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1.
Yoshimitsu Itoh 《Tetrahedron》2006,62(30):7199-7203
It has generally been believed that highly basic Li enolates cannot be applied as substrates for radical trifluoromethylation due to defluorination of the α-CF3 product. However, Li enolates can be in fact employed for radical trifluoromethylation. Moreover, the reaction is extremely fast and the minimum reaction time is only ∼1 s. 相似文献
2.
Yuri N. Belokon’Devayani Bhave Daniela D'AddarioElizabetta Groaz Viktor MaleevMichael North Armine Pertrosyan 《Tetrahedron letters》2003,44(10):2045-2048
Copper(salen) complex 1 has been found to catalyse the asymmetric alkylation of enolates derived from a variety of amino acids. There is a clear relationship between the size of the side chain in the substrate and the enantioselectivity of the process, so that the enantioselectivity decreases in the order alanine>aminobutyric acid>allylglycine>leucine>phenylalanine>valine. A transition state model which accounts for the influence of the size of the side chain on the enantioselectivity of the reactions is presented. 相似文献
3.
Edward S. TasberRobert M. Garbaccio 《Tetrahedron letters》2003,44(51):9185-9188
Following 1,4-reduction of 2-substituted dihydropyridones (1), the requisite ‘kinetic’ enolate can be isomerized upon warming to allow the isolation of the thermodynamic enolate as its vinyl triflate (3). This enolate interconversion is dependent on the dihydropyridone C-2 substituent and can be interpreted in terms of conformational analysis. This novel scaffold (3) opens another avenue for the strategic deployment of dihydropyridones into both natural product synthesis and drug discovery. To this end, this method is highlighted by its use as a key step in a total synthesis of (+/−) epiuleine (14). 相似文献
4.
Knöevenagel-type reaction between diketene and aldehydes proceeded in the presence of Ti(O-i-Pr)4. This reaction proceeded via titanium enolate derived from Ti(O-i-Pr)4 and diketene. As for the stereoselectivity of the products, E-isomers were produced predominantly in the case of aromatic aldehydes. 相似文献
5.
Mark L. Hlavinka 《Tetrahedron letters》2006,47(29):5049-5053
Simple amides and esters are conveniently deprotonated by Zn(tmp)2 (tmp = 2,2,6,6-tetramethylpiperidinyl anion) to generate Zn enolates. Enolates formed by this method are suitable for use in aldol reactions that tolerate base-sensitive functional groups. Additionally, the Zn enolates are readily coupled with aryl bromides using typical Pd-catalyzed coupling methods. 相似文献
6.
Shimpei Sugiyama 《Tetrahedron letters》2005,46(39):6771-6775
Treatment of optically active 1-chlorovinyl p-tolyl sulfoxides, which were synthesized from symmetrical ketones and (R)-(−)-chloromethyl p-tolyl sulfoxide in three steps, with lithium enolate of carboxylic acid tert-butyl esters gave optically active adducts having a substituent at the α-position with high 1,4-chiral induction from the sulfur chiral center in high yields. The adducts were converted to optically active esters and carboxylic acids having a chiral center at the α-position. When this addition reaction was carried out with the ester enolate generated from excess carboxylic acid tert-butyl ester with LDA in the presence of HMPA, the diastereomer of the adduct was obtained. By using the two reaction conditions for the generation of the ester enolates, a new method for asymmetric synthesis of both enantiomers of carboxylic acid derivatives having a substituent at the α-position from the one chiral source, (R)-(−)-chloromethyl p-tolyl sulfoxide, was realized. 相似文献
7.
Stereoselective alkylation of the enolate derived from benzyl (2R,3S)-(−)-6-oxo-2,3-diphenyl-4-morpholinecarboxylate (1) with cyclopentyl iodide afforded anti-α-monosubstituted product, benzyl (2R,3S,5S)-(−)-6-oxo-2,3-diphenyl-5-cyclopentyl-4-morpholinecarboxylate (3) in 60% yield. Catalytic hydrogenolysis over PdCl2 cleaved the auxiliary ring system to give l-cyclopentylglycine (4) in 84% yield. Subsequent protection of the α-amino function with Fmoc-OSu gave Fmoc-l-cyclopentylglycine (5) in high yield. 相似文献
8.
Stereospecific Palladium-Catalyzed Acylation of Enantioenriched Alkylcarbastannatranes: A General Alternative to Asymmetric Enolate Reactions
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Chao-Yuan Wang Glenn Ralph Joseph Derosa Prof. Dr. Mark R. Biscoe 《Angewandte Chemie (International ed. in English)》2017,56(3):856-860
We report the development of a Pd-catalyzed process for the cross coupling of unactivated primary, secondary, and tertiary alkylcarbastannatrane nucleophiles with acyl electrophiles. Reactions involving optically active alkylcarbastannatranes occur with exceptional stereofidelity and with net retention of absolute configuration. Because the stereochemistry of the resulting products is entirely reagent-controlled, this process may be viewed as a general, alternative approach to the preparation of products typically accessed via asymmetric enolate methodologies. Additionally, we report a new method for the preparation of optically active alkylcarbastannatranes, which should facilitate their future use in stereospecific reactions. 相似文献
9.
Enantioselective Total Synthesis of Dysidavarone A,a Novel Sesquiterpenoid Quinone from the Marine Sponge Dysidea avara
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Yurie Fukui Koichi Narita Prof. Dr. Tadashi Katoh 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(9):2436-2439
Dysidavarone A, a structurally unprecedented sesquiterpenoid quinone, was synthesized in 30 % overall yield in a longest liner sequence of 13 steps from commercially available o‐vanillin. A highly strained and bridged eight‐membered carbocyclic core was established by the C7?C21 carbon bond formation through a copper enolate mediated Michael addition to the internal quinone ring. 相似文献
10.
Pei-Hsun Wei Mukulesh Mondal Gero D. Harzmann Kraig A. Wheeler 《Tetrahedron letters》2010,51(51):6690-6694
The mechanism of PBu3-catalyzed homodimerization of ketoketenes has been explored and compared with that of the previously reported trialkylphosphite-mediated reactions. NMR studies of the PBu3-catalyzed reaction implicated the involvement of tetravalent phosphonium intermediates. Phosphonium intermediates in the catalytic cycle were trapped through reaction with trimethylsilyl chloride and 4-chlorobenzaldehyde, and the resulting products were characterized. A method for the stoichiometric generation of phosphonium enolates was developed as a result of these studies. No evidence was obtained for the involvement of pentacovalent phosphorane intermediates in trialkylphosphine-catalyzed ketoketene homodimerization reactions, in contrast with the mechanism of the trialkylphosphite-mediated homodimerization of dimethylketene. An X-ray crystal structure analysis of methylphenylketene dimer showed that it possesses Z-geometry about the exocyclic olefin. 相似文献