- Chiral Supramolecular U-Shaped Catalysts Induce the Multiselective Diels-Alder Reaction of Propargyl Aldehyde
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The Diels-Alder reaction, which is a traditional [4 + 2] cycloaddition with two carbon-carbon bond formations, is one of the most powerful tools to synthesize versatile and unique six-membered rings. We show that chiral supramolecular U-shaped boron Lewis acid catalysts promote the unprecedented multiselective Diels-Alder reaction of propargyl aldehyde with cyclic dienes. Independent from the substrate control, enantio-, endo/exo-, π-facial-, regio-, site-, and substrate-selectivities could be controlled by the present U-shaped catalysts. The obtained reaction products could access the concise synthesis of chiral diene ligands and a key intermediate of (+)-sarkomycin. The results presented here might partially contribute to the development of artificial enzyme-like supramolecular catalysts for multiselective reactions, which will be able to target organic compounds that have thus far eluded synthesis.
- Hatano, Manabu,Sakamoto, Tatsuhiro,Mizuno, Tomokazu,Goto, Yuta,Ishihara, Kazuaki
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supporting information
p. 16253 - 16263
(2018/11/27)
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- (Guanidine)copper Complex-Catalyzed Enantioselective Dynamic Kinetic Allylic Alkynylation under Biphasic Condition
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Highly enantioselective allylic alkynylation of racemic bromides under biphasic condition is furnished in this report. This approach employs functionalized terminal alkynes as pro-nucleophiles and provides 6- and 7-membered cyclic 1,4-enynes with high yields and excellent enantioselectivities (up to 96% ee) under mild conditions. Enantioretentive derivatizations highlight the synthetic utility of this transformation. Cold-spray ionization mass spectrometry (CSI-MS) and X-ray crystallography were used to identify some catalytic intermediates, which include guanidinium cuprate ion pairs and a copper-alkynide complex. A linear correlation between the enantiopurity of the catalyst and reaction product indicates the presence of a copper complex bearing a single guanidine ligand at the enantio-determining step. Further experimental and computational studies supported that the alkynylation of allylic bromide underwent an anti-SN2′ pathway catalyzed by nucleophilic cuprate species. Moreover, metal-assisted racemization of allylic bromide allowed the reaction to proceed in a dynamic kinetic fashion to afford the major enantiomer in high yield.
- Cui, Xi-Yang,Ge, Yicen,Tan, Siu Min,Jiang, Huan,Tan, Davin,Lu, Yunpeng,Lee, Richmond,Tan, Choon-Hong
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supporting information
p. 8448 - 8455
(2018/06/22)
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- Arenophile-Mediated Dearomative Reduction
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A dearomative reduction of simple arenes has been developed which employs a visible-light-mediated cycloaddition of arenes with an N-N-arenophile and in situ diimide reduction. Subsequent cycloreversion or fragmentation of the arenophile moiety affords 1,3-cyclohexadienes or 1,4-diaminocyclohex-2-enes, compounds that are not synthetically accessible using existing dearomatization reactions. Importantly, this strategy also provides numerous opportunities for further derivatization as well as site-selective functionalization of polynuclear arenes.
- Okumura, Mikiko,Nakamata Huynh, Stephanie M.,Pospech, Jola,Sarlah, David
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p. 15910 - 15914
(2016/12/16)
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- Reaction of cyclic allylic acetates with aliphatic alcohols in the presence of cerium(III) chloride
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The reactions of selected allylic acetates with methanol, ethanol, n-propyl alcohol, isopropyl alcohol and tert-butyl alcohol in the presence of catalytic amounts of cerium(III) chloride are described. Allylic alkyl ethers, bis-allylic ethers and 1,3-dienes were obtained depending on the structure of the acetates.
- Uzarewicz,Dresler
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p. 1921 - 1930
(2007/10/03)
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- A Versatile Route to 2-Substituted Cyclic 1,3-Dienes via a Copper(I)-Catalyzed Cross-Coupling Reaction of Dienyl Triflates with Grignard Reagents
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A general synthesis of 2-substituted cyclic 1,3-dienes in two steps from α,β-unsaturated ketones has been developed. Formation of a dien-2-yl triflate followed by a copper(I)-catalyzed cross-coupling reaction with a Grignard reagent gives 2-substituted dienes in fair to excellent yields. Alkyl, aryl, and allyl Grignard reagents can be used.
- Karlstroem, A. Sofia E.,Roenn, Magnus,Thorarensen, Atli,Baeckvall, Jan-E.
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p. 2517 - 2522
(2007/10/03)
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- The reaction of cyclic allylic alcohols with aliphatic alcohols in the presence of cerium(III) chloride
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Cyclic secondary and tertiary allylic alcohols react with primary aliphatic alcohols in the presence of cerium(III) chloride heptahydrate to give alkyl allylic ethers. When secondary or tertiary aliphatic alcohols are used 1,3-dienes are obtained from allylic alcohols heaving the 3-methyl-2-en-1-ol moiety (3-8, 13-15).
- Uzarewicz,Dresler
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p. 181 - 195
(2007/10/03)
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- Isomer differentiation by tri-osmium cluster complexation of substituted 1,3-cyclohexadienes
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A series of methyl- and dimethyl-substituted 1,3-cyclohexadienes have been prepared from their aromatic analogues via Birch reduction and subsequent isomerisation with Fe(CO)3 fragments. These ligands were reacted with [Os3(CO)10(CH3CN)2] to form tri-osmium decacarbonyl cluster compounds containing the η4-coordinated substituted 1,3-cyclohexadienes. The various isomers of the substituted dienes show a dramatic difference in their reactivity towards the tri-osmium cluster and it is likely that this is due to the steric interactions between the methyl substituents and the cluster framework, with this effect being more marked for the di-substituted ligands.
- Ingham,Johnson,Sadler,Nairn
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p. 237 - 242
(2007/10/03)
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- Regioselectivity in the gas - phase nucleophilic attack on O - protonated 3-methyl-2-cyclohexen-1-ol and 1-methyl-2-cyclohexen-1-ol
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Our radiolytic study of the occurrence in the gas phase of concerted SN2' reactions on several open-chain allylic oxonium ions generated in the gas phase from the attack of gaseous GA+ acids (GA+ = CnH+5 (n = 1, 2), iC3H+7, and (CH3)2F+) on suitable substrates is now continued with cyclic allylic alcohols, such as 3-methyl-2-cyclohexen-1-ol (1) and 1-methyl-2-cyclohexen-1-ol (2), with both MeOH and NMe3 as neutral nucleophiles.With MeOH as the nucleophile, the substitution reaction exclusively takes place on 1 as the starting compound, whereas when the substrate is 2 it is accompanied by extensive elimination.With NMe3, only the elimination reaction is observed in the same systems.The analysis of the isomeric distribution of the substitution and elimination products allows definition of the corresponding reaction patterns.As for open-chain oxonium ions, the nucleophilic attack on O-protonated 1 and 2 is preceded by significant intramolecular interconversion.Partial unimolecular dissociation of the same ionic intermediates also takes place.After careful evaluation of the extent of these side processes, it is demonstrated that the O-protonated 1 undergoes the concerted SN2 process with MeOH almost exclusively ( 99percent).With O-protonated 2, however, the concerted SN2' pathway (84-95percent) prevails over the classical SN2 one (6-17percent).Concomitant (E2) and elimination (E2') pathways involve attack of the selected nucleophiles on the oxonium ions from 1 and 2.Their relative extent (E2'/E2:1.78-1.96 (1); 1.43-1.70 (2)) appears only slightly dependent on the nature of the ionic substrate, the nucleophile (whether MeOH or NMe3), and the leaving group (whether H2O or MeOH).The effects of both intrinsic structural factors and experimental conditions in determining the SN2'/SN2 and E2'/E2 branchings in the selected oxonium ions is discussed and compared with related gas-phase data. - Keywords: cyclohexenols; elimination reactions; gas-phase chemistry; mechanistic studies; nucleophilic substitutions
- Dezi, Emanuela,Lombardozzi, Antonietta,Renzi, Gabriele,Pizzabiocca, Adriano,Speranza, Maurizio
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p. 323 - 334
(2007/10/03)
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- Synthesis of Alkyl Allylic Ethers and 1,3-Dienes by the Reaction of Conjugated Cyclohexenones with Sodium Borohydride-Cerium(III) Chloride in Aliphatic Alcohols
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The reaction of conjugated cyclohexenones 1,3-containing 3-methyl-2-en-1-one moiety with NaBH4/CeCl3*7H2O in primary aliphatic alcohols (MeOH, EtOH, n-PrOH) affords alkyl allylic ethers and 1,3-dienes.In isopropanol or tert-butanol only 1,3-dienes are obtained.Ketones 4-6 containing 2-methyl-2-en-1-one moiety are reduced under the same conditions to the corresponding allylic alcohols irrespective of the alcohol used.Key words: reduction, α,β-unsaturated ketones, allylic alcohols, alkyl allylic ethers, sodium borohydride, cerium(III) chloride
- Uzarewicz, A.,Dresler, R.
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p. 1655 - 1658
(2007/10/03)
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- Thermal Decomposition of 2,3-Dihydro-1,4-benzodioxin and 1,2-Dimethoxybenzene
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Rates and mechanisms of decomposition of 2,3-dihydro-1,4-benzodioxin (1) and 1,2-dimethoxybenzene (27) have been investigated in the gas phase near atmospheric pressure between 750 and 900 K in a tubular flow reactor in a large excess of radical trapping agents.The following rate expressions for decomposition have been determined: log kt/s-1 (1) = 15.7 - (271 kJ mol-1/2.303 RT); log kt/s-1 (27) = 15.7 - (251 kJ mol-1/2.303 RT).The main decomposition routes for 1 are the formation of o-benzoquinone (2) and 2-methyl-1,3-benzodioxole (7) through a biradical intermediate.The measured activation energy is 20 kJ mol-1 above the required C-O bond dissociation energy.Compound 2 rapidly loses CO to form cyclopenta-2,4-dien-1-one (6) which after dimerisation decomposes mainly into 3-phenylprop-2-enal (12) and indenols (14).The main product of the thermolysis of 27 is o-hydroxybenzaldehyde (33).The O-methyl bond is weakened by 16 kJ mol-1 compared to methoxybenzene as a result of the o-methoxy-substitution.
- Schraa, Gerrit-Jan,Arends, Isabel W. C. E.,Mulder, Peter
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p. 189 - 198
(2007/10/02)
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- Hydrogen Transfer Reactions, 19. - The Catalysis of Hydrogen Transfer and 1,5-H Shift by Rhodium(III) Chloride in Homogeneous Organic Systems
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In homogeneous solution, partly in the presence of a phase-transfer catalyst, rhodium(III) chloride catalyzes the disproportionation of 1,3-cyclohexadiene and to a lesser extent 1,5-H shifts.In the start phase the catalyst is reduced to the active monovalent state.In these catalytic systems the dehydrogenation proceeds stereoselectively. - This was shown by tracer experiments and isotopes effects using deuterated 1,3-cyclohexadienes 1a-d, which were synthesized with high isotopomeric purity.Key Words: Rhodium chloride / Hydrogen transfer / Deuterated 1,3-cyclohexadienes / Isotope effects
- Wehage, Hubert,Heesing, Albert
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p. 209 - 215
(2007/10/02)
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- Rotational Barriers of Vinyl-Substituted Olefines
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For the vinyl-substituted olefines 1-14 activation parameters for the geometrical isomerisation have been determined in the gas-phase.By comparison of these barriers with the corresponding ones of the isolated double bonds, each corrected by the contribution of the steric energy to the ground and transition state, a value of 13.5 +/- 1.1 kcal mol-1 for the allyl stabilisation energy (ASE), defined as replacement of alkyl by vinyl, has been derived.
- Doering, William von E.,Roth, Wolfgang R.,Bauer, Frank,Boenke, Martin,Breuckmann, Rolf,et al.
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p. 1461 - 1470
(2007/10/02)
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- Platinacyclobutane chemistry: Cis-disubstituted platinacyclobutane complex from bicyclo[4.1.0] heptane
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The methodology for the preparation, isolation, and characterization of platinacyclobutanes from cis-disubstituted cyclopropane derivatives is established. In this case the metallacyclobutane was successfully prepared and characterized from bicyclo[4.1.0]
- Parsons,Jennings
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p. 1435 - 1437
(2008/10/08)
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- Synthesis of Substituted Dibenzophospholes. Part 5. Synthesis of Intermediates for 4- and 6-Aryl Substituents
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6-Iodo-5-methoxy-8-methyl-1,2,3,4-tetrahydro-1,4-ethanonaphthalene was prepared from the Diels-Alder adduct of benzoquinone and cyclohexadiene.Diels-Alder condensation of 2-acetamimido-benzoquinone and 2-iodobenzoquinone (convenient, new syntheses of both quinones are described) with 2-methylcyclohexa-1,3-diene led to mixtures of adducts; the major adduct from the iodoquinone was isolated and found by X-ray analysis to have the methyl and iodo substituents at the 2- and 7-positions, respectively, of the 1,4-ethanonaphthalene skeleton.Addition of 2-acetamidobenzoquinone to mentha-2,6,8(9)-triene derived from (-)-carvone gave two regioisomers (structures determined by n.m.r. spectroscopy).In a smooth 4-step synthesis from 6,6-dimethylfulvene and benzoquinone, 6-iodo-9-syn-isopropyl-5,8-dimethoxy-1,2,3,4-tetrahydro-1,4-methanonaphthalene was prepared and its stucture confirmed by X-ray analysis.
- Buttrus, Nabeel H.,Cornforth, Sir John,Hitchcock, Peter B.,Kumar, Ashok,Stuart, Alan S.
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p. 851 - 858
(2007/10/02)
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- Stereo-and Regioselective Palladium-Catalyzed 1,4-Diacetoxylation of 1,3-Dienes
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Palladium-catalyzed oxidation of 1,3-dienes in acetic acid using an oxidation system of MnO2 and catalytic amounts of p-benzoquinone selectively gives 1,4-diacetoxy-2-alkenes.The reaction proceeds with high stereo-and regioselectivity, and by ligand control the reaction can be made to take place with either cis or trans 1,4-diacetoxylation across the diene in cyclic systems.Also in an acyclic system the 1,4-relative stereochemistry can be controlled as shown by the stereoselective oxidation of (E,E)- and (E,Z)-2,4-hexadiene to their corresponding dl (>88percent dl) and meso (>95percent meso) diacetates 15 and 18, respectively.Evidence is provided that supports a mechanism involving a trans acetoxypalladation of the conjugated diene to give an intermediate (?-allyl)palladium complex, followed by either a cis or trans attack by acetate on the allyl group.The cis attack is best explained by a cis migration from a (?-allyl)palladium intermediate.The diacetoxylation reaction was applied to the preparation of a key intermediate for the synthesis of dl-shikimic acid.
- Baeckvall, Jan-E.,Bystroem, Styrbjoern E.,Nordberg, Ruth E.
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p. 4619 - 4631
(2007/10/02)
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- Generation of Bicycloheptatrienes
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Derivatives of bicycloheptatriene have been generated in solution by the base-induced dehydrochlorination of gem-dichlorocyclopropanes.Reaction of 7,7-dichlorodibenzobicycloheptane with potassium tert-butoxide in tetrahydrofuran at 0 deg C gives mainly products derived from solvent incorporation by carbene insertion.Evidence that the carbene results from rearrangement of the bicycloheptatriene derives from the successful interception of the bicycloheptatriene with nucleophile (MeS-). endo-7-Chlorodibenzobicycloheptane failed to reactwith potassium tert-butoxide in tetrahydrofuran.Generation of benzobicycloheptatrienes was also accomplished via the base-induced dehydrochlorination of gem-dichlorocyclopropanes. 1-Methylbenzobicycloheptatriene gives products derived from multiple carbene-carbene rearrangements.In contrast, nonannelated methylbicycloheptatrienes generated by the dehydrochlorination route give only carbene-derived products resulting from the initially produced bicycloheptatriene.
- Billups, W. E.,Reed, Larry E.,Casserly, Edward W.,Lin, L. P.
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p. 1326 - 1333
(2007/10/02)
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- Electronic Control of Stereoselectivity. 9. The Stereochemical Course of Electrophilic Additions to Aryl-Substituted Benzobicyclooctadienes
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Product and relative reactivity data have been obtained for the photooxygenation, epoxidation, cyclopropanation, oxymercuration, and hydroboration of three differently substituted (aryl) 2-methylbenzobicyclooctadienes.Syn stereoselectivity was observed in every case, with the level of syn attack being highest with the tetrafluoro derivative 2c (except in the Simmons-Smith reaction where a single isomer was produced in every case).Only small differences in rate were seen with a given reagent.Electronic interactions in these molecules were explored by photoelectron spectroscopy and MINDO/3 calculations.These combined tools served to show that through-space interaction is absent in these molecules.However, through-bond coupling in 2a and 2b leads to olefinic ?-bond disrotation.The relative importance of this effect as well as long-range Coulomb and charge-transfer interactions is discussed.A connection between such subtle electronic influences and stereoselectivity is established, although prevailing steric effects do serve to compress somewhat the syn/anti range available to these systems.
- Paquette, Leo A.,Bellamy, Francois,Wells, Gregory J.,Boehm, Michael C.,Gleiter, Rolf
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p. 7122 - 7133
(2007/10/02)
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