- Asymmetric synthesis of α,β-substituted γ-amino acids via conjugate addition
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The first conjugate addition reaction of organocuprates to N-enoyl oxazolidinone where a N-protected γ-nitrogen atom and an α-methyl group are present into α, β-unsaturated system is described. This reaction gave anti-products in moderate yields and high diastereomeric ratios. The anti-products have two contiguous stereogenic centers, one formed by the conjugate addition reaction and the other by a diastereoselective protonation reaction. The removal of chiral oxazolidinone moiety and N-deprotection of amino group furnished chiral α, β-disubstituted γ-amino acids.
- Sabala, Rocío,Assad, Salomon,Mendoza, ángel,Jiménez, Jacqueline,Sansinenea, Estibaliz,Ortiz, Aurelio
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p. 1741 - 1744
(2019/06/05)
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- 2-alkyl substituted crotonic acid and ester synthesis method thereof
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The invention provides a 2-alkyl substituted crotonic acid and an ester synthesis method thereof.The ester synthesis methodincludes the following steps that 2-alkyl butyric acid, a first catalyst and halogen are used as raw materials to synthesize 2-halogeneated-alkyln-butyric acid; the 2-halogeneated-alkyln-butyric acid, a solvent and inorganic base are used as raw materials to synthesize 2-alkyl crotonic acid; the 2-alkyl crotonic acid, a second catalyst and alcohol are used as raw materials to synthesize 2-alkyl crotonic acid ester. The 2-alkyl substituted crotonic acid and the ester synthesis method have the advantages that the solvents used in all reaction steps are recyclable, a water phase is recycled after finished product filtering, no wastewater is discharged, and a byproduct haloid acid (particularly referring to hydrobromic acid and hydrochloric acid) is obtained after halogen hydridetail gas is absorbed.
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Paragraph 0057; 0058
(2017/02/17)
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- Highly enantioselective iridium-catalyzed hydrogenation of α,β-unsaturated esters
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α,β-Unsaturated esters have been employed as substrates in iridium-catalyzed asymmetric hydrogenation. Full conversions and good to excellent enantioselectivities (up to 99 % ee) were obtained for a broad range of substrates with both aromatic- and aliphatic substituents on the prochiral carbon. The hydrogenated products are highly useful as building blocks in the synthesis of a variety of natural products and pharmaceuticals. Asymmetric hydrogenation: A variety of α,β-unsaturated esters were hydrogenated with high enantioselectivities (see scheme). The hydrogenated products have been used in synthetic transformations as well as in formal total syntheses. Copyright
- Li, Jia-Qi,Quan, Xu,Andersson, Pher G.
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supporting information
p. 10609 - 10616
(2012/11/07)
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- Rh-catalyzed asymmetric hydroformylation of functionalized 1,1-disubstituted olefins
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The first method for the highly enantioselective rhodium-catalyzed hydroformylation of 1,1-disubstituted olefins has been developed. By employing either of the P-chirogenic phosphine ligands BenzP* and QuinoxP*, linear aldehydes with β-chirality can be prepared in a highly enantioselective fashion with good chemo- and regioselectivities.
- Wang, Xiao,Buchwald, Stephen L.
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supporting information; experimental part
p. 19080 - 19083
(2012/01/05)
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- Efficient preparation of α,α-dialkyl-α-(phenylselanyl) acetates and α,β-unsaturated esters from the corresponding α,α-dialkyl-α-cyanoacetates by a lithium naphthalenide induced reductive selenenylation process
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An array of α,α-dialkyl-α-(phenylselanyl)acetates has been synthesized very efficiently from readily available α,α- dialkyl-α-cyanoacetates, by use of lithium naphthalenide induced reductive α-selenenylation as a key operation. Moreover, the selanyl esters thus generated in situ could be converted further, in a one-pot treatment with hydrogen peroxide and acetic acid, into the corresponding α,β- unsaturated esters in moderate to high yields. The C=C bond formation was highly regio- and/or diastereoselective in some cases. Georg Thieme Verlag Stuttgart.
- Ko, Yen-Chun,Zhu, Jia-Liang
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p. 3659 - 3665
(2008/09/19)
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- Synthesis and resolution of 2-methyl analogues of GABA
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E-4-Amino-2-methylbut-2-enoic acid, (±)-4-amino-2-methylbutanoic acid, (+)-(S)- and (-)-(R)-4-amino-2-methylbutanoic acid, which are analogues of the inhibitory neurotransmitter GABA (γ-aminobutyric acid, 4-aminobutanoic acid), were synthesised from ethyl 2-methyl-4-phthalimidobut-2- enoate, ethyl 2-methyl-4-phthalimidobutanoate, (+)-[(2R-(3,3-dimethylbutyro-1,4- lactonyl)]-(2S)-methyl-4-phthalimidobutanoate and (-)-[(2R-(3,3-dimethylbutyro- 1,4-lactonyl)]-(2R)-methyl-4-phthalimidobutanoate, respectively. The assignment of the absolute configuration of (+)-(S)- and (-)-(R)-4-amino-2-methylbutanoic acid was based on the X-ray crystallographic structure of the (+)-(R,S)-diastereoisomer, and direct comparison of specific rotations with the published data for (-)-(R)-4-amino-2-methylbutanoic acid.
- Duke, Rujee K.,Chebib, Mary,Hibbs, David E.,Mewett, Kenneth N.,Johnston, Graham A.R.
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p. 1745 - 1751
(2007/10/03)
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- A concise synthesis of siphonodictidine
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Siphonodictidine (1) has been synthesized for the first time in a concise and regiocontrolled manner by using 2-(tert-butyldimethylsiloxy)-3-methylfuran (6) as the crucial building block. The silver trifluoro-acetate-induced alkylation of 6 with Ω-bromogeranyl acetate 7 gave the key γ-lactone intermediate 8, which on subsequent reduction, conversion of the hydroxyl into the amino group, and amidination afforded siphonodictidine (1) in an overall yield of 25.7% from 6.
- Jefford, Charles W.,Rossier, Jean-Claude,Boukouvalas, John,Sledeski, Adam W.,Huang, Ping-Zhong
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p. 1383 - 1386
(2007/10/03)
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- Structure-cytoprotective activity relationship of simple molecules containing an α,β-unsaturated carbonyl system
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In previous reports we attributed the cytoprotective activity of several sesquiterpene lactones to the presence of a nonhindered electrophilic acceptor in their structure. We suggested that the mechanism of protection would be, at least in part, mediated through a reaction between the electrophilic acceptor and the sulfhydryl-containing groups of the mucosa. We report here the gastric cytoprotective effect of simple molecules containing an α,β-unsaturated carbonyl group. In the present paper, we undertake the study of molecular accessibility and molecular shape, in addition to conformational, electronic, and steric factors. Our results helped to establish two important facts connecting chemical structure with cytoprotective effect. Firstly, an adequate molecular accessibility appears to be necessary to produce the biological response, and secondly, the α,β- unsaturated carbonyl system has to be included in a cyclic structure or, at least, in the proximity of a cyclic system.
- Rodríguez, Ana M.,Enriz, Ricardo D.,Santagata, Luis N.,Jáuregui, Esteban A.,Pestchanker, Mauricio J.,Giordano, Oscar S.
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p. 1827 - 1834
(2007/10/03)
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- Stereocontrol of stereogenic centres para on a benzene ring using the SE2″ reaction of a pentadienylsilane
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The pentadienylsilane 9 and the dimethyl acetal 2 of isobutyraldehyde react with high (80:20) anti stereospecificity to give largely the diene 10a, which was converted into the Para-disubstituted benzene 11a, having 1,6-related stereogenic centres.
- Fleming, Ian,Leslie, Colin P.
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p. 1197 - 1203
(2007/10/03)
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- Preparation et etude de nouveaux derives organozinciques allyliques fonctionnels
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Stable organozinc compounds derived from alkyl-3-alkyl-2-(bromomethyl)-propenoates have been prepared.NMR 13C, 1H and IR studies show only one Z stereoisomer (no methylenic form) with a strong chelation between zinc and the carbonyl oxygen of the ester and solvated by only one solvent molecule.Hydrolysis can be achieved by two concurrent mechanisms with or without transposition.
- Lambert, Francois,Kirschleger, Bernard,Villieras, Jean
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p. 273 - 286
(2007/10/02)
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- Preparation des organozinciques derives de l'α-bromomethyl acrylate d'ethyle et de ses homologues
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The preparation of the bromozinc derivatives of various α-bromoalkyl acrylates (aliphatic and alicyclic) results in high yields when carried out on 30 mesh activated granular zinc, between 14 and 20 deg C in ethereal solvents (THF, DME, ether).Under these conditions duplication can be minimized (5-15 percent) especially with t-butyl acrylates.These α-functional allylic orgazinc derivatives have been characterized by hydrolysis and coupling with benzaldehyde.
- Alami, Najat El,Belaud, Chantal,Villieras, Jean
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- Lewis Acid Catalysis of Photochemical Reactions. 5. Selective Isomerization of Conjugated Butenoic and Dienoic Esters
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The effects of Lewis and Broensted acids upon the photoisomerization reactions of several conjugated butenoic and dienoic esters have been investigated.Lewis acid inhibit the photochemical deconjugation of α,β- to β,γ-unsaturated butenoic esters and shift the photoequilibrium between E and Z isomers toward the Z isomer.As such, irradiation of E α,β-unsaturated esters in the presence of EtAlCl2 provides a convenient method for the preparation of the thermodynamically less stable Z isomer.Irradiation of methyl (E,E)-2,4-hexadienoate and methyl (E,E)-5-phenyl-2,4-pentadienoate in the absence of added catalysts results in nonselective E,Z isomerization to give mixtures of all four stereoisomers in roughly comparable yields.In the presence of the Broensted acid trifluoroacetic acid, quantitative conversion of methyl 2,4-hexadienoates to methyl 3,4-hexadienoate is observed.The acid serves as a catalyst for the thermal 1,3-hydrogen shift of an allenic enol ester formed via a photochemical 1,5-hydrogen shift of the conjugated esters.Irradiation of the ground-state complexes of the conjugated esters with the Lewis acids EtAlCl2 or BF3 results in selective E,Z isomerization about the α,β-double bond in methyl 2,4-hexadienoate and the γ,δ-double bond in methyl 5-phenyl-2,4-pentadienoate.The mechanistic bases for the observed effects of Lewis acids are selective excitation of the more strongly absorbing E complex and more efficient isomerization of the excited E vs.Z complex.
- Lewis, Frederick D.,Howard, Daniel K.,Barancyk, Steven V.,Oxman, Joe D.
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p. 3016 - 3023
(2007/10/02)
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- ETUDE DE LA REACTION CHLOROCARBENE-ACETALS DE CETENES. I. SYNTHESE D'ESTERS α,β-ETHYLENIQUES.
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The reaction of chloro, chloromethyl and chlorophenyl carbenoids with ketene alkylsilylacetals has been studied.Excellent yields of cyclopropanation were observed and the unstable chlorocyclopropanone acetals formed were thermally rearranged in high yield into α-substituted α,β-ethylenic esters.This new method for the synthesis of unsaturated esters appeared complementary of the known-ones.
- Slougui, N.,Rousseau, G.
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p. 2643 - 2652
(2007/10/02)
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- Hydrogenolysis of Small Cycloalkanes, XI. - Hydrogenation of Bicyclobutane-1- and -2-carboxylates
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Hydrogenation of ethyl bicyclobutane-2-carboxylate (1) with Pd/C in ethanol at normal conditions leads to 95 percent of ethyl 2-methylbutyrate (2) and 5 percent of ethyl n-valerate (3).The corresponding 1-carboxylic acid ester 8 yields 99 percent of 2 but less than 1 percent of cyclobutane as well as the cis- and trans-2-methylcyclopropanecarboxylates 5 and 9.In this case 2-methylenebutyric and cis- and trans-2-methylcrotonic acid esters (10, 11a, and 12) can be detected as intermediates.From these, conclusions can be made about the mechanism at the catalyst. 5 is the main product with a poisoned catalyst.
- Hertzsch, Winfried,Musso, Hans
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p. 1485 - 1491
(2007/10/02)
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- Phenyl 2-(Trimethylsilyl)ethynyl Sulfone as a New Vinyl Cation Synthon
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Phenyl 2-(trimethylsilyl)ethynyl sulfone (PhSO2CCSiMe3, 1) is provided as a new vinyl cation synthon for an efficient introduction of the vinyl group to a variety of carbanionic nucleophiles (see Table I), including a highly hindered one, 29, an important precursor for the synthesis of Aspidosperma alkaloids.Another attractive feature of this reagent, which can be easily prepared in a large scale, is particularly demonstrated by its utility under rather strong basic conditions such as NaH, t-BuOK, KF, etc.
- Ohnuma, Takeshi,Hata, Noriaki,Fujiwara, Hiroyuki,Ban, Yoshio
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p. 4713 - 4717
(2007/10/02)
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