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Chiral N‐Heterocyclic Carbene Ligands Bearing a Pyridine Moiety for the Copper‐Catalyzed Alkylation of N‐Sulfonylimines with Dialkylzinc Reagents 下载免费PDF全文
Dr. Takahiro Soeta Tomohiro Ishizaka Yuta Tabatake Prof. Dr. Yutaka Ukaji 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16773-16778
Amino acid‐derived chiral imidazolium salts, each bearing a pyridine ring, were developed as N‐heterocyclic carbene ligands. The copper‐catalyzed asymmetric alkylation of various N‐sulfonylimines with dialkylzinc reagents in the presence of these chiral imidazolium salts afforded the corresponding alkylated products with high enantioselectivity (up to 99 % ee). The addition of HMPA to the reaction mixture as a co‐solvent is critical in terms of chemical yield and enantioselectivity. A wide range of N‐sulfonylimines and dialkylzinc reagents were found to be applicable to this reaction. 相似文献
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The cyclohexene‐derived aziridine 7‐tosyl‐7‐azabicyclo[4.1.0]heptane ( 1 ) reacts with Grignard reagents in the presence of chiral nonracemic Cu‐catalysts to afford sulfonamides 3a – e (Scheme 3) in up to 91% ee under optimized conditions (Table 2). No activation of the aziridine by Lewis acids is required. The reaction may be extended to other bicyclic N‐sulfonylated aziridines, but aziridines derived from acyclic olefins, cyclooctene, and trinorbornene are unreactive under standard conditions (Scheme 5). Exposure of 1 to s‐BuLi in the presence of (−)‐sparteine (2.8 equiv.) affords the allylic sulfonamide 31 in 35% yield and 39% ee (Scheme 6). Under the same conditions, the aziridines 33 and 35 yield products 34 and 36 derived from intramolecular carbenoid insertion with 75 and 43% ee, respectively. 相似文献
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Ring opening reactions of N‐sulfonyl aziridines by primary and secondary amines in silica gel (SG)‐water system were achieved, which provided a mild, practical and environmentally benign method to synthesize mono‐ and bis‐sulfonyl substituted amines. When primary and secondary amines were used in excess, they reacted with N‐sulfonyl aziridines smoothly at room temperature, mainly affording 1:1 ring opening products. Reactions of primary amines with 2 equiv. of aziridines produced 2:1 ring opening products. Some 1:1 products can be cyclized with CS2 to synthesize N‐sulfonyl cyclothioureas also in water. 相似文献
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Stereoelectronic Basis for the Kinetic Resolution of N‐Heterocycles with Chiral Acylating Reagents 下载免费PDF全文
Sheng‐Ying Hsieh Benedikt Wanner Dr. Philip Wheeler Prof. Dr. André M. Beauchemin Prof. Dr. Tomislav Rovis Prof. Dr. Jeffrey W. Bode 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(24):7228-7231
The kinetic resolution of N‐heterocycles with chiral acylating agents reveals a previously unrecognized stereoelectronic effect in amine acylation. Combined with a new achiral hydroxamate, this effect makes possible the resolution of various N‐heterocycles by using easily prepared reagents. A transition‐state model to rationalize the stereochemical outcome of this kinetic resolution is also proposed. 相似文献
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Dr. Roman Savka M. Sc. Marvin Bergmann Yuki Kanai Sabine Foro Prof. Dr. Herbert Plenio 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(28):9667-9675
Based on 1‐amino‐4‐hydroxy‐triptycene, new saturated and unsaturated triptycene‐NHC (N‐heterocyclic carbene) ligands were synthesized from glyoxal‐derived diimines. The respective carbenes were converted into metal complexes [(NHC)MX] (M=Cu, Ag, Au; X=Cl, Br) and [(NHC)MCl(cod)] (M=Rh, Ir; cod=1,5‐cyclooctadiene) in good yields. The new azolium salts and metal complexes suffer from limited solubility in common organic solvents. Consequently, the introduction of solubilizing groups (such as 2‐ethylhexyl or 1‐hexyl by O‐alkylation) is essential to render the complexes soluble. The triptycene unit infers special steric properties onto the metal complexes that enable the steric shielding of selected areas close to the metal center. Next, chiral and meso‐triptycene based N‐heterocyclic carbene ligands were prepared. The key step in the synthesis of the chiral ligand is the Buchwald–Hartwig amination of 1‐bromo‐4‐butoxy‐triptycene with (1S,2S)‐1,2‐diphenyl‐1,2‐diaminoethane, followed by cyclization to the azolinium salt with HC(OEt)3. The analogous reaction with meso‐1,2‐diphenyl‐1,2‐diaminoethane provides the respective meso‐azolinium salt. Both the chiral and meso‐azolinium salts were converted into metal complexes including [(NHC)AuCl], [(NHC)RhCl(cod)], [(NHC)IrCl(cod)], and [(NHC)PdCl(allyl)]. An in situ prepared chiral copper complex was tested in the enantioselective borylation of α,β‐unsaturated esters and found to give an excellent enantiomeric ratio (er close to 90:10). 相似文献
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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(41):12828-12831
Aziridines activated by N‐acylation are opened to the higher substituted radical through electron transfer from titanocene(III) complexes in a novel catalytic reaction. This reaction is applicable in conjugate additions, reductions, and cyclizations and suited for the construction of quaternary carbon centers. The concerted mechanism of the ring opening is indicated by DFT calculations. 相似文献
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Jompol Thongpaen Romane Manguin Olivier Basl 《Angewandte Chemie (International ed. in English)》2020,59(26):10242-10251
The asymmetric functionalization of C?H bond is a particularly valuable approach for the production of enantioenriched chiral organic compounds. Chiral N‐heterocyclic carbene (NHC) ligands have become ubiquitous in enantioselective transition‐metal catalysis. Conversely, the use of chiral NHC ligands in metal‐catalyzed asymmetric C?H bond functionalization is still at an early stage. This minireview highlights all the developments and the new advances in this rapidly evolving research area. 相似文献
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Comparing Cyclophellitol N‐Alkyl and N‐Acyl Cyclophellitol Aziridines as Activity‐Based Glycosidase Probes 下载免费PDF全文
Jianbing Jiang Thomas J. M. Beenakker Dr. Wouter W. Kallemeijn Prof. Dr. Gijsbert A. van der Marel Hans van den Elst Dr. Jeroen D. C. Codée Prof. Dr. Johannes M. F. G. Aerts Prof. Dr. Herman S. Overkleeft 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(30):10861-10869
The synthesis and evaluation as activity‐based probes (ABPs) of three configurationally distinct, fluorescent N‐alkyl cyclophellitol aziridine isosteres for profiling GH1 β‐glucosidase (GBA), GH27 α‐galactosidase (GLA) and GH29 α‐fucosidase (FUCA) is described. In comparison with the corresponding acyl aziridine ABPs reported previously, the alkyl aziridine ABPs are synthesized easily and are more stable in mild acidic and basic media, and are thus easier to handle. The β‐glucose‐configured alkyl aziridine ABP proves equally effective in labeling GBA as its N‐acyl counterpart, whereas the N‐acyl aziridines targeting GLA and FUCA outperform their N‐alkyl counterparts. Alkyl aziridines can therefore be an attractive alternative in retaining glycosidase ABP design, but in targeting a new retaining glycosidase both N‐alkyl and N‐acyl aziridines are best considered at the onset of a new study. 相似文献
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Mascha Jäkel Dr. Jianping Qu Prof. Dr. Günter Helmchen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(49):16746-16755
Enantioselective iridium‐catalyzed allylic substitutions were used to prepare N‐allyl hydroxamic acid derivatives that were suitable for ring‐closing metathesis, giving N‐methoxylactams. Reactions of these derivatives with Grignard or organolithium compounds gave hemiaminals, which could be reduced diastereoselectively via acyliminium intermediates to give cis‐piperidines or cis‐pyrrolidines with substituents in the 2,6‐ or 2,5‐positions, respectively. In addition, compounds with a quaternary carbon center could be synthesized by corresponding reactions with potassium cyanide/AcOH. The procedures were applied in the syntheses of alkaloids (?)‐209D and (+)‐prosophylline. 相似文献
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Stereoselective Synthesis and Reactions of Secondary Alkyllithium Reagents Functionalized at the 3‐Position 下载免费PDF全文
Kohei Moriya Dr. Dorian Didier Meike Simon Jeffrey M. Hammann Dr. Guillaume Berionni Prof. Dr. Konstantin Karaghiosoff Prof. Hendrik Zipse Prof. Dr. Herbert Mayr Prof. Dr. Paul Knochel 《Angewandte Chemie (International ed. in English)》2015,54(9):2754-2757
Secondary alkyllithium reagents bearing an OTBS group (TBS=tert‐butyldimethylsilyl) at the 3‐position can be prepared stereoconvergently through an I/Li exchange from a diastereomeric mixture of the corresponding secondary alkyl iodides. These lithium reagents react with a range of electrophiles, including carbon electrophiles, with retention of configuration to yield various 1,3‐difunctionalized derivatives with good diastereoselectivities. Kinetic studies show that the 3‐siloxy group strongly accelerates the epimerization at the lithium‐substituted carbon atom. This method offers a new way to construct chiral open‐chain molecules with excellent stereoselectivity. 相似文献