Search results for "Stereocenter"
showing 10 items of 123 documents
ChemInform Abstract: Enantioselective Friedel-Crafts Alkylation of Indoles with (E)-1-Aryl-4-benzyloxybut-2-en-1-ones Catalyzed by an (R)-3,3′-Br2BIN…
2013
A highly enantioselective Friedel–Crafts reaction of unprotected indoles with (E)-1-aryl-4-benzyloxybut-2-en-1-ones catalyzed by a new chiral [Hf{(R)-3,3′-Br2-BINOL}(OtBu)2]2 complex has been developed to functionalize the C-3 position of the indole nucleus with a side chain bearing a 1,4-difunctionalized moiety and a benzylic stereogenic center. The reaction proceeds in good to excellent yields and excellent enantioselectivities (up to 97 % ee). The usefulness of this approach was illustrated with the synthesis of a tryptophol derivative.
Enantioselective Friedel-Crafts Alkylation of Indoles with (E)-1-Aryl-4-benzyloxybut-2-en-1-ones Catalyzed by an (R)-3,3′-Br2BINOLate-Hafnium(IV) Com…
2013
A highly enantioselective Friedel–Crafts reaction of unprotected indoles with (E)-1-aryl-4-benzyloxybut-2-en-1-ones catalyzed by a new chiral [Hf{(R)-3,3′-Br2-BINOL}(OtBu)2]2 complex has been developed to functionalize the C-3 position of the indole nucleus with a side chain bearing a 1,4-difunctionalized moiety and a benzylic stereogenic center. The reaction proceeds in good to excellent yields and excellent enantioselectivities (up to 97 % ee). The usefulness of this approach was illustrated with the synthesis of a tryptophol derivative.
Synthesis of Functionalized Indoles with a Trifluoromethy-Substituted Stereogenic Tertiary Carbon Atom Through an Enantioselective Friedel-Crafts Alk…
2010
[EN] Chiral complexes of BINOL-based ligands with zirconium tert-butoxide catalyze the Friedel-Crafts alkylation reaction of indoles with beta-trifluoromethyl-alpha,beta-unsaturated ketones to give functionalized indoles with an asymmetric tertiary carbon center attached to a trifluoromethyl group. The reaction can be applied to a large number of substituted alpha-trifluoromethyl enones and substituted indoles. The expected products were obtained with good yields and ees of up to 99%.
Bioconjugates of 1’-Aminoferrocene-1-carboxylic Acid with (S)-3-Amino-2-methylpropanoic Acid and L-Alanine
2010
Formal CH 2 insertion in bioconjugates composed of 1'-aminoferrocene-1-carboxylic acid (Fca) and alanine Boc-Ala-Fca-Ala-OCH 3 gives Fca bioconjugates with the β-amino acid (S)-3-amino-2-methylpropanoic acid (Aib). The novel homologous conjugates of ferrocene were fully characterized by spectroscopic and analytical methods. NMR, CD and IR spectroscopy in concert with DFT calculations suggest that the formal "L-Ala-to-(S)-β-Aib mutations" can exert ferrocene helix inversion due to the different stereogenic carbon atoms of L -Ala and (S)-β-Aib. Furthermore, the mutation (de-)stabilizes the conserved secondary structure with two intramolecular hydrogen bonds, depending on the "mutation site". …
The First P ‐Stereogenic 1D Coordination Polymers with the Metal Centers in the Backbone
2011
The enantiomeric ligands (R,R)- and (S,S)-bis(o-anisylphenylphosphanyl)methane (R,R-22 and S,S-22) and (R,R)- and (S,S)-bis(phenyl-m-xylylphosphanyl)methane (R,R-23 and S,S-23; dppm*), were treated with [Cu(NCCH3)4](BF4) and AgBF4 to produce the binuclear complexes [Cu2(dppm*)2(NCCH3)4](BF4)2 or [Ag2(dppm*)2](BF4)2, respectively. Then, these complexes were used as building blocks to prepare the first P-chirogenic 1D coordination polymers {[M2(dppm*)2(dmb)2](BF4)2}n [dppm* = (R,R)-22, (S,S)-22, (R,R)-23, (S,S)-23, M = Cu, Ag, dmb = 1,8-diisocyano-p-menthane] where M is part of the backbone of the polymer chain. The isostructural nature of these new polymers with the achiral parent polymers, …
Stereochemistry of terpene derivatives. Part 5: Synthesis of chiral lactones fused to a carane system—insect feeding deterrents
2006
Abstract Chiral iodo- 9, bromo- 10 and hydroxylactones 12 condensed with the carane system were obtained. In each case, the synthetic pathway led to an enantiomerically pure diastereoisomer to generate two stereogenic centers. Iodo- 9 and bromolactone 10 possess a γ-lactone group while the hydroxylactone 12 possesses a δ-lactone moiety situated trans to the gem-dimethylcyclopropyl ring. The structures of the products were confirmed by X-ray crystallography. These lactones were tested for antifeedant activity against storage pest insects.
Synthesis and stereochemistry of some new derivatives of cis-dihydropinol
1999
Abstract The synthesis of four new derivatives of cis-hydroxy-cis-dihydropinol with allyl-, epoxyalkyl-, hydroxyalkyl- and ketoalkyl-groups substituted on the cyclohexane ring is presented. The cis-orientation of hydroxyl group at C-2 and the configuration of all stereogenic centers is confirmed by X-ray crystallography.
Synthesis, crystal structures and magnetic properties of a P-stereogenic ortho-(4-amino-tempo)phosphinic amide radical and its CuII complex
2021
The synthesis of phosphinic amides containing one 4-amino-TEMPO substituent at the ortho position has been achieved through copper(I) catalyzed cross-coupling reactions of ortho-iodophosphinic amides with 4-amino-TEMPO. The method has been extended to the preparation of the first example of a P-stereogenic ortho-(4-amino-tempo)phosphinic amide radical 10. The reaction of 10 with Cu(hfac)2 afforded the P-stereogenic CuII complex 19. The crystal structure of both chiral compounds is reported. The molecular structure of 10 consists of a supramolecular zig-zag chain formed by intermolecular hydrogen bonds between the NH group of the phosphinic amide moiety and the nitroxide oxygen atom. In comp…
Organocatalytic Enantioselective Synthesis of Pyrazoles Bearing a Quaternary Stereocenter
2016
An efficient one-pot asymmetric synthesis of pyrazoles bearing a chiral quaternary stereocenter has been developed. Quinine-derived thiourea catalyzed the enantioselective addition of pyrazolones to isatin-derived ketimines, providing the corresponding acetylated pyrazoles after in situ treatment with Ac2O/Et3N. The corresponding pyrazoles were afforded in high yields and excellent enantioselectivities.
Resveratrol-Related Dehydrodimers: Laccase-Mediated Biomimetic Synthesis and Antiproliferative Activity
2012
Seven resveratrol-related monomeric stilbenoids were submitted to biomimetic oxidative coupling in the presence of laccase from Trametes versicolor (TvL), and gave racemic dihydrobenzofuran dehydrodimers (±)-15 to (±)-21. These products, after spectral characterization, were submitted to an antiproliferative activity bioassay against SW480 human colon cancer cells. Five racemates were found to be active, and were resolved by chiral HPLC. The pure enantiomers were subjected to circular dichroism measurements to establish their absolute configurations at C-7 and C-8. These enantiomerically pure compounds were submitted to the antiproliferative activity assay towards SW480 cells, and were all …