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1.
Kyoungmin Kang Kosuke Sakamoto Dr. Yoshihiro Nishimoto Prof. Dr. Makoto Yasuda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(22):4930-4934
The regioselective anti-carboindation of ynamides by using InBr3 and silylated nucleophiles was developed to synthesize (Z)-β-(carbonylamino)alkenylindiums. The X-ray crystallographic analysis of an alkenylindium suggested that the reaction proceeded in an anti-addition fashion. In contrast to reported syn-carbometalations of ynamides by using organometallics, a cooperation of InBr3 and silylated nucleophiles to ynamides achieved an anti-addition, which was supported by DFT calculations. The scope of substrates included various ynamides and silylated nucleophiles, such as silyl ketene acetals and silyl ketene imines. The transformation of synthesized alkenylindiums by iodination, radical coupling, and Pd-catalyzed cross-coupling successfully afforded trisubstituted enamines with high regio- and stereoselectivities. 相似文献
2.
《Tetrahedron: Asymmetry》2001,12(16):2343-2349
The BF3·OEt2-promoted aldol reaction of chiral syn- and anti-α-methyl-β-siloxy aldehydes with a silyl ketene acetal resulted in essentially complete syn Felkin selection. Even in the asymmetric aldol reaction using chiral oxazaborolidinones, the substrate control with respect to diastereoselection was found to overcome the promoter (catalyst) control which would normally occur depending on the stereocenter of the chiral boranes. 相似文献
3.
Otera J Fujita Y Sakuta N Fujita M Fukuzumi S 《The Journal of organic chemistry》1996,61(9):2951-2962
Mechanism of Mukaiyama-Michael reaction of ketene silyl acetal has been discussed. The competition reaction employing various types of ketene silyl acetals reveals that those bearing more substituents at the beta-position react preferentially over less substituted ones. However, when ketene silyl acetals involve bulky siloxy and/or alkoxy group(s), less substituted compounds react preferentially. The Lewis acids play an important role in these reactions. Enhanced preference for the more sterically demanding Michael adducts is obtained with Bu(2)Sn(OTf)(2), SnCl(4), and Et(3)SiClO(4) in the former reaction while TiCl(4) gives the highest selectivity for the less sterically demanding products in the latter case. These results are interpreted in terms of alternative reaction mechanisms. The reaction of less bulky ketene silyl acetals are initiated by electron transfer from these compounds to a Lewis acid. On the other hand, bulkier ketene silyl acetals undergo a ubiquitous nucleophilic reaction. Such a mechanistic change is discussed based on a variety of experimental results as well as the semiempirical PM3 MO calculations. 相似文献
4.
《Magnetic resonance in chemistry : MRC》2002,40(4):261-272
The Nicholas reaction of chiral 1‐alkoxy‐dicobalthexacarbonyl‐propargylium cations with linear and/or cyclic silyl enol ethers resulted in the formation of two pairs of diastereoisomers (syn‐1, syn‐2 and anti‐1, anti‐2), depending on the relative stereochemistry of the two new stereocenters formed in the reaction products. Here, we present a model to establish the relative stereochemistry of those stereocenters on the basis of a correlation of their 1H and 13C NMR spectra, together with their conformational analysis and a study of the stereoelectronic interactions conditioning the chemical shifts and coupling constants. The importance of this method is based on its applicability to the assignment of the relative stereochemistry of non‐separable components of a diastereomeric mixture or, when diastereomers are non‐crystallizable oily products, not suitable for X‐ray diffraction analysis. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
5.
A Powerful Chiral Phosphoric Acid Catalyst for Enantioselective Mukaiyama–Mannich Reactions 下载免费PDF全文
Dr. Fengtao Zhou Prof. Dr. Hisashi Yamamoto 《Angewandte Chemie (International ed. in English)》2016,55(31):8970-8974
A new BINOL‐derived chiral phosphoric acid bearing 2,4,6‐trimethyl‐3,5‐dinitrophenyl substituents at the 3,3′‐positions was developed. The utility of this chiral phosphoric acid is demonstrated by a highly enantioselective (ee up to >99 %) and diastereoselective (syn/anti up to >99:1) asymmetric Mukaiyama–Mannich reaction of imines with a wide range of ketene silyl acetals. Moreover, this method was successfully applied to the construction of vicinal tertiary and quaternary stereogenic centers with excellent diastereo‐ and enantioselectivity. Significantly, BINOL‐derived N‐triflyl phosphoramide constitutes a complementary catalyst system that allows the title reaction to be applied to more challenging imines without an N‐(2‐hydroxyphenyl) moiety. 相似文献
6.
Stereospecific epoxide-opening reactions of 1,1-dibromo-3,4-epoxy-1-alkenes with carbon nucleophiles
Fumihiko Yoshimura 《Tetrahedron letters》2008,49(49):6991-6994
The stereospecific epoxide-opening reactions of 1,1-dibromo-3,4-epoxy-1-alkenes with allyltributylstannane and with ketene silyl acetals in the presence of a Lewis acid are described. Both the reactions occurred regioselectively at the allylic position via an SN2 process giving rise to a single product, respectively. Treatment of the products by the latter reaction with p-TsOH afforded various 3,4-anti- and 3,4-syn-disubstituted γ-lactones in a highly stereoselective manner and high yields. 相似文献
7.
《Tetrahedron: Asymmetry》1998,9(11):1883-1890
A mixture of syn- and anti-aldol products containing an α-methylthio group were obtained in good yields with high enantioselectivities in the chiral oxazaborolidinone-promoted aldol reactions of a novel silyl ketene acetal, derived from ethyl 2-(methylthio)propionate, with aldehydes. Subsequent desulfurization resulted in an effective preparation of essentially enantiopure syn- and anti-propionate aldols which were separable. 相似文献
8.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(51):16560-16564
A novel approach for the umpolung α‐arylation of amides is presented. By the nucleophilic phenylation of O‐silyl N,O‐ketene acetals, generated in situ from N‐alkoxy amides, a phenyl group can be introduced onto the α‐carbon atom of amides through N−O bond cleavage in a two‐step, one‐pot process. The asymmetric synthesis of α‐aryl amides through the diastereoselective arylation of a chiral N,O‐ketene acetal is also described. 相似文献
9.
The title compounds were prepared by aldol reaction of anisaldehyde and the respective N,N‐dibenzyl glycinates. Deprotection of the nitrogen atom with Pearlman’s catalyst delivered the unprotected β‐hydroxytyrosine esters, which were further N‐protected as N,N‐phthaloyl (Phth) and N‐fluorenylmethylcarbonyloxy (Fmoc) derivatives. The Friedel–Crafts reaction with various arenes was studied employing these alcohols as electrophiles. It turned out that the facial diastereoselectivitiy depends on the nitrogen protecting group and on the ester group. The unprotected substrates (NH2) gave preferentially syn‐products but the anti‐selectivity increased when going from NHFmoc over NPhth to NBn2. If the ester substituent was varied the syn‐preference increased in the order Me <Et <iPr. The reactions were shown to be fully stereoconvergent and proceeded under kinetic product control. A model is suggested to explain the facial diastereoselectivity based on a conformationally locked benzylic cation intermediate. The reactions are preparatively useful for the N‐unprotected isopropyl ester, which gave Friedel–Crafts alkylation products with good syn‐selectivity (anti/syn=21:79 to 7:93), and for the N,N‐dibenzyl‐protected methyl ester, which led preferentially to anti‐products (anti/syn=80:20 to >95:5). Upon acetylation of the latter compound to the respective acetate, Bi(OTf)3‐catalyzed alkylation reactions became possible, in which silyl enol ethers served as nucleophiles. The respective alkylation products were obtained in high yield and with excellent anti‐selectivitiy (anti/syn≥95:5). 相似文献
10.
Shahriar H. Emami Ronald Salovey Thieo E. Hogen‐Esch 《Journal of polymer science. Part A, Polymer chemistry》2002,40(17):3021-3026
The crosslinking of poly(ethylene oxide) (PEO) with a difunctional peroxide such as 2,5‐bis(tert‐butylperoxy)‐2,5‐dimethylhexane (Luperox 101) may proceed through at least two different pathways. Thus, the thermally formed alkoxy radicals abstract hydrogen from PEO, and the resulting PEO radicals may combine or react with the peroxide radicals to give ether or acetal crosslinks. However, these reactions also produce noncrosslinking acetals and vinyl ethers. The acetals may react further with peroxy or other radicals and yield orthoesters and ketene acetals. These and similar groups, in the presence of dilute acids, are susceptible to acid hydrolysis, leading to the disintegration of the gels. The gels, upon swelling in dilute acids, undergo a slow degradation process that is not observed for unmodified PEO. The acid hydrolysis is confirmed by a combination of size exclusion chromatography and dynamic mechanical analysis. IR analysis shows the presence of hydroxyl end groups and the presence of carboxylates rather than aldehyde groups, this is consistent with orthoesters and ketene acetal intermediates. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3021–3026, 2002 相似文献
11.
Matthias Welker 《Tetrahedron》2010,66(52):9954-9963
Enantioselective approaches to the formation of α,β-disubstituted ketones through aldol reactions are compared. A one-pot ACA/aldol domino process is lower yielding than alternative procedures involving enantiomerically pure β-substituted silyl enol ethers. The use of chiral acetals derived from hydrobenzoin provides access to syn and anti diols in moderate to good yields and high diastereoselectivities. A novel synthesis of functionalized β,γ-unsaturated acetals is also described. 相似文献
12.
Klaus Neuschütz Jean‐Mary Simone Thomas Thyrann Reinhard Neier 《Helvetica chimica acta》2000,83(10):2712-2737
We report the synthesis of N‐benzyl‐N‐[(E)‐buta‐1,3‐dienyl]propanamide ( 6 ) and its corresponding O‐silyl‐substituted ketene N,O‐acetal 7 and their Diels‐Alder reaction. Propanamide 6 reacted smoothly, whereas the yield obtained from 7 was low, probably due to polymerization of the dienophile induced by electron transfer. The ketene N,O‐acetals 27a – g were synthesized starting from the corresponding benzamides 25a – e (Scheme 9). The ketene N,O‐acetals 27a – g showed increased stabilities and underwent amino‐Claisen rearrangements under thermal conditions. Using catalysts, interesting side reactions leading either to the annulated systems rac‐ 35 – 37 or to a β‐lactam rac‐ 34 were observed. 相似文献
13.
Robert J. Hinkle Yajing Lian Lee C. Speight Heather E. Stevenson Melissa M. Sprachman Lauren A. Katkish M. Christa Mattern 《Tetrahedron》2009,65(34):6834-9277
The rapid synthesis of cis-2,6-disubstituted dihydropyrans is achieved in a three-component, one-pot cascade reaction. BiBr3-mediated addition of ketene silyl acetals or silyl enol ethers to β,γ-unsaturated cis-4-trimethylsilyl-3-butenal provides a Mukaiyama aldol adduct containing a vinylsilane moiety tethered to a silyl ether. Addition of a second aldehyde initiates a domino sequence involving intermolecular addition followed by an intramolecular silyl-modified Sakurai (ISMS) reaction. Isolated yields of this one-pot reaction vary from 44 to 80% and all compounds were isolated as the cis-diastereomers (10 examples). 相似文献
14.
Trimethyl Orthoacetate and Ethylene Glycol Mono‐Vinyl Ether as Enolate Surrogates in Enantioselective Iridium‐Catalyzed Allylation 下载免费PDF全文
Yeshua Sempere Prof. Dr. Erick M. Carreira 《Angewandte Chemie (International ed. in English)》2018,57(26):7654-7658
Trimethyl orthoacetate and ethylene glycol mono‐vinyl ether are employed in iridium‐catalyzed enantioselective allylation reactions. The method documented enables their convenient use as surrogates for silyl ketene acetals and silyl enol ethers to prepare γ,δ‐unsaturated esters and protected aldehydes with excellent enantioselectivity. The utility of this novel method has been demonstrated by its implementation in a formal enantioselective synthesis of the meroterpenoid (+)‐conicol. 相似文献
15.
Seiji ShirakawaKeiji Maruoka 《Tetrahedron letters》2003,44(2):281-284
A stable glyoxylate can be successfully applied to both syn- and anti-selective aldol reactions by using two different kinds of ordinary Lewis acids. Thus, treatment of bowl-shaped tris(2,6-diphenylbenzyl)silyl glyoxylate 1 with enol silyl ether under the influence of BF3·OEt2 gave syn-aldol product, while the use of TiCl4 afforded anti-aldol product with >97% selectivity. 相似文献
16.
The multieffects of DMF and DBU on the [5 + 1] benzannulation of nitroethane and α‐alkenoyl ketene‐(S,S)‐acetals: Hydrogen bonding and electrostatic interactions 下载免费PDF全文
Haiyan Yuan Yiying Zheng Bo Li Wenliang Li Jingping Zhang 《Journal of computational chemistry》2015,36(10):731-738
A density functional theory (DFT) study was performed to elucidate the mechanism for the [5 + 1] benzannulation of nitroethane and α‐alkenoyl ketene‐(S,S)‐acetals. The calculation results are consistent with experimental findings, showing that the reaction proceeds via deprotonation of nitroethane, nucleophilic addition, intramolecular cyclization, elimination of HNO2, and the keto‐enol tautomerization sequence. It was disclosed that N,N‐dimethylformamide (DMF) and 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) act as not only solvent and nonnucleophilic base, respectively, but also catalysts in the reaction by stabilizing the transition states (TSs) and intermediates via intermolecular hydrogen bonds and electrostatic interactions. Besides, the effective orbital interaction of the reaction site in TS also contributes to the intramolecular cyclization step. The new mechanistic insights obtained by DFT calculations highlight that the hydrogen bonds and electrostatic interactions are key factors for the [5 + 1] benzannulation of nitroethane and α‐alkenoyl ketene‐(S,S)‐acetals. © 2015 Wiley Periodicals, Inc. 相似文献
17.
Indium Tribromide Catalyzed Coupling Reaction of Enol Ethers with Silyl Ketene Imines toward the Synthesis of β,γ‐Unsaturated Nitriles 下载免费PDF全文
Dr. Yoshihiro Nishimoto Takashi Nishimura Prof. Dr. Makoto Yasuda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(50):18301-18308
Herein, a coupling reaction of enol ethers with silyl ketene imines in the presence of catalytic amounts of InBr3 and Me3SiBr is described. Kinetic studies have revealed that an indium catalyst and Me3SiBr accelerated the coupling process and the regeneration of the catalyst, respectively. Various types of enol ethers and silyl ketene imines are applicable. In addition, a formal synthesis of verapamil was achieved by using this novel coupling reaction. 相似文献
18.
Tetsuji Yata Dr. Yoshihiro Nishimoto Prof. Dr. Makoto Yasuda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(7):e202103852
Strong main-group Lewis acids such as silylium ions are known to effectively promote heterolytic C(sp3)−F bond cleavage. However, carrying out the C(sp2)−F bond transformation of vinylic C−F bonds has remained an unmet challenge. Herein, we describe our development of a new and simple strategy for vinylic C−F bond transformation of α-fluorostyrenes with silyl ketene acetals catalyzed by B(C6F5)3 under mild conditions. Our theoretical calculations revealed that a stabilized silylium ion, which is generated from silyl ketene acetals by carboboration, cleaves the C−F bond of α-fluorostyrenes. A comparative study of α-chloro or bromostyrenes demonstrated that our reaction can be applied only to α-fluorostyrenes because the strong silicon-fluorine affinity facilitates an intramolecular interaction of silylium ions with fluorine atom to cleave the C−F bond. A broad range of α-fluorostyrenes as well as a range of silyl ketene acetals underwent this C−F bond transformation. 相似文献
19.
Oisaki K Zhao D Kanai M Shibasaki M 《Journal of the American Chemical Society》2006,128(22):7164-7165
An enantioselective aldol reaction between ketones and ketene silyl acetals is described using CuF-chiral phosphine as a catalyst. The key for high enantioselectivity was the development of a novel ligand derived from Taniaphos combined with the unique accelerative effect of PhBF3K. These conditions are applicable to various substrates such as aromatic, aliphatic, and heteroaromatic ketones. In the case of substituted nucleophiles, the reaction proceeds well. The diastereoselectivity is independent of ketene silyl acetal geometry. This is the first example of a catalytic enantio- and diastereoselective aldol reaction to ketones using ketene silyl acetals. 相似文献
20.
Gen Onodera 《Tetrahedron》2010,66(46):9021-9031
A cationic iridium complex [Ir(cod)2]SbF6 was found to be a new and efficient Lewis acid catalyst for Mukaiyama aldol and Mannich reactions. Aldehydes react smoothly with silyl enol ethers to give β-siloxy ketones in the presence of 0.5 mol % of [Ir(cod)2]SbF6. The reaction of N-alkyl arylaldimines with ketene silyl acetals in the presence of 5 mol % [Ir(cod)2]SbF6/P(OPh)3 gave β-amino esters. After Mannich reaction was complete, stirring of the reaction mixture for 24 h led to cyclization to give β-lactam. The reaction of N-aryl benzaldimine with silyl enol ether derived from acetophenone gave a tetrahydroquinoline derivative as a single diastereomer. 相似文献