- Modular enantioselective synthesis of cis-cyclopropanes through self-sensitized stereoselective photodecarboxylation with benzothiazolines
-
Chiral cis-cyclopropanes are strained rigid analogues of alkyl chains, whose study and application are limited by their difficult synthesis. A modular approach from olefin materials is enabled by the discovery of the electron donor-acceptor (EDA) interaction between 2-substituted benzothiazolines and N-hydroxyphthalimide esters. These complexes are activated by visible light without photocatalysts, and the benzothiazoline reagent plays a triple role as a photoreductant, a stereoselective hydrogen-atom donor, and a Br?nsted acid. Beyond the enantioselective synthesis of cis-cyclopropanes, these results introduce benzothiazolines as accessible and easily tunable self-sensitized photoreductants.
- Costantini, Matteo,Mendoza, Abraham
-
p. 13312 - 13319
(2021/11/20)
-
- All at once arrangement of both oxygen atoms of dioxygen into aliphatic C(sp3)-C(sp3) bonds for hydroxyketone difunctionalization
-
Both β- and γ- hydroxyketone structures are important units in biologically active molecules, synthetic drugs and fine chemicals. Although there are some routes available for their manufacture from pre-functionalized groups on one or two matrix molecule(s), the approaches to simply and simultaneously deposit two oxygen atoms from dioxygen into two specific C(sp3) positions of pure saturated hydrocarbons have rarely succeeded because they are involved in the targeted activation of three inert C-H σ bonds all at once. Here, we show that a TiO2-CH3CN photocatalytic suspension system enables the insertion of dioxygen into one C(sp3)-C(sp3) bond of strained cycloparaffin derivatives, by which difunctionalized hydroxyketone products are obtained in a one-pot reaction. With the cleavage event to release strain as the directional driving force, as-designed photocatalytic reaction systems show 21 examples of β-hydroxyketone products with 31%–76% isolated yields for three-membered ring derivatives and 5 examples of γ-hydroxyketone products with 30%–63% isolated yields for four-membered ring substrates. 18O isotopic labeling experiments using 18O2, Ti18O2 and intentionally added H218O, respectively, indicated that both oxygen atoms of hydroxyketone products were exclusively from dioxygen, suggesting a previously unknown H+/TiO2-e? catalyzed arrangement pathway of the hydroperoxide intermediate to convert dioxygen into hydroxyketone units. [Figure not available: see fulltext.]
- Qiao, Xiaofeng,Lin, Yuhan,Li, Jiazhen,Ma, Wanhong,Zhao, Jincai
-
p. 770 - 777
(2021/04/09)
-
- Reductive Ring-Opening 1,3-Difunctionalizations of Arylcyclopropanes with Sodium Metal
-
Sodium dispersion promotes reductive ring opening of arylcyclopropanes. The presence of a reduction-resistant electrophile, such as methoxypinacolatoborane, epoxide, oxetane, paraformaldehyde, or chlorotrimethylsilane, during the reductive ring opening event leads to the formation of 1,3-difunctionalized 1-arylalkanes by immediate trappings of the resulting two reactive carbanions. In particular, the ring-opening 1,3-diborylations of arylcyclopropanes afford 1,3-diborylalkanes with high syn selectivity.
- Wang, Shuo,Kaga, Atsushi,Yorimitsu, Hideki
-
supporting information
p. 219 - 223
(2020/11/04)
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- The Versatile Reaction Chemistry of an Alpha-Boryl Diazo Compound
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The first α-boryl diazo compound that is capable of engaging in classic synthetic organic diazo reaction chemistry is described. The diazomethyl-1,2-azaborine 1, which is a BN isostere of phenyldiazomethane, is significantly more stable than phenyldiazomethane; its reaction chemistry ranges from C-H activation, O-H activation, [3+2] cycloaddition, and halogenation, to Ru-catalyzed carbonyl olefination. The demonstrated broad range of reactivity of diazomethyl-1,2-azaborine 1 makes it an exceptionally versatile synthetic building block for the 1,2-azaborine heterocyclic motif.
- Cuenca, Ana Belén,Li, Bo,Liu, Shih-Yuan,Liu, Yao,Puig De La Bellacasa, Raimon
-
supporting information
p. 14059 - 14064
(2021/09/15)
-
- Gold Sulfonium Benzylide Complexes Undergo Efficient Benzylidene Transfer to Alkenes
-
The gold sulfonium benzylide complexes [(P1)AuCHPh(SR1R2)]+ {B[3,5-CF3C6H3]4}? [P1=P(tBu)2o-biphenyl; R1, R2=-(CH2)4- (1 a); R1=Et, R2=Ph (1 b); R1=R2=Ph (1 c)] were synthesized by reaction of the gold α-chloro benzyl complex (P1)AuCHClPh with sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate and excess sulfide. Complexes 1 undergo efficient benzylidene transfer to alkenes and DMSO under mild conditions without external activation. Kinetic analysis of the reaction of 1 c with styrene was consistent with the intermediacy of the cationic gold benzylidene complex [(P1)AuCHPh]+ (I).
- Carden, Robert G.,Widenhoefer, Ross A.
-
supporting information
p. 11026 - 11030
(2019/08/12)
-
- Iron-catalyzed synthesis of cyclopropanes by in situ generation and decomposition of electronically diversified diazo compounds
-
The modular synthesis of a variety of trans 1,2-disubstituted cyclopropanes in a safe and user-friendly one-pot iron-catalyzed cyclopropanation reaction is described. Easily synthesized N-nosylhydrazones are used as diazo precursors, allowing the in situ generation of electron-rich diazo compounds under mild reaction conditions and their direct participation in the cyclopropanation reaction.
- Allouche, Emmanuelle M. D.,Al-Saleh, Afnan,Charette, André B.
-
p. 13256 - 13259
(2018/12/11)
-
- Mild Ring-Opening 1,3-Hydroborations of Non-Activated Cyclopropanes
-
The Brown hydroboration reaction, first reported in 1957, is the addition of B?H across an olefin in an anti-Markovnikov fashion. Here, we solved a long-standing problem on mild 1,3-hydroborations of non-activated cyclopropanes. A three-component system including cyclopropanes, boron halides, and hydrosilanes has been developed for borylative ring-opening of cyclopropanes following the anti-Markovnikov rule, under mild reaction conditions. Density functional theory (M06-2X) calculations show that the preferred pathway involves a cationic boron intermediate which is quenched by hydride transfer from the silane.
- Wang, Di,Xue, Xiao-Song,Houk, Kendall N.,Shi, Zhuangzhi
-
supporting information
p. 16861 - 16865
(2018/11/27)
-
- Nanoscaled copper metal-organic framework (MOF) based on carboxylate ligands as an efficient heterogeneous catalyst for aerobic epoxidation of olefins and oxidation of benzylic and allylic alcohols
-
Aerobic epoxidation of olefins at a mild reaction temperature has been carried out by using nanomorphology of [Cu3(BTC)2 ] (BTC = 1,3,5-benzenetricarboxylate) as a high-performance catalyst through a simple synthetic strategy. An aromatic carboxylate ligand was employed to furnish a heterogeneous copper catalyst and also serves as the ligand for enhanced catalytic activities in the catalytic reaction. The utilization of a copper metal-organic framework catalyst was further extended to the aerobic oxidation of aromatic alcohols. The shape and size selectivity of the catalyst in olefin epoxidation and alcohol oxidation was investigated. Furthermore, the as-synthesized copper catalyst can be easily recovered and reused several times without leaching of active species or significant loss of activity.
- Qi, Yue,Luan, Yi,Yu, Jie,Peng, Xiong,Wang, Ge
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p. 1589 - 1597
(2015/01/30)
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- Encapsulated cobalt-porphyrin as a catalyst for size-selective radical-type cyclopropanation reactions
-
A cobalt-porphyrin catalyst encapsulated in a cubic M8L 6 cage allows cyclopropanation reactions in aqueous media. The caged-catalyst shows enhanced activities in acetone/water as compared to pure acetone. Interestingly, the M8L6 encapsulated catalyst reveals size-selectivity. Smaller substrates more easily penetrate through the pores of the "molecular ship-in-a-bottle catalysts" and are hence converted faster than bigger substrates. In addition, N-tosylhydrazone sodium salts are easy to handle reagents for cyclopropanation reactions under these conditions.
- Otte, Matthias,Kuijpers, Petrus F.,Troeppner, Oliver,Ivanovic-Burmazovic, Ivana,Reek, Joost N. H.,De Bruin, Bas
-
supporting information
p. 4880 - 4884
(2014/05/06)
-
- Improved zinc-catalyzed simmons-smith reaction: Access to various 1,2,3-trisubstituted cyclopropanes
-
The Simmons-Smith reaction of zinc carbenoids with alkenes is a powerful method to access cyclopropanes containing various substitution patterns. This work exploits the high reactivity of aryldiazomethanes toward zinc halides to generate aryl-substituted carbenoids catalytically. These carbenoids are able to cyclopropanate various alkenes diastereoselectively, including unfunctionalized substrates such as styrenes. The zinc catalyst can be modified to tolerate the use of free allylic alcohols.
- Levesque, Eric,Goudreau, Sebastien R.,Charette, Andre B.
-
supporting information
p. 1490 - 1493
(2014/04/03)
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- Electron transfer to benzenes by photoactivated neutral organic electron donor molecules
-
Powerful reduction reactions: Simple organic electron donors, composed solely of the elements carbon, hydrogen, and nitrogen, reduce ground-state benzene rings to their radical anions by electron transfer upon photoactivation (DMF=dimethylformamide).
- Cahard, Elise,Schoenebeck, Franziska,Garnier, Jean,Cutulic, Sylvain P. Y.,Zhou, Shengze,Murphy, John A.
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p. 3673 - 3676
(2012/06/01)
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- Intermolecular metal-free cyclopropanation of alkenes using tosylhydrazones
-
We describe the first general method for the metal-free cyclopropanation of alkenes by using N-tosylhydrazones as an in situ source of diazo compounds. This new method works with a wide variety of alkenes (styrene derivatives, dienes, enynes, and electron-deficient alkenes) by using N-tosylhydrazones derived from various ketones or aldehydes (aromatic, aliphatic, enones). The reaction is performed with the use of K2CO3 as a base to form the diazo species and is compatible with a wide array of functional groups. A new procedure for the synthesis of cyclopropanes by the formal cyclopropanation of carbonyl compounds and alkenes is described. This metal-free reaction proceeds through the base-promoted decomposition of tosylhydrazones. There is significant tolerance of the functional groups, enabling cyclopropanation in the presence of functionalities often not compatible with other methodologies.
- Barluenga, Jose,Quinones, Noelia,Tomas-Gamasa, Maria,Cabal, Maria-Paz
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supporting information; experimental part
p. 2312 - 2317
(2012/06/01)
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- Olefin cyclopropanation with aryl diazocompounds upon catalysis by a dirhodium(II) complex
-
A dirhodium(II) complex with N-perfluorooctylsulfonylprolinate ligands is found to catalyze the cyclopropanation of olefins with simple aryl diazomethanes. In contrast to previously reported dirhodium(II) catalysts, the present complex works well not only with very electron-rich olefins such as enol ethers, but also with styrenes. Consequently, the present catalyst allows to prepare functionalized diarylcyclopropanes in moderate yields with good diastereoselectivity for the cis product, whereas the enantioselectivity of the reaction appears negligible.
- Verdecchia, Mirella,Tubaro, Cristina,Biffis, Andrea
-
p. 1136 - 1139
(2011/03/22)
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- Catalytic reactions of carbene precursors on bulk gold metal
-
Bulk gold metal powder, consisting of particles (5-50 μm) much larger than nanoparticles, catalyzes the coupling of carbenes generated from diazoalkanes (R2C=N2) and 3,3-diphenylcyclopropene (DPCP) to form olefins. It also catalyzes cyclopropanation reactions of these carbene precursors with styrenes. The catalytic activity of the gold powder depends on the nature of the gold particles, as determined by TEM and SEM studies. The reactions can be understood in terms of mechanisms that involve the generation of carbene R2C: intermediates adsorbed on the gold surface.
- Zhou, Yibo,Trewyn, Brian G.,Angelici, Robert J.,Woo, L. Keith
-
experimental part
p. 11734 - 11743
(2009/12/08)
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- A Novel Class of Tunable Zinc Reagents (RXZnCH2Y) for Efficient Cyclopropanation of Olefins
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A class of zinc reagents (RXZnCH2Y) generated with an appropriate organozinc is very effective for the cyclopropanation of olefins. The reactivity and selectivity of these reagents can be regulated by tuning the electronic and steric nature of the RX group on Zn. A reasonable level of enantioselectivity was obtained for the cyclopropanation of unfunctionalized olefins when a chiral (iodomethyl)zinc species was used, providing a valuable approach for the asymmetric cyclopropanation of unfunctionalized olefins.
- Lorenz, Jon C.,Long, Jiang,Yang, Zhiqiang,Xue, Song,Xie, Yinong,Shi, Yian
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p. 327 - 334
(2007/10/03)
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- Electronically tuned chiral ruthenium porphyrins: Extremely stable and selective catalysts for asymmetric epoxidation and cyclopropanation
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We report the use of three enantiomerically pure and electronically tuned ruthenium carbonyl porphyrin catalysts for the asymmetric cyclopropanation and epoxidation of a variety of olefinic substrates. The D4-symmetric ligands carry a methoxy, a methyl or a trifluoromethyl group at the 10-position of each of the 9-[anti-(1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracene)]-substituents at the meso-positions of the porphyrin. Introduction of a CF 3-substituent in this remote position resulted in greatly improved catalyst stability, and turnover numbers of up to 7500 were achieved for cyclopropanation, and up to 14200 for epoxidation, with ee values typically >90% and ≈80%, respectively. In one example, the axial CO ligand at the ruthenium was exchanged for PF3, resulting in the first chiral ruthenium porphyrin with a PF3 ligand reported to date. In cyclopropanations with ethyl diazoacetate, the latter catalyst performed exceedingly well, and gave a 95% ee in the case of 1,1-diphenylethylene as substrate.
- Berkessel, Albrecht,Kaiser, Patrick,Lex, Johann
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p. 4746 - 4756
(2007/10/03)
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- Catalytic cyclopropanation of alkenes using diazo compounds generated in situ. A novel route to 2-arylcyclopropylamines
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(Equation presented) A user-friendly, one-pot process for catalytic cyclopropanation of alkenes from tosylhydrazones is described. The cyclopropanation of N-vinylphthalimide provides a new route to 2-arylcyclopropylamines, and this is exemplified in the efficient synthesis of the HIV-1 reverse transcriptase inhibitor 6.
- Aggarwal, Varinder K.,De Vicente, Javier,Bonnert, Roger V.
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p. 2785 - 2788
(2007/10/03)
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- Di-π-methane photorearrangement of trans-1,3-diphenylpropene upon excitation to higher singlet states in polar solvents
-
A dramatic enhancement of the di-π-methane rearrangement is observed upon excitation of trans-1,3-diphenylpropene (1) to its higher singlet states in acetonitrile, which leads to trans-1,2-diphenylcyclopropane (3) as a major photoproduct.
- Jimenez,Miranda,Tormos
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p. 2341 - 2342
(2007/10/03)
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- Oxidation of aryl- and diarylcyclopropanes in a pentasil zeolite: Ring opening with deprotonation or net hydrogen migration
-
Incorporation of trans-1,2-diphenylcyclopropane (1) and its 3,3-D2- isotopomer into the channels of a redox-active pentasil zeolite (Na-ZSM-5) resulted in the formation of exo,exo-1,3-diphenylallyl radical (2.) and its 2-D1 isotopomer, respectively. This conversion requires oxidation, ring opening, and deprotonation, in an unspecified sequence. The allyl radical 2. is also formed upon incorporation of trans-1,3-diphenylpropene (3). A comparison with the solution photochemistry, in the presence or absence of added base, shows the conversion of 1 into 2. to be a zeolite-specific reaction. Incorporation of arylcyclopropanes 9 (R = H, OCH3) into ZSM-5 generated trans-propenylbenzene radical cations 10.+ (R = H, OCH3); the 2,2-D2 isotopomer of 9 (R = OCH3) gave rise to three different isotopomers of 10.+) (R = OCH3).
- Herbertz, Torsten,Lakkaraju, Prasad Sreeramachandra,Blume, Florian,Blume, Matthias,Roth, Heinz Dieter
-
p. 467 - 472
(2007/10/03)
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- The nickel and palladium catalyzed stereoselective cross coupling of cyclopropyl nucleophiles with aryl halides
-
The reaction of 2-phenylcyclopropylzinc chloride with some substituted (het)aryl halides gave the corresponding coupling products with good yields and stereoselectivities under the influence of a catalytic amount of Pd(PPh3)4. Other Ni- and Pd-catalysts were less efficient. Alkyl-substituted cyclopropyl nucleophiles gave lower yields.
- De Lang,Brandsma
-
p. 225 - 232
(2007/10/03)
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- A four-member ring hypervalent iodine radical
-
A four-member ring hypervalent iodine radical has been detected in the laser flash photolysis of 1,3-diiodo-1,3-diphenylpropane. This species absorbs at 320 nm, has a lifetime of ~9.5 μs in cyclohexane, and is not quenchable by oxygen. Excitation of this radical by means of laser-drop photolysis results the formation of trans-1,2-diphenylcyclopropane through concerted iodine extrusion.
- Miranda, Miguel A.,Perez-Prieto, Julia,Font-Sanchis, Enrique,Konya, Klara,Scaiano
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p. 9975 - 9977
(2007/10/03)
-
- Exploring new reactive species for cyclopropanation
-
An organozinc species RXZnCH2I generated by reacting Zn(CH2I)2 with RXH was found to be an efficient reagent for the cyclopropanation of olefins at room temperature. A 50.7% ee was obtained for the cyclopropanation of trans-β-methylstyrene when a chiral alcohol was used.
- Yang, Zhiqiang,Lorenz, Jon C.,Shi, Yian
-
p. 8621 - 8624
(2007/10/03)
-
- Conversion of non-activated alkenes into cyclopropanes with lithiated sulfones under nickel catalysis
-
Summary -Lithiated alkyl ierf-butyl sulfones convert alkenes into cyclopropane derivatives under nickel catalysis. The new reaction appears to differ from the known cyclopropanation reactions from both the stereochemical and the electronic points of view. Elsevier.
- Gai, Yonghua,Julia, Marc,Verpeaux, Jean-Noel
-
p. 817 - 829
(2007/10/03)
-
- Beta Secondary Deuterium Kinetic Isotope Effects on the Thermal Stereomutations of 1,2-Diphenylcyclopropanes
-
(+)-(1S,2S)-trans-1,2-Diphenylcyclopropane and (-)-(1R,2R)-trans-1,2-diphenyl-3,3-d2-cyclopropane at 234°C interconvert reversibly with the corresponding enantiomers and cis-1,2-diphenylcyclopropanes. For the unlabeled trans isomer, the ratio of rate constants for one-center epimerization (k1) and two-center turnover (k12) was found to be 1.1. A small normal kH/kD effect, 3% per deuterium, was observed for the rate constant for one-center epimerization (k1); a substantial normal kH/kD effect, 17% per deuterium, was observed for the rate constant for two-center turnover (k12). Thus different transition structures, presumably EF and EE 1,3-diphenyltrimethylene diradicals, dominate the two sorts of stereomutations.
- Asuncion, Lisa A.,Baldwin, John E.
-
p. 1421 - 1436
(2007/10/03)
-
- Enantioselective synthesis of γ-hydroxysilanes, 1,3-diols and cyclopropanes by reaction of a chiral epoxide with a racemic α-silyl organolithium reagent
-
The racemic α-silyl organolithium reagents 2a and 2b react with (R)-styrene oxide enantioselectively to produce the chiral γ-hydroxysilanes 3a and 3b, respectively. The chiral 1,3-diol 4 and cyclopropane 7 are readily obtained in enantiomerically pure form from these γ-hydroxysilanes.
- Corey,Chen, Zhuoliang
-
p. 8731 - 8734
(2007/10/02)
-
- Iron Lewis acid catalyzed reactions of phenyldiazomethane and olefins: Formation of cyclopropanes with very high cis selectivity
-
The irol Lewis acid, [(η5-C5H5)Fe(CO)2(THF)]+ (1) catalyzes the cyclopropanation reaction of phenyldiazomethane with olefins to provide cis cyclopropanes in high selectivity.
- Seitz, William J.,Hossain, M. Mahmun
-
p. 7561 - 7564
(2007/10/02)
-
- Kinetische und mechanistische Untersuchungen von Uebergangsmetall-Komplex-Reactionen.XVII. Untersuchungenen zur Substituentenabhaengigkeit der cis/trans-Cyclopropan-Produktherhaeltnisse bei der Uebertragung von Benzylidenliganden auf Styrole
-
The benzylidene complexes (CO)5M=C(C6H4R-p)H react with styrenes, H2C=C(C6H4R-p)H (R = F, Cl, Br, H, Me, OMe), α-methylstyrene, vinylcyclohexane and 2-methyl-2-butene, respectively, by transfer of the benzylidene ligand to the C=C bond and formation of cis- and trans-cyclopropanes.From the temperature dependence of the cis/trans isomer ratios the differences in the activation enthalpies ΔΔH* = Δ(Hcis)* - Δ(Htrans)* and activation entropies ΔΔS* = Δ(Scis)* - Δ(Strans)* weredetermined.With all reactions the formation of the cis-isomer is favoured by the lower activation enthalpy.The formation of the trans-isomers, however, is generally favoured by the lower activation entropy.Exceptions are the reactions of 1a with styrene and of 1c with 2-methyl-2-butene.These two opposing influences determine the cis/trans isomer ratio observed.The results are discussed on the basis of stabilizing electronic and destabilizing steric interactions.
- Fisher, Helmut,Jaeger, Monika
-
p. 205 - 212
(2007/10/02)
-
- Stereochemical outcome of benzyllithiums synthesis from selenides
-
Epimerisation usually occurs during the synthesis of arylalcanes from the corresponding benzylselenides which involves benzyllithiums as intermediates. This has been used to produce stereoselectively arylcyclopentanes and arylcyclopropanes. γ-Benzenesulfonyloxyalkyl selenides substituted on the carbon bearing the benzenesulfonyl group behave differently and lead stereospecifically to arylcyclopropane derivatives.
- Krief, Alain,Hobe, Myriam,Dumont, Willy,Badaoui, Elie,Guittet, Eric,Evrard, Guy
-
p. 3381 - 3384
(2007/10/02)
-
- On the synthesis of aryl cyclopropanes from γ-benzenesulfonylalkyl tin derivatives and n-butyllithium
-
γ-Benzenesulfonyloxyalkyl tin derivatives readily available from γ-hydroxyalkyl selenides, n-butyllithium and trialkyl tin chlorides react with n-butyllithium and stereospecifically lead to aryl cyclopropanes. The transformation is quite general and allows the synthesis of α,β-di- and trisubstituted ones.
- Krief,Hobe
-
p. 6527 - 6528
(2007/10/02)
-
- cis-1,2-Diphenylcyclopropane: Molecular Structure and Attempted Chelate Complexation of Gallium(I)
-
In an attempt to design a chelating bis(arene) ligand for metals in an s2 electron configuration, the synthesis of cis-1,2-diphenylcyclopropane (1) from ω-benzylideneacetophenone and hydrazine hydrate (followed by pyrolysis) has been optimized.The crystal structure of 1 has been determined by X-ray diffraction 12121, a = 5.823(1), b = 11,962(2), c = 15.727(3) Angstroem, Z = 4>.The molecules have the expected geometry and dimensions and appear to be ideally suited for complexation of cations like Ga+, as judged from the geometries encountered with non-chelating bis(arene) complexes. 71Ga-NMR spectra of solutions of equimolar quantities of 1 and Ga (X = Cl, Br) in benzene indeed indicate the presence of complexes with monoalkylated arenes, but no crystalline products could be isolated.
- Schmidtbaur, Hubert,Bublak, Wolfgang,Schier, Anette,Reber, Gabriele,Mueller, Gerhard
-
p. 1373 - 1376
(2007/10/02)
-
- The Photochemical Debromination of Bromocyclopropane in the Presence of Amine
-
The irradiation of bromocyclopropanes (1) in the presence of tertiary amine rresulted in the formation of the debrominated cyclopropanes as a mixture of geometrical isomers, whose ratios were essentially similar regardless of the stereochemistry of the bromide.The reactions were not, however, observed in the absence of amine.The results are interpreted as indicating that the reactions proceed through an initial single-electron transfer to the excited 1, followed by debromination and hydrogen-abstraction.
- Tomioka, Hideo,Inoue, Osamu
-
p. 3725 - 3726
(2007/10/02)
-
- OLEFIN REACTIONS WITH HMn(CO)5: PRODUCT SELECTIVITY BY MICELLE SEQUESTERING
-
The reaction of HMn(CO)5 with certain cyclopropenes, when carried out in a detergent medium gives a different mixture of hydroformylated and hydrogenated products than is obtained when the same reaction is carried out in a homogeneous medium.These results are consistent with the intermediacy of caged geminate radical pairs whose escape from the cage is retarded by micelle sequestering.
- Matsui, Yasushi,Orchin, Milton
-
p. 369 - 374
(2007/10/02)
-
- THE MATRIX EFFECT ON STEREOSELECTIVITY OF OLEFIN CYCLOPROPANATION BY ARYLCARBENE
-
Temperature studies of addition of phenylcarbene to styrene showed that stereoselectivity changed rather dramatically as the reaction phase changed.
- Tomioka, Hideo,Ozaki, Yasuji,Koyabu, Yasuhiro,Izawa, Yasuji
-
p. 1917 - 1920
(2007/10/02)
-
- Chemistry at Rigid Surfaces, 6. - Photochemically Induced Reactions with Surface-bound Sensitizers
-
AerosilR reacts with 3-triethoxysilylpropylamine to give Aminoaerosil (1) which can be converted into aerosils 2a - f by means of sensitizers containing carboxyl groups.The density of the functional groups on the surface which was determined by several methods clearly effects the reaction.On irradiation in 2-propanol, acetone was produced as well as the surface-bound pinacol, e. g. 4, which could be reoxidized by lead tetraacetate to give 2b.Hydrodimerization on the surface of 2b proceeds three times more slowly than with the homogeneous analogues.The photoreduction of 2b with a minor surface density, gave - in addition to 4 - the carbinol 8 and the mixed pinacol 9. - The aerosil with surface-bound p-acetylbenzoic acid (modified aerosil 2b) is investigated in comparison to the homogeneous system: experiments were made in (S)-p-menth-3-yl lactate and (R,S)-p-menth-3-yl-lactate.In both cases the surface-bound pinacol 4 was formed, and in the latter case a decrease in the optical activity of the lactate was observed. - With surface-bound sensitizers the following photochemically induced reactions were studied: a) the photosensitized addition of 2-propanol to maleic acid and diethyl maleate to give terebinic acid (12a) or its methyl ester, respectively; b) the sensitized cis/trans isomerization of maleic acid or diethyl fumarate; c) the sensitized cis/trans isomerization of 1,2-diphenylcyclopropane; d) the sensitized autoxidation of 2,5-dimethylfuran. - All four reactions, although slower, yield the same products as in the analogous homogeneous system.In reaction b), c), and d) the efficiency factor WF (ratio of reaction rates in homo- and heterogeneous system) and the reutilization factor SF (ratio of co nversions after a given time in the first and second experiment) was determined for the heterogeneous sensitizer.
- Horner, Leopold,Klaus, Joachim
-
p. 792 - 810
(2007/10/02)
-
- Kinetic Study of the Homolytic Brominolysis of 1,2-Diarylcyclopropanes
-
The rate constants for the photolytic brominolysis of 22 trans-1,2-diarylcyclopropanes in carbon disulfide relative to an internal standard, p-chlorotoluene, have been determined.The products of the brominolysis are 1,3-dibromo-1,3-diarylpropanes.The rate constants range over 5 orders of magnitude, being enhanced by electrondonating substituents on one or both benzene rings.The quantitative size of the substituent effect (ρ) at either involved carbon center is a function of the substituent at the other center.This fact suggests a continuum of transition-state structures with varying degrees of bond breaking and charge separation.
- Applequist, Douglas E.,Gdanski, Rick D.
-
p. 2502 - 2510
(2007/10/02)
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- cis- And trans-N-Nitroso-2,4-diphenylazetidines
-
The synthesis of cis- and trans-2,4-diphenylazetidines as well as that of their N-nitroso derivatives is described.The "abnormal" reduction of the N-nitrosamines gives a cis-trans mixture of the expected 1,2-diphenylcyclopropanes.However, no stereochemical correlations could be made owing to the base-induced isomerisation of the starting N-nitrosamines during the course of the reaction.
- Powell, Burwell F.,Reichenthal, Jules,Overberger, C. G.,Anselme, J.-P.
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p. 219 - 224
(2007/10/02)
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- Photolysis of cis- and trans-3,5-Diphenyl-1-pyrazolines: Competing Trimethylene and Cycloreversion Pathways
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In the photolysis of the title compounds up to 30percent of the reactions are proceeding via cycloreversions producing styrene and phenyldiazomethane.
- Schneider, Manfred P.,Bippi, Herbert,Rau, Hermann,Ufermann, Dieter,Hoermann, Michael
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p. 957 - 958
(2007/10/02)
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- Synthesis of clyclopropyl analogs of stilbene and stilbenediol as possible antiestrogens.
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Conformationally rigid analogs of stilbene and stilbenediol were prepared via gem-dichlorocyclopropyl precursors utilizing two different synthetic methods: a two-phase catalytic method and an organomercurial method. These precursors were reduced to the corresponding cyclopropyl analogs using sodium and methanol. All compounds are being tested to discriminate between estrogenic and antiestrogenic ability, to determine estrogen binding ability, and to evaluate tissue culture anticancer activity.
- Magarian,Benjamin
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p. 1626 - 1632
(2007/10/12)
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