesis. 相似文献
3.
A general method for the synthesis of 5-substituted indolizidines based on intramolecular cyclization oftrans- andcis-2-allyl-6-R-1,2,3,6-tetrahydropyridines, obtained from pyridine and triallylborane, has been elaborated. The closure of the
five-membered ring is carried out by hydroboration-oxidation followed by cyclization of the resulting δ-amino alcohols in
the presence of the Ph3P−CBr4−Et3N system. (Pr2BH)2 and Pr3B are used as the hydroborating reagents, and H2O2 in an acid medium is used for the oxidation of 2-[3-(dipropylboryl]-Δ2-piperideines formed. This method has been used for the synthesis of two natural alkaloids: indolizidine 209D (cis-5-hexylindolizidine) and itstrans-isomer were prepared fromcis- andtrans-2-allyl-6-hexyl-1,2,3,6-tetrahydropiridine, respectively; indolizidine 167B andtrans-5-propylindolizidine were synthesized fromcis- andtrans-2,6-diallyl-1,2,3,6-tetra-hydropyridine, respectively.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 971–979, May, 1998. 相似文献
4.
The first stereoselective syntheses of the naturally occurring, ,β-unsaturated lactone hyptolide 1 and of its nonnatural epimer at C-6 are described. Ethyl l-lactate was the chiral starting material. Key steps of these syntheses were a Brown's asymmetric allylation, a Carreira's asymmetric ethynylation and a ring closing metathesis. 相似文献
5.
Highly Diastereoselective Synthesis of Methylenecyclobutanes by Merging Boron‐Homologation and Boron‐Allylation Strategies
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Michael Eisold Dr. Dorian Didier 《Angewandte Chemie (International ed. in English)》2015,54(52):15884-15887
A highly diastereoselective synthesis of methylenecyclobutanes possessing a quaternary stereocenter is reported, in which boron homologation of an easily‐generated cyclobutenylmetal species is performed, followed by an allylation reaction. Combining three steps in a one‐pot process further optimized the method, which afforded the expected adducts in excellent yields and stereoselectivity, starting from commercially available 4‐bromobutyne. 相似文献
6.
《Tetrahedron》2019,75(31):4110-4117
Enantioselective allylboration of aldehydes with α-substituted β-methyl allylboronate was reported. By using BF3·OEt2 as the catalyst, γ,δ-disubstituted homoallylic alcohols were obtained in good yields with high E-selectivities and enantioselectivities. Transition state analysis revealed that the disfavored transition state suffers from a syn-pentane interaction between the BF3 catalyst and axially oriented α-substituent of the allylboron reagent. Such a syn-pentane interaction is severe enough to overcome the A1,2 allylic strain between the β-methyl group and the α-substituent of the boron reagent that is present in the favored competing transition state. Consequently, the reaction proceeded with equatorial placement of the α-substituent to furnish γ-methyl substituted homoallylic alcohols with high E-selectivity. 相似文献
7.
Bubnov Yu. N. Klimkina E. V. Starikova Z. A. Ignatenko A. V. 《Russian Chemical Bulletin》2001,50(6):1078-1084
Reductive allylation of the bis(pyridine)dihydropyridyllithium dimer containing the 1,2- and 1,4-dihydropyridine fragments by triallylborane results mainly in trans- and cis-2,6-diallylpiperidines (60—85%), their ratio depending on the nature of the solvent. The minor reactions products are 2-allyl-1,2,3,6-tetrahydropyridine and 4,10-diallyl-3,9-diazatricyclo[6.2.2.02,7]dodecane. The unexpected formation of the latter is due to hetero-Diels—Alder condensation of intermediate products formed in the allylboration of dihydropyridines. The stereochemistry of trans- and cis-2,6-diallylpiperidines was determined from the 1H and 13C NMR spectra of the respective N,N-dimethylpiperidinium iodides. The structure of 4,10-diallyl-3,9-diazatricyclo[6.2.2.02,7]dodecane dipicrate was established by X-ray diffraction analysis. 相似文献
8.
An efficient, enantioselective total synthesis of (−)-lasubine I (1) has been achieved in an overall 8.8% yield from readily available starting materials. The important features of this approach include the creation of stereogenic centers through two sequential highly stereoselective Roush allylborations and the use of SN2 cyclization and ring-closing metathesis reactions for the construction of the quinolizidine skeleton. 相似文献
9.
Cross‐Metathesis/Isomerization/Allylboration Sequence for a Diastereoselective Synthesis of Anti‐Homoallylic Alcohols from Allylbenzene Derivatives and Aldehydes
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Dr. Rémy Hemelaere Dr. François Carreaux Dr. Bertrand Carboni 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(44):14518-14523
We describe a highly diastereoselective approach to anti‐homoallylic alcohols from allylbenzene derivatives and aldehydes. The strategy is based on a cross‐metathesis/isomerization/allylboration sequence catalyzed successively by ruthenium and iridium. This methodology provides another way to access this class of compounds, which leads to the preparation of hitherto‐unknown homoallylic alcohols without the requirement to control the stereochemistry of the 1‐alkenyl boronate intermediates. Our study towards an enantioselective version of this sequential reaction is also reported. 相似文献
10.
Vorontsova N. V. Rozenberg V. I. Vorontsov E. V. Antonov D. Yu. Starikova Z. A. Bubnov Yu. N. 《Russian Chemical Bulletin》2002,51(8):1483-1490
The nucleophilic addition of butyllithium, phenyllithium, methyllithium, and triallylborane to [2.2]paracyclophane-4,7-quinone (1) proceeded regio- and stereospecifically to give the corresponding cis-4,7-disubstituted 4,7-dihydroxy-4,7-dihydro[2.2]paracyclophanes 2—5 with the endo orientation of the hydroxy groups. The structures of quinone 1 and diols 2, 4, and 5 were established by X-ray diffraction analysis. 相似文献