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Dr. Marzia Dell'Aera Dr. Filippo Maria Perna Dr. Paola Vitale Dr. Angela Altomare Prof. Alessandro Palmieri Dr. Lewis C. H. Maddock Leonie J. Bole Dr. Alan R. Kennedy Prof. Eva Hevia Prof. Vito Capriati 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(40):8742-8748
We report the first transition metal catalyst- and ligand-free conjugate addition of lithium tetraorganozincates (R4ZnLi2) to nitroolefins. Displaying enhanced nucleophilicity combined with unique chemoselectivity and functional group tolerance, homoleptic aliphatic and aromatic R4ZnLi2 provide access to valuable nitroalkanes in up to 98 % yield under mild conditions (0 °C) and short reaction time (30 min). This is particularly remarkable when employing β-nitroacrylates and β-nitroenones, where despite the presence of other electrophilic groups, selective 1,4 addition to the C=C is preferred. Structural and spectroscopic studies confirmed the formation of tetraorganozincate species in solution, the nature of which has been a long debated issue, and allowed to unveil the key role played by donor additives on the aggregation and structure of these reagents. Thus, while chelating N,N,N’,N’-tetramethylethylenediamine (TMEDA) and (R,R)-N,N,N’,N’-tetramethyl-1,2-diaminocyclohexane (TMCDA) favour the formation of contacted-ion pair zincates, macrocyclic Lewis donor 12-crown-4 triggers an immediate disproportionation process of Et4ZnLi2 into equimolar amounts of solvent-separated Et3ZnLi and EtLi. 相似文献
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Preparation of Enantiomerically Pure 4,4,4-Trifluoro-3-hydroxy-butanoic Acid Derivatives, Branched in the 2- or 3-Position, from 6-Trifluoromethyl-1,3-dioxan- and -dioxin-4-ones Enantiomerically pure 3-hydroxy-3-trifluoromethyl-propionic acid and esters, substituted in the 2- or 3-position, are prepared (13 examples) from (R)- or (S)-4,4,4-trifluoro-3-hydroxy-butanoic acid. Key intermediates are the 2-t-butyl-6-trifluoromethyl-1,3-dioxan- and -dioxin-4-ones. The Li enolate of the cis-dioxanone is generated with t-BuLi and reacts with electrophiles (alkyl halides, aldehydes, imines, nitroolefins, Br2, I2) with predominant formation of trans,trans-2,5,6-trisubstituted dioxanones (9 examples). Elimination of HBr from the 5-Br-substituted dioxanone gives the (R)- or (S)-dioxinone, a chiral derivative of 4,4,4-trifluoro-3-oxo-butanoic acid (trifluoro-acetoacetate). Michael additions of cuprates or of CuCl-doped Grignard reagents to the dioxinone produce 6,6-disubstituted dioxanones (10 examples) bearing a CF3 group in the 6-position. In most cases this addition is highly diastereoselective, with the new substituent winding up in the trans position. There are, however, surprising exceptions, such as the product formed with benzylmagnesium chloride which is an abnormal adduct with a p-quinoid structure ( 26 ) and with the newly introduced group in the cis position with respect to the t-Bu group. The structures of four trisubstituted dioxanones bearing CF3 groups are determined by X-ray crystal structure analysis (Figure 1, Table 1), one of them including the absolute configuration (by anomalous diffraction). Besides the well-known sofa, a twist-boat conformation of dioxanones appears to be favorable. The solution conformations of the different types of CF3-substituted dioxanones are derived from Nuclear Overhauser NMR measurements and compared with the crystal structures (Figure 3). 相似文献
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Organocatalytic Strategy for the Enantioselective Cycloaddition to Trisubstituted Nitroolefins to Create Spirocyclohexene‐Oxetane Scaffolds 下载免费PDF全文
Dr. Alicia Monleón Dr. Florian Glaus Stefania Vergura Prof. Dr. Karl Anker Jørgensen 《Angewandte Chemie (International ed. in English)》2016,55(7):2478-2482
The first catalytic enantioselective cycloaddition reaction to α,β,β‐trisubstituted nitroolefins is reported. For this purpose, nitroolefin oxetanes were employed in the reaction with 2,4‐dienals promoted by trienamine catalysis. This methodology provides a facile and efficient strategy for the synthesis of highly functionalized chiral spirocyclohexene‐oxetanes with two adjacent tetrasubstituted carbon atoms in high yields and excellent selectivities. This strategy also enabled access to chiral spirocyclohexene‐cyclobutanes and ‐azetidines. Additionally, the obtained scaffolds can undergo diverse transformations leading to complex structures with up to four stereocenters, and we demonstrate that the nitro group, under nucleophilic conditions, can be applied for ring‐opening of the oxetane. 相似文献
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Known as electrophiles, maleimides are often used as acceptors in Michael additions to produce succinimides. However, reactions with maleimides as nucleophiles for enantioselective functionalization are only rarely performed. In this paper, a series of bifunctional Takemoto’s catalysts were used to organocatalyze the enantioselective Michael reaction of aminomaleimides with nitroolefins. The resulting products were obtained in good yields (76–86%) with up to 94% enantiomer excess (ee). The catalyst type and the substrate scope were broadened using this methodology. 相似文献
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Mustafa Durmaz 《Supramolecular chemistry》2013,25(5):292-301
The synthesis of calix[4]arene-based chiral bifunctional primary amine–thiourea catalysts has been described from p-tert-butylcalix[4]arene for the first time. The calix[4]arene-based catalysts were successfully applied to promote Michael addition of aldehydes with nitroalkenes affording preferentially the (R)- or (S)-adducts in high yields (up to 95%) and excellent enantioselectivities (up to 99% ees). 相似文献
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Organocatalytic Enantio‐ and Diastereoselective Conjugate Addition to Nitroolefins: When β‐Ketoamides Surpass β‐Ketoesters 下载免费PDF全文
Haiying Du Prof. Dr. Jean Rodriguez Dr. Xavier Bugaut Prof. Dr. Thierry Constantieux 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(27):8458-8466
Our findings on the bifunctional squaramide‐catalyzed enantioselective conjugate addition of β‐ketoamides to nitroolefins are disclosed. It appears that simple acyclic methylene β‐ketoamides, unlike the extensively studied β‐ketoesters, afford the products in excellent diastereoselectivities, and maintain high yields and enantioselectivities. Moreover, competition and kinetic studies were conducted to rationalize the observed reactivity and selectivity. The high level of diastereocontrol, along with the amenability of the amide group to postfunctionalization, dramatically increase the synthetic usefulness of the transformation. 相似文献
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Hong-Ying Tang Zhong-Biao Zhang 《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2038-2046
Abstract Asymmetric Michael-type Friedel–Crafts (F–C) alkylations of indoles with nitroolefins catalyzed by a chiral H8-BINOL-based phosphoric acid were investigated. The reactions took place very smoothly in the presence of only 5 mol-% of catalyst at room temperature to afford the desired F–C alkylation products in good yields and with moderate enantioselectivities. GRAPHICAL ABSTRACT 相似文献
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Conjugate addition reactions of aldehydes to α,β-disubstituted nitroolefins are important because they provide synthetically useful γ-nitroaldehydes bearing three consecutive stereogenic centers. Such reactions are challenging due to the drastically lower reactivity of α,β-disubstituted nitroolefins compared to, for example, β-monosubstituted nitroolefins. The testing of a small collection of peptides of the type Pro-Pro-Xaa (Xaa=acidic amino acid) led to the identification of H-Pro-Pro-D-Gln-OH and H-Pro-Pro-Asn-OH as excellent stereoselective catalysts for this transformation. In the presence of 5 mol% of these peptides different combinations of aldehydes and α,β-disubstituted nitroolefins react readily with each other providing γ-nitroaldehydes in good yields and diastereoselectivities as well as excellent enantioselectivities. Chiral pyrrolidines as well as fully substituted γ-butyrolactams and γ-amino acids are easily accessible from the γ-nitroaldehydes. Mechanistic studies demonstrate that the configuration at all three stereogenic centers is induced by the peptidic catalysts. Only a minimal amount of products from homo-aldol reactions is observed demonstrating the high chemoselectivity of the peptidic catalysts. 相似文献