1011-12-7Relevant articles and documents
1,1-DICYCLOPENTADIENYL-3,3-DIMETHYLVANADA(IV)CYCLOBUTANE
Seetz, J. W. F. L.,Heisteeg, B. J. J. Van De,Schat, G.,Akkerman, O. S.,Bickelhaupt, F.
, p. 173 - 182 (1984)
The reaction of 1,3-bis(bromomagnesio)-2,2-dimethylpropane (1b) with dichlorodicyclopentadienylvanadium(IV) (5) gave 1,1-dicyclopentadienyl-3,3-dimethylvanada(IV)cyclobutane (4) in 30percent yield, contaminated with dicyclopentadienylneopentylvanadium(III) (12).Attempts to purify 4 were only partially successful due to its limited stability (t1/2 = 4 h at 25 deg C in cyclopentane).Identification of 4 is therefore based on its having sufficient thermal stability for isolation, on its reaction with bromine to give 1,3-dibromo-2,2-dimethylpropane (2b), and especially on its ESR and 1H NMR spectra.The reaction of 4 with cyclohexanone (15) gave 17 and 18 as the main products; 17 is the aldol dimer of 15, while 18 may be derived from either 4 or 12.Because methylenecyclohexane (16) is not one of the reaction products, it is concluded that 4 does not have a pronounced tendency to fragment to give a metallacarbene (20).
Optimization of a cyclohexanone distillation stage in the presence of alkali
Glazko,Levanova,Martynenko,Sokolova
, p. 1767 - 1771 (2011)
Kinetics of two reactions: hydrolysis of esters and condensation of cyclohexanone in an alkaline environment, was studied in model mixtures. Derived kinetic equations were used to assess optimal parameters of proceeding cyclohexanone distillation in the presence of alkali.
Koch
, p. 6295 (1968)
The introduction of a double bond on the steroid skeleton - The preparation of enol silyl ether derivatives from vicinal diols
Marek, Ales,Klepetarova, Blanka,Elbert, Tomas
, p. 443 - 456 (2011)
The ways of converting steroid vicinal diol into an unsaturated derivative were studied with the intention of preparing suitable precursors for the introduction of deuterium or tritium into the molecules of brassinosteroids. The model vicinal diol compound, 2α,3α-dihydroxy-5α-pregnane-6, 20-dione (3), was converted with high regioselectivity to the α-hydroxy ketone derivative, 2α-hydroxy-5α-pregnane-3,6,20-trione (8), in a 75% yield. The attempts to convert α-hydroxy ketone 8 to the dioxolene derivative, 2α,3α-(isopropylidenedioxy)-5α-pregn-2-ene-6,20- dione (6), failed. The conditions for the conversion of ketone to the corresponding enol trialkylsilyl ether were optimized using cyclohexanone as a model compound. The best and reproducible results were obtained by using tert-butyldimethylsilyl trifluoromethansulfonate (TBDMSiOTf) as the silylating reagent and triethylamine as the base. Under these conditions, the 3,6,20-trione (8) was converted to 2,3-bis(tert-butyldimethylsilyloxy)-5α-pregn-2-ene- 6,20-dione (14) with a 66% yield.
Alkylenation with Geminal Dialuminoalkane Reagents: The Synthesis of Olefins from Ketones
Piotrowski, Andrzej M.,Malpass, Dennis B.,Boleslawski, Marek P.,Eisch, John J.
, p. 2829 - 2835 (1988)
Bis(dichloroalumino)methane (BDAM, 1) has been synthesized in high yield from aluminum powder and methylene chloride by a published procedure carefully modified for safety.By the screening away of aluminum metal fine particles and the gradual addition of methylene bromide promoter over the course of reaction, a safe procedure was attained.Although 1 itself was a poor methylenating agent for ketones, its dietherate complex was distinctly more reactive.By exchanging half the halogens of 1 with Me3Al, MeMgBr, or Et3Al, two very effective methylenating agents for ketones, namely CH2(AlClMe)2 (2) and CH2(AlClEt)2 (3), were obtained.As diether ates with Et2O or THF, 2 and 3 smoothly converted a broad variety of ketones (aliphatic, alicyclic, and aromatic) into their corresponding methylene derivatives, with little or no competitive alkylation or reduction.A titanium-modified reagent, Cl2AlCH2TiCl3 (4), was also effective toward ketones, but gave only low conversions of esters to vinyl ethers.Finally, as an example of a multicarbon, alkylenating agent, the reagents 5-7 ((R2Al)2CH(CH2)4CH3, 5, R = Et; 6, R = Cl; and 7, R = Cl or Et) were examined.Good to fair yields of alkylenation were obtained with aromatic ketones, but aliphatic ketones underwent alkylation, hydride reduction, and/or aldol condension.The great influence of alkyl groups and donor solvent on the reactivity of 1-3 is briefly discussed.
Thermal decomposition of quaternary oxazolidinium bases
Kukharev
, p. 885 - 889 (1996)
Thermal decomposition of the quaternary oxazolidinium bases is accompanied by the nucleophilic attack of the hydroxyl group at the C(2) carbon atom of the cycle to afford carbonyl compounds and aminoalcohols.
ZUR HERSTELLUNG UND REAKTIVITAET VON BIS(TRIMETHYLSILYL)DILITHIOMETHAN
Eikema Hommes, N. J. R. van,Bickelhaupt, F.,Klumpp, G. W.
, p. 5237 - 5240 (1988)
At -90 deg C in THF or similar media bis(trimethylsilyl)dichloromethane 2 reacts with lithium-4,4'-di-tert-butylbiphenyl (LiDBB) or suspensions of freshly sublimed lithium to give the title compound 1 that can bind two equivalents of various electrophiles. 1 has a great propensity for proton abstraction and it is markedly less reactive towards ethyl iodide than (Me3Si)2EtCLi 6.
Mg-Al layered double hydroxides: Synthesis, structure, and catalytic potential in condensation of cyclohexanone with acetonitrile
Belov,Markov,Sova,Stolyarova,Prikhod'Ko
, p. 1013 - 1020 (2014)
Basic properties of synthetic Mg-Al layered double hydroxides were studied. It was shown that these properties strongly depend on the chemical composition and calcination temperature and are of key importance for determining the activity of catalysts based on these compounds. A relationship was found between the basic properties of these materials and the selectivity of conversion of the starting reagents to N-cyclohexylideneacetonitrile in condensation of cyclohexanone with acetonitrile.
Aldol-type condensation reactions of cyclic ketones by the W(CO)6/CCl4/UV system
Bozkurt
, p. 252 - 255 (2000)
The cyclic ketones can be converted to their aldol-type condensation products by the W(CO)6/CCl4/UV system. The reaction was monitored by recording the IR and GC-MS spectra of the reaction mixture. The results support a mechanism that includes an intermediate carbene complex of tungsten.
The influence of the preparation method on the physico-chemical properties and catalytic activities of ce-modified ldh structures used as catalysts in condensation reactions
Birjega, Ruxandra,Breze?tean, Ioana,Dumitru, Marius,Marcu, Ioan-Cezar,Matei, Andreea,Osiac, Mariana,Pavel, Octavian Dumitru,Stamate, Alexandra-Elisabeta,Z?voianu, Rodica
, (2021/10/25)
Mechanical activation and mechanochemical reactions are the subjects of mechanochem-istry, a special branch of chemistry studied intensively since the 19th century. Herein, we comparably describe two synthesis methods used to obtain the following layered double hydroxide doped with cerium, Mg3 Al0.75 Ce0.25 (OH)8 (CO3)0.5·2H2 O: the mechanochemical route and the co-precipitation method, respectively. The influence of the preparation method on the physico-chemical properties as determined by multiple techniques such as XRD, SEM, EDS, XPS, DRIFT, RAMAN, DR-UV-VIS, ba-sicity, acidity, real/bulk densities, and BET measurements was also analyzed. The obtained samples, abbreviated HTCe-PP (prepared by co-precipitation) and HTCe-MC (prepared by mechanochemical method), and their corresponding mixed oxides, Ce-PP (resulting from HTCe-PP) and Ce-MC (result-ing from HTCe-MC), were used as base catalysts in the self-condensation reaction of cyclohexanone and two Claisen–Schmidt condensations, which involve the reaction between an aromatic aldehyde and a ketone, at different molar ratios to synthesize compounds with significant biologic activity from the flavonoid family, namely chalcone (1,3-diphenyl-2-propen-1-one) and flavone (2-phenyl-4H-1benzoxiran-4-one). The mechanochemical route was shown to have indisputable advantages over the co-precipitation method for both the catalytic activity of the solids and the costs.
Ketalization of ketones to 1,3-dioxolanes and concurring self-aldolization catalyzed by an amorphous, hydrophilic SiO2-SO3H catalyst under microwave irradiation
Barbosa, Sandro L.,Ottone, Myrlene,De Almeida, Mainara T.,Lage, Guilherme L.C.,Almeida, Melina A.R.,Nelson, David Lee,Dos Santos, Wallans T.P.,Clososki, Giuliano C.,Lopes, Norberto P.,Klein, Stanlei I.,Zanatta, Lucas D.
, p. 1663 - 1671 (2018/06/29)
The amorphous, mesoporous SiO2-SO3H catalyst with a surface area of 115 m2 g-1 and 1.32 mmol H+ per g was very efficient for the protonation of ketones on a 10percent (m/m) basis, and the catalyst-bound intermediates can be trapped by polyalcohols to produce ketals in high yields or suffer aldol condensations within minutes under low-power microwave irradiation. The same catalyst can easily reverse the ketalization reaction. Printed in Brazil-
Synthesis and catalytic properties of ZSM-5 zeolite with hierarchical pores prepared in the presence of n-hexyltrimethylammonium bromide
Bai, Peng,Wu, Pingping,Xing, Wei,Liu, Daolan,Zhao, Lianming,Wang, Youhe,Xu, Benjing,Yan, Zifeng,Zhao, Xiu Song
, p. 18586 - 18597 (2015/09/15)
ZSM-5 samples with hierarchical pores (macropores, mesopores and micropores) were synthesized in the presence of n-hexyltrimethylammonium bromide (HTAB) and tetrapropylammonium hydroxide (TPAOH). The effect of synthesis conditions including the Si/Al ratio, crystallization temperature and time, and the amount of HTAB added to the synthesis system on the final products was examined. The catalytic properties of the hierarchical zeolite were investigated in reactions of Claisen-Schmidt condensation of benzaldehyde and acetophenone, self-condensation of cyclohexanone and methanol conversion. The hierarchical zeolite exhibits superior catalytic performance in Claisen-Schmidt condensation of benzaldehyde and acetophenone and self-condensation of cyclohexanone and has a remarkably high selectivity for dimethyl ether in the methanol conversion reaction at relatively low temperatures, which was attributed to the fast mass transport in the three-dimensional hierarchical pore network. A cooperative assembly mechanism accounting for the formation of the hierarchical zeolite was proposed based on experimental results.
