Ene Reaction Products Research Articles

Nitrosocarbonyl Carbohydrate Derivatives: Hetero Diels–Alder and Ene Reaction Products for Useful Organic Synthesis

AbstractThe generation and trapping of two new nitrosocarbonyl intermediates bearing carbohydrate-based chiral substituents is achieved by the mild oxidation of the corresponding nitrile oxides with tertiary amine N-oxides. Their capture with suitable dienes and alkenes afforded the corresponding hetero Diels–Alder cycloadducts and ene adducts from fair to excellent yields. The entire methodology looks highly promising by the easy conversion of aldoximes into hydroxymoyl halides, widening the access to nitrosocarbonyls, versatile tools in organic synthesis.

Computational Study of the Ene/Rearrangement Reaction between (F3C)2B═NMe2, 1, and Acetonitrile: Reactant-Catalyzed Mechanism of the Ketenimine–Nitrile-Like Rearrangement

The reaction between (F3C)2B═NMe2, 1, and acetonitrile at low temperature in pentane yields a bora-acetonitrile rather than the expected coordination complex. This appears to arise from the two undergoing an ene reaction followed by a rearrangement analogous to a ketenimine-nitrile rearrangement. Computational studies indicate that mechanistic steps suggested for the latter require energies too large for the reaction to take place under the experimental conditions. Instead, a mechanism in which the ene reaction product is attacked by a second molecule of 1, followed by hydrogen transfer and decomposition, exhibits barriers lower than that for the ene reaction. The mechanism implies that the fragment of 1 in the observed product is not the one that underwent the ene reaction. The ene reaction barrier is rate-determining, and it is low enough to conform to the experimental conditions.

Synthesis of 3-trimethylsiloxy-1-(furan-3-yl)butadiene and its reactions with dienophiles

3-Trimethylsilyloxy-1-(furan-3-yl)butadiene was synthesized and studied in reactions with 2,2-dimethyl-5-methylidene-1,3-dioxane-4,6-diones, 5-methylenepyrimidine-2,4,6-triones, as well as with imines. Reactions with dienophiles containing an exo-methylene double bond in the presence of L-proline occurred regio- and stereoselectively with the formation of 7-(furan-3-yl)spiro[5,5]undecane-1,5,9-triones or 7-(furan-3-yl)-2,4-diazaspiro[5.5]undecane-1,3,5,9-tetraones. The reaction of diene with methylene imine, obtained from L-phenylalanine methyl ester and formaldehyde, in the presence of Lewis acids led to the formation of 2-(furan-3-yl)piperidin-4-one or the product of ene reaction, methyl (2S)-2-{[(4E)-5-(furan-3-yl)-3-oxopent-4-en-1-yl]amino}-3-phenylpropanoate. The structures of three compounds were confirmed by X-ray structural analysis.

Crystal structure and thermal decomposition of the Silanimine tBu2Si=N-SitBu3·thf

Abstract The thf-complexed silanimine tBu2Si=N–Sit- Bu3·thf (1(thf); monoclinic, space group C2/c) was prepared by the reaction of 1 equivalent of tBu2SiClN3 with 1 equivalent of Na[SitBu3] in Bu2O and subsequent addition of thf. By heating a benzene solution over a period of 11 d –140 °C, 1(thf) slowly released the thf donor to form the uncomplexed silanimine 1. However, under these conditions the silanimine 1 is unstable and is thermolized to give the ene reaction product of 1 with isobutene, H2C=C(CH2SitBu2–NH–SitBu3)2. By contrast, the thermolysis reaction of Me2Si=N–SitBu3·thf yielded the silanimine dimer (Me2SiNSitBu3)2 in 51 % and the vinyl ether Me2Si(OCH=CH2)NHSitBu3 in 49 % yield.

ChemInform Abstract: The Hexadehydro‐Diels—Alder Reaction: A New Chapter in Aryne Chemistry

AbstractReview: 22 refs.

A General Approach to Mechanism in Multiproduct Reactions: Product-Specific Intermolecular Kinetic Isotope Effects

Here we report a general method for the measurement of (13)C kinetic isotope effects at natural abundance for reactions that yield two or more products concurrently. We use, as an example, a recently reported Co-catalyzed reaction between cyclopentene and 1-phenyl-1-propyne. High-precision intermolecular (13)C isotope effects are reported for both the formal [2+2] cycloaddition (major) and Alder-ene (minor) reaction products. Mechanistic possibilities that are in accord with observed isotope effect measurements are discussed.

Completely OH-Selective FeCl3-Catalyzed Prins Cyclization: Highly Stereoselective Synthesis of 4-OH-Tetrahydropyrans

The completely OH-selective Prins cyclization has been realized from the enantioselective ene reaction product. A variety of 4-hydroxyl-tetrahydropyrans were exclusively generated via FeCl(3)-catalyzed Prins reaction. Excellent stereoselectivities (up to >99:1 dr and >99.5:0.5 er) were obtained for a remarkably broad range of substrates under mild reaction conditions. The control experiments, including NOE effects and (18)O-labeling studies, as well as DFT calculations were conducted to provide fundamental insights into the mechanism of the reaction. A different [2 + 2] cycloaddition process was suggested to rationalize the observed OH-selectivity.

Melt‐grafting mechanism study of maleic anhydride onto polypropylene with 1‐decene as the second monomer

AbstractAlthough polypropylene (PP) grafted by maleic anhydride (MAH) has been successfully commercialized, the grafting mechanism under the existence of a second monomer is not very clear. To simulate the grafting process of MAH onto PP with 1‐decene as the second monomer, the MAH/1‐decene copolymer and Alder ene reaction product were prepared and grafted onto PP with dicumyl peroxide as the initiator. We found that the grafting of the copolymer and the reactive product greatly improved the grafting degree of MAH. Particularly, the grafting degree with a 3% content of the Alder ene reactive product was 1.89%, which was 178% higher than that of pure MAH‐g‐PP, the maximum value of which was 0.68%. The molecular weight of the synthesized product affected the grafting efficiency and crystallization behavior of the grafted system. The system grafted with the Alder ene reaction product showed a higher crystallization temperature and crystalline degree. When the molecular weight of the copolymer was higher than 1700, the improvement of the grafting degree could be neglected. For MAH‐g‐PP with 1‐decene as the second monomer, the possible grafting mechanisms were as follows: first, the formation of MAH/1‐decene copolymer or the Alder ene reaction product, and second, the grafting of the previously formed product onto PP, in which, the effect of the Alder ene reaction product was more pronounced. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

ChemInform Abstract: Reaction of Aromatic N-Oxides with Dipolarophiles. Part 15. Formation of the 1,5-Sigmatropic Products and Their Double Ene Reaction Products.

ChemInform Abstract: Reaction of Aromatic N-Oxides with Dipolarophiles. Part 15. Formation of the 1,5-Sigmatropic Products and Their Double Ene Reaction Products.

ChemInform Abstract: Synthesis of Trifluoromethylated Tetrahydropyrans from Ene Reaction Products of Trifluoromethyl Ketones: Synthesis of Fluorine Analogs of a Sesquiterpene.

ChemInform Abstract: Synthesis of Trifluoromethylated Tetrahydropyrans from Ene Reaction Products of Trifluoromethyl Ketones: Synthesis of Fluorine Analogs of a Sesquiterpene.

ChemInform Abstract: Reaction of Sterically Congested Thiones with Benzyne. The First Isolation of a Thioaldehyde-Benzyne Adduct.

Reaction of 2,4,6-tri-tert-butylthiobenzaldehyde (3) with benzyne prepared from phenyl[2-(trimethylsilyl)phenyl]iodonium trifluoromethanesulfonate (1) and tetrabutylammonium fluoride afforded 5,7-di-tert-butyl-3,3-dimethylindan-1-yl phenyl sulfide (5) in 92% yield, whereas a [2 + 2] cycloadduct and an ene-reaction product were obtained by the reaction of sterically congested aliphatic thiones with benzyne.

Ene Réaction et Réaction de Substitution sur Des Hétérocycles Catalysées par les Sels de Bi(III)

Carbonylated electrophiles react with furan, thiophene, or pyrrole derivatives in the presence of catalytic amounts of bismuth triflate or chloride, leading to either electrophilic substitution or ene reaction products.

Disilene R*XSiSiXR* (R*=Si tBu 3) mit siliciumgebundenen H- und Hal-Atomen X: Bildung, Isomerisierung, Reaktionen

Dehalogenations of 1,2-disupersilyldisilanes R*H 2SiSiHalHR*, R*HHalSiSiHalHR*, R*HHalSiSiHal 2R* and R*Hal 2SiSiHal 2R* in THF with equimolar amounts of supersilyl sodium NaR* (R*=Si tBu 3=Supersilyl) lead slowly at room temperature (Hal=Cl) or fast even at −78°C (Hal=Br, I) under exchange of one halogen Hal for sodium Na to yellow–orange disilanides R*H 2SiSiNaHR*, R*HHalSiSiNaHR*, R*HHalSiSiNaHalR* and R*Hal 2SiSiNaHalR* (identification by protonation, methylation, silylation). These then, in the latter three cases, eliminate NaHal under formation of trans-1,2-disupersilyldisilenes R*XSiSiXR* with silicon-bound H and Hal atoms as X. Actually produced are R*HSiSiHR*, R*HSiSiBrR*, R*ClSiSiClR*, R*BrSiSiBrR* and R*ISiSiIR*. The intermediate existence of the disilenes could be proved by trapping them with diphenylacetylene (formation of [2+2] cycloadducts), with anthracene (formation of [4+2] cycloadducts), with benzophenone (formation of [2+2] cycloadducts), and/or with 2,3-dimethylbutadiene (formation of [2+2] and [4+2] cycloadducts as well as ene reaction products). Obviously, isomerization of the disilenes R*HalSiSiHalR* to silylenes R*Hal 2SiSiR* is possible, the latter of which may be trapped by Et 3SiH. In the absence of the mentioned traps, R*HSiSiHR* thermolizes under formation of cyclotrisilanes R* 3Si 3H 3 and R* 3Si 3H 2R with R=SiH 2R* as well as cyclotetrasilanes R* 4Si 4H 4, whereas R*HSiSiBrR* and R*BrSiSiBrR* react to an unidentified mixture of substances. The disilene R*ClSiSiClR* forms in the presence of its source R*Cl 2SiSiNaClR* cyclotetrasilanes R* 4Si 4Cl 4 obviously by way of insertion into the SiNa bond of the latter followed by elimination of NaCl. Finally, R*ISiSiIR* goes over into the cyclotrisilane R* 3Si 3I 2R with R=SiI 2R*, the formation of which could take place by way of [2+1] cycloaddition of the mentioned disilene and its isomer R*I 2SiSiR*. In the presence of NaR*, the disilene R*HSiSiBrR* forms endo, exo- and endo, endo-bicyclotetrasilanes R* 4Si 4H 2. Thereby, at room temperature the pure endo, endo isomer slowly transforms into an equilibrium mixture of the endo, endo and the endo, exo isomer in the mole ratio of 1:9 (the reactions of R* 4Si 4H 2 with I 2 lead to cyclotrisilanes R* 3Si 3HIR with R=SiHIR* and cyclotetrasilanes R* 4Si 4H 2I 2). On the other hand, the disilenes R*HalSiSiHalR* (Hal=Cl, Br, I) in the presence of NaR* quantitatively transform, possibly via the disilenides R*HalSiSiNaR* and cyclotetrasilenes R* 4Si 4Hal 2, into the tetrahedrotetrasilane R* 4Si 4 (the tetrahedrane reacts with O 2, I 2, Na under formation of R* 4Si 4O 2, R* 4Si 4I 2, R* 4Si 4Na 2). X-ray structure analyses are presented for cis, cis, trans-R* 4Si 4H 2I 2 as well as cis, trans, cis-R* 4Si 4Cl 4 and the [2+2] cycloadducts of R*BrSiSiBrR* with Ph 2CO and of R*ClSiSiClR* with CH 2CMeCMeCH 2.

Adducts of sila-, germa-, and stannaethenes Me2E=C(SiMe3)2 (E = Si, Ge, Sn) with anthracene: syntheses, structures, thermolyses

The [4 + 2] cycloadducts of Me2E=C(SiMe3)2 (E = Si, Ge, Sn) and anthracene are prepared by reaction of an excess of anthracene in benzene with the [2 + 2] cycloadduct of Me2Si=C(SiMe3)2 and Ph2C=NSiMe3 at 130°C, with Me2Ge(OPh)-CLi(SiMe3)2 at 100°C, and with Me2SnBr-CNa(SiMe3)2 at 80°C, respectively. The mentioned adducts act as sources for the ethenes Me2E=C(SiMe3)2 above 100°C, the intermediate formation of which has been demonstrated by trapping experiments with 2,3-dimethylbutadiene (formation of a [4 + 2] and an ene reaction product). The half life time of the anthracene adducts with E = Si, Ge, and Sn in the presence of DMB (= 2,3-dimethylbutadiene) in benzene on thermolysis at 130°C (first order reactions) is found to be 141, 12, and 0.3 h, respectively. In the absence of DMB, thermolysis of the cycloadducts leads in benzene as reaction medium exclusively to the dimers of the Me2E=C(SiMe3)2 intermediates. In toluene as reaction medium ene products of Me2E=C(SiMe3)2 are observed in addition to the dimers. The ene products are not isolable as such, but only after migration of the Me2E-CH(SiMe3)2 substituents. The formed derivatives C6H5CH2EMe2CH(SiMe3)2 of toluene in part give a second ene reaction with another Me2E=C(SiMe3)2 molecule. X-ray structure analyses of the mentioned sources in fact prove the latter to be normal [4 + 2] cycloadducts of Me2E=C(SiMe3)2 and anthracene.Key words: silaethene, germaethene, stannaethene, [4 + 2] anthracene adducts, [4 + 2] cycloadditions and reversions, ene reactions, X-ray structure analyses.

Adducts of sila-, germa-, and stannaethenes Me<sub>2</sub>E=C(SiMe<sub>3</sub>)<sub>2</sub> (E = Si, Ge, Sn) with anthracene: syntheses, structures, thermolyses

The [4 + 2] cycloadducts of Me2E=C(SiMe3)2 (E = Si, Ge, Sn) and anthracene are prepared by reaction of an excess of anthracene in benzene with the [2 + 2] cycloadduct of Me2Si=C(SiMe3)2 and Ph2C=NSiMe3 at 130°C, with Me2Ge(OPh)-CLi(SiMe3)2 at 100°C, and with Me2SnBr-CNa(SiMe3)2 at 80°C, respectively. The mentioned adducts act as sources for the ethenes Me2E=C(SiMe3)2 above 100°C, the intermediate formation of which has been demonstrated by trapping experiments with 2,3-dimethylbutadiene (formation of a [4 + 2] and an ene reaction product). The half life time of the anthracene adducts with E = Si, Ge, and Sn in the presence of DMB (= 2,3-dimethylbutadiene) in benzene on thermolysis at 130°C (first order reactions) is found to be 141, 12, and 0.3 h, respectively. In the absence of DMB, thermolysis of the cycloadducts leads in benzene as reaction medium exclusively to the dimers of the Me2E=C(SiMe3)2 intermediates. In toluene as reaction medium ene products of Me2E=C(SiMe3)2 are observed in addition to the dimers. The ene products are not isolable as such, but only after migration of the Me2E-CH(SiMe3)2 substituents. The formed derivatives C6H5CH2EMe2CH(SiMe3)2 of toluene in part give a second ene reaction with another Me2E=C(SiMe3)2 molecule. X-ray structure analyses of the mentioned sources in fact prove the latter to be normal [4 + 2] cycloadducts of Me2E=C(SiMe3)2 and anthracene.Key words: silaethene, germaethene, stannaethene, [4 + 2] anthracene adducts, [4 + 2] cycloadditions and reversions, ene reactions, X-ray structure analyses.

Studies on Lewis acid-mediated intramolecular cyclization reactions of allene-ene systems.

The Lewis acid-mediated reactions of allene-ene compounds, derived from 3-methylcitronellal or dimethyl malonate, were carried out using various Lewis acids such as ethylaluminum dichloride, diethylaluminum chloride, titanium chloride, zinc chloride etherate, or boron trifluoride etherate, affording unexpectedly intramolecular [2+2]cycloaddition products under some particular reaction conditions without any formation of intramolecular ene reaction products.

A Highly Diastereoselective Dioxetane Formation by the Hydroxy-Directed [2+2] Cycloaddition of Singlet Oxygen to a Chiral Allylic Alcohol

The adamantylidene-substituted allylic alcohol 1a reacts diastereoselectively with singlet oxygen in CDCl3 to yield the dioxetane threo-2a, accompanied by the dioxolane 4, which is formed as a subsequent product of an initial ene reaction. In the more polar CD3OD/CCl4 solvent mixture, the diastereoselectivity drops to 89:11, but the ene mode (dioxolane 4) is completely suppressed. In contrast, the photooxygenation of the acetate 1b in CDCl3 and in CD3OD yielded only ene product 3b. The observed threo-selective hydroxy-group directivity is explained in terms of hydrogen bonding in the exciplex between the singlet oxygen and the hydroxy group, and the latter is appropriately conformationally aligned in the substrate by 1,3-allylic strain. This synergism between conformational strain and hydrogen bonding controls not only the stereochemical course but also the mode selectivity (ene, [4+2], and [2+2]) in all three reaction types of singlet oxygen.

Reaction of sterically congested thiones with benzyne. The first isolation of a thioaldehyde–benzyne adduct

Reaction of 2,4,6-tri-tert-butylthiobenzaldehyde (3) with benzyne prepared from phenyl[2-(trimethylsilyl)phenyl]iodonium trifluoromethanesulfonate (1) and tetrabutylammonium fluoride afforded 5,7-di-tert-butyl-3,3-dimethylindan-1-yl phenyl sulfide (5) in 92% yield, whereas a [2 + 2] cycloadduct and an ene-reaction product were obtained by the reaction of sterically congested aliphatic thiones with benzyne.

The carbonyl-Diels-Alder reaction catalyzed by bismuth (III) chloride

In presence of bismuth (III) chloride, a carbonylated electrophile (ethyl mesoxalate or glyoxylate) and usual diene led selectively (65 to 100%) the hetero carbonyl-Diels-Alder reaction with the ene reaction product. BiCl 3 exhibits strong catalytic activity and, compared with previous literature, reacts under mild conditions.

Erzeugung, nachweis und stabilisierung isomerer silaethene R 2Si [dbnd]C(SiR 3) 2 mit jeweils sechs Me- und zwei Ph-substituenten R

Bromotrisilylmethanes Me 2SiBr CBrRR 2 ( 2b), PhMeSiBr CBrRR 1 ( 3b, two diastereomers) and Me 2SiBr CBrR 2 1 ( 4b) (R SiMe 3, R 1 SiMe 2Ph, R 2 SiMePh 2) - sources of silaethenes Me 2Si CRR 2 ( 2), PhMeSi CRR 1 ( 3, two isomers), and Me 2Si CR 2 2 ( 4) - are formed by bromination of Me 2SiH CBrRR 2 ( 2a), PhMeSiH CBrRR 1 ( 3a, two diastereomers; bromination takes place stereospecifically), and Me 2SiH CBrR 2 2 ( 4a), which themselves are formed from CBr 4 by introducing three silyl groups step by step according to: ≤Cz.sbnd;Br+R′Li+≤SiCl→≤C Si≤+R′Br+LiCl(R′ = ″Bu, (Me 3Si) 2CH). The structure of one of the two diastereomeric compounds, 3a, has been solved by X-ray analysis. PhLi converts 2b–4b by Br/Li-exchange to lithium organyls Me 2SiBr CLiRR 2 ( 2c). PhMeSiBr CLiRR 1 ( 3b, two diastereomers), and Me 2SiBr CLiR 2 1 ( 4c), which in Et 2O at −78°C are in equilibrium with silaethenes 2, 3 and 4 in very low concentrations. The intermediacy of the silaethenes has been established chemically by trapping 2, 3 and 4 with 2,3-dimethyl-1,3-butadiene (DMB): formation of[4 + 2] cycloadducts 2d, 3d (two diastereomers) and 4d, of ene reaction products 2e, 3e (two diastereomers), and 4e as well as of[4 + 2] cycloadducts 2f (diastereomers), 3f (diastereomers), and 4f of the formed ene reaction products. The structure of one of the two diastereomeric compounds, 3d, has been solved by X-ray analysis. By warming the etheral solutions of 2c, 3c and 4c,[2 + 2] cycloadducts 2 × 2, 2 × 4 and 4 × 4 of silaethenes 2 and 4 are found. Considering the types and yields of the products of silaethenes - including Ph 2Si CR 2 ( 1) - in the absence and the presence of DMB, the following is concluded; (i) silaethenes 1, 2, 3, 4 are in equilibrium by methyl and phenyl group migrations; (ii) the relative thermodynamic silaethene stability increases in the order 1 < 3 < 4 < 4 (phenyl groups at unsaturated silicon destabilize the silaethenes as a consequence of electronic effects of phenyl; (iii) silaethenes 1–4 are kinetically more stable against [2 + 2] cycloadditions than silaethene Me 2Si C(SiMe 3) 2 (as a consequence of steric effects of phenyl); (iv) the rate of methyl and phenyl group migration is equal; (v) substitution of methyl groups at unsaturated silicon (saturated silicons) in Me 2Si C(SiMe 3) 2 increases (does not increase) the SiC double bond polarity.