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Crotonaldehyde hydrogenation by gold supported on TiO2: Structure sensitivity and mechanism
The catalytic properties of two series of Au/TiO2 catalysts prepared by deposition-precipitation with NaOH (DP NaOH) (～3 wt%) and by deposition-precipitation with urea (DP Urea) (～8 wt%) were evaluated for the reaction of crotonaldehyde hydrogenation at atmospheric pressure. There is no difference in activity (molgAu-1s-1) and selectivity between the DP Urea and DP NaOH samples for a given activation treatment. This is due to the fact that the DP Urea and DP NaOH samples exhibit a similar gold particle size distribution, although the gold loading in DP Urea catalysts is much higher than in DP NaOH. The DP Urea samples were reduced under H2 at different temperatures (120-500°C) or treated in air at 300°C with various flow rates, to vary the average particle size within a large range, 1.7 to 8.7 nm. The selectivity to crotyl alcohol (selective hydrogenation of the carbonyl bond), in the 5-50% conversion range, is high, 60-70 %, and is independent of the reduction temperature, and almost constant as a function of the particle size. In contrast, the TOF depends on the gold particle size, drastically increasing when the gold particle size is ～2 nm. These characteristic features of Au/TiO2 catalysts in this reaction are compared with those of Pt/TiO2. The possible adsorption modes of crotonaldehyde are discussed. Hydrogen dissociation is proposed to be the rate-determining step, and to take place on the low-coordinated atoms of the gold particles.
Zanella, Rodolfo,Louis, Catherine,Giorgio, Suzanne,Touroude, Raymonde
p. 328 - 339
(2004)
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Using NMR to determine the relative stereochemistry of 7,7-diaryl-8,8′-dimethylbutan-1-ol lignans
Due to their linear, freely rotatable, structure many natural 7,7-diaryl-8,8′-dimethylbutan-7′-ol lignans are reported without any stereochemical assignment. Analysis of synthetic 8,8′-dimethylbutanol lignans and analogues reveals significant differences between the NMR data of syn- and anti-isomers. This information was then used to determine the relative stereochemistry of the C-8 and C-8′ methyl groups in previously undefined natural products.
Davidson, Samuel J.,Rye, Claire E.,Barker, David
p. 138 - 142
(2015)
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Alkyne Aminopalladation/Heck and Suzuki Cascades: An Approach to Tetrasubstituted Enamines
Alkyne aminopalladation reactions starting from tosylamides are reported. The emerging vinylic Pd species are converted either in an intramolecular Heck reaction with olefinic units or in an intermolecular Suzuki reaction by using boronic acids exhibiting broad functional group tolerance. Tetra(hetero)substituted tosylated enamines are obtained in a simple one-pot process.
Geffers, Finn J.,Jones, Peter G.,Kurth, Florens R.,Werz, Daniel B.
supporting information
p. 14846 - 14850
(2021/10/19)

Regiospecific Synthesis of Calcium-Independent Daptomycin Antibiotics using a Chemoenzymatic Method
Daptomycin (DAP) is a calcium (Ca2+)-dependent FDA-approved antibiotic drug for the treatment of Gram-positive infections. It possesses a complex pharmacophore hampering derivatization and/or synthesis of analogues. To mimic the Ca2+-binding effect, we used a chemoenzymatic approach to modify the tryptophan (Trp) residue of DAP and synthesize kinetically characterized and structurally elucidated regiospecific Trp-modified DAP analogues. We demonstrated that the modified DAPs are several times more active than the parent molecule against antibiotic-susceptible and antibiotic-resistant Gram-positive bacteria. Strikingly, and in contrast to the parent molecule, the DAP derivatives do not rely on calcium or any additional elements for activity.
Mupparapu, Nagaraju,Lin, Yu-Hsin Cindy,Kim, Tae Ho,Elshahawi, Sherif I.
supporting information
p. 4176 - 4182
(2021/02/01)

Molecular Recognition and Cocrystallization of Methylated and Halogenated Fragments of Danicalipin A by Enantiopure Alleno-Acetylenic Cage Receptors
Enantiopure (P)4- and (M)4-configured alleno-acetylenic cage (AAC) receptors offer a highly defined interior for the complexation and structure elucidation of small molecule fragments of the stereochemically complex chlorosulfolipid danicalipin A. Solution (NMR), solid state (X-ray), and theoretical investigations of the formed host-guest complexes provide insight into the conformational preferences of 14 achiral and chiral derivatives of the danicalipin A chlorohydrin core in a confined, mostly hydrophobic environment, extending previously reported studies in polar solvents. The conserved binding mode of the guests permits deciphering the effect of functional group replacements on Gibbs binding energies ΔG. A strong contribution of conformational energies toward the binding affinities is revealed, which explains why the denser packing of larger apolar domains of the guests does not necessarily lead to higher association. Enantioselective binding of chiral guests, with energetic differences ΔΔG293 K up to 0.7 kcal mol-1 between diastereoisomeric complexes, is explained by hydrogen- and halogen-bonding, as well as dispersion interactions. Calorimetric studies (ITC) show that the stronger binding of one enantiomer is accompanied by an increased gain in enthalpy ΔH but at the cost of a larger entropic penalty TΔS stemming from tighter binding.
Carreira, Erick M.,Diederich, Fran?ois,Fischer, Stefan,Gropp, Cornelius,Husch, Tamara,Trapp, Nils
supporting information

(2020/03/13)

Visible-Light-Promoted Intramolecular α-Allylation of Aldehydes in the Absence of Sacrificial Hydrogen Acceptors
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
supporting information
p. 7369 - 7372
(2020/10/05)

Formal synthesis of borrelidin: A highly enantio- and diastereoselective access to the Morken's C2-C12 intermediate
In contrast to methyl and isobutyl phenyl sulfone, condensing under basic conditions higher alkyl sulfones and trans-2,3-epoxy-butanol 13c (or its O-benzyl and O-silyl derivatives) proved unfeasible, a difficulty that was overcome by using mono ethers of trans-2,3-epoxy-butane-1,4-diol 35c as the electrophilic reagents. Thus, adding excess BuLi to a mixture of the benzyl ether 35b and sulfone ent-12a, a stereodiad sulfone prepared in pure state from the R-Roche ester, via the O-trityloxy-sulfone ent-12c (X-ray), gave, after elimination by column chromatography of the side-formed regioisomer, a diolsulfone that was next converted to sulfone 20 by means of conventional functional-group modifications. Reacting like-wise this sulfone with the parent O-PMB derivative 35a, and then proceeding to the same purification process and function adjustment, delivered the title fragment in virtually pure state.
Gembus, Vincent,Karmazin, Lydia,Uguen, Daniel,Zoller, Thomas
supporting information
p. 359 - 380
(2019/02/25)

New Zinc Catalyst for Hydrosilylation of Carbonyl Compounds
A new zinc complex was synthesized and applied in the catalytic hydrosilylation of carbonyl compounds. Optimization of the reaction conditions showed that the presence a substoichiometric amount of methanol accelerates the process significantly. The reaction can proceed at very low catalyst load (down to 0.1 molpercent) under mild reaction conditions. The reaction tolerates the presence of C=C bonds, and thus can be useful for the synthesis of allylic alcohols from α,β-unsaturated aldehydes and ketones.
Alshakova, Iryna D.,Nikonov, Georgii I.
p. 3305 - 3312
(2019/08/28)

Vapor-phase catalytic dehydration of butanediols to unsaturated alcohols over yttria-stabilized zirconia catalysts
Vapor-phase catalytic dehydration of butanediols (BDOs) such as 1,3-, 1,4-, and 2,3-butanediol was investigated over yttria-stabilized tetragonal zirconia (YSZ) catalysts as well as monoclinic zirconia (MZ). BDOs were converted to unsaturated alcohols with some by-products over YSZ and MZ. YSZ is superior to MZ for these reactions in a view point of selective formation of unsaturated alcohols. Calcination temperature of YSZ significantly affected the products selectivity as well as the conversion of BDOs: high selectivity to unsaturated alcohols was obtained over the YSZ calcined at high temperatures over 800 °C. In the conversion of 1,4-butanediol at 325 °C, the highest 3-buten-1-ol selectivity of 75.3% was obtained over the YSZ calcined at 1050 °C, whereas 2,3-butanediol was less reactive than the other BDOs. In the dehydration of 1,3-butanediol at 325 °C, in particular, it was found that a YSZ catalyst with a Y2O3 content of 3.2 wt.% exhibited an excellent stable catalytic activity: the highest selectivity to unsaturated alcohols such as 2-buten-1-ol and 3-buten-2-ol over 98% was obtained at a conversion of 66%. Structures of active sites for the dehydration of 1,3-butanediol were discussed using a crystal model of tetragonal ZrO2 and a probable model structure of active site was proposed. The well-crystalized YSZ inevitably has oxygen defect sites on the most stable surface of tetragonal ZrO2 (101). The defect site, which exposes three cations such as Zr4+ and Y3+, is surrounded by six O2? anions. The selective dehydration of 1,3-butanediol to produce 3-buten-2-ol over the YSZ could be explained by tridentate interactions followed by sequential dehydration: the position-2 hydrogen is firstly abstracted by a basic O2? anion and then the position-1 hydroxyl group is subsequently or simultaneously abstracted by an acidic Y3+ cation. Another OH group at position 3 plays an important role of anchoring 1,3-butanediol to the catalyst surface. Thus, the selective dehydration of 1,3-butanediol could proceed via the speculative base-acid-concerted mechanism.
Ohtsuka, Shota,Nemoto, Takuma,Yotsumoto, Rikako,Yamada, Yasuhiro,Sato, Fumiya,Takahashi, Ryoji,Sato, Satoshi
p. 48 - 57
(2019/02/19)

Asymmetric Reductive Carbocyclization Using Engineered Ene Reductases
Ene reductases from the Old Yellow Enzyme (OYE) family reduce the C=C double bond in α,β-unsaturated compounds bearing an electron-withdrawing group, for example, a carbonyl group. This asymmetric reduction has been exploited for biocatalysis. Going beyond its canonical function, we show that members of this enzyme family can also catalyze the formation of C?C bonds. α,β-Unsaturated aldehydes and ketones containing an additional electrophilic group undergo reductive cyclization. Mechanistically, the two-electron-reduced enzyme cofactor FMN delivers a hydride to generate an enolate intermediate, which reacts with the internal electrophile. Single-site replacement of a crucial Tyr residue with a non-protic Phe or Trp favored the cyclization over the natural reduction reaction. The new transformation enabled the enantioselective synthesis of chiral cyclopropanes in up to >99 % ee.
Heckenbichler, Kathrin,Schweiger, Anna,Brandner, Lea Alexandra,Binter, Alexandra,Toplak, Marina,Macheroux, Peter,Gruber, Karl,Breinbauer, Rolf
supporting information
p. 7240 - 7244
(2018/06/15)

Selective Base-free Transfer Hydrogenation of α,β-Unsaturated Carbonyl Compounds using iPrOH or EtOH as Hydrogen Source
Commercially available Ru-MACHOTM-BH is an active catalyst for the hydrogenation of several functional groups and for the dehydrogenation of alcohols. Herein, we report on the new application of this catalyst to the base-free transfer hydrogenation of carbonyl compounds. Ru-MACHOTM-BH proved to be highly active and selective in this transformation, even with α,β-unsaturated carbonyl compounds as substrates. The corresponding aliphatic, aromatic and allylic alcohols were obtained in excellent yields with catalyst loadings as low as 0.1–0.5 mol % at mild temperatures after very short reaction times. This protocol tolerates iPrOH and EtOH as hydrogen sources. Additionally, scale up to multi-gram amounts was performed without any loss of activity or selectivity. An outer-sphere mechanism has been proposed and the computed kinetics and thermodynamics of crotonaldehyde and 1-phenyl-but-2-en-one are in perfect agreement with the experiment.
Farrar-Tobar, Ronald A.,Wei, Zhihong,Jiao, Haijun,Hinze, Sandra,de Vries, Johannes G.
supporting information
p. 2725 - 2734
(2018/02/28)

Encapsulation of Crabtree's Catalyst in Sulfonated MIL-101(Cr): Enhancement of Stability and Selectivity between Competing Reaction Pathways by the MOF Chemical Microenvironment
Crabtree's catalyst was encapsulated inside the pores of the sulfonated MIL-101(Cr) metal–organic framework (MOF) by cation exchange. This hybrid catalyst is active for the heterogeneous hydrogenation of non-functionalized alkenes either in solution or in the gas phase. Moreover, encapsulation inside a well-defined hydrophilic microenvironment enhances catalyst stability and selectivity to hydrogenation over isomerization for substrates bearing ligating functionalities. Accordingly, the encapsulated catalyst significantly outperforms its homogeneous counterpart in the hydrogenation of olefinic alcohols in terms of overall conversion and selectivity, with the chemical microenvironment of the MOF host favouring one out of two competing reaction pathways.
Grigoropoulos, Alexios,McKay, Alasdair I.,Katsoulidis, Alexandros P.,Davies, Robert P.,Haynes, Anthony,Brammer, Lee,Xiao, Jianliang,Weller, Andrew S.,Rosseinsky, Matthew J.
supporting information
p. 4532 - 4537
(2018/03/26)

Rhenium-catalyzed deoxydehydration of renewable triols derived from sugars
An efficient method for the catalytic deoxydehydration of renewable triols, including those obtained from 5-HMF, is described. The corresponding unsaturated alcohols were obtained in good yields using simple rhenium(vii)oxide under neat conditions and ambient atmosphere at 165 °C.
Wozniak, Bartosz,Li, Yuehui,Tin, Sergey,De Vries, Johannes G.
supporting information
p. 4433 - 4437
(2018/10/17)

Manganese-Catalyzed Upgrading of Ethanol into 1-Butanol
Biomass-derived ethanol is an important renewable feedstock. Its conversion into high-quality biofuels is a promising route to replace fossil resources. Herein, an efficient manganese-catalyzed Guerbet-type condensation reaction of ethanol to form 1-butanol was explored. This is the first example of upgrading ethanol into higher alcohols using a homogeneous non-noble-metal catalyst. This process proceeded selectively in the presence of a well-defined manganese pincer complex at the parts per million (ppm) level. The developed reaction represents a sustainable synthesis of 1-butanol with excellent turnover number (>110 000) and turnover frequency (>3000 h-1). Moreover, mechanistic studies including control experiments, NMR spectroscopy, and X-ray crystallography identified the essential role of the "N-H moiety" of the manganese catalysts and the major reaction intermediates related to the catalytic cycle.
Fu, Shaomin,Shao, Zhihui,Wang, Yujie,Liu, Qiang
supporting information
p. 11941 - 11948
(2017/09/07)

Influence of Metal Doping on the Lewis Acid Catalyzed Production of Butadiene from Ethanol Studied by using Modulated Operando Diffuse Reflectance Infrared Fourier Transform Spectroscopy and Mass Spectrometry
As a result of the increasing gap between the supply and demand of butadiene, the catalytic coupling of ethanol has regained the attention of the scientific and industrial community as an “on-purpose” production route to butadiene. The most promising systems are based on bifunctional catalysts that comprise metal sites that can dehydrogenate ethanol to acetaldehyde and Lewis acid sites that catalyze the aldol condensation between two aldehyde molecules and the Meerwein–Ponndorf–Verley reduction of the intermediate crotonaldehyde. Here, we investigate the role of Ag in an established Ag-Zr-BEA catalyst using modulated operando diffuse reflectance infrared Fourier transform spectroscopy and mass spectrometry experiments. We obtain insights into the complex reaction network that involves several consecutive and parallel reactions. Based on our investigations, we formulate suggestions for catalyst optimization.
Müller, Philipp,Wang, Shao-Chun,Burt, Samuel P.,Hermans, Ive
p. 3572 - 3582
(2017/09/27)

METHOD FOR PRODUCING UNSATURATED ALCOHOL AND CATALYST
PROBLEM TO BE SOLVED: To provide a method for the selective production of allyl type unsaturated alcohol from 1,3-diol. SOLUTION: As shown in the following reaction formula, a catalyst comprising zirconium oxide (ZrO2) and calcium oxide (CaO) acts on diol, to produce allyl type unsaturated alcohol (where R1-R4 independently represent H, a C1-5 alkyl group or the like). SELECTED DRAWING: None COPYRIGHT: (C)2017,JPOandINPIT
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Paragraph 0038; 0043

(2017/07/31)

Vapor-phase dehydration of C4 unsaturated alcohols to 1,3-butadiene
Vapor-phase dehydration of C4 unsaturated alcohols such as 3-buten-1-ol, 2-buten-1-ol and 3-buten-2-ol were performed to produce 1,3-butadiene over various solid catalysts including ordinary solid acid catalysts such as Al2O3, SiO2-Al2O3, and TiO2 and basic rare earth metal oxides such as Yb2O3 and CeO2. In the reaction of 3-buten-1-ol, 1,3-butadiene could not be selectively produced because the acid catalysts decomposed 3-buten-1-ol into propylene. In contrast to the acid catalysts, CeO2 inhibited the decomposition of 3-buten-1-ol and showed a relatively high performance for the formation of 1,3-butadiene. In the dehydration of 2-buten-1-ol and 3-buten-2-ol, however, acid catalysts were effective for the formation of 1,3-butadiene. Among the tested catalysts, commercial SiO2-Al2O3 showed a relatively high catalytic performance, although it deactivated rapidly. We prepared a series of SiO2/Al2O3 catalysts by depositing SiO2 species onto Al2O3 support, and the SiO2/Al2O3 with a SiO2 content of 10?wt.% showed more stable catalytic activity than the commercial SiO2-Al2O3. Furthermore, modification of SiO2/Al2O3 with Ag at a loading of 3–5?wt.% was found to be efficient for inhibiting the coke formation and improving the catalytic stability of SiO2/Al2O3 in the dehydration of both 2-buten-1-ol and 3-buten-2-ol under hydrogen flow conditions.
Sun, Daolai,Arai, Shigenori,Duan, Hailing,Yamada, Yasuhiro,Sato, Satoshi
p. 21 - 28
(2016/12/09)

Asymmetric Enzymatic Synthesis of Allylic Amines: A Sigmatropic Rearrangement Strategy
Sigmatropic rearrangements, while rare in biology, offer opportunities for the efficient and selective synthesis of complex chemical motifs. A "P411" serine-ligated variant of cytochrome P450BM3 has been engineered to initiate a sulfimidation/[2,3]-sigmatropic rearrangement sequence in whole E. coli cells, a non-natural function for any enzyme, providing access to enantioenriched, protected allylic amines. Five mutations in the enzyme substantially enhance its activity toward this new function, demonstrating the evolvability of the catalyst toward challenging nitrene transfer reactions. The evolved catalyst additionally performs the highly enantioselective imidation of non-allylic sulfides.
Prier, Christopher K.,Hyster, Todd K.,Farwell, Christopher C.,Huang, Audrey,Arnold, Frances H.
supporting information
p. 4711 - 4715
(2016/04/19)

An acyl-Claisen/Paal-Knorr approach to fully substituted pyrroles
The synthesis of fully substituted pyrroles using the Paal-Knorr reaction on acyl-Claisen derived 2,3-syn-disubstituted-1,4-diketones is reported. The use of the acyl-Claisen rearrangement allows the synthesis of wide variety of syn-substituted 1,4-diketones which are shown to be better substrates for pyrrole condensation than their corresponding anti isomers. When the reaction was performed open to air the use of nucleophilic amines in the pyrrole forming step leads to auto-oxidation of the 5-methyl group giving exclusively 5-formyl pyrroles.
Dittrich, Nora,Jung, Eun-Kyung,Davidson, Samuel J.,Barker, David
p. 4676 - 4689
(2016/07/15)

Comparison of “on water” and solventless procedures in the rhodium-catalyzed hydroformylation of diolefins, alkynes, and unsaturated alcohols
Catalytic systems containing Rh(acac)(CO)2 or Rh/PAA (PAA?=?polyacrylic acid) and hydrophobic phosphine (PPh3) were used in the hydroformylation of diolefins, alkynes, and unsaturated alcohols under solventless and “on water” conditions. The total yield of dialdehydes obtained from 1,5-hexadiene and 1,7-octadiene reached 99%, and regioselectivity towards linear dialdehydes was higher in the “on water” system. The tandem hydroformylation-hydrogenation of phenylacetylene led to the formation of saturated aldehydes (3-phenylpropanal and 2-phenylpropanal) at 98% conversion with a good regioselectivity towards the linear aldehyde in the “on water” reaction. In contrast, solventless conditions appeared better in the hydroformylation of 1-propen-3-ol. 4-Hydroxybutanal, formed in this reaction with an excellent selectivity, was next transformed to tetrahydrofuran-2-ol via a ring-closure process. Cyclic products were also obtained in hydroformylation of 1-buten-3-ol. In reaction of undec-1-ol and 2-allylphenol linear aldehydes were formed with the yield 69–87%. The hydroformylation of 3-buten-1-ol performed under “on water” conditions showed very good regioselectivity towards a linear aldehyde, 5-hydroxypentanal. Further cyclization of the aldehyde to tetrahydropyran-2-ol was observed.
Alsalahi,Trzeciak
p. 41 - 48
(2016/07/06)

Selective Pinacol-Coupling Reaction using a Continuous Flow System
The first continuous flow pinacol coupling reaction of carbonyl compounds was successfully achieved within only 2 min during a single pass through a cartridge filled with zinc(0). The optimized method allowed the efficient production of gram-scale value-added compounds with high productivity. The developed methodology is efficient for aromatic or α,β-unsaturated aldehydes but gives moderate results for more stable acetophenone derivatives. Moreover, the flow method displayed better results in terms of yield and selectivity in comparison to the corresponding batch methodology.
Sotto, Nicolas,Cazorla, Clément,Villette, Carole,Billamboz, Muriel,Len, Christophe
p. 11065 - 11071
(2016/11/28)

Enantioselective allylation of (2E,4E)-2,4-dimethylhexadienal: Synthesis of (5R,6S)-(+)-Pteroenone
Abstract Allylation, trans- and cis-crotylation of (2E,4E)-2,4-dimethylhexadienal, a representative α,β,γ,δ-unsaturated aldehyde, was carried out under different catalytic and stoichiometric conditions. The reactions catalyzed by organocatalysts TRIP-PA and N,N′-dioxides gave the best results with respect to yields, asymmetric induction, and catalyst load in comparison to other procedures. The developed methodology was applied in the enantioselective synthesis of (5R,6S)-(+)-pteroenone, a defensive metabolite (ichthyodeterrent) of the Antarctic pteropod Clione antarctica. Allylation and crotylation of an α,β,γ,δ-unsaturated aldehyde was studied under various conditions. The asymmetric induction was as high as 96 % ee. The anti-crotylation product was used as the crucial intermediate for the enantioselective synthesis of (5R,6S)-(+)-pteroenone, a defensive metabolite of Clione Antarctica.
Koukal, Petr,Kotora, Martin
supporting information
p. 7408 - 7412
(2015/05/13)

Method for Producing Alpha, Beta-Unsaturated Alcohol
A method of producing an α,β-unsaturated alcohol at a high conversion ratio and a high selectivity is provided, which comprises continuously supplying a gas mixture containing an α,β-unsaturated aldehyde and at least an equimolar amount of a secondary alcohol using zirconium oxide as a catalyst to thereby produce the corresponding α,β-unsaturated alcohol through a hydrogen transfer reaction from the secondary alcohol. According to this method, crotyl alcohol can be produced at a high yield from crotonaldehyde using isopropanol as a hydrogen source, the crotonaldehyde being obtained by dehydrogenating bioethanol to produce acetaldehyde and then subjecting acetaldehyde to aldol condensation.
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Paragraph 0051-0052

(2016/03/11)

Selective Pinacol Coupling on Regeneratable Supported Acids in Sole Water
Efficient pinacol coupling was developed in sole water, using a reusable heterogeneous supported acid source and zinc as cheap available metal source. This medium can be easily regenerated up to 10-fold without loss of activity. Moreover, supported acids enhance the selectivity of the pinacol coupling reaction compared with homogeneous acids.
Sotto, Nicolas,Billamboz, Muriel,Chevrin-Villette, Carole,Len, Christophe
p. 6375 - 6380
(2015/06/30)

The first stereoselective total synthesis of the immunosuppressive decalin derivative monascusic acid B 1
The first stereoselective total synthesis of the immunosuppressive decalin derivative monascusic acid B has been accomplished from (R)-(+)-pulegone involving Horner-Wadsworth-Emmons and Julia-Kocienski olefination reactions and Lewis acid catalyzed intramolecular Diels-Alder cyclization. Georg Thieme Verlag Stuttgart New York.
Kumar, Jayprakash Narayan,Das, Biswanath
p. 863 - 865
(2014/04/17)

Asymmetric cascade reaction to allylic sulfonamides from allylic alcohols by palladium(II)/base-catalyzed rearrangement of allylic carbamates
A regio- and enantioselective tandem reaction is reported capable of directly transforming readily accessible achiral allylic alcohols into chiral sulfonyl-protected allylic amines. The reaction is catalyzed by the cooperative action of a chiral ferrocene palladacycle and a tertiary amine base and combines high step-economy with operational simplicity (e.g. no need for inert-gas atmosphere or catalyst activation). Mechanistic studies support a Pd II-catalyzed [3,3] rearrangement of allylic carbamates - generated in situ from the allylic alcohol and an isocyanate - as the key step, which is followed by a decarboxylation.
Bauer, Johannes Moritz,Frey, Wolfgang,Peters, Rene
supporting information
p. 7634 - 7638
(2014/08/05)

Asymmetric chiral ligand-directed alkene dioxygenation
A Pd-catalyzed asymmetric alkene 1,2-dioxygenation reaction is described. The diastereoselectivity of the reaction is controlled by tethering a chiral oxime ether directing group to the alkene substrate. The best selectivities are obtained with 8-substituted menthone-derived oxime ether auxiliaries.
Neufeldt, Sharon R.,Sanford, Melanie S.
supporting information
p. 46 - 49
(2013/04/10)

Multimetallic Ir-Sn3-catalyzed substitution reaction of π-activated alcohols with carbon and heteroatom nucleophiles
An atom economic and catalytic substitution reaction of π-activated alcohols by a multimetallic IreSn3 complex has been demonstrated. The multimetallic IreSn3 complex can be easily synthesized from the reaction between [Cp*IrCl2]2 and SnCl2. In presence of as little as 1 mol % of the catalyst three different types of π-activated alcohols, namely benzyl, allyl, and propargyl alcohols, have been successfully transformed into alkylated products using carbon (arenes, heteroarenes, allyltrimethylsilane, and 1,3-dicarbonyls), nitrogen (sulfonamides), oxygen (alcohols), and sulfur (thiols) nucleophiles in very high yields. An electrophilic mechanism is proposed from the Hammett correlation study.
Maity, Arnab Kumar,Chatterjee, Paresh Nath,Roy, Sujit
p. 942 - 956
(2013/07/25)

Total synthesis of infectopyrone, aplysiopsenes A-C, ent-aplysiopsene D, phomapyrones A and D, 8,9-dehydroxylarone, and nectriapyrone
The total synthesis of the 2-pyrone natural products nectriapyrone, aplysiopsenes A-C, ent-aplysiopsene D, phomapyrones A and D, and of 8,9-dehydroxylarone were achieved by Wittig olefination starting with vermopyrone. Infectopyrone was synthesized by Horner-Wadsworth-Emmons reaction starting with phomapyrone D. Racemic phomapyrone C methyl ether was obtained by hydrogenation of nectriapyrone. The total syntheses were achieved starting from commercially available 3,5-heptanedione and led to the desired natural products in 18-46% over 5-6 steps, whereupon all five-step syntheses were carried out with a single chromatographic workup. The total synthesis of infectopyrone, aplysiopsenes A-D, of phomapyrones A and D, and of 8,9-dehydroxylarone were achieved for the first time, giving unambiguous proof for the proposed structures of these natural products.
Geiseler, Oliver,Podlech, Joachim
experimental part
p. 7280 - 7287
(2012/09/11)

Aromatic cations from oxidative carbon-hydrogen bond cleavage in bimolecular carbon-carbon bond forming reactions
Chromenes and isochromenes react quickly with 2,3-dichloro-5,6-dicyano-1,4- benzoquinone (DDQ) to form persistent aromatic oxocarbenium ions through oxidative carbon-hydrogen cleavage. This process is tolerant of electron-donating and electron-withdrawing groups on the benzene ring and additional substitution on the pyran ring. A variety of nucleophiles can be added to these cations to generate a diverse set of structures.
Clausen, Dane J.,Floreancig, Paul E.
experimental part
p. 6574 - 6582
(2012/10/08)

Dehydration of 1,5-pentanediol over bixbyite Sc2-xYb xO3 catalysts
Vapor-phase dehydration of 1,4- and 1,5-alkanediols was investigated over three scandium ytterbium mixed oxides, Sc2-xYbxO 3 (x = 0.5, 1.0, and 1.5), to produce the corresponding unsaturated alcohols. In the dehydration of
Sato, Fumiya,Sato, Satoshi
p. 129 - 133
(2013/01/13)

Benign catalysis with iron: Unique selectivity in catalytic isomerization reactions of olefins
The use of noble metal catalysts in homogeneous catalysis has been well established. Due to their price and limited availability, there is growing interest in the substitution of such precious metal complexes with readily available and bio-relevant catalysts. In particular, iron is a "rising star" in catalysis. Herein, we present a general and selective iron-catalyzed monoisomerization of olefins, which allows for the selective generation of 2-olefins. Typically, common metal complexes give mixtures of various internal olefins. Both bulk-scale terminal olefins and functionalized terminal olefins give the corresponding products under mild conditions in good to excellent yields. The proposed reaction mechanism was elucidated by in situ NMR studies and supported by DFT calculations and extended X-ray absorption fine structure (EXAFS) measurements.
Jennerjahn, Reiko,Jackstell, Ralf,Piras, Irene,Franke, Robert,Jiao, Haijun,Bauer, Matthias,Beller, Matthias
experimental part
p. 734 - 739
(2012/06/04)

Effects of NaCl on Pt/ZrO2 catalysts for selective hydrogenation of crotonaldehyde
A series of NaCl-modified Pt/ZrO2 catalysts were prepared and tested for vapor phase selective hydrogenation of crotonaldehyde. It was found that the reactivities of the catalysts increased with NaCl contents, with the highest selectivity to crotyl alcohol (60%) at a NaCl content of 1%. Ammonia temperature programmed desorption and Fourier transmission infrared spectra of pyridine adsorption results indicated that the strengths of surface Lewis acids of the catalysts were weakened with increasing NaCl contents, such weakening was responsible for the enhancement of the reactivity. Diffuse reflectance infrared transform spectra of CO adsorption and X-ray photoelectron spectrometer results suggested that increased electron density on Pt species with the NaCl modification was responsible for the enhanced selectivity. However, high NaCl content (>3%) in the catalyst resulted in the growth of Pt particles and fewer interfacial Pt sites contacting with the surface Lewis acid sites, such changes were unfavorable for the selectivity.
Wang, Xiao-Xia,Zheng, Hai-Ying,Liu, Xi-Jing,Xie, Guan-Qun,Lu, Ji-Qing,Jin, Ling-Yun,Luo, Meng-Fei
experimental part
p. 134 - 140
(2011/01/12)

Gosteli-claisen rearrangement: Substrate synthesis, simple diastereoselectivity, and kinetic studies
The results of kinetic studies on the uncatalyzed [3,3]-sigmatropic rearrangement of 2-alkoxycarbonyl- substituted allyl vinyl ethers are reported. Apparently first reported by Gosteli in 1972, this variation of a Claisen rearrangement enjoyed a shadowy existence for three decades until its potential for the development of a catalytic asymmetric Claisen rearrangement was discovered. Inspired by this development, we have studied substituent and solvent rate effects, and we provide evidence that a chairlike transition state is highly favorable for the uncatalyzed Gosteli-Claisen rearrangement.
Rehbein, Julia,Leick, Sabine,Hiersemann, Martin
supporting information; experimental part
p. 1531 - 1540
(2009/09/05)

Sodium tetraalkoxyborates: Intermediates for the quantitative reduction of aldehydes and ketones to alcohols through ball milling with NaBH4
Stoichiometric molecular solid-state vibrational ball milling, solvent-free kneading ball milling, and mechanochemical ball milling of varied aldehydes and ketones with unmodified sodium borohydride under temperature control uses all hydrogen atoms of the reducing agent in fast reactions. It provides quantitative yields of thermally stable sodium tetraalkoxyborates. The easily isolated solids are extremely sensitive towards hydrolysis, leading to quantitative yields of the corresponding alcohols. The rapid syntheses are regiospecific and stereoselective. Varied substituents are not attacked, including the bromine of α-bromo ketones. Conjugated aldehydes and ketones provide quantitative yields of the allylic alcohols free of contamination by saturated alcohols that would occur by reaction in solution. Depending on the stoichiometric ratio, benzil is quantitatively reduced to benzoin (4:1 ratio) or dihydrobenzoin (2:1 ratio).
Naimi-Jamal, M. Reza,Mokhtari, Javad,Dekamin, Mohammad G.,Kaupp, Gerd
experimental part
p. 3567 - 3572
(2009/10/26)

An acyl-claisen approach to tetrasubstituted tetrahydrofuran lignans: Synthesis of fragransin A2, talaumidin, and lignan analogues
A simple and stereocontrolled synthesis of racemic 2,3,4,5-tetrasubstituted tetrahydrofurans was achieved from acyl-Claisen derived syn-disubstituted amides. Georg Thieme Verlag Stuttgart New York.
Rye, Claire E.,Barker, David
experimental part
p. 3315 - 3319
(2010/03/04)

Hydrogenation of the α,β-unsaturated aldehydes acrolein, crotonaldehyde, and prenal over Pt single crystals: A kinetic and sum-frequency generation vibrational spectroscopy study
Sum-frequency generation vibrational spectroscopy (SFG-VS) and kinetic measurements using gas chromatography have been used to study the surface reaction intermediates during the hydrogenation of three α,β- unsaturated aldehydes, acrolein, crotonaldehyde,
Kliewer, Christopher J.,Bieri, Marco,Somorjai, Gabor A.
experimental part
p. 9958 - 9966
(2009/12/08)

An efficient method for one-pot reductive cleavage of acetals to primary alcohols using a bimetal redox couple CoCl2.6H2O-Zn
Acyclic or cyclic O, O-acetals and O, S-acetals underwent reductive cleavage to give primary alcohols efficiently on treatment with Zn-CoCl 2.6H2O-bimetal redox system in dry tetrahydrofuran at ambient temperature to give good to excellent yields.
Sarma, Kuladip,Goswami, Amrit
experimental part
p. 568 - 572
(2010/04/23)

Regioselective hydroformylation of sulfonamides using a scaffolding ligand
A highly regloselectlve hydroformylatlon of allyllc sulfonamides has been developed by employing a catalytic directing group. The reaction tolerates a wide range of electronically and sterlcally modified olefins, and only 10% of the scaffolding llgand Is required to effectively control the regloselectlvlty.
Worthy, Amanda D.,Gagnon, Morlah M.,Dombrowski, Michael T.,Tan, Kian L.
supporting information; scheme or table
p. 2764 - 2767
(2009/11/30)

Cross-coupling of aromatic bromides with allylic silanolate salts
The sodium salts of allyldimethylsilanol and 2-butenyldimethylsilanol undergo palladium-catalyzed cross-coupling with a wide variety of aryl bromides to afford allylated and crotylated arenes. The coupling of both silanolates required extensive optimization to deliver the expected products in high yields. The reaction of the allyldimethylsilanolate takes place at 85°C in 1,2-dimethoxyethane with allylpalladium chloride dimer (2.5 mol %) to afford 73-95% yields of the allylation products. Both electron-rich and sterically hindered bromides reacted smoothly, whereas electron-poor bromides cross-coupled in poor yield because of a secondary isomerization to the 1-propenyl isomer (and subsequent polymerization). The 2-butenyldimethylsilanolate (E/Z, 80:20) required additional optimization to maximize the formation of the branched (γ-substitution) product. A remarkable influence of added alkenes (dibenzylideneacetone and norbornadiene) led to good selectivities for electron-rich and electron-poor bromides in 40-83% yields. However, bromides containing coordinating groups (particularly in the ortho position) gave lower, and in one case even reversed, selectivity. Configurationally homogeneous (E)-silanolates gave slightly higher γ-selectivity than the pure (Z)-silanolates. A unified mechanistic picture involving initial γ-transmetalation followed by direct reductive elimination or σ-π isomerization can rationalize all of the observed trends.
Denmark, Scott E.,Werner, Nathan S.
scheme or table
p. 16382 - 16393
(2009/05/08)

The regio- and stereo-chemistry of 1,3-dipolar cycloaddition of a chiral methylenenitrone to 1,2-disubstituted alkenes
A study of regio- and stereo-selectivity in the cycloaddition reactions of a series of symmetrical and unsymmetrical 1,2-disubstituted alkenestothechiral, internally H-bonded N-(2-hydroxy-1-phenyl)methylenenitrone, has been carried out. The regioselectivity observed in the addition reactions is explained in terms of frontier orbital interactions. The alkenes having a hydroxymethyl substituent at the allylic position are found to undergo regio- as well as highly stereo-selective cycloaddition reactions in the presence of anhydrous magnesium bromide.
Ali, Shaikh A.,Iman, Muhammad Z.N.
p. 38 - 47
(2008/12/21)

Hydrogenation of crotonaldehyde on different Au/CeO2 catalysts
The gas-phase hydrogenation of crotonaldehyde was carried out at 120, 150, and 180 °C over Au catalysts supported on ceria with low and medium surface areas (150 and 80 m2 g-1, respectively). An initial deactivation period was observed, followed by a steady-state regime. Ethanol was the main product in the deactivation period, whereas crotyl alcohol, butanal, butanol, and condensation products were produced under steady-state conditions. The activity and selectivity to crotyl alcohol (in the 20-32% range) were lower than those for the high-surface area ceria catalysts studied previously [B. Campo, M. Volpe, S. Ivanova, R. Touroude, J. Catal. 242 (2006) 162]. Samples were characterized by TPR, XPS, TEM, and XRD. The analysis of catalytic and characterization results indicates that gold particles supported on low- and medium-surface area ceria were relatively large, and the promotional effect of Ce3+ species was not achieved for the corresponding catalysts. Moreover, under reductive conditions, sintering still increased gold particle size.
Campo, Betiana,Petit, Corinne,Volpe, Maria A.
p. 71 - 78
(2008/09/18)

One-pot synthesis of heterocyclic compounds initiated by chemoselective addition to β-acyl substituted unsaturated aldehydes with nucleophilic tin complexes
β-Acyl substituted unsaturated aldehydes 1 were revealed to be good precursors for the synthesis of various heterocyclic compounds by the combination with tin nucleophiles. Various 2-monosubstituted pyrroles were prepared in an one-pot procedure via the reductive amination of formyl groups of 1 by using Bu2SnIH-HMPA complex. One-pot synthesis of heterocycles was carried out initiated by chemoselective reduction of 1 with Bu3SnH-HMPA complex and the subsequent reaction with heterocumulenes. Furthermore, the one-pot synthesis of nitrogen heterocyclic compounds accompanying chemo-, regio- and diastereoselective carbon-carbon bond formation in side chain moieties was effectively accomplished initiated by the regio- and diastereoselective allylation of the formyl group of 1 with allylic tin species.
Shibata, Ikuya,Kato, Hirofumi,Yasuda, Makoto,Baba, Akio
p. 604 - 619
(2008/02/06)

METHOD FOR PRODUCING CITRAL HYDRIDE
Provided is a method for producing a citral hydride, which comprises hydrogenating citral in the presence of hydrogen and a supported-type noble metal catalyst by the use of carbon dioxide in a subcritical or supercritical state as a reaction medium. The method is a novel technique for producing a citral hydride, which allows the synthesis of a citral hydride, in particular, a citral hydride having a high content of geraniol which has a trans isomer purity higher than 98% from citral (which is a cis/trans mixture) with high conversion and high selectivity.
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Page/Page column 24-25

(2008/06/13)

Deconvoluting the memory effect in Pd-catalyzed allylic alkylation: Effect of leaving group and added chloride
An analysis of product distributions in the Tsuji-Trost reaction indicates that several instances of reported "memory effects" can be attributed to slow interconversion of the initially formed syn- and anti- [Pd(η3-allyl)] complexes. Addition of chloride triggers a true memory effect, in which the allylic terminus originally bearing the leaving group has a higher reactivity. The latter effect, termed regioretention, can be rationalized by ionization from a palladium complex bearing a chloride ion, forming an unsymmetrically substituted [Pd(η3-allyl)] complex. DFT calculations verify that the position trans to the phosphine ligand is more reactive both in the initial ionization and in the subsequent nucleophilic attack.
Fristrup, Peter,Jensen, Thomas,Hoppe, Jakob,Norrby, Per-Ola
p. 5352 - 5360
(2008/02/13)

On water and in air: Fast and highly chemoselective transfer hydrogenation of aldehydes with iridium catalysts
(Chemical Equation Presented) Water as solvent: A fast, selective, and high-yielding transfer hydrogenation of a wide range of aldehydes is achieved using IrIII catalysts containing simple ethylene-diamine (en) ligands (see scheme; Ts = p-toluenesulfonyl, TOF = turnover frequency). This procedure is suitable for aldehydes with a wide range of functional groups.
Wu, Xiaofeng,Liu, Jianke,Li, Xiaohong,Zanotti-Gerosa, Antonio,Hancock, Fred,Vinci, Daniele,Ruan, Jiwu,Xiao, Jianliang
p. 6718 - 6722
(2007/10/03)

In situ synthesis of gold nanoparticles inside the pores of MCM-48 in supercritical carbon dioxide and its catalytic application
Gold nanoparticles are deposited into the channels of MCM-48 through a simple H2-assisted reduction of HAuCl4 (aqueous solution) in supercritical carbon dioxide medium at 70 °C within 2-4 h. The nanoparticles were characterized by powder X-ray diffraction (PXRD), N 2 adsorption-desorption, transmission electron microscopy (TEM), and UV-Vis spectroscopy. The particle size of the synthesized material is tunable with the pressure (density) of the supercritical carbon dioxide medium. At the fixed temperature (70°C) and hydrogen pressure [P(H2) = 2 MPa], the Au particle size varies from ca. 25 nm to ca. 2 nm with the change in CO2 pressure from 7 MPa to 17 MPa. At the low solvent density conditions, larger particles of ～25 nm were obtained. On the contrary, a high solvent density of CO2 slows down particle aggregation, resulting in the small particle size within the range of 2-5 nm. This change in particle size with CO2 pressure and the interaction of the particles with the silica support were correlated well with long-range van der Waals interactions and consequently the Hamaker constant for the gold nanoparticle-CO2 (A131) and silica-gold core-CO 2 (A132), respectively. Supercritical carbon dioxide alone can provide a unique environment for stabilizing gold nanoparticles in the channels of the cubic mesoporous MCM-48 support and exquisite control of the particle size without perturbing the support structure. The synthesized material is highly stable, recyclable and no metal nanoparticle leaching was observed. The selective hydrogenation of crotonaldehyde with the synthesized material provides convincing evidence that the particles are inside the pores and available to the reactant molecules.
Chatterjee,Ikushima,Hakuta,Kawanami
p. 1580 - 1590
(2007/10/03)

A simple, efficient and highly selective deprotection of t-butyldimethylsilyl (TBDMS) ethers using silica supported sodium hydrogen sulfate as a heterogeneous catalyst
t-Butyldimethylsilyl (TBDMS) ethers have been efficiently and selectively deprotected using silica supported sodium hydrogen sulfate (NaHSO4·SiO2) as a heterogeneous catalyst at room temperature to regenerate the parent alcohols in high yields.
Das, Biswanath,Reddy, K. Ravinder,Thirupathi
p. 5855 - 5857
(2007/10/03)

Sodium borohydride-solid LiClO4: An effective reagent for reducing aldehydes and ketones in aprotic solvent
An efficient and simple method for the reduction of aldehydes, ketones and acid chlorides has been accomplished by using NaBH4-solid LiClO 4 in mild conditions at ambient temperature with complete chemoselectivity in reduction of α,β-unsaturated aldehydes and ketones. The reaction is fast with high yield and simple workup. Copyright Taylor & Francis, Inc.
Halimjani, Azim Ziyaei,Saidi, Mohammad R.
p. 2271 - 2276
(2007/10/03)

Iridium-catalyzed intermolecular allylic etherification with aliphatic alkoxides: Asymmetric synthesis of dihydropyrans and dihydrofurans
Hindered chiral ethers with one or two stereocenters are now readily available by allylic etherification of primary and secondary alkoxides (see reaction). When an Ir-phosphoramidite complex is used as the catalyst, the reaction proceeds with high regio-, enantio-, and diastereoselectivity. Np = 1-naphthyl.
Shu, Chutian,Hartwig, John F.
p. 4794 - 4797
(2007/10/03)