- Chemoselective Nucleophilic Functionalizations of Aromatic Aldehydes and Acetals via Pyridinium Salt Intermediates
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The development of a novel chemoselective functionalization can diversify the strategy for synthesizing the target molecules. The perfect chemoselectivity between aromatic and aliphatic aldehydes is difficult to achieve by the previous methods. The aromatic aldehyde-selective nucleophilic addition in the presence of aliphatic aldehydes was newly accomplished. Namely, the aromatic aldehyde-selective nucleophilic addition using arenes and allyl silanes proceeded in the presence of trialkylsilyl triflate and 2,2′-bipyridyl, while the aliphatic aldehydes completely remained unchanged. The reactive pyridinium-type salt intermediate derived from an aromatic aldehyde chemoselectively underwent the nucleophilic substitution. Moreover, the aromatic acetals as the protected aldehydes could be directly transformed into similar pyridinium salt intermediates, which reacted with various nucleophiles coexisting with the aliphatic aldehydes.
- Kawajiri, Takahiro,Kato, Maho,Nakata, Hiroki,Goto, Ryota,Aibara, Shin-Yo,Ohta, Reiya,Fujioka, Hiromichi,Sajiki, Hironao,Sawama, Yoshinari
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p. 3853 - 3870
(2019/03/07)
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- Unique chemoselective Mukaiyama aldol reaction of silyl enol diazoacetate with aldehydes and acetals catalyzed by MgI2 etherate
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Functionalized diazo acetoacetates are prepared by an efficient Mukaiyama aldol reaction between 3-TBSO-2-diazo-3-butenoate with aldehydes and acetals under mild reaction conditions. A variety of substituted aldehydes and the corresponding acetals are both accessible in good to excellent yields through this methodology. MgI2 etherate (MgI2·(OEt2)n) is the preferred catalyst and, the addition proceeds without decomposition of the diazo moiety. In addition, this MgI2·(OEt2)n-catalyzed Mukaiyama aldol reaction shows unique chemoselectivity towards aldehydes and acetals.
- Meng, Xiangwei,Pan, Haokun,Zhong, Tengjiang,Zhang, Xingxian
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- Preparation of acetals from aldehydes and alcohols under basic conditions
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A new, simple protocol for the synthesis of acetals under basic conditions from non-enolizable aldehydes and alcohols has been reported. Such reactivity is facilitated by a sodium alkoxide along with a corresponding trifluoroacetate ester, utilizing formation of sodium trifluoroacetate as a driving force for acetal formation. The usefulness of this protocol is demonstrated by its orthogonality with various acid-sensitive protecting groups and by good compatibility with functional groups, delivering synthetically useful acetals complementarily to the synthesis under acidic conditions from aldehydes and alcohols.
- Grabowski, Jakub,Granda, Jaros?aw M.,Jurczak, Janusz
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p. 3114 - 3120
(2018/05/17)
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- Ru(II)-functionalized SBA-15 as highly chemoselective, acid free and sustainable heterogeneous catalyst for acetalization of aldehydes and ketones
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Combining electron deficient Ru(II) coordination sites with organofunctionalized SBA-15, (L)Ru(II)@SBA-15, result in a mild, neutral, water scavenger free and chemo-selective acetalization catalyst for cyclic/acyclic acetals. Vacant coordination sites of ruthenium in (L)Ru(II)@SBA-15 activates protecting groups as well as reactants simultaneously and restricts the reverse acetalization reaction. Synthesized (L)Ru(II)@SBA-15 catalyst has been thoroughly characterized and act as competitive catalyst compared to conventional acid catalysts. (L)Ru(II)@SBA-15 performs high catalytic activity as well as selectivity within 20 min with high TOF. The catalyst can be recycled and reaction parameters are optimized.
- Lazar, Anish,Betsy,Vinod,Singh
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- Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions
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We report here on the use of ethyl nitroacetate as a glycine template to produce α-amino esters. This started with a study of its condensation with various arylacetals to give ethyl 3-aryl-2-nitroacrylates followed by a reduction (NaBH4 and then zinc/HCl) into α-amino esters. The scope of this method was explored as well as an alternative with arylacylals instead. We also focused on various [2 + 3] cycloadditions, one leading to a spiroacetal, which led to the undesired ethyl 5-(benzamidomethyl)isoxazole-3-carboxylate. The addition of ethyl nitroacetate on a 5-methylene-4,5-dihydrooxazole using cerium(IV) ammonium nitrate was also explored and the synthesis of other oxazole-bearing α-amino esters was achieved using gold(I) chemistry.
- Gagnot, Glwadys,Hervin, Vincent,Coutant, Eloi P.,Desmons, Sarah,Baatallah, Racha,Monnot, Victor,Janin, Yves L.
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supporting information
p. 2846 - 2852
(2018/11/27)
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- Phosphorylated Polyacrylonitrile Fibers as an Efficient and Greener Acetalization Catalyst
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A novel solid acid catalyst (PANEAPF) is developed by immobilization of phosphoric acid on polyacrylonitrile fiber through covalent bonding. Various characterization techniques such as elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), etc. are utilized to confirm the successful grafting and the stability of the fiber catalysts during application. PANEAPF shows high catalytic activity in the acetalization of aldehydes owing to the high utilization efficiency of its functionalized acid sites. In addition, the strong polarity micro-environment in the surface layers of PANEAPF make it highly suitable for catalytic application in both water and alcohol. Furthermore, the fiber catalyst can be applied to the acetalization of aldehydes in a continuous-flow process at room temperature, and shows excellent reactivity and superior recyclability (over 20 times). The many advantages of PANEAPF such as simple preparation, convenient regulation of acid amount, high durability, and eco-friendly process make it very attractive for fixed-bed reactors in the chemical industry.
- Xu, Gang,Cao, Jian,Zhao, Yali,Zheng, Lishuo,Tao, Minli,Zhang, Wenqin
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supporting information
p. 2565 - 2575
(2017/09/25)
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- Photochemical Approaches to the Bilobalide Core
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Bilobalide is a tetracyclic sesquiterpene containing three contiguous γ-lactone rings and an unusual tert-butyl group, which is found in the leaves of the ginkgo tree (Ginkgo biloba). Three different photochemical approaches towards bilobalide's unique sk
- Emsermann, Jens,Opatz, Till
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p. 3362 - 3372
(2017/06/29)
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- Dialkyl Ether Formation by Nickel-Catalyzed Cross-Coupling of Acetals and Aryl Iodides
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A new substrate class for nickel-catalyzed C(sp3) cross-coupling reactions is reported. α-Oxy radicals generated from benzylic acetals, TMSCl, and a mild reductant can participate in chemoselective cross-coupling with aryl iodides using a 2,6-bis(N-pyrazolyl)pyridine (bpp)/Ni catalyst. The mild, base-free conditions are tolerant of a variety of functional groups on both partners, thus representing an attractive C-C bond-forming approach to dialkyl ether synthesis. Characterization of a [(bpp)NiCl] complex relevant to the proposed catalytic cycle is also described.
- Arendt, Kevin M.,Doyle, Abigail G.
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supporting information
p. 9876 - 9880
(2015/08/19)
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- The asymmetric Cu(ii)-indolinylmethanol complex catalyzed Diels-Alder reaction of 2-vinylindoles with β,γ-unsaturated α-ketoesters: An efficient route to functionalized tetrahydrocarbazoles
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An efficient asymmetric Diels-Alder reaction of 2-vinylindoles with β,γ-unsaturated α-ketoesters has been developed for the construction of functionalized tetrahydrocarbazoles. The products were obtained in high yields (up to 96%) with good stereoselectiv
- Ouyang, Banlai,Yu, Tingting,Luo, Renshi,Lu, Gui
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supporting information
p. 4172 - 4176
(2014/06/10)
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- Syn-selective kobayashi aldol reaction using acetals
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The Kobayashi aldol reaction has been used to construct anti-aldol products by remote stereoinduction. Since the product of the Kobayashi aldol reaction has a typical polyketide structure, this reaction has been applied to the total synthesis of natural p
- Tsukada, Hiroyuki,Mukaeda, Yuki,Hosokawa, Seijiro
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supporting information
p. 678 - 681
(2013/04/10)
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- Efficient enantioselective synthesis of dihydropyrans using a chiral N, N ′-dioxide as organocatalyst
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The bifunctional organocatalyst C3 N,N′-dioxide has been successfully applied to the asymmetric cascade Michael/hemiacetalization reaction of α-substituted cyano ketones and β,γ-unsaturated α-ketoesters for the synthesis of multifunctionalized chiral dihydropyrans. The corresponding products were obtained in excellent yields (up to 99%) with high to excellent enantioselectivities (up to 99% ee).
- Feng, Juhua,Fu, Xuan,Chen, Zhenling,Lin, Lili,Liu, Xiaohua,Feng, Xiaoming
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supporting information
p. 2640 - 2643
(2013/07/19)
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- Role of the 4,6-O-acetal in the regio-and stereoselective conversion of 2,3-di-O-sulfonyl-b-D-galactopyranosides to D-idopyranosides
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The recently reported conversion of 2,3-di-O-sulfonyl-D-galactopyranosides to D-idopyranosides has provided an efficient route to obtaining orthogonally-protected idopyranoside building blocks with a b-1,2-cis glycosidic linkage. In an effort to expand th
- Hevey, Rachel,Chen, Xining,Ling, Chang-Chun
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- Enantioselective copper-catalyzed conjugate addition of trimethylaluminium to β,γ-unsaturated α-ketoesters
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Not a cop out: The copper-catalyzed asymmetric conjugate addition of organometallic reagents to Michael acceptors is an important methodology for forming a C-C bond in an enantioselective manner. Such an addition of Me 3Al to β,γ-unsaturated α-
- Gremaud, Ludovic,Alexakis, Alexandre
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supporting information; experimental part
p. 794 - 797
(2012/03/09)
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- Mesoporous aluminosilicate-catalyzed allylation of carbonyl compounds and acetals
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A mesoporous aluminosilicate (Al-MCM-41) was found to be an effective heterogeneous catalyst for the reaction of both carbonyl compounds and acetals with allylsilanes to afford the corresponding homoallyl silyl ethers and homoallyl alkyl ethers, respectively. Both the mesoporous structure and the presence of aluminum moiety were indispensable for the high catalytic activity of Al-MCM-41. Moreover, Al-MCM-41 could catalyze the reaction of acetals chemoselectively in the presence of the corresponding carbonyl compounds. The solid acid catalyst Al-MCM-41 could be recovered easily by filtration and could be reused three times without a significant loss of catalytic activity.
- Ito, Suguru,Hayashi, Akira,Komai, Hirotomo,Yamaguchi, Hitoshi,Kubota, Yoshihiro,Asami, Masatoshi
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supporting information; experimental part
p. 2081 - 2089
(2011/04/19)
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- Dichotomous reactivity in the reaction of triethyl- and triphenylphosphane HBr salts with dimethyl acetals: A novel entry to α-alkoxy-functionalized ylides and general synthesis of vinyl ethers and alkoxy dienes
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The discovery of dichotomous reactivity in the reaction of trialkyl- vs. triphenylphosphane HBr salts with acetals allows entry to functionalized α-methoxy phosphonium salts and a novel process for tertiary phosphane methylation. The new protocol opens a general entry to the synthesis of vinyl ethers and differentially substituted 1,3-dienes via Wittig reactions of the functionalized ylides derived from the α-methoxy phosphonium salts.
- Das, Priyabrata,McNulty, James
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supporting information; experimental part
p. 3587 - 3591
(2010/09/05)
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- Efficient acetalisation of aldehydes catalyzed by titanium tetrachloride in a basic medium
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The acetalisation of aliphatic and aromatic aldehydes is achieved in a basic medium by using catalytic amount of Ti(IV) chloride in MeOH in the presence of NH3 or Et3N. The present protocol shows many advantages over the well known base or acid catalysis: in fact, in contrast to base-promoted acetalisation, aldehydes with electron-rich carbonyl groups react easily, enolizable aldehydes do not undergo aldol condensation and, in contrast to acid-catalysis, migration of the double bond does not occur in the preparation of α,β-unsaturated acetals.
- Clerici, Angelo,Pastori, Nadia,Porta, Ombretta
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p. 15679 - 15690
(2007/10/03)
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- Unexpected products in the LiA1H4/AlCl3-reduction of 3-O-substituted and N-benzyloxycarbonyl-protected 4,6-O-[2-methoxybenzylidene]-α-D-glucosamine derivatives
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The reductive cleavage of benzyl 2-benzyloxycarbonylamino-2-deoxy-4,6-O-(2-methoxybenzylidene)-α-D- glucopyranoside 2 with LiA1H4-AlCl3 gave the corresponding 4-O-(2-methoxybenzyl) ether along with the 6-O-ether as expected. When, ho
- Wessel, Hans Peter,Plessis, Isabelle,Cassel, Stephanie,Arnold, Wolf
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p. 789 - 806
(2007/10/03)
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- DIHYDROPYRANS OBTAINED IN THE REACTION BETWEEN 2-(ACENAPHTHYLEN-1-YL)ETHANOL AND CABONYLIC DERIVATIVES
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The reaction of 2-(acenaphthylen-1-yl)ethanol with a series of aldehydes or ketones, as well as with dimethylketals or vinylic ethers, was investigated. Structure proofs for the dihydropyrans obtained in this reaction are presented; possible mechanisms explaining the reaction course are proposed.
- Razus, Alexandru C.,Gheorghiu, Mircea D.,Bartha, Emeric
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p. 215 - 228
(2007/10/03)
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- 2-METHOXYBENZYLIDENE ACETALS, EFFICIENT PROTECTING GROUPS FOR ALDOHEXOPYRANOSIDES
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2-Methoxybenzaldehyde dimethyl acetal is an excellent protecting group for aldohexopyranosides by way of the formation of their 4,6-O-(2-methoxybenzylidene) acetals.
- Box, Vernon,Hollingsworth, Rawle,Roberts, Earle
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p. 1713 - 1716
(2007/10/02)
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