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1.
1H-, 13C-, and 17O-NMR spectra for the 2-substituted enaminones MeC(O)C(Me)?CHNH(t-Bu) ( 1 ), EtC(O)C(Me)?CHNH(t-Bu) ( 2 ), PhC(O)C(Me)?CHNH(t-Bu) ( 3 ), and MeC(O)C(Me)?CHNH(t-Bu) ( 4 ) are reported. These data show that 3 exists mainly in the (E)-form, 4 in (Z)-form, and 1 and 2 as mixtures of both forms. Polar solvents favour the (E)-form. The (Z)- and (E)-forms exist in the 1,2-syn,3,N-anti and 1,2-anti,1,N-anti conformations A and B , respectively. The structures of the (E)- and (Z)-form are confirmed by X-ray crystal-structure determinations of 3 and 4. The shielding of the carbonyl O-atom in the 17O-NMR spectrum by intramolecular H-bonding (ΔλHB) ranging from ?28 to ?41 ppm, depends on the substituents at C(l) and C(2). Crystals of 3 at 90 K are monoclinic. with a = 9.618(2) Å, b = 15.792(3) Å, c = 16.705(3) Å, and β = 94.44(3)°, and the space group is P21/c with Z = 8 (refinement to R = 0.0701 on 3387 independent reflections). Crystals of 4 at 101 K are monoclinic, with a = 16.625(8) Å, b = 8.637(6) Å, c = 11.024(7) Å, and β = 101.60(5)°, and the space group is Cc with Z = 4 (refinement to R = 0.0595 on 2106 independent reflections). 相似文献
2.
Ashot Khrimian 《Tetrahedron》2005,61(15):3651-3657
All eight geometric isomers of methyl 2,4,6-decatrienoate were synthesized from readily accessible starting materials by fully exploiting Wittig-type olefinations, and taking advantage of an easy separation of 2E and 2Z unsaturated esters. The aggregation pheromone of the brown-winged green bug, Plautia stali, methyl (E,E,Z)-2,4,6-decatrienoate (also a cross-attractant for the brown marmorated stink bug, Halyomorpha halys), was expediently produced in two easy steps from (E)-4,4-dimethoxy-2-butenal in 55% yield. The sex pheromone of the red-shouldered stink bug, Thyanta pallidovirens, methyl (E,Z,Z)-2,4,6-decatrienoate, was conveniently synthesized from 2,4-octadiyn-1-ol in 32% yield using in situ manganese dioxide oxidation-Wittig condensation in a key step. 相似文献
3.
Utility and limitation of the title reaction was studied. When (E)-3-(4-t-butyl- and 4-phenylcyclohex-1-en-1-yl)-2-(trimethylsilylmethyl)prop-2-en-1-ols were treated with Ms2O or MsCl, 3-t-butyl- and 3-phenyl-8-methylbicyclo[4.3.0]nona-1(6),7-dienes were obtained, respectively. The corresponding (Z)-isomer afforded a complex mixture, among which an elimination product was detected. (E)-4-(4-t-Butylcyclohexylidene)-2-(trimethylsilylmethyl)but-2-en-1-ol afforded only elimination product. 相似文献
4.
《Tetrahedron: Asymmetry》2001,12(18):2581-2587
From stereoisomeric α,β-unsaturated nitriles (E,Z)-1, the recombinant nitrilase AtNIT1 from Arabidopsis thaliana hydrolyses the (E)-isomers exclusively to the corresponding (E)-carboxylic acids (E)-2 with high specificity. The (E)-selectivity can also be utilised for the preparation of the isomerically pure nitriles (Z)-1. From (E,Z)-2-hydroxycinnamonitrile (E,Z)-3, the otherwise difficult obtainable (Z)-3 was prepared in 66% isolated yield. With β,γ-unsaturated (E,Z)-3-heptenenitrile (E,Z)-4, however, (E)-selectivity was not observed. AtNIT1 exhibits not only diastereoselectivity but also regioselectivity. From a mixture of the four isomers A–D of 3-(2-cyanocyclohex-3-enyl)propenenitrile 6, exclusively isomer D ((E)-cis-6) was hydrolysed to 3-(2-cyanocyclohex-3-enyl)propenoic acid (E)-cis-7, as stated by X-ray crystal structure. Only after complete conversion of D and high enzyme concentrations, isomer C ((E)-trans-6) was hydrolysed to a small extent. 相似文献
5.
(E)-β-ionone oximc ethyl ether [(E, E)-4] upon direct irradiation with λ either254or 313 nm yields the geometrical isomer (E, Z)-4 and (Z)-retro-γ-ionone oxime ethyl ether (Z,E)-5 as the sole primary products, illustrating (E)-(Z) isomerization (φ313 =0.49) and a 1, 5-hydrogen shift (φ313 =0.15) respectively. From studies with triplet photosensitizers and with ethyl iodide (to enhance the singlet-triplet intersystem crossing) it is concluded that these two products in the direct irradiation result only from the singlet excited state, and that the inter-system crossing quantum yield is relatively low. Upon prolonged irradiation of (E,E)-4 with λ 313 nm the eventual products are (Z,E)-5 and (Z,Z)-5, whereas with λ 254 nm they are (E,E)-5 and [(Z,E)-5 and/or (E,Z)-5]. Upon triplet photosensitization (E,E)-4 undergoes only (E)-(Z) isomerization, leading to a mixture of all the four geometrical isomers of4. From the dependence of the geometrical isomer distribution in the photostationary state on the triplet energy of the sensitizer the triplet energies of (E,E)-4, (E, Z)-4, (Z, E)-4, and (Z, Z)-4 have been determined to be ca 55, < 55,57, and 57 respectively. 相似文献
6.
Carlos Pérez-Balado 《Tetrahedron letters》2005,46(29):4883-4886
syn-Hydroalumination of 2,4,6-triisopropylphenylselanyl-1-alkynes 22 with DIBAL-H, followed by Al/I exchange with I2, afforded selectively the corresponding (E)-1-iodo-1-selenoalkenes in good yields. The sterically hindered 2,4,6-triisopropylphenyl group proved to be mandatory and prevented the formation of undesired by-products. 相似文献
7.
2,3-Diarylbenzofurans are efficiently generated by the cyclization of ortho-benzyloxybenzophenones using the hindered phosphazene base P4-t-Bu. 相似文献
8.
《Tetrahedron》2003,59(7):1021-1032
The conjugate (E)- and (Z)-(4′-pyridylethenyl)-4-phenylethyne (E-4 and Z-4) has been satisfactorily prepared by two different routes: (a) by dehydrohalogenation of 4′-pyridylethenyl-4-phenyl-β-chloroethene; (b) by the Wittig reaction between p-(iodobenzyl)(triphenyl)phosphine ylide and 4-pyridinecarboxaldehyde, E/Z isomer separation, and cross-coupling with 2-methyl-but-3-yn-2-ol followed the propanone elimination. The Glaser oxidative dimerization of (Z)-4 yields (Z,Z)-1,4-di[(4′-pyridylethenyl)-4-phenyl]-buta-1,3-diyne in good yield, (Z,Z)-5. (E,E)-5 was obtained by phase transfer oxidative dimerisation of (E)-4 in presence of their N-methyl salt (E)-10. Mono- and di-N-methylated salts of conjugate (E,E)-5 and (Z,Z)-5, were obtained by quaternation with iodomethane. The (Z,Z)-5 di-N-methylated salt forms charge-transfer complexes with TCNE, TCNQ and TMPD. 相似文献
9.
6-Methyl-6-hepten-2-one (3) on reaction with ethyl α-dimethylphosphonate/NaH gives a mixture of (E)-and (Z)-conjugated esters. The major (E)-isomer, (E)-ethyl-3,7-dimethyl-2,7-octadienoate (4), on reduction with LiAlH4 at room temperature furnishes (E)-3,7-dimethyl-2,7-octadien-l-ol (5) which on propionylation affords (E)-3,7-dimethyl-2,7-octadienyl propionate (1). Carbinol (5) is converted into its silyl ether (E)-2,6-dimethyl-8-t-butyldimethylsilyloxy-l,6-octadiene (6) witht-Bu(Me)2SiCl in CH2Cl2, which on hydroboronation-oxidation with 9-BBN/NaOH-H2O2 followed by disilylalion with (n-Bu)4N+ F− at room temperature, gives (E)-3,7-dimethyl-2-octen-l,8-diol (2). 相似文献
10.
Carlos Pérez-Balado 《Tetrahedron》2006,62(10):2331-2349
syn-Hydroalumination of 2,4,6-triisopropylphenylselanyl-1-alkynes with DIBAL-H followed by Al/I exchange with I2 afforded exclusively (E)-1-iodo-1-selenoalkenes in good yields. 1-Iodo-1-selenopropene 10 proved to be a convenient 1,1 dianion equivalent, leading to the stereodivergent synthesis of allylsilanes (Z)-6 and (E)-6. Adduct 3, an intermediate in the synthesis of the tetrahydropyran subunit of polycavernoside A, was efficiently synthesised from allylsilane (Z)-6 and aldehyde 7 via an intramolecular Sakurai cyclisation. 相似文献
11.
Thorsten Lifka 《Tetrahedron》2008,64(27):6551-6560
(E,E)-3,6-Bis(styryl)pyridazines (3a-t) bearing 2, 4 or 6 alkoxy chains were prepared by applying the Siegrist reaction of 3,6-dimethylpyridazine (13) and the corresponding azomethines 10a-t. The transversal dipole moment of these calamitic compounds effects an extremely high tendency for self-organization in thermotropic LC phases (N, SA, SB, SC, SE, SI/F, and Cub). The conjugated core structure represents moreover a chromophore with a high photosensitivity for (E,E)?(E,Z) isomerization reactions: this property makes the compounds interesting for optical imaging and switching techniques. 相似文献
12.
Sergey M. Ivanov 《Journal of heterocyclic chemistry》2021,58(6):1371-1378
Reactions of 2-(6-tert-butyl-5-oxo-4,5-dihydro-1,2,4-triazin-3(2H)-ylidene)-3-oxo-3-R-propanenitriles (R = t-Bu, Ad-1) with tert-butyl bromoacetate gave the corresponding N(2), C(5)O bis-alkylation products. Treatment of the latter with t-BuLi, in the case of R = t-Bu, led to intramolecular condensation at the exocyclic nitrile group. However, in the case of R = Ad-1, the condensation with the sterically more hindered carbonyl group was observed to give diastereomerically pure 8-cyanopyrrolo[1,2-b][1,2,4]triazine-6-carboxylate derivatives. The structures of the isolated products were confirmed by spectral methods and X-ray single-crystal diffraction. 相似文献
13.
Natacha Mariet 《Tetrahedron》2004,60(12):2829-2835
The structures of eleven 1-substituted benzocyclobutenes and corresponding (E)-o-xylylenes and (Z)-o-xylylenes have been calculated at the Becke3LYP/6-311G(d,p) level. Some o-xylylenes are plane and even some (Z)-isomers. In three cases (substituent: methoxy, amino and formamido groups), the (Z)-isomer is more stable than the (E)-isomer. The regioselectivity of the Diels-Alder reaction between (o)-xylylenes and propene or ethylvinylether is discussed according to the frontier OM coefficients. 相似文献
14.
Evidence is presented for the intermediacy of a terminal phosphinidene complex, [2,4,6-(t-Bu)3C6H2]PFe(CO)4, in the reaction of [2,4,6-(t-Bu)3C6H2]PCO with Fe2(CO)9. 相似文献
15.
Alexandre Lumbroso Anna Blonska Isabelle Beaudet Slawomir Jarosz Jean-Paul Quintard 《Tetrahedron》2010,66(8):1570-1580
Ethyl glyoxylate was reacted with α-substituted γ-(t-butyldimethylsilyloxy)-allyltributyltin in order to obtain selectively each diastereomer of ethyl 3-(t-butyldimethylsilyloxy)-2-hydroxyhex-4-enoate and subsequently the corresponding diols. Diastereomers syn-E, anti-E and anti-Z were obtained in good yields with good to high selectivities and the obtained results were rationalized by consideration of cyclic or open transition states in agreement with the experimental conditions and with the structure of the starting reagents. 相似文献
16.
The p-methoxybenzylation of hydroxy and amide groups by p-methoxybenzyl chloride utilizing NaOt-Bu in DMSO is described. p-Methoxybenzylation of sterically hindered menthol using NaOt-Bu in DMSO proceeded faster than the commonly used methods which use NaH in THF or DMF for p-methoxybenzylation of hydroxy and amide groups. The described method was applicable for sterically hindered substrates at room temperature without adding any activating reagents such as tetrabutylammonium iodide. 相似文献
17.
An iron-catalyzed regio- and stereoselective chlorosulfonylation of aryl chloroalkynes has been described, producing cis-1,2-dichlorovinylsulfones in satisfactory yields with good to excellent stereoselectivity (Z/E up to 95:5). A variety of functional groups such as F, NO2, Cl, Br, OMe, and t-Bu are found to be compatible under the reaction conditions. 相似文献
18.
Ahmed El-GokhaGerhard Maas 《Tetrahedron》2011,67(16):2849-2857
A diastereomeric mixture of dimethyl (2-formyl-2-methyl-1-phenylcyclopropyl)phosphonate ((Z)-6, (E)-6) was obtained by thermally induced cyclopropanation of α-methylacrolein with α-diazobenzylphosphonate 5. Application of proline or proline-derived organocatalysts accelerated the reaction, but had a minor effect on the Z/E ratio of 6. By reaction with benzylamine or methyl esters of glycine, (S)-alanine, and (S)-phenylalanine, the Z/E-mixture of 6 was converted into cyclopropylaldimines, which after reduction gave the corresponding N-substituted (2-aminomethyl-cyclopropyl)phosphonates. 相似文献
19.
The stereoisomers (3 and 4) of O-ethyl O-phenyl O-(1-methyl-2-ethoxycarbonyl) vinyl phosphorothionate have been synthesized by the reaction of optically active O-ethyl O-phenyl phosphorothiochloride 2 with ethyl acetoacetate under different conditions. 3 (100% Z-isomer, determined by 1H NMR) was synthesized by the reaction of 2 with ethyl sodio-acetoacetate in the mixed solvent of 1:3 toluene-dioxane at 50°C. 4 (>95% E-isomer) was obtained by the reaction of 2 with ethyl acetoacetate in presence of t-BuOK in DMSO at 15°C. 100% E-isomer 4 was separated from crude 4(>95% E-isomer) by column chromatography on silica gel (petroleum ether-ether 6:1). By this reaction either Z- or E-isomers were formed with inversion of the configuration at phosphorus atom. Thus, six stereoisomers of 3 and 4 which were prepared from 2 (RS, S, R) by the above method namely (RS)-Z, (R)-Z, (S)-Z and (RS)-E, (R)-E, (S)-E. 相似文献
20.
Reactions of mixtures of t-butyl E- and Z-3-substituted glycidates 1a-h with 50% aq. sodium hydroxide and a catalyst, benzyltriethylammonium chloride, TEBAC in dichloromethane (phase-transfer catalysis, PTC) led to preferential hydrolysis of the E-isomers to afford pure (90-98%) t-butyl Z-3-substituted glycidates 1a-i in good yields; PTC cleavage of glycidates additionally substituted at C-2, 1g or C-3, 1h,i suggests that an aryl group in the Z isomers hampers attack of HO− on the carbonyl carbon atom. As described in the literature, the diastereoselective PTC synthesis of Z-3-substituted glycidates and glycidonitriles consists of fast hydrolysis of E isomers present in mixtures with Z ones. 相似文献