- An Intramolecular Iodine-Catalyzed C(sp3)?H Oxidation as a Versatile Tool for the Synthesis of Tetrahydrofurans
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The formation of ubiquitous occurring tetrahydrofuran patterns has been extensively investigated in the 1960s as it was one of the first examples of a non-directed remote C?H activation. These approaches suffer from the use of toxic transition metals in overstoichiometric amounts. An attractive metal-free solution for transforming carbon-hydrogen bonds into carbon-oxygen bonds lies in applying economically and ecologically favorable iodine reagents. The presented method involves an intertwined catalytic cycle of a radical chain reaction and an iodine(I/III) redox couple by selectively activating a remote C(sp3)?H bond under visible-light irradiation. The reaction proceeds under mild reaction conditions, is operationally simple and tolerates many functional groups giving fast and easy access to different substituted tetrahydrofurans.
- Br?se, Stefan,Koch, Vanessa
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supporting information
p. 3478 - 3483
(2021/07/22)
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- Site- And enantiodifferentiating C(sp3)-H oxidation enables asymmetric access to structurally and stereochemically diverse saturated cyclic ethers
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A manganese-catalyzed site- and enantiodifferentiating oxidation of C(sp3)-H bonds in saturated cyclic ethers has been described. The mild and practical method is applicable to a range of tetrahydrofurans, tetrahydropyrans, and medium-sized cyclic ethers with multiple stereocenters and diverse substituent patterns in high efficiency with extremely efficient site- and enantiodiscrimination. Late-stage application in complex biological active molecules was further demonstrated. Mechanistic studies by combined experiments and computations elucidated the reaction mechanism and origins of stereoselectivity. The ability to employ ether substrates as the limiting reagent, together with a broad substrate scope, and a high level of chiral recognition, represent a valuable demonstration of the utility of asymmetric C(sp3)-H oxidation in complex molecule synthesis.
- Liu, Lei,Sun, Shutao,Yang, Yiying,Zhang, Dongju,Zhao, Ran
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supporting information
p. 19346 - 19353
(2020/12/01)
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- Heterocyclization involving benzylic C(sp3)-H functionalization enabled by visible light photoredox catalysis
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A general and efficient method for heterocyclization involving benzylic C(sp3)-H functionalization enabled by visible light photoredox catalysis to access a wide range of structurally diverse oxygen as well as nitrogen heterocycles up to a gram scale is reported. The potential application of this new methodology is demonstrated by the total synthesis of (-)-codonopsinine and (+)-centrolobine. Herein it is proposed that selectfluor, unlike a fluorinating reagent, acts as an oxidative quencher and a hydrogen radical acceptor.
- Pandey, Ganesh,Laha, Ramkrishna,Mondal, Pradip Kumar
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p. 9689 - 9692
(2019/08/15)
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- Aryl Boronic Acid Catalysed Dehydrative Substitution of Benzylic Alcohols for C?O Bond Formation
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A combination of pentafluorophenylboronic acid and oxalic acid catalyses the dehydrative substitution of benzylic alcohols with a second alcohol to form new C?O bonds. This method has been applied to the intermolecular substitution of benzylic alcohols to form symmetrical ethers, intramolecular cyclisations of diols to form aryl-substituted tetrahydrofuran and tetrahydropyran derivatives, and intermolecular crossed-etherification reactions between two different alcohols. Mechanistic control experiments have identified a potential catalytic intermediate formed between the aryl boronic acid and oxalic acid.
- Estopi?á-Durán, Susana,Donnelly, Liam J.,Mclean, Euan B.,Hockin, Bryony M.,Slawin, Alexandra M. Z.,Taylor, James E.
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p. 3950 - 3956
(2019/02/16)
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- The Combination of Benzaldehyde and Nickel-Catalyzed Photoredox C(sp3)?H Alkylation/Arylation
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Herein we report a highly selective photoredox C(sp3)?H alkylation/arylation of ethers through the combination of a photo-organocatalyst (benzaldehyde) and a transition-metal catalyst (nickel). This method provides a simple and general strategy for the C(sp3)?H alkylation/arylation of ethers. A selective late-stage modification of (?)-ambroxide has also been conducted to demonstrate the applicability of the method.
- Zhang, Lumin,Si, Xiaojia,Yang, Yangyang,Zimmer, Marc,Witzel, Sina,Sekine, Kohei,Rudolph, Matthias,Hashmi, A. Stephen K.
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supporting information
p. 1823 - 1827
(2019/01/14)
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- Palladium nanoparticles: Chemoselective control for reductive Heck with aryl triflates and 2,3-dihydrofuran
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The reductive-Heck reaction offers a unique entry to formal Csp2-Csp3 cross-coupling reactions that proceed in the absence of a main group organometallic coupling partner. Consequently, further development of new variants would be transformative. Unfortunately, controlling the relative rates of the organopalladium intermediates has proven difficult with homogenous, single-site Pd catalysts. This work describes a selective reductive Heck reaction catalyzed by Pd-nanoparticles. The reaction works well with electron-deficient aryl triflates at room temperature in the absence of ligands. This work addresses some of the challenges found in the reductive-Heck literature.
- Rosas Vargas, Daisy,Cook, Silas P.
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supporting information
p. 3314 - 3317
(2018/05/04)
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- Glycosyl Cross-Coupling of Anomeric Nucleophiles: Scope, Mechanism, and Applications in the Synthesis of Aryl C-Glycosides
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Stereoselective manipulations at the C1 anomeric position of saccharides are one of the central goals of preparative carbohydrate chemistry. Historically, the majority of reactions forming a bond with anomeric carbon has focused on reactions of nucleophiles with saccharide donors equipped with a leaving group. Here, we describe a novel approach to stereoselective synthesis of C-aryl glycosides capitalizing on the highly stereospecific reaction of anomeric nucleophiles. First, methods for the preparation of anomeric stannanes have been developed and optimized to afford both anomers of common saccharides in high anomeric selectivities. We established that oligosaccharide stannanes could be prepared from monosaccharide stannanes via O-glycosylation with Schmidt-type donors, glycal epoxides, or under dehydrative conditions with C1 alcohols. Second, we identified a general set of catalytic conditions with Pd2(dba)3 (2.5 mol%) and a bulky ligand (JackiePhos, 10 mol%) controlling the β-elimination pathway. We demonstrated that the glycosyl cross-coupling resulted in consistently high anomeric selectivities for both anomers with mono- and oligosaccharides, deoxysugars, saccharides with free hydroxyl groups, pyranose, and furanose substrates. The versatility of the glycosyl cross-coupling reaction was probed in the total synthesis of salmochelins (siderophores) and commercial anti-diabetic drugs (gliflozins). Combined experimental and computational studies revealed that the β-elimination pathway is suppressed for biphenyl-type ligands due to the shielding of Pd(II) by sterically demanding JackiePhos, whereas smaller ligands, which allow for the formation of a Pd-F complex, predominantly result in a glycal product. Similar steric effects account for the diminished rates of cross-couplings of 1,2-cis C1-stannanes with aryl halides. DFT calculations also revealed that the transmetalation occurs via a cyclic transition state with retention of configuration at the anomeric position. Taken together, facile access to both anomers of various glycoside nucleophiles, a broad reaction scope, and uniformly high transfer of anomeric configuration make the glycosyl cross-coupling reaction a practical tool for the synthesis of bioactive natural products, drug candidates, allowing for late-stage glycodiversification studies with small molecules and biologics.
- Zhu, Feng,Rodriguez, Jacob,Yang, Tianyi,Kevlishvili, Ilia,Miller, Eric,Yi, Duk,O'Neill, Sloane,Rourke, Michael J.,Liu, Peng,Walczak, Maciej A.
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supporting information
p. 17908 - 17922
(2017/12/26)
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- Remote migratory cross-electrophile coupling and olefin hydroarylation reactions enabled by in situ generation of nih
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A highly efficient strategy for remote reductive cross-electrophile coupling has been developed through the ligand-controlled nickel migration/arylation. This general protocol allows the use of abundant and bench-stable alkyl bromides and aryl bromides for the synthesis of a wide range of structurally diverse 1, 1-diarylalkanes in excellent yields and high regioselectivities under mild conditions. We also demonstrated that alkyl bromide could be replaced by the proposed olefin intermediate while using n-propyl bromide/Mn0 as a potential hydride source.
- Chen, Fenglin,Chen, Ke,Zhang, Yao,He, Yuli,Wang, Yi-Ming,Zhu, Shaolin
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supporting information
p. 13929 - 13935
(2017/11/07)
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- A Re2O7catalyzed cycloetherification of monoallylic diols
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A Re2O7catalyzed cycloetherification of monoallylic diols is described. The reaction features short reaction time, mild reaction conditions and exclusive E selectivity. A wide range of monoallylic alcohols with alkyl or aryl substituents on olefin smoothly undergo ring closure to deliver corresponding oxa-heterocycles. The reaction is also operationally simple and not sensitive to air and moisture.
- Wan, Xiaolong,Hu, Jiadong,Xu, Dongyang,Shang, Yang,Zhen, Yanxia,Hu, Chenchen,Xiao, Fan,He, Yu-Peng,Lai, Yisheng,Xie, Weiqing
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p. 1090 - 1093
(2017/03/02)
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- Cyclic ether synthesis from diols using trimethyl phosphate
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Cyclic ethers have been effectively synthesized via the intramolecular cyclization of diols using trimethyl phosphate and NaH. The present cyclization could proceed at room temperature to produce 5-7 membered cyclic ethers in good to excellent yields. Substrates possessing a chiral secondary hydroxy group were transformed into the corresponding chiral cyclic ethers along with the retention of their stereochemistries.
- Asai, Shota,Kato, Maho,Monguchi, Yasunari,Sajiki, Hironao,Sawama, Yoshinari
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p. 4787 - 4790
(2017/07/06)
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- Preparation of arylmagnesium/lithium from aryl bromides and their coupling and substitution reactions in tetrahydrofuran
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One-pot synthesis of 2-aryltetrahydrofurans was achieved by a coupling reaction between arylmagnesium bromides prepared in situ and tetrahydrofuran under mild conditions. The reaction between ArBr and n-BuLi gave unexpected butylbenzene derivatives in mod
- Gundogdu, Ozlem,Altundas, Ramazan,Kara, Yunus
-
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- Visible-Light-Induced Cyclization of Electron-Enriched Phenyl Benzyl Sulfides: Synthesis of Tetrahydrofurans and Tetrahydropyrans
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A new approach to the preparation of tetrahydrofurans and tetrahydropyrans through a photoredox catalytic process is described. The introduction of a phenylsulfanyl auxiliary group permits the substrates to be readily oxidized to form cationic intermediates for sequential intramolecular cyclization. The method features mild reaction conditions and operational simplicity.
- Li, Wei,Yang, Chao,Gao, Guo-Lin,Xia, Wujiong
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p. 1391 - 1396
(2016/06/01)
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- Photochemical Nickel-Catalyzed C-H Arylation: Synthetic Scope and Mechanistic Investigations
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An iridium photocatalyst and visible light facilitate a room temperature, nickel-catalyzed coupling of (hetero)aryl bromides with activated α-heterosubstituted or benzylic C(sp3)-H bonds. Mechanistic investigations on this unprecedented transformation have uncovered the possibility of an unexpected mechanism hypothesized to involve a Ni-Br homolysis event from an excited-state nickel complex. The resultant bromine radical is thought to abstract weak C(sp3)-H bonds to generate reactive alkyl radicals that can be engaged in Ni-catalyzed arylation. Evidence suggests that the iridium photocatalyst facilitates nickel excitation and bromine radical generation via triplet-triplet energy transfer.
- Heitz, Drew R.,Tellis, John C.,Molander, Gary A.
-
supporting information
p. 12715 - 12718
(2016/10/13)
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- Triphenylphosphine-N-bromosuccinimide mediated chemoselective cyclodehydration of diols
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A triphenylphosphine-N-bromosuccinimide mediated chemoselective cyclodehydration of diols is presented for the synthesis of polysubstituted tetrahydrofurans. 1,4-Diols and their derivatives can be rapidly cyclized to furnish tetrahydrofurans in high yields with one equivalent of Ph3P/NBS. Higher amount of Ph3P/NBS leads to the formation of dibromobutanes.
- Zhao, Shuo,Wu, You,Sun, Qi,Cheng, Tie-Ming,Li, Run-Tao
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p. 1154 - 1162
(2015/04/14)
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- Practical and highly selective C-H functionalization of structurally diverse ethers
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A trityl ion mediated C-H functionalization of ethers with a wide range of nucleophiles at ambient temperature has been developed. The reaction displays high chemo-selectivity and good functional group tolerance. The protocol also exhibits excellent regio- and diastereoselectivities for the unsymmetric ethers, thus stereoselectively generating highly functionalized disubstituted 2,5-trans tetrahydrofurans (THF), 2,6-trans tetrahydropyrans (THP), 2,6-trans dihydropyrans (DHP), and 1,3-trans isochromans, and highlighting the capacity of the protocol in complex molecule synthesis.
- Wan, Miao,Meng, Zhilin,Lou, Hongxiang,Liu, Lei
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supporting information
p. 13845 - 13849
(2015/01/16)
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- Reductive cross-coupling of nonaromatic, heterocyclic bromides with aryl and heteroaryl bromides
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Reductive cross-coupling allows the direct C-C bond formation between two organic halides without the need for preformation of an organometallic reagent. A method has been developed for the reductive cross-coupling of nonaromatic, heterocyclic bromides with aryl or heteroaryl bromides. The developed conditions use an air-stable Ni(II) source in the presence of a diamine ligand and a metal reductant to allow late-stage incorporation of saturated heterocyclic rings onto aryl halides in a functional-group tolerant manner.
- Molander, Gary A.,Traister, Kaitlin M.,ONeill, Brian T.
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p. 5771 - 5780
(2014/07/08)
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- Mn-catalyzed three-component reactions of imines/nitriles, grignard reagents, and tetrahydrofuran: An expedient access to 1,5-amino/keto alcohols
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An expedient Mn-catalyzed three-component synthesis of 1,5-amino/keto alcohols from Grignard reagents, imines/nitriles, and tetrahydrofuran (THF) is described, which deviates from the classic Grignard addition to imines/nitriles in THF solvent. THF is split and sewn in an unprecedented manner in the reaction, leading to the formation of two geminal C-C bonds via C-H and C-O cleavage. Mechanistic experiments and DFT calculations reveal radical and organo-Mn intermediates in the catalytic cycle and the α-arylative ring-opening of THF as the key reaction step.
- He, Ruoyu,Jin, Xiqing,Chen, Hui,Huang, Zhi-Tang,Zheng, Qi-Yu,Wang, Congyang
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p. 6558 - 6561
(2014/05/20)
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- Activation of sp3 and sp2 C-H bonds of oxygen containing heterocyclic molecules for alkylation and arylation reactions catalyzed by an iron complex
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Activation of both sp3 and sp2 CH bonds is reported using an efficient iron(III) complex (1) of a ligand (N2,N6-bis(2,6- diisopropylphenyl)pyridine-2,6-dicarboxamide: L). The iron(III) complex showed catalytic activity of CC coupling reaction of oxygen containing heterocycles, e.g. tetrahydrofuran (THF), with various alkyl, allyl and aryl Grignard reagents under ambient reaction conditions. Complex 1 demonstrated excellent activity and reactions were completed within 30 min to 1 h. A high turnover frequency (TOF) of 1700 h-1 using a low catalyst loading of 0.02 mol% was obtained for the reaction. Interestingly, the catalyst was selective in activation of the CH bond adjacent to the oxygen in various oxygen containing heterocyclic molecules to yield 2-substitituted products.
- Gartia, Yashraj,Ramidi, Punnamchandar,Cheerla, Sreevishnu,Felton, Charlette M.,Jones, Darin E.,Das, Bhaskar C.,Ghosh, Anindya
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p. 253 - 259
(2014/07/07)
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- Nickel complex catalyzed efficient activation of sp3and sp 2c-h bonds for alkylation and arylation of oxygen containing heterocyclic molecules
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A nickel(II) complex (1) of N,N'-bis(2,6-diisopropylphenyl)-2,6- pyridinedicarboxamido (L) ligand was examined for catalytic coupling of Grignard reagents with the C-H bond of oxygen containing heterocyclic compounds such as tetrahydrofuran and furan. The nickel( II) complex showed excellent activity in catalyzing C-H activation and further coupling with various Grignard reagents. The effective activation of the C-H bond proceeded under ambient reaction conditions with a short reaction time (1-2 h). The catalyst (1) displays high turnover frequency of 4,130 h-1with catalyst loading as low as 0.01 mol%. This catalytic route could prove to be an efficient mode of activation of sp3and sp2C-H bonds in various heterocycles for the preparation of synthetically and pharmaceutically relevant molecules. Springer Science+Business Media New York 2013.
- Gartia, Yashraj,Ramidi, Punnamchandar,Jones, Darin E.,Pulla, Sharon,Ghosh, Anindya
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p. 507 - 515
(2014/06/24)
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- Direct functionalization of tetrahydrofuran and 1,4-dioxane: Nickel-catalyzed oxidative C(sp3)-H arylation
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CHoose nickel: The nickel-catalyzed oxidative arylation of C(sp 3)-H bonds has been achieved. Several substituted arylboronic acids and various C(sp3)-H bonds were found to be suitable substrates for this novel transformation, which is likely to proceed through a radical pathway. This method allows the introduction of simple ether derivatives to construct α-arylated ethers. FG=functional group. Copyright
- Liu, Dong,Liu, Chao,Li, Heng,Lei, Aiwen
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supporting information
p. 4453 - 4456
(2013/05/21)
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- Direct benzylic C-H activation for C-O bond formation by photoredox catalysis
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Power of light: 1,4-dicyanonaphthalene (DCN) and light directly activates benzylic C-H bonds for intra- and intermolecular C-O bond formation. Arylalkyls have also been transformed directly into aryl ketones using water as a source of oxygen. EDG=electron-donating group, EWG=electron-withdrawing group. Copyright
- Pandey, Ganesh,Pal, Sujit,Laha, Ramkrishna
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p. 5146 - 5149
(2013/07/11)
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- Boronic acid catalysis as a mild and versatile strategy for direct carbo- and heterocyclizations of free allylic alcohols
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BAC to the future: Boronic acid catalysis (BAC) was applied to the direct activation of alcohols leading to the preparation of carbocycles (see scheme), benzofurans, tetrahydrofurans, pyrrolidines, pyrans, piperidines, and various polycyclic compounds. The reactions proceed under mild conditions that circumvent the use of reactive leaving groups like halides. Copyright
- Zheng, Hongchao,Ghanbari, Sina,Nakamura, Shinji,Hall, Dennis G.
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p. 6187 - 6190
(2012/08/13)
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- New method for C-H arylation/alkylation at α-position of cyclic aliphatic ethers by iron-oxide mediated reaction
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We report a new and efficient iron oxide catalyzed cross-coupling reaction between organometallic species such as alkyl/arylmagnesium halides or organolithium species and α-hydrogen bearing cyclic unbranched and branched aliphatic ethers via activation of C(sp3)-H. In the presence of 1 mol% of iron oxide, five and six membered unbranched cyclic ethers such as tetrahydrofuran and tetrahydropyran gave good to excellent yields of cross-coupled products. Whereas, in case of branched ether such as 2-methyltetrahydrofuran, it was observed that the arylation occurred at both the sides and gave moderate yields of a mixture of regioisomers. Among the organometallic species used, alkyl organometallic reagents gave less yields as compared to aryl organometallics.
- Singh, Parvinder Pal,Gudup, Satish,Aruri, Hariprasad,Singh, Umed,Ambala, Srinivas,Yadav, Mahipal,Sawant, Sanghapal D.,Vishwakarma, Ram A.
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experimental part
p. 1587 - 1597
(2012/03/22)
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- Alternative pathways for heck intermediates: Palladium-catalyzed oxyarylation of homoallylic alcohols
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The oxidative Heck arylation of homoallylic alcohols affords adducts in good yields and regioselectivities owing largely to coordination between the catalyst and hydroxy group (see scheme). Moreover, the Heck intermediate can be intercepted by an intramol
- Zhu, Chen,Falck, John R.
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supporting information; experimental part
p. 6626 - 6629
(2011/09/12)
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- Iron oxide mediated direct C-H arylation/alkylation at α-position of cyclic aliphatic ethers
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We report a new and efficient iron oxide catalyzed cross-coupling reaction between organometallic species such as alkyl/arylmagnesium halides or organolithium species and α-hydrogen bearing cyclic aliphatic ethers via activation of C(sp3)-H. This is the first example of iron oxide mediated direct C-C bond formation without expensive or toxic ligands.
- Singh, Parvinder Pal,Gudup, Satish,Ambala, Srinivas,Singh, Umed,Dadhwal, Sumit,Singh, Baldev,Sawant, Sanghapal D.,Vishwakarma, Ram A.
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supporting information; experimental part
p. 5852 - 5854
(2011/06/26)
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- Gold-catalysed cyclic ether formation from diols
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Gold(I) and (III) salts have been found to be highly effective at the catalysis of ether formation from alcohols. Intramolecular ether formation of a 1,5-diol was also achieved, with a stereoselectivity that indicates that an SN1 mechanism predominates. In an attempt to form a seven-membered ring, a stable 14-membered dimer product was also formed. Attempts to control the diastereoselectivity of the reaction using a chiral anionic counterion did not give products with a high de.
- Jiang, Xiaolu,London, Emma K.,Morris, David J.,Clarkson, Guy J.,Wills, Martin
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experimental part
p. 9828 - 9834
(2011/02/23)
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- Photochemical arylation of alkenols: Role of intermediates and synthetic significance
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A one-pot, tandem synthesis of cyclic ethers is obtained by addition of photogenerated phenyl cations to hydroxyalkenes. Thus, 2- (or 3-) phenyl-substituted tetrahydrofurans were prepared by irradiation of 4-chloro-N,N-dimethylaniline, -anisole, and -phenol with β-hydroxyalkenes and 2-benzyltetrahydrofurans with λ-hydroxyalkenes. With nonterminal alkenes [diastereomeric (E)- and (Z)-3-hexen-1-ols] trans-2-ethyl-3- aryltetrahydrofuran derivatives were stereoselectively formed from both isomers. The output of the photoreaction is structure and solvent dependent and is rationalized through the intermediacy of a phenonium ion from the addition of the primarily formed triplet phenyl cation to the alkenol double bond. Intramolecular addition of the OH group to form benzyl (aryl) tetrahydrofurans is favored in polar protic solvents, where hydride shifts to form aryltetrahydropyrans also occur, whereas in ethyl acetate, intermolecular addition of the chloride anion to the phenonium ion takes place. The mechanism of the above reactions is also discussed on the basis of computational data. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.
- Protti, Stefano,Dondi, Daniele,Fagnoni, Maurizio,Albini, Angelo
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scheme or table
p. 2240 - 2247
(2009/04/07)
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- Tandem olefin metathesis/hydrogenation at ambient temperature: Activation of ruthenium carbene complexes by addition of hydrides
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Sodium hydride activates ruthenium carbene complexes to catalyze hydrogenation reactions subsequent to ring closing olefin metathesis. Under these conditions, hydrogenation of cyclopentenols proceeds smoothly at ambient temperature and under 1 atm of hydrogen in toluene. An alternative protocol was developed that involves the formation of hydrogen in situ by reaction of excess sodium hydride with protic functional groups and water.
- Schmidt, Bernd,Pohler, Michael
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p. 2512 - 2517
(2007/10/03)
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- Oxygen versus carbon acidity in the side-chain fragmentation of 2-, 3-, and 4-arylalkanol radical cations in aqueous solution: The influence of the distance between the OH group and the aromatic ring
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The decay of 2-, 3-, and 4-(4-methoxyphenyl) alkanol radical cations in water has been kinetically investigated by pulse radiolysis, the reaction products being determined either by steady-state γ-radiolysis experiments or by reactions promoted by potassium 12-tungstocobalt(III)ate, a bona fide one-electron oxidant. It was found that all 2-arylalkanol radical cations react with -OH at a diffusion-controlled rate leading to Cα-Cβ bond cleavage products. This suggests a reaction induced by deprotonation at the alcoholic OH group. In acidic medium (pH = 4), the rates of decay of these radical cations are much lower leading to Cα-H deprotonation (for 2-(4-methoxyphenyl)ethanol (1.+) and 1-(4-methoxyphenyl)-2-propanol (4.+)) or Cα-Cβ bond cleavage products (for 1-phenyl-2-(4-methoxyphenyl)ethanol (5.+) and 2-methyl-1-phenyl-3-(4-methoxyphenyl)-2-propanol (6.+)). The 3-(4-methoxyphenyl)propanol radical cation (2.+) reacts in acidic medium (pH = 4) at a rate close to that of 1.+, undergoing Cα-H deprotonation. In contrast, in basic medium (pH = 10) 2.+ produces 3-(4-methoxyphenyl)propanal, with a rate ~5-fold lower than that of 1.+, again indicating a reaction promoted by O - H deprotonation. With 4-(4-methoxyphenyl)-1-butanol radical cation (3.+), products of Cα - H deprotonation were observed both in the presence and in the absence of -OH. These results are discussed in terms of a mechanistic dichotomy, that is, carbon versus oxygen acidity, which appears to be operating for 2-and 3-arylalkanols whereas with 4-arylalkanol radical cations only carbon acidity is observed.
- Baciocchi, Enrico,Bietti, Massimo,Manduchi, Laura,Steenken, Steen
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p. 6624 - 6629
(2007/10/03)
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- An unprecedented coupling reaction of arylmagnesium compounds with tetrahydrofuran providing 2-aryltetrahydrofuran mediated by an iodoalkane- EtMgBr system
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An extremely facile coupling reaction between arylmagnesium compounds and THF by means of an iodoalkane-EtMgBr system provides 2- aryltetrahydrofurans. One-pot synthesis of 2thienyltetrahydrofuran is achieved from thiophene and THF using this coupling reaction.
- Inoue, Atsushi,Shinokubo, Hiroshi,Oshima, Koichiro
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p. 1582 - 1584
(2007/10/03)
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- A mild method for generation of p-methoxybenzyl cation through NIS- mediated activation of p-methoxybenzyl 4-pentenyl ether
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A mild and facile method for generation of p-methoxybenzyl cation through NIS-mediated activation of p-methoxybenzyl 4-pentenyl ether was achieved. Under the present activation conditions, various alcohols were convened to the corresponding p-methoxybenzyl ethers. A scope and limitation of the present p-methoxybenzylation reaction was also investigated.
- Okada,Kitagawa,Fujita,Taguchi
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p. 8135 - 8142
(2007/10/03)
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- γ-Lithioalkoxides via Reductive Lithiation of Oxetanes by Aromatic Radical Anions
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Oxetanes are cleaved at 0 deg C in tetrahydrofuran by lithium 4,4'-di-tert-butylbiphenylide, giving lithium γ-lithioalkoxides which can provide 2-substituted tetrahydrofurans by trapping with aldehydes and ketones followed by acid cyclization of the resulting 1,4-diols; the cuprates of these dianions undergo conjugate addition and nucleophilic substitution reactions.
- Mudryk, Boguslaw,Cohen, Theodore
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p. 5657 - 5659
(2007/10/02)
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- PREPARATION OF CYCLIC ETHERS VIA OXIDATIVE CYCLISATION OF 2-(4-HYDROXYALKYL) AND 2-(5-HYDROXYALKYL)FURANS WITH DDQ.
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Reaction of 2-(4- or 5-hydroxyalkyl)furans with DDQ leads to the smooth formation of cyclic ethers under neutral conditions, but aromatic analogues do not give useful yields of desired products.
- Harwood, Laurence M.,Robertson, Jeremy
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p. 5175 - 5176
(2007/10/02)
-
- Thallium in Organic Synthesis. 61. Intramolecular Capture of Radical Cations from Thallium(III) Trifluoroacetate Oxidation of Arylalkanoic Acids and Arylalkanols. New Routes to Oxygen Heterocycles
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Treatment of electron-rich arylpropionic acids with TTFA in TFA containing a small amount of BF3*etherate results in the formation of dihydrocoumarins and spirocyclohexadienone lactons by initial formation of aromatic radical cations followed by intramolecular cyclization involving the side-chain carboxyl group.The scope and limitations of this reaction with respect to aromatic substitution and the length of the alkanoic acid side chain have been examined; the reaction has been extended with analogous results to 1-naphthalenylalkanoic acids.Oxidation of a series of homologous phenyl- and naphthalenyl-1-alknols with TTFA under similar conditions results in intramolecular cyclization to give fused or pendant cyclic esters.It is suggested that the observed propensity for intramolecular cyclization may due to complexation of both the aryl group and the side-chain basic substituent (-COOH or -OH) with thallium(III).
- Taylor, Edward C.,Andrade, Juan G.,Rall, Gerhardus J. H.,Turchi, Ignatius J.,Steliou, Kosta,et al.
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p. 6856 - 6863
(2007/10/02)
-