1667-00-1Relevant articles and documents
The Question of Cyclic Versus Acyclic Ions: The Structure of +. Gas Phase Ions
Dass, Chhabil,Gross, Michael L.
, p. 34 - 40 (1985)
The extent of isomerization of acyclic and cyclic gas phase radical cations of composition +. has been investigated by using collisionally activated dissociation spectroscopy.Both electron and charge exchange ionization were employed to form the ions with various internal energies.The +. ions investigated consisted of ionized phenylbutenes, ring-substituted methyl derivatives of allylbenzene and phenylpropene, 1-methyl-isopropenylbenzene, benzylcyclopropane, phenylcyclobutane, tetralin and 1-methylindan.The 1-methylindan and tetralin radical cations are the most stable of the C10H12 isomeric radical ions.The +. formed from acyclic olefins having the double bond in conjugation with the aromatic ring retain the initial structure to a significant extent.However, ions derived from olefins with the double bond out of conjugation with the benzene ring preferentially cyclize to stable five- and six-membered cyclic ions.Ring opening of small-ring cyclic ions, such as ionized benzylcyclopropane and phenylcyclobutane, occurs, followed by ring closure to the tetralin radical cation.
Metal-Organic Framework-Confined Single-Site Base-Metal Catalyst for Chemoselective Hydrodeoxygenation of Carbonyls and Alcohols
Antil, Neha,Kumar, Ajay,Akhtar, Naved,Newar, Rajashree,Begum, Wahida,Manna, Kuntal
supporting information, p. 9029 - 9039 (2021/06/28)
Chemoselective deoxygenation of carbonyls and alcohols using hydrogen by heterogeneous base-metal catalysts is crucial for the sustainable production of fine chemicals and biofuels. We report an aluminum metal-organic framework (DUT-5) node support cobalt(II) hydride, which is a highly chemoselective and recyclable heterogeneous catalyst for deoxygenation of a range of aromatic and aliphatic ketones, aldehydes, and primary and secondary alcohols, including biomass-derived substrates under 1 bar H2. The single-site cobalt catalyst (DUT-5-CoH) was easily prepared by postsynthetic metalation of the secondary building units (SBUs) of DUT-5 with CoCl2 followed by the reaction of NaEt3BH. X-ray photoelectron spectroscopy and X-ray absorption near-edge spectroscopy (XANES) indicated the presence of CoII and AlIII centers in DUT-5-CoH and DUT-5-Co after catalysis. The coordination environment of the cobalt center of DUT-5-Co before and after catalysis was established by extended X-ray fine structure spectroscopy (EXAFS) and density functional theory. The kinetic and computational data suggest reversible carbonyl coordination to cobalt preceding the turnover-limiting step, which involves 1,2-insertion of the coordinated carbonyl into the cobalt-hydride bond. The unique coordination environment of the cobalt ion ligated by oxo-nodes within the porous framework and the rate independency on the pressure of H2 allow the deoxygenation reactions chemoselectively under ambient hydrogen pressure.
Nickel-catalyzed reductive deoxygenation of diverse C-O bond-bearing functional groups
Cook, Adam,MacLean, Haydn,St. Onge, Piers,Newman, Stephen G.
, p. 13337 - 13347 (2021/11/20)
We report a catalytic method for the direct deoxygenation of various C-O bond-containing functional groups. Using a Ni(II) pre-catalyst and silane reducing agent, alcohols, epoxides, and ethers are reduced to the corresponding alkane. Unsaturated species including aldehydes and ketones are also deoxygenated via initial formation of an intermediate silylated alcohol. The reaction is chemoselective for C(sp3)-O bonds, leaving amines, anilines, aryl ethers, alkenes, and nitrogen-containing heterocycles untouched. Applications toward catalytic deuteration, benzyl ether deprotection, and the valorization of biomass-derived feedstocks demonstrate some of the practical aspects of this methodology.
Copper-Catalyzed Direct C-H Alkylation of Polyfluoroarenes by Using Hydrocarbons as an Alkylating Source
Xie, Weilong,Heo, Joon,Kim, Dongwook,Chang, Sukbok
supporting information, p. 7487 - 7496 (2020/08/06)
Construction of carbon-carbon bonds is one of the most important tools in chemical synthesis. In the previously established cross-coupling reactions, prefunctionalized starting materials were usually employed in the form of aryl or alkyl (pseudo)halides or their metalated derivatives. However, the direct use of arenes and alkanes via a 2-fold oxidative C-H bond activation strategy to access chemoselective C(sp2)-C(sp3) cross-couplings is highly challenging due to the low reactivity of carbon-hydrogen (C-H) bonds and the difficulty in suppressing side reactions such as homocouplings. Herein, we present the new development of a copper-catalyzed cross-dehydrogenative coupling of polyfluoroarenes with alkanes under mild conditions. Relatively weak sp3 C-H bonds at the benzylic or allylic positions, and nonactivated hydrocarbons could be alkylated by the newly developed catalyst system. A moderate-to-high site selectivity was observed among various C-H bonds present in hydrocarbon reactants, including gaseous feedstocks and complex molecules. Mechanistic information was obtained by performing combined experimental and computational studies to reveal that the copper catalyst plays a dual role in activating both alkane sp3 C-H bonds and sp2 polyfluoroarene C-H bonds. It was also suggested that the noncovalent π-πinteraction and weak hydrogen bonds formed in situ between the optimal ligand and arene substrates are key to facilitating the current coupling reactions.
Lewis Base-Promoted Ring-Opening 1,3-Dioxygenation of Unactivated Cyclopropanes Using a Hypervalent Iodine Reagent
Gieuw, Matthew H.,Ke, Zhihai,Yeung, Ying-Yeung
supporting information, p. 3782 - 3786 (2018/03/13)
A facile and effective system has been developed for the regio- and chemoselective ring-opening/electrophilic functionalization of cyclopropanes through C?C bond activation by [bis(trifluoroacetoxy)iodo]benzene with the aid of the Lewis basic promoter p-toluenesulfonamide. The p-toluenesulfonamide-promoted system works well for a wide range of cyclopropanes, resulting in the formation of 1,3-diol products in good yields and regioselectivity.
Asymmetric Photocatalytic C-H Functionalization of Toluene and Derivatives
Mazzarella, Daniele,Crisenza, Giacomo E. M.,Melchiorre, Paolo
supporting information, p. 8439 - 8443 (2018/07/25)
Reported herein is a visible-light-mediated organocatalytic direct C-H functionalization of toluene derivatives to afford enantioenriched β-benzylated aldehydes from the corresponding enals. The process combines the oxidative power of a chiral excited-state iminium ion and the basic nature of its counteranion to trigger the generation of benzylic radicals by means of a sequential multisite proton-coupled electron transfer mechanism. This study shows that feedstock chemicals generally used as solvents, such as toluene and xylene derivatives, can be used as substrates for making chiral molecules with high enantioselectivity.
Facile coupling of propargylic, allylic and benzylic alcohols with allylsilane and alkynylsilane, and their deoxygenation with Et3SiH, catalyzed by Bi(OTf)3 in [BMIM][BF4] ionic liquid (IL), with recycling and reuse of the IL
Narayana Kumar,Laali, Kenneth K.
experimental part, p. 7347 - 7355 (2012/09/25)
Allyltrimethylsilane (allyl-TMS) reacts with propargylic alcohols 1a-1d in the presence of 10% Bi(OTf)3 in [BMIM][BF4] solvent to furnish the corresponding 1,5-enynes in respectable isolated yields (87-93%) at room temperature. The utility of Bi(OTf)3 as a superior catalyst was demonstrated in a survey study on coupling of allyl-TMS with 1a employing several metallic triflates (Bi, Ln, Al, Yb) as well as, B(C6F 5)3, Zn(NTf2)2 and Bi(NO 3)3·5H2O. Coupling of cyclopropyl substituted propargylic alcohol 1e with allyl-TMS gave the skeletally intact 1,5-enyne and a ring opened derivative as a mixture. Coupling of propargylic/allylic alcohol 1f with allyl-TMS resulted in allylation at both benzylic (2 isomers) and propargylic positions, as major and minor products respectively. The scope of this methodology for allylation of a series of allylic and benzylic alcohols was explored. Chemoselective reduction of a host of propargylic, propagylic/allylic, bis-allylic, allylic, and benzylic alcohols with Et3SiH was achieved in high yields with short reaction times. The same approach was successfully applied to couple representative propargylic and allylic alcohols with 1-phenyl-2-trimethylsilylacetylene. The recovery and reuse of the ionic liquid (IL) was gauged in a case study with minimal decrease in isolated yields after six cycles.
Suzuki coupling of potassium cyclopropyl- and alkoxymethyltrifluoroborates with benzyl chlorides
Colombel, Virginie,Rombouts, Frederik,Oehlrich, Daniel,Molander, Gary A.
scheme or table, p. 2966 - 2970 (2012/06/01)
Efficient Csp3-Csp3 Suzuki couplings have been developed with both potassium cyclopropyl- and alkoxymethyltrifluoroborates. Moderate to good yields have been achieved in the cross-coupling of potassium cyclopropyltrifluoroborate with benzyl chlorides possessing electron-donating or electron-withdrawing substituents. Benzyl chloride was also successfully cross-coupled to potassium alkoxymethyltrifluoroborates derived from primary, secondary, and tertiary alcohols.
Deoxygenation of benzylic alcohols using chloroboranes
Yao, Min-Liang,Pippin, Adam B.,Kabalka, George W.
scheme or table, p. 853 - 855 (2010/03/24)
New boron-based methods for deoxygenating benzylic alcohols via the corresponding alkoxides are reported.
Copper-catalyzed cross-coupling reaction of Grignard reagents with primary-alkyl halides: Remarkable effect of 1-phenylpropyne
Terao, Jun,Todo, Hirohisa,Begum, Shameem Ara,Kuniyasu, Hitoshi,Kambe, Nobuaki
, p. 2086 - 2089 (2008/02/14)
(Chemical Equation Presented) A general get-together: The Cu-catalyzed cross-coupling reaction of primary-alkyl halides with primary-, secondary-, and tertiary-alkyl and phenyl Grignard reagents proceeds efficiently in THF under reflux in the presence of 1-phenylpropyne (see scheme). The reaction is also applicable to alkyl mesylates (OMs) and tosylates (OTs). The reactivities of alkyl-X with a Grignard reagent increase in the order X = Cl F OMs OTs Br.
