- Visible-Light-Promoted Intramolecular α-Allylation of Aldehydes in the Absence of Sacrificial Hydrogen Acceptors
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We report herein an unprecedented protocol for radical cyclization of aldehydes with pendant alkenes via synergistic photoredox, cobaloxime, and amine catalysis. The transformation was achieved in the absence of external oxidants, providing a variety of 5-, 6-, and 7-membered ring products with alkene transposition in satisfactory yields. The reaction exhibits wide functional group compatibility and occurs under mild conditions with extrusion of H2.
- Liu, Feng,Liu, Jia-Li,tu, Jia-Lin
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supporting information
p. 7369 - 7372
(2020/10/05)
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- Fabrication of Ni3N nanorods anchored on N-doped carbon for selective semi-hydrogenation of alkynes
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Nickel is a highly active catalyst for the semi-hydrogenation of alkynes. However, the low selectivity of the alkene product caused by the over-hydrogenation reaction on Ni has hindered its practical applications. In this work, we report a new nickel nitride (Ni3N)-catalyzed semi-hydrogenation of alkynes to the corresponding alkenes. The Ni3N nanorods were facilely fabricated via a direct pyrolysis of the solid mixture of nickel acetate tetrahydrate and melamine (Mlm). The Ni3N phase in the optimum catalyst (Ni3N/NC-6/5-550) is shown to be effective and stable in the semi-hydrogenation of alkynes, with a high yield and good selectivity for alkenes (Z/E ratios up to >99/1). Both terminal and internal alkynes bearing a broad scope of functional groups are readily converted into alkenes with good chemo- and stereoselectivity. Notably, it was found that the over-hydrogenation can be markedly suppressed even at high conversion of alkyne. Density functional theory (DFT) calculations reveal that the low interaction between the alkene product and the Ni3N might plays a critical role in the selectivity enhancement.
- Shi, Xiaozhen,Wen, Xin,Nie, Shilin,Dong, Jie,Li, Jingde,Shi, Yongqing,Zhang, Huiling,Bai, Guoyi
-
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- Copper-catalyzed, stereoconvergent,: Cis -diastereoselective borylative cyclization of ω -mesylate- α, β -unsaturated esters and ketones
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The Cu(i)-catalyzed stereoconvergent borylative cyclization of ω-mesylate-α,β-unsaturated compounds is facilitated by a simple Cu-bisphosphine catalyst. This reaction provides a novel route to cis-β-boron-substituted five- and six-membered carbocycle and heterocycle esters. Mechanistic studies indicate that stereoconvergence and cis-substitution likely stem from the rapid enolation of the borylcopper adduct with the substrate double bond and the formation of a five-membered intermediate, respectively.
- Zuo, Ya-Jie,Chang, Xiao-Tong,Hao, Zhi-Ming,Zhong, Chong-Min
-
supporting information
p. 6323 - 6327
(2017/08/10)
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- MONOMER, POLYMER, RESIST COMPOSITION, AND PATTERNING PROCESS
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A polymer comprising recurring units derived from a (meth)acrylate monomer of tertiary ester type having branched alkyl on alicycle is used to form a resist composition. When subjected to exposure, PEB and organic solvent development, the resist composition is improved in dissolution contrast.
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- Virtually complete E-selective α,β-unsaturated ester synthesis by Hg(OTf)2-catalyzed hydration of sec-ethoxyalkynyl acetate
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The reaction of alkyl-substituted sec-ethoxyalkynyl acetates with water catalyzed by Hg(OTf)2 afforded α,β-unsaturated esters in excellent yield with high catalytic turnover up to 1000 times under very mild reaction conditions with virtually complete E-selectivity, superior even to that of the HWE reaction.
- Nishizawa, Mugio,Hirakawa, Hiroko,Nakagawa, Yuki,Yamamoto, Hirofumi,Namba, Kosuke,Imagawa, Hiroshi
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p. 5577 - 5580
(2008/09/17)
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- Efficient large scale stereoinversion of (R)-ethyl 3-hydroxybutyrate
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A three step method for the large scale preparation of enantiomerically pure ethyl (S)-3-hydroxybutyrate is reported starting from the commercial biopolymer poly[(R)-hydroxybutyrate]. The key step depends on the ability to cleanly invert the stereochemistry of (R)-ethyl 3-hydroxybutyrate via its mesylate ester under neutral conditions, avoiding the competing elimination process. This has been achieved in good (75%) yield on >100g scale by controlled addition of the mesylate to a stirred slurry of calcium carbonate in water at 80°C.
- Carnell, Andrew J.,Head, Robert,Bassett, Derek,Schneider, Michael
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p. 821 - 825
(2007/10/03)
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- Reaction of silyl ketene acetals with epoxides: A new method for the synthesis of γ-butanolides
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Titanium tetrachloride promoted reaction of silyl ketene acetals with epoxides, followed by acidic work-up, affords butanolides in moderate/good yields. With epihalohydrins the reaction is regioselective and occurs at the less substituted end of the epoxide; the γ-haloalkyl-γ-butanolides thus obtained can be further transformed into various products. Graphical Abstract
- Maslak, Veselin,Matovi?, Radomir,Sai?i?, Radomir N.
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p. 8957 - 8966
(2007/10/03)
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- Indium-mediated reductive elimination of halohydrins
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Olefin formation has been successfully carried out by reductive elimination reactions of halohydrins with Pd(PPh3)4/In/InCl3 in aqueous media.
- Cho, Sangwon,Kang, Soyeon,Keum, Gyochang,Kang, Soon Bang,Han, So-Yeop,Kim, Youseung
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p. 180 - 182
(2007/10/03)
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- On the stereochemistry of β-elimination of β-silyl azides
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Fluoride-mediated elimination of syn and anti β-silyl azides was shown to afford the corresponding (Z)- and (E)-olefins, respectively, demonstrating that β-elimination of β-silyl azides is stereospecifically anti.
- Chabaud, Laurent,Landais, Yannick
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p. 6995 - 6998
(2007/10/03)
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- New insight into the mechanism of catalytic hydrogenation allows the structure of the key intermediate in asymmetric hydrogenation to be predicted
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An approach has been developed to determine the regioselectivity of hydrometalation in homogeneous and heterogeneous hydrogenation of alkenes. By studying the electronic effects on the orientation of hydrometalation it is found with palladium and rhodium that this key step is a two electron process that can occur by two modes (a Pd(δ*+-) H(δ-) or b Pd(δ-)- H(δ+)). This provides valuable information about the structure of the metal-alkyl intermediate and helps rationalise how chiral induction occurs.
- Yu, Jinquan,Spencer, Jonathan B.
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p. 15821 - 15832
(2007/10/03)
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- Conversion of 2-methylthio-4-trifluoroacetyl-5,6-dihydro-4H-1,3,4-thiadiazines intoα,β-unsaturated esters via carbanion-induced ring opening and desulfurization
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A convenient conversion of 2-methylthio-5,6-dihydro-4H-1,3,4-thiadiazines 1 into α,β-unsaturated esters was achieved through the procedure including trifluoroacetylation of 1, carbanion-induced ring opening of trifluoroacetamides 2, and reductive removal of heteroatom functionality of the resulting S-alkenyl hydrazinecarbodithioates 3. Treatment of 3 with a base under an aqueous condition also gave the corresponding 6-alkylidene-4H-1,3,4-thiadiazin-5-ones 6.
- Shimada, Kazuaki,Otaki, Akihiro,Yanakawa, Masaki,Mabuchi, Shosuke,Yamakado, Naoya,Shimoguchi, Takeshi,Takikawa, Yuji
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p. 329 - 330
(2007/10/03)
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- Esterification in dry media using ferric perchlorate adsorbed on silica gel
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Adsorption of Fe(ClO4)3(H2O)6 onto chromatographic grade silica gel in the presence of alcohol ( to be used for esterification ) produces a supported reagent, Fe(ClO4)3(ROH)6/SiO2. This reagent, has been found effective for the rapid and high yield of esters, on grinding in the presence of carboxylic acids using pestle and mortar in the solid state.
- Parmar, Anupama,Kaur, Jatinder,Goyal, Rita,Kumar, Baldev,Kumar, Harish
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p. 2821 - 2826
(2007/10/03)
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- The carbonylation of allylic halides and prop-2-en-1-ol catalysed by triethylphosphine complexes of rhodium
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In ethanol, [RhX(CO)(PEt3)2] added directly or formed in situ from [Rh2(OAc)4]·2MeOH (OAc = O2CMe) and PEt3 or [Rh(OAc)(CO)(PEt3)2] catalysed the carbonylation of CH2=CHCH2X (X = Cl, Br or I) to ethyl but-3-enoate with CH2=CHCH2OEt as a side product. Small amounts of the isomerisation product, ethyl but-2-enoate were produced but no base was required for the reaction. The selectivity of the reaction is in the order Cl > Br > I and prop-2-en-1-ol can be successfully carbonylated to prop-2-enyl but-3-enoate by the same system using 3-chloroprop-1-ene as a promoter. 3-Fluoropropene was not carbonylated, but in the presence of H2 underwent hydroformylation to produce acetals. 3-Chlorobut-1-ene and 1-chlorobut-2-ene both produced ethyl pent-3-enoate and 3-ethoxybut-1-ene. In situ and ex situ NMR and IR spectroscopic studies have been used to show that the first step of the reaction is oxidative addition to give [Rh(CH2CH=CH2)Cl2(CO)(PEt3) 2] for which thermodynamic parameters have been obtained. Both 3-chlorobut-1-ene and 1-chlorobut-2-ene give [Rh(CH2CH=CHMe)Cl2-(CO)(PEt3)2] but with different E:Z ratios. The detailed mechanism of the oxidative addition is discussed. The CO inserts into the Rh-C bond to give [Rh(COCH2CH=CH2)Cl2(CO)(PEt3) 2], from which but-3-enoyl chloride reductively eliminates to react with ethanol to give the observed products. High-pressure IR and high-pressure NMR studies reveal that [RhX(CO)(PEt3)2] (X = Cl or Br) reacts with CO to give [RhX(CO)2(PEt3)2], which exists as two isomeric forms. The compound [Rh(OAc)(CO)(PEt3)2] catalyses the formation of prop-2-enyl ethanoate from 1-chloroprop-2-ene and sodium ethanoate. A mechanism is proposed.
- Payne, Marc J.,Cole-Hamilton, David J.
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p. 3167 - 3175
(2007/10/03)
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- Carbon-carbon bond forming reactions of rhenium enolates with terminal alkynes. Evidence for an alkyne C-H oxidative addition mechanism and observation of highly stereoselective base-catalyzed proton transfer reactions in rhenium metallacycles
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The acetonitrile-substituted complexes fac-(MeCN)(OC)3(PPh3)ReCH(R2)CO(R1) (4, R1 = OEt R2 = H; 5, R1 = OEt R2 = Me) and the chelating amide complex 6 react with terminal alkynes (R3 C≡CH) to afford five-membered metallacycles 7-9 The metallacycles possess an exocyclic double bond which exists in the less thermodynamically stable Z stereochemistry, in which the alkyl group R3 is oriented proximate to the metal center. These complexes rearrange in the presence of a Lewis base to form the endocyclic isomers 10-12. The structure of the metallacycle 10g was determined by a single-crystal X-ray diffraction study. Labeling studies demonstrated that the 1,3-hydrogen shift involved in this rearrangement is intramolecular and stereospecific with respect to the rhenium center, even though it is mediated by an external reagent. Deuterium incorporation into the 7-position of the endo metallacycles can also be induced by base and once again occurs stereospecifically (anti to the phosphine ligand). Treatment of the metallacycles with acid results in removal of the metal and yields the unsaturated esters as a mixture of stereo- and regioisomers. Kinetic studies demonstrated that the reaction of 4 with terminal alkynes involves reversible dissociation of the coordinated acetonitrile to form an unsaturated intermediate 29 (R1 = CO2Et) This intermediate reacts faster with more electron-rich alkynes (HC≡CCMe3) than electron-deficient alkynes (HC≡CCO2Me) and displays a R3C≡CH/R3C≡CD kinetic isotope effect kH/kD of 2.0. On the basis of these results and information about reactions of related rhenium complexes, we suggest that formation of the metallacycles is best accommodated by the mechanism shown in Scheme VIII: insertion of 29 into the alkyne C-H bond leading to a 7-coordmate rhenium acetylide hydride 31, 1,3-migration of the hydride to the acetylide β-carbon, providing vinylidene complex 32, and then migration of the enolate ligand to the a-carbon of the vinylidene group, giving the exo metallacycle.
- Stack, Jeffrey G.,Simpson, Robert D.,Hollander, Frederick J.,Bergman, Robert G.,Heathcock, Clayton H.
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p. 2716 - 2729
(2007/10/02)
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- Palladium-Catalyzed, Atmospheric Pressure Ethoxycarbonylation of Allylic Halides under the Influence of Sodium Ethoxide. A Facile Synthesis of β,γ-Unsaturated Esters
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Atmospheric pressure ethoxycarbonylation of allylic halides is realized under the influence of sodium ethoxide.This reaction is catalyzed by Na2PdCl4-bis(diphenylphosphino)ethane (dppe) and offers a convenient synthetic method to β,γ-unsaturated esters.
- Kiji, Jitsuo,Okano, Tamon,Konishi, Hisatoshi,Nishiumi, Wataru
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p. 1873 - 1876
(2007/10/02)
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- Synthesis of indoles and L-tryptophans specifically 2H- or 13C-labelled in the six-membered ring
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(4-2H)-, (5-2H)-, (6-2H)-, (7-2H)-, (4-13C)- and (5-13C)-1H-indole and the corresponding six L-tryptophans have been synthesized from simple labelled starting materials via a single reaction scheme.The L-tryptophans were prepared from the indoles via a quantitative one-step biosynthetic conversion.A scheme leading to the synthesis of three other indoles, mono-13C-enriched in the six-membered ring, has been developed and optimized.Indole and L-tryptophan, 13C- or 2H-enriched at the positions 4 or 5, have been synthesized with 99percent isotope incorporation without scrambling. (6-2H)-1H-Indole and -tryptophan have been synthesized with 95percent deuterium incorporation and (7-2H)-1H-indole and -tryptophan with 96percent.The reactions have been carried out on a gram scale and, in the case of the 4-13C system, they have been scaled up to the ten-gram level with no deterioration in yield.
- Berg, Ellen M. M. van den,Liemt, Willem B. S. van,Heemskerk, Bram,Lugtenburg, Johan
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p. 304 - 313
(2007/10/02)
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- α-Bromo-, α-chloro-, and α-trimethylsilyl-zinc ester enolates. New and universal Reformatsky-type Darzens and Peterson reactions
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Low temperature reactions of ethyl dihaloacetates with carbonyl compounds in the presence of zinc/silver-graphite give α-halo-β-hydroxyalkanoates, which are readily converted into glycidates by base.Unser the same conditions ethyl(bromo)(trimethylsilyl) acetate with aldehydes and ketones forms α,β-unsaturated esters by a Reformatsky-Peterson reaction combination.
- Fuerstner, Alois
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p. C33 - C36
(2007/10/02)
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- WITTIG-HORNER REACTION CATALYZED BY ACTIVATED BARIUM HYDROXIDE IN THE PRESENCE OF ULTRASOUND
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The sonochemical Wittig-Horner reaction, catalyzed by an activated barium hydroxide catalyst in interfacial solid-liquid conditions leads to E-acrylates with very good yields.The sonochemical process takes place at room temperature and with lower catalyst weight and reaction time than the thermal process.
- Fuentes, A.,Marinas, J.M.,Sinisterra, J.V.
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p. 2951 - 2954
(2007/10/02)
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- STEREOSPECIFIC RHODIUM(I) CATALYZED DESULFURIZATION OF THIIRANES
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The first metal catalyzed route for the desulfurization of thiiranes (episulfides) is described.
- Calet, Serge,Alper, Howard
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p. 3573 - 3576
(2007/10/02)
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- ELECTROOXIDATIVE DESULFENYLATION OF MICHAEL-TYPE THIOL ADDUCTS OF α,β-UNSATURATED ESTERS, KETONES, AND NITRILES
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Michael adducts of ethanethiol with α,β-unsaturated esters ketones,and nitriles are conveniently desulfenylated under neutral conditions by an electrooxidation involving bromonium ion mediation.
- Kimura, Makoto,Matsubara, Shinichi,Sawaki, Yasuhiko,Iwamura, Hiizu
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p. 4177 - 4178
(2007/10/02)
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- A Simple, Mild Elimination of Hydrogen Halide from Primary Alkyl Bromides and Iodides
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Addition of a solution of a primary alkyl bromide or iodide and 1,8-diazabicycloundec-7-ene in tetrahydrofuran (THF) to a solution prepared from dichlorobis(triphenylphosphine)nickel, triphenylphosphine, and n-butyl-lithium in THF results in an elimination at room temperature to give, in most cases, the terminal alkene.
- Jeropoulos, Sotiris,Smith, Edward H.
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p. 1621 - 1622
(2007/10/02)
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- A VERSATILE ROUTE TO MIXED VINYLKETENE ACETALS : USE OF 1-t-BUTYLDIMETHYLSILOXY-1-ETHOXY BUTADIENE IN CYCLOHEXENONE SYNTHESIS
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The successful entry to the diverse mixed vinylketene acetals 3 extends the participation of these intermediates in cyclohexenone synthesis.
- Lombardo, Luciano
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p. 381 - 384
(2007/10/02)
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- SYNTHESIS OF α,β UNSATURATED ESTERS USING A SOLID-LIQUID PHASE TRANSFER IN A SLIGHTLY HYDRATED APROTIC MEDIUM
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The condensation reaction of alkylphosphonates with variously functionnalysed aldehydes in the presence of solid potassium carbonate in low hydrated aprotic media leads to the selective formation of αβ-unsaturated esters E in high yield.
- Mouloungui, Zephirin,Delmas, Michel,Gaset, Antoine
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p. 701 - 706
(2007/10/02)
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- FACILE ESTERIFICATION OF CARBOXYLIC ACIDS WITH ORGANOPHOSPHORUS REAGENTS. NOVEL APPLICATION OF ALKYLPHOSPHORIC ESTERS (APE)
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A mixture of alkyl phosphate esters (APE) obtained from P4O10 and alkanols taken in 1:6 mole ratio is an excellent esterification reagent for several classes of carboxylic acids.This new reagent offers several advantages compared to conventional reagents.
- Balasubramaniyan, V.,Bhatia, V. G.,Wagh, S. B.
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p. 1475 - 1485
(2007/10/02)
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- STEREOSPECIFIC SYNTHESIS OF ISOMERIC 4-SUBSTITUTED 9-(2,3-DIHYDROXYBUTYL)ADENINES
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Reduction of ethyl 2,3-O-isopropylidene-D-tartrate with sodium borohydride afforded (4S,5S)-2,2-dimethyl-1,3-dioxolane-4,5-dimethanol (Va) which was benzoylated to give monobenzoyl derivative Vd and further transformed into p-toluenesulfonyl derivative Ve.Reaction of the compound Ve with sodium salt of adenine followed by methanolysis gave 2,3-O-isopropylidene derivative Vf which on acid hydrolysis afforded 9-(2S,3S)-(2,3,4-trihydroxybutyl)adenine (Ia).The enantiomer IIa was obtained from 3,4-O-isopropylidene-D-mannitol via (4R,5R)-2,2-dimethyl-1,3-dioxolane-4,5-dimethanol (VIa) using the same procedure.Reaction of compounds Vf and VIf with p-toluenesulfonyl chloride afforded 4-O-p-toluenesulfonyl derivatives Vg and VIg.These compounds were also obtained from Va and VIa via di-p-toluenesulfonyl derivatives Vc and VIc by reaction with sodium salt of adenine.Treatment of compounds Vg and VIg with sodium iodide gave 4-iodo derivatives Vh and VIh which on reaction with tri-n-butyltin hydride, followed by acid hydrolysis, afforded enantiomeric threo-2,3-dihydroxybutyl derivatives Ib and IIb.Compounds Vg and VIg on treatment with sodium azide, subsequent catalytic hydrogenation of the intermediates Vj and VIj and acid hydrolysis afforded enantiomeric threo-9-(4-amino-2,3-dihydroxybutyl)adenines (Ic, IIc).Reaction of methyl threo-3-phenylglycerate (VIIb) with acetone, followed by reduction with lithium aluminum hydride, gave 2,2-dimethyl-4-phenyl-1,3-dioxolane-5-methanol (VIIIb) which was converted by reaction with p-toluenesulfonyl chloride, condensation with sodium salt of adenine and acid hydrolysis into 9-(RS)-threo-(3-phenyl-2,3-dihydroxypropyl)adenine (I, IId).Methyl ester of D-eritadenine (IXb) was transformed into 2,3-O-isopropylidene derivative XIa which on reduction with sodium borohydride afforded the alcohol XIb.Its acid hydrolysis gave 9-(2R,3S)-erythro-(2,3,4-trihydroxybutyl)adenine (IIIa); tosylation of compound XIb, successive treatment with sodium iodide and tri-n-butyltin hydride and acid hydrolysis afforded 9-(2R,3S)-erythro-(2,3-dihydroxybutyl)adenine (IIIb).The enantiomers IVa and IVb were obtained analogously from L-eritadenine.The racemic derivative Ib + IIb was prepared from (RS)-threo-2,3-dihydroxybutyric acid via p-toluenesulfonyl derivative of racemic 2,2,4-trimethyl-1,3-dioxolane-5-methanol (IIIc) by reaction of sodium salt of adenine followed by acid hydrolysis.
- HOLY, Antonin
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p. 173 - 189
(2007/10/02)
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- Dialkyl sulphites: Convenient Reagents for Esterification of Carboxylic Acids
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Several mono and dicarbocylic acids undergo esterification with dimethyl/ diethyl sulphite in the presence of traces of sulphuric acid in a one-pot reaction.
- Bhatia, V. G.,Shaik, A. S.,Tongare, D. B.,Balasubramaniyan, V.
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p. 259 - 260
(2007/10/02)
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- Base-Catalyzed Reactions of α,β-Unsaturated Esters and Nitriles. 4. Dimerization of β-Alkyl-Substituted Acrylates
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2-Butenoates 1-C4 alkyl, cyclohexyl, or 1-bornyl> and higher β-alkyl-substituted acrylates 2-C9 n-alkyl> undergo highly selective (>95percent) dimerization in the presence of promoted potassium or sodium catalysts to yield corresponding 2-alkylidene-3-alkylglutarates (3).The reaction involves metalation of the β-alkylacrylate at the C-2 position, followed by addition at C-3 of a second monomeric molecule.Changes in the relative extent of dimerization (Kr) as a function of structural and experimentalvariables were determined.Kr is strongly dependent upon the inductive and steric characteristics of the alcoholic (R) group and of the β-alkyl substituent (R').For an n-alkyl group as R' the Kr value increases with increase in chain length from C1 to C4 but then decreases for longer substituents (C5-C9).Among the two geometric isomers in the dimeric product 3, the isomer with an α-vinylic hydrogen cis to the carboalkoxy group is predominant in all cases, but its relative concetration decreases with an increase in the size of R'.Branched or cyclic β-substituents in 2 prevent dimerization due to steric hindrance in the rate-determining addition step.Promoted potassium or sodium catalysts show much higher dimerization activity compared to supported alkali metals or to alkoxides.For conversions of up to 60percent, Kr values in proton-exchanging alkylbenzene solvents and in nonexchanging alkylcyclohexanes are closely similar, indicating faster abstraction of an α-vinylic hydrogen from the monomer, rather than a benzylic hydrogen from the solvent, in the chain regeneration step of the reaction.
- Shabtai, Joseph,Ney-Igner, Eva
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p. 3795 - 3802
(2007/10/02)
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- SUBSTITUTION NUCLEOPHILE VINYLIQUE PAR LE REACTIF DE REFORMATSKY CATALYSSE PAR DES COMPLEXES DU NICKEL ET DU PALLADIUM ZEROVALENTS. SYNTHESE D'ESTERS β,γ-ETHYLENIQUES
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Zerovalent complexes of palladium and nickel catalyse vinylic nucleophilic substitution by the Reformatsky reagent giving β,γ-ethylenic esters.Formation of a ?-vinylpalladium complex is the rate-determining step of the reaction.
- Fauvarque, J.F.,Jutand, A.
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p. 109 - 114
(2007/10/02)
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- Chemistry of Substituted cuprates and Their Synthetic Application to Cyclopentenone Annulations
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The conjugate addition of mixed alkyl cuprates to ethyl propiolate generates substituted cuprates that readily react with acid chlorides of α,β-unsaturated acids to produce α,α'-dienones.These unsaturated ketones bearing an α-carboethoxy group can serve as precursors to annulated cyclopentenones via a Nazarov-type cyclization.With this two-step sequence, it is possible to efficiently prepare substituted cyclopentenones fused to five-, six-, and seven-membered rings.As part of an effort to optimize yields in the Nazarov cyclizations, trimhylsilyl iodide was shown to be a new and effective reagent for this transformation.
- Marino, Joseph Paul,Linderman, Russell J.
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p. 3696 - 3702
(2007/10/02)
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- Stereochemistry of the Reaction of Diorganocuprate(I) Complexes Derived from Grignard Reagents with α,β-Acetylenic Esters
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Diorganocuprate(I) complexes RCH3CuMgX, prepared from methylcopper and Grignard reagents (i-PrMgBr and t-BuMgCl) gave mainly cis-1,4-addition of the alkyl group originally present in the Grignard reagents and small amounts of cis- and trans-1,4-addition of the methyl group introduced by methylcopper, when they were allowed to react with ethyl propiolate and ethyl phenylpropiolate.The proportion of cis-1,4-addition products did not change when the reaction temperature was raised from -78 deg C to room temperature.The configurations of the main reaction products from the reaction with ethyl phenylpropiolate, ethyl (Z)-β-isopropylcinnamate and ethyl (Z)-β-t-butylcinnamate, were established by conversion of the corresponding acids to β-isopropylindenone and β-t-butylindenone.
- Jalander, Lars,Iambolieva, Kostadinka,Sundstroem, Viola
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p. 715 - 720
(2007/10/02)
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- A Comparison of the Effects of Steric Crowding at Phosphorus on the Steric Course of Wittig Reactions of Stabilised and Semistabilised Ylides
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The cis-trans ratio of the alkenes formed in Wittig reactions of semistabilised ylides (derived from benzyltriarylphosphonium salts in ethanolic sodium ethoxide) with benzaldehyde, acetaldehyde or trimethylacetaldehyde increases as steric crowding at phosphorus increases.In contrast, the cis-trans ratio of the unsaturated esters formed in the related reactions of the stabilised ethoxycarbonylmethylene ylides decreases as steric crowding at phosphorus increases.The relevance of these results to recent proposals for the mechanism of the Wittig reaction is considered. - Keywords: Alkene cis-trans Ratio, Reaction Mechanism
- Allen, David W.
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p. 1455 - 1458
(2007/10/02)
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- The Chemistry of Heteroarylphosphorus Compounds, Part 14 Effects of Heteroaryl Substituents at Phosphorus on the Steric Course of Wittig Reactions of Semistabilised and Stabilised Ylides
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The cis-trans ratio of the stilbenes formed in Wittig reactions of semistabilised ylides (derived from benzyltri(hetero)arylphosphonium salts in ethanolic ethoxide) with benzaldehyde decreases markedly in the series 2-furyl > 2-thienyl > phenyl > 1-methylpyrrol-2-yl.The 2-furyl group favours a greater proportion of the cis-isomer than m-trifluoromethylphenyl, whereas the 1-methylpyrrol-2-yl group favours a greater proportion of the trans isomer than p-methoxyphenyl.Similarly, in Wittig reactions of carbonyl-stabilised ylides with benzaldehyde and acetaldehyde, the presence at phosphorus of 2-furyl groups results in a significant increase in the proportion of the cis-alkene compared to that formed from the related triphenylphosphonium ylide.These results are discussed in terms of both betaine and cycloaddition mechanisms for the Wittig reaction.Also discussed is their relevance to recent proposals concerning the eliminaton of alkene from the intermediate oxaphosphetan. - Keywords: Alkene cis-trans Ratio, Betaine Mechanism, Cycloaddition Mechanism
- Allen, David W.,Ward, Helen
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p. 754 - 757
(2007/10/02)
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- Novel Synthetic Reactions Using Bis(2,2,2-trifluoroethoxy)diorganosulfuranes
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Alkoxy- or acyloxysulfuranes prepared in situ by the ligand exchange of bis(2,2,2-trifluoroethoxy)diorganosulfuranes with alcohols or carboxylic acids were found to behave as a potential alkylating or acylating reagent for the preparation of unsymmetrical sulfides, ketones, and esters.
- Kitazume, Tomoya,Ishikawa, Nobuo
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p. 2064 - 2066
(2007/10/02)
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