- Metal-free approach for hindered amide-bond formation with hypervalent iodine(iii) reagents: application to hindered peptide synthesis
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A new bio-inspired approach is reported for amide and peptide synthesis using α-amino esters that possess a potential activating group (PAG) at the ester residue. To activate the ester functionality under mild metal-free conditions, we exploited the facile dearomatization of phenols with hypervalent iodine(iii) reagents. Using a pyridine-hydrogen fluoride complex, highly reactive acyl fluoride intermediates can be successfully generated, thereby allowing for the smooth formation of sterically hindered amides and peptides from bulky amines and α-amino esters, respectively.
- Lee, Hyo-Jun,Huang, Xiao,Sakaki, Shigeyoshi,Maruoka, Keiji
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supporting information
p. 848 - 855
(2021/02/09)
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- Nickel-catalyzed deallylation of aryl allyl ethers with hydrosilanes
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An efficient and mild catalytic deallylation method of aryl allyl ethers is developed, with commercially available Ni(COD)2 as catalyst precursor, simple substituted bipyridine as ligand and air-stable hydrosilanes. The process is compatible with a variety of functional groups and the desired phenol products can be obtained with excellent yields and selectivity. Besides, by detection or isolation of key intermediates, mechanism studies confirm that the deallylation undergoes η3-allylnickel intermediate pathway.
- Ding, Guangni,Fan, Sijie,Wang, Jingyang,Wang, Yu,Wu, Xiaoyu,Xie, Xiaomin,Yang, Liqun,Zhang, Zhaoguo
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- Direct hydroxylation of benzene and aromatics with H2O2 catalyzed by a self-assembled iron complex: Evidence for a metal-based mechanism
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An iminopyridine Fe(ii) complex, easily prepared in situ by self-assembly of cheap and commercially available starting materials (2-picolylaldehyde, 2-picolylamine, and Fe(OTf)2 in a 2 : 2 : 1 ratio), is shown to be an effective catalyst for the direct hydroxylation of aromatic rings with H2O2 under mild conditions. This catalyst shows a marked preference for aromatic ring hydroxylation over lateral chain oxidation, both in intramolecular and intermolecular competitions, as long as the arene is not too electron poor. The selectivity pattern of the reaction closely matches that of electrophilic aromatic substitutions, with phenol yields and positions dictated by the nature of the ring substituent (electron-donating or electron-withdrawing, ortho-para or meta-orienting). The oxidation mechanism has been investigated in detail, and the sum of the accumulated pieces of evidence, ranging from KIE to the use of radical scavengers, from substituent effects on intermolecular and intramolecular selectivity to rearrangement experiments, points to the predominance of a metal-based SEAr pathway, without a significant involvement of free diffusing radical pathways.
- Capocasa, Giorgio,Olivo, Giorgio,Barbieri, Alessia,Lanzalunga, Osvaldo,Di Stefano, Stefano
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p. 5677 - 5686
(2017/12/07)
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- An efficient and chemoselective deprotection of aryl tert-butyldimethylsilyl (TBDMS) ethers by NaCN
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Phenolic tert-butyldimethylsilyl (TBDMS) ethers can be deprotected to yield phenols in excellent yield using sodium cyanide (NaCN) as catalyst in ethanol. The deprotectation of various phenolic TBDMS ethers were found to be very convenient, fast, high yielding and chemoselective.
- Qiao, Xue-Jun,Hou, Xiao,Fang, Wu-Hong,Bao, Xue-Fei,Chen, Guo-Liang
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p. 899 - 904
(2016/05/19)
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- Cross Redox Coupling of Aryl-Aldehydes and p-Benzoquinone
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Herein, we report an unprecedented Cross Redox Coupling (CRC) reaction catalyzed by Cu(OAc)2·H2O. As a proof-of-concept, direct coupling of aromatic aldehydes (or alcohols) and p-benzoquinone led to an ester in the presence of the Cu(II)-TBHP combination. During the coupling process, the C-H bond of the aldehydes was converted directly to a C-O bond. Mechanistically, we propose that the reaction proceeded via a radical pathway. In addition, atom and electron economies were well-conserved during this CRC reaction.
- Bose, Anima,Mal, Prasenjit
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p. 11219 - 11225
(2015/11/18)
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- Synthesis of industrially important aromatic and heterocyclic ketones using hierarchical ZSM-5 and Beta zeolites
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Hierarchical ZSM-5 and Beta zeolites were investigated in the synthesis of wide range of industrially important aromatic/heterocyclic ketones by Friedel-Crafts acylation and benzoylation reactions. For comparative study, conventional ZSM-5 and Beta, and amorphous mesoporous Al-MCM-41 were investigated. Hierarchical zeolites were prepared by multi-ammonium structure directing agents whereas conventional zeolites were prepared by mono-ammonium structure directing agents. Among the catalysts investigated in this study, hierarchical Beta exhibited the highest reactant conversion in the acylation and benzoylation reactions. In this study, the systematic assessment of the catalytic activity of acid catalysts for wide range of aromatic and heterocyclic compounds is shown under one umbrella. To the best of our knowledge, these reactions over hierarchical zeolites (ZSM-5 and Beta) are reported here for the first time. Structure activity relationship is explained based on the physico-chemical properties, molecular size, reactivity of reactants, and reaction mechanism. Catalysts can be easily recovered and reused with negligible loss in the catalytic activity.
- Kore, Rajkumar,Srivastava, Rajendra,Satpati, Biswarup
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p. 129 - 141
(2015/09/28)
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- Synthesis of tricyclic precursors of cyclitols
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Stereoselective syntheses of three tricyclic cyclohexenones are described. These compounds were conceived as novel precursors of synthetic conduritols, quercitols, and inositols because they allow diastereoselective C=O reductions, C=C osmylations, and C=C epoxidations to be performed. These functionalizations created up to three uniformly configured oxygen-bearing stereocenters. One of the follow-up products was a tricycle that was amenable to successive cleavages of its 1,4-dioxane and 1,3-dioxane rings. This rendered the pentaesters of neo-quercitol, which contain five stereogenic C-O bonds, with ds = 85:15. Georg Thieme Verlag Stuttgart New York.
- Aucktor, Johannes,Anselmi, Chiara,Brückner, Reinhard,Keller, Manfred
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p. 1312 - 1318
(2014/06/10)
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- Cerium(IV) sulfate tetrahydrate: A catalytic and highly chemoselective deprotection of THP, MOM, and BOM ethers
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Tetrahydropyranyl (THP), methoxymethyl (MOM), and benzyloxymethyl (BOM) phenyl/alkyl ethers were efficiently cleaved to the corresponding parent hydroxyl compounds in good yields using catalytic amounts of Ce(SO 4)2·4H2O by microwave-assisted or conventional heating in methanol solution. Intramolecular and competitive experiments demonstrated the chemoselective deprotection of THP ethers in the presence of triisopropylsilyl (TIPS) and tert-butyldiphenylsilyl (TBDPS) phenyl ethers.
- González-Calderón, Davir,González-González, Carlos A.,Fuentes-Benítez, Aydeé,Cuevas-Yá?ez, Erick,Corona-Becerril, David,González-Romero, Carlos
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p. 7164 - 7166
(2013/12/04)
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- First total chemical synthesis of natural acyl derivatives of some phenolglycosides of the family Salicaceae
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The total synthesis of certain natural phenolglycosides of the family Salicaceae, namely: salireposide, populosides A, B, and C and not occurring in plants desoxysalireposide (2-(β-d-glucopyranosyloxy)-benzylbenzoate) and per-acetate of iso-salireposide (2-(β-d-glucopyranosyloxy)-5-benzoyloxy benzyl alcohol), starting from readily available phenols and glucose was accomplished. A simple method for the synthesis of phenolglycosides derivatives of 2-acyloxy salicyl and gentisyl alcohol was developed. The key step of these natural products' synthesis is a selective removal of acetyl groups in the presence of other acyl groups.
- Belyanin, Maxim L.,Stepanova, Elena V.,Ogorodnikov, Vladimir D.
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- An improved synthesis of hydroxy aryl ketones by fries rearrangement with methanesulfonic acid/methanesulfonic anhydride
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Methanesulfonic acid treated with methanesulfonic anhydride effectively mediates the Fries rearrangement of aryl esters to give hydroxy aryl ketones with high yields. Georg Thieme Verlag Stuttgart · New York.
- Jeon, Ingyu,Mangion, Ian K.
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experimental part
p. 1927 - 1930
(2012/10/08)
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- HF-Pyridine: A versatile promoter for monoacylation/sulfonylation of phenolic diols and for direct conversion of t-butyldimethylsilyl ethers to the corresponding acetates
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Monoacylation and trifluoromethanesulfonylation of phenolic diols were achieved by the aid of HF-pyridine, whereas diacylation occurred with pyridine alone. Furthermore, HF-pyridine was found to promote the direct conversion of t-butyldimethylsilyl ethers to the corresponding acetates.
- Michigami, Kyosuke,Yoshimoto, Kazuya,Hayashi, Masahiko
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scheme or table
p. 138 - 139
(2012/03/09)
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- Unsymmetric main-chain liquid crystal elastomers with tuneable phase behaviour: Synthesis and mesomorphism
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The synthesis of a new series of polysiloxane-based, main-chain liquid crystal elastomers (MC-LCEs) containing unsymmetric mesogenic units is described. The structure of the mesogenic monomers, spacers and cross-linkers has been varied systematically in order to tune the thermotropic behaviour of the networks. Three unsymmetric mesogens were studied, characterised by having two aromatic rings as the rigid core and two different alkoxy chains. Smectic A or nematic phases were observed, depending on the length of the alkoxy chains. These mesogens were combined with three different spacers, a flexible hexamethyltrisiloxane (S1) and two aromatic bis(dimethylsilyloxy)benzene with the silyl groups disposed para (S2) or meta (S3). To form the MC-LCEs, two cross-linkers were chosen, one flexible 2,4,6,8-tetramethylcyclooctasiloxane (C1) and a rigid, aromatic tris(dimethylsilyl)benzene (C2). The elastomers showed low glass transition temperatures (below 0 °C) and low clearing temperatures (between 30 and 72 °C), as such presenting liquid crystalline properties at room temperature. The transition temperatures could be tuned by a simple choice of the components; for instance, the clearing temperature decreased as aromatic spacers or cross-linkers were introduced. In contrast, the glass transition temperature did not depend on the cross-linker or mesogen used and showed only a small dependence on the structure of the spacer. The phase behaviour of the MC-LCEs was affected greatly by the spacer used and networks containing the trisiloxane spacer systematically exhibited the smectic C phase. The insertion of aromatic spacers favoured the formation of a nematic phase over a smectic phase when the flexible cross-linker, C1, was used. This behaviour was enhanced by the addition of the aromatic cross-linker C3, so that the smectic C phase was suppressed totally and only a nematic phase was observed. The synthesis of the components of MC-LCEs is presented and the structure-thermal properties relationships of the MC-LCEs are discussed.
- Amela-Cortes, Maria,Heinrich, Benoit,Donnio, Bertrand,Evans, Kenneth E.,Smith, Chris W.,Bruce, Duncan W.
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experimental part
p. 8427 - 8435
(2012/01/17)
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- Mesomorphic properties of chiral nematic star-shaped liquid crystals containing melitose as cores
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Three star-shaped compounds (SSCs, c1-c3), are synthesized by using melitose as the chiral core and monacid (b1, b2 and b3) as side arms, respectively. The side arms (b1, b2 and b3), in which terminal chains are different, are introduced into the hydroxyl groups of melitose by esterification, respectively. The chemical structures of c1-c3 are confirmed by FT-IR and 1H NMR. The roles played by the chiral core and the side arms in the mesomorphic properties of the SSCs are studied. b1 is not a liquid crystal (LC), while b2 and b3 are nematic LCs. c1 is not a LC, while c2 and c3 are star-shaped LCs (SSLCs) and exhibit fingerprint texture of chiral nematic. c1, c2 and c3 are all levo-SSCs, which are different from their parent cores. The absolute value of their specific rotation increases with the increase of the terminal chain length of the side arms. The melting temperature of SSCs decreases with the increase of the terminal chain length of the side arms. For c2-c3, their mesomorphic region increases with the increase of the terminal chain length of the side arms. The results suggest that the LC properties of the side arms play an important role in inducing LC properties of the SSCs and the chiral core induces the chiral nematic of SSLCs, which contain the nematic LCs as the side arms.
- Tian, Mei,Zhang, Bao-Yan,Cong, Yue-Hua,He, Xiao-Zhi,Zhang, Bing
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experimental part
p. 131 - 135
(2010/03/25)
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- Synthesis and properties of 2-phenylbenzoxazole-based luminophores for in situ photopolymerized liquid-crystal films
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We report the synthesis of a series of blue-emitting 2-phenylbenzoxazoles (PBOs) substituted at either the 5- or 6-position of the benzoxazole ring and the para-position of the phenyl substituent. The thermal and optical properties of the materials can be rationalized in terms of the position of the substituent at the benzoxazole moiety and the electron-withdrawing or electron-donating character of the substituents. From the results, we conclude that the combination of an electron-donating substituent at the benzoxazole fragment and an electron-withdrawing one at the phenyl fragment has a more marked effect on the electronic properties of the aromatic PBO core than other possibilities. This particular combination gives luminophores that are suitable for optical applications on the basis of their high emission efficiency and photostability. In view of that, oriented films were prepared by in situ polymerization of a mixture of a liquid crystalline direactive matrix containing 5% (w/w) of the luminophore. The films exhibit linearly polarized emission.
- Gimenez, Raquel,Oriol, Luis,Pinol, Milagros,Serrano, Jose Luis,Vinuales, Ana I.,Fisher, Thomas,Stumpe, Joachim
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p. 304 - 319
(2007/10/03)
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- Quinoxalines. Part 13: Synthesis and mass spectrometric study of aryloxymethylquinoxalines and benzo[b]furylquinoxalines
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A series of new aryloxymethylquinoxalines, benzo[b]- and naphtho[2,1-b]furylquinoxalines, possessing potential biological activity, was prepared, characterized by IR and NMR spectroscopy and their electron ionization (EI) mass spectra studied in detail. The aryloxymethylquinoxalines were obtained by reacting halogenomethylquinoxalines with bifunctional O-nucleophiles. The benzo[b]furylquinoxalines and naphtho[2,1-b] furylquinoxalines were prepared via two routes, which differed in the order of the two cyclization steps involved in the syntheses. The composition of the ions obtained by EI mass spectrometry were determined by accurate mass measurements and the fragmentation pathways clarified by B/E linked scans and collision induced dissociation. The mass spectrometric behaviour of the compounds studied as to the possible loss of OH· radicals proved to be very characteristic.
- Starke, Ines,Sarodnick, Gerhard,Ovcharenko, Vladimir V.,Pihlaja, Kalevi,Kleinpeter, Erich
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p. 6063 - 6078
(2007/10/03)
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- Effects of chemical variations on the mesophase behavior of new fluorinated poly(vinylcyclopropane)s
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Several new structures of fluorinated polymers poly(1)-poly(9) were prepared by free radical ring opening polymerization of vinylcyclopropane monomers 1-9 containing different fluorinated side groups of the type -(CH2)n(CF2) pF. While in poly(1)-poly(3) p varied from 6 to 10 for a fixed n=2, in poly(4)-poly(6) n increased from 3 to 5 at the given p=8. In poly(7) and poly(8) a phenyl ring was incorporated to elongate the mesogenic side group (n=2; p=6 and 8, respectively), that was further separated from the polymer backbone by a methylene spacer (m=11) in poly(9). Therefore, the effects of various chemical variations of the polymer structure on the mesophase behavior could be assessed. The polymers were in fact co-polymers comprising both 1,5-linear and cyclobutane-ring isomer units. In any case they formed smectic mesophase(s) owing to the special character of the perfluorinated chains. The order and the isotropization temperature (Ti) of the mesophase were enhanced by increasing p, but Ti lowered with increasing n. Extension of the side group by insertion of a phenyl ring improved Ti. Wide angle X-ray diffraction studies clarified the nature of the different smectic phases, the occurrence of which was discussed in terms of the ability of the fluorinated side groups to pack antiparallel in either a partly or fully interdigitated structure. Co-polymers of 3 with a non-mesogenic, not fluorinated co-monomer 10 were also prepared with different chemical compositions. Co-polymerization was found to be another effective means of modifying the mesophase behavior of the poly(vinylcyclopropane)s.
- Ragnoli, Marina,Pucci, Elena,Bertolucci, Massimo,Gallot, Bernard,Galli, Giancarlo
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p. 283 - 292
(2007/10/03)
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- An efficient strategy for the synthesis of chiral liquid crystals using Evans' methodology
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The synthesis of liquid crystal compound 2 was achieved using Evans' methodology. The strategy was based on three key synthetic reactions: alkylation of chiral amide enolates, Mitsunobu and, finally, esterification. The final compound presents a stable smectic A phase.
- Merlo, Aloir A.,Fernandes, Mirele S.
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p. 1167 - 1178
(2007/10/03)
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- Facile and selective deprotection of aryl acetates using sodium perborate under mild and neutral conditions
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A variety of aryl acetates are cleaved to the corresponding phenols using sodium perborate in methanol under mild conditions (25°C). The effectiveness of this protocol is manifested in its tolerance of different functional groups and selectivity of deprotection towards aryl acetates whereas alkyl acetates are found to be unreactive under these reaction conditions.
- Bandgar, Babasaheb P.,Uppalla, Lavkumar S.,Sadavarte, Vaibhav S.,Patil, Suresh V.
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p. 1273 - 1276
(2007/10/03)
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- The mesophase structure of chiral liquid crystalline polysiloxanes for electro-optical applications
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Homopolysiloxanes poly(1) and poly(2) and copolysiloxanes poly(1-co-3) were synthesized. Their mesophase structures were investigated by X-ray diffraction, and the electron density profiles along the layer normal were derived. A linear response with the applied electric field was detected in the chiral smectic (C* or A*) phases of poly(1) and poly(2).
- Galli,Cesarino,Gallot,Komitov,Chiellini
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p. 147 - 160
(2007/10/03)
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- Lipase PS-C catalysed hydrolysis of aryl diesters: A new route to the synthesis of achiral half esters
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Pseudomonas cepacia lipase supported on ceramic particles (PS-C) offers a simple alternative route for the synthesis of achiral half esters, with very high yields, easy work up and remarkable substrate selectivity, as it cleaves only phenolic esters having a phenyl group (i.e. C6H5-O-CO-C6H5).
- Nair, Ranjeet V.,Shukla, Manojkumar R.,Patil, Prashant N.,Salunkhe, Manikrao M.
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p. 1671 - 1677
(2007/10/03)
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- Dihalopropene compounds, insecticidal/acaricidal agents containing same, and intermediates for their production
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The dihalopropene compounds of the general formula ?I! have excellent insecticidal/acaricidal activity, so that they are satisfactorily effective for the control of noxious insects, mites and ticks.
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- Effects of nitro substituents on the properties of a ferroelectric liquid crystalline side chain polysiloxane
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The syntheses of chiral liquid crystalline side chain polysiloxanes with lateral nitro substituents in the mesogenic core are described. The influence of the substituents and substituent positions on phase behaviour and electro-optical properties are investigated and compared. The lateral nitro groups strongly affect the phase behaviour of the side chain precursors as well as the liquid crystalline polymers. Properties in smectic A and C* phases are discussed with respect to substituent position. One side chain precursor exhibits very large spontaneous polarization of ～700 nC cm-2.
- Svensson, Magnus,Helgee, Bertil,Skarp, Kent,Andersson, Gunnar
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p. 353 - 362
(2007/10/03)
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- F--induced decomposition of 3-[(tert-Butyldimethylsiloxy)phenoxy]-3-phenyl-1,2- dioxetanes without C-C bond cleavage of the dioxetane ring
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F--induced decomposition of 3-[3-tert-butyldimethylsiloxy)phenoxy]-3-phenyl-1,2- dioxetane (5c) yielded an intramolecular redox product (7b), whereas 3-phenoxy-3-(3-siloxyphenyl)-1,2-dioxetane (3) gave normal carbonyl fragments with intense light emission. An isomer (5a) gave light with normal decomposition by CIEEL, though the major process was one to yield an acyloin (7a).
- Matsumoto, Masakatsu,Azami, Mitsunori
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p. 8947 - 8950
(2007/10/03)
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- Preparation of a novel cross-linked polymer for second-order nonlinear optics
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A novel cross-linked pyroelectric polymer with pronounced second-order nonlinear optical properties has been prepared. A multistep synthesis with several selective transformations including a kinetic resolution (transesterification) with the highly enantioselective Candida antarctica lipase B, yielded the monomer 4''-{(R)-(-)-2[(10-acryloyloxy)decyl]oxy}-3-nitrophenyl 4-{4'-[(11-acryloyloxy)undecyloxy]phenyl}benzoate A2c which displayed a ferroelectric chiral smectic C phase with large spontaneous polarization (175 nC/cm2). The monomer was poled and subsequently cross-linked by in-situ photopolymerization in the surface-stabilized ferroelectric liquid crystalline state. The cross-linked pyroelectric polymer exhibited an electro-optical coefficient (r22-r12) of 15-35 pm/V.
- Trolls?s, Mikael,Orrenius, Christian,Sahlén, Fredrik,Gedde, Ulf W.,Norin, Torbj?rn,Hult, Anders,Hermann, David,Rudquist, Per,Komitov, Lachezar,Lagerwall, Sven T.,Lindstr?m, Jan
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p. 8542 - 8548
(2007/10/03)
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- HYDROXYLATION DIRECTE D'ESTERS DE PHENYLE ET D'ANILIDES PAR LE PEROXYDE D'HYDROGENE EN MILIEU SUPERACIDE
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In SbF5-HF, hydrogen peroxide reacts on the aromatic ring of esters 1a-5a and anilides 11a-15a to give monohydroxylated derivatives in good yields.With compounds 2a, 4a and 5a, meta or para isomers are by far the major products, whereas with formate 1a and benzoate 3a, the proportion of the ortho isomer is more important.With anilides, the reaction is less selective, the three isomers being obtained in comparable amounts.Thus, the relative proportions of ortho, meta and para-hydroxylated derivatives obtained using 70 percent H2O2 with acetate 2a and acetanilide 12a are 6/51/43 and 36.5/30/33.5, respectively.The important proportion of meta hydroxylation is the result of the reaction of protonated hydrogen peroxide H3O2+ on the protonated substrate.
- Berrier, Christian,Jacquesy, Jean-Claude,Jouannetaud, Marie-Paule,Morellet, Guy
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p. 158 - 164
(2007/10/02)
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- Process for the autoxidation of an isopropylphenyl ester
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Isopropylphenyl esters are converted to di- or trihydric phenols via a novel autoxidation of the esters at high conversion rates to the corresponding hydroperoxyisopropylphenyl esters in the presence of a catalyst combination comprising at least two members selected from the group consisting of (i) a metal phthalocyanine; (ii) a di-tertiary alkyl peroxide; and (iii) a tertiary alkyl hydroperoxide. Rearrangement of the hydroperoxyisopropylphenyl esters to the corresponding hydroxyphenyl esters and the hydrolysis of the latter compounds provides the phenols in overall yields (from the starting esters) heretofore not obtainable. Novel bis(hydroperoxyisopropylphenyl)carbonates are described which are attractive intermediates for the intermediate bisphenol carbonate or the final hydroquinone hydrolysis product.
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