- Three-component reaction of aryl diazoacetates, alcohols, and aldehydes (or imines): Evidence of alcoholic oxonium ylide intermediates
-
(Chemical Equation Presented) The Rh(II)-catalyzed three-component reaction of aryl diazoacetates, alcohols and aldehydes was explored, which provided evidence of alcoholic oxonium ylide formation for O-H insertion. A new C-C bond formation reaction where alcoholic oxonium ylides were trapped by electron-deficient aryl aldehydes (or imines) was realized.
- Lu, Chong-Dao,Liu, Hui,Chen, Zhi-Yong,Hu, Wen-Hao,Mi, Ai-Qiao
-
-
Read Online
- N-SUBSTITUTED ALPHA-AMINO AND ALPHA-HYDROXY CARBOXAMIDE DERIVATIVES
-
Disclosed are N-substituted α-amino and α-hydroxy carboxamides, pharmaceutical compositions comprising them, and methods of using them.
- -
-
Paragraph 130-131
(2021/10/30)
-
- Synthesis of Overloaded Cyclopentadienyl Rhodium(III) Complexes via Cyclotetramerization of tert-Butylacetylene
-
Herein we describe the synthesis and reactivity of rhodium catalysts with the very bulky cyclopentadienyl ligand C8H3tBu4 (designated as tBu4Cp). The reaction of [Rh(cod)Cl]2 with tert-butylacetylene in the presence of Et3N gives the complex (tBu4Cp)Rh(cod) (60-65% yield), in which the cyclopentadienyl ligand tBu4Cp is assembled from four alkyne molecules. The oxidation of (tBu4Cp)Rh(cod) with chlorine or bromine gives the corresponding halide complexes (tBu4Cp)RhX2 (X = Cl (85%), Br (95%)), which have unusual 16-electron monomeric structures due to the steric shielding provided by tBu groups. A similar reaction with iodine gives the ionic dinuclear complex [(tBu4Cp)RhI3Rh(tBu4Cp)]I (99%) with halide bridges. The bromide complex (tBu4Cp)RhBr2 reacts with phosphorus ligands such as P(OMe)3, P(OPh)3, PMe2Ph, and PMePh2 to give the 18-electron adducts (tBu4Cp)RhBr2(PR3), but no reaction occurs with larger phosphines such as PPh3. The racemic chloride (tBu4Cp)RhCl2 can be separated into enantiomers by preparative TLC of its diastereomeric adducts with (R)-phenylglycinol. The complex (tBu4Cp)RhBr2 catalyzes C-H activation and annulation of O-pivaloyl-hydroxamate as well as insertion of phenyldiazoacetate into E-H bonds, although the reaction rates and the substrate scope are limited by the bulky tBu4Cp ligand.
- Kolos, Andrey V.,Nelyubina, Yulia V.,Perekalin, Dmitry S.,Sundararaju, Basker
-
supporting information
p. 3712 - 3719
(2021/09/18)
-
- Photocatalytic Alkylation of Pyrroles and Indoles with α-Diazo Esters
-
This article describes the photoalkylation of electron-rich aromatic compounds with diazo esters. C-2-alkylated indoles and pyrroles are obtained with good yields even though the photocatalyst loading is as low as 0.075 mol %. For EWG-substituted substrates, the addition of a catalytic amount of N,N-dimethyl-4-methoxyaniline is required. Both EWG-EWG- and EWG-EDG-substituted diazo esters are suitable as alkylating agents. The reaction selectivity and mechanistic experiments suggest that carbenes/carbenoid intermediates are not involved in the reaction pathway.
- Ciszewski, Lukasz W.,Durka, Jakub,Gryko, Dorota
-
supporting information
p. 7028 - 7032
(2019/09/12)
-
- Bis(imino)pyridine iron complexes for catalytic carbene transfer reactions
-
The bis(imino)pyridine iron complex, for the first time, is developed as an effective metal carbene catalyst for carbene transfer reactions of donor-acceptor diazo compounds. Its broad catalytic capability is demonstrated by a range of metal carbene reactions, from cyclopropanation, cyclopropenation, epoxidation, and Doyle-Kirmse reaction to O-H insertion, N-H insertion, and C-H insertion reactions. The asymmetric cyclopropanation of styrene and methyl phenyldiazoacetate was successfully achieved by the new chiral bis(imino)pyridine iron catalyst, which delivers a new gateway for the development of chiral iron catalysis for metal carbene reactions.
- Wang, Ban,Howard, Isaac G.,Pope, Jackson W.,Conte, Eric D.,Deng, Yongming
-
p. 7958 - 7963
(2019/09/06)
-
- FeII-catalysed insertion reaction of α-diazocarbonyls into X-H bonds (X = Si, S, N, and O) in dimethyl carbonate as a suitable solvent alternative
-
The insertion reaction of a broad range of diazo compounds into Si-H bonds was found to be efficiently catalysed by Fe(OTf)2 in an emerging green solvent i.e. dimethyl carbonate (DMC). The α-silylated products were obtained in good to excellent yields (up to 95%). Kinetic studies showed that the extrusion of N2 to form an iron carbene intermediate is rate-limiting. The iron-catalysed insertion reaction of methyl α-phenyl-α-diazoacetate into polar X-H bonds (S-H, N-H, and O-H) was also established in DMC.
- Tanbouza, Nour,Keipour, Hoda,Ollevier, Thierry
-
p. 31241 - 31246
(2019/10/19)
-
- Asymmetric Counter-Anion-Directed Aminomethylation: Synthesis of Chiral β-Amino Acids via Trapping of an Enol Intermediate
-
A novel enantioselective aminomethylation reaction of diazo compound, alcohol and α-aminomethyl ether enabled by asymmetric counteranion-directed catalysis is disclosed that offers an efficient and convenient access to furnish optically active α-hydroxyl-β-amino acids in high yield with high to excellent enantioselectivities. Control experiments and DFT calculations indicate that the transformation proceeds through trapping the in situ generated enol intermediate with methylene iminium ion, and the asymmetric induction was enabled by chiral pentacarboxycyclopentadiene anion via H-bonding and electrostatic interaction.
- Kang, Zhenghui,Wang, Yongheng,Zhang, Dan,Wu, Ruibo,Xu, Xinfang,Hu, Wenhao
-
supporting information
p. 1473 - 1478
(2019/01/26)
-
- Silylium-Catalyzed Carbon–Carbon Coupling of Alkynylsilanes with (2-Bromo-1-methoxyethyl)arenes: Alternative Approaches
-
The catalytic activation of alkynylsilanes towards 2-halo-1-alkoxyalkyl arenes gives β-halo-substituted alkynes. It involves the chemoselective substitution of an alkoxide by an alkyne in the presence of a neighboring C(sp3)–Br bond in a cationic C–C bond-forming event. Two complementary protocols to accomplish this new transformation are reported. The outcome of a direct approach based on mixing the precursors with a freshly prepared solution of the active catalytic species (TMSNTf2) is compared with an alternative based on smooth release of the required silylium ions upon selective activation of the alkyne by gold(I) (JohnPhosAuNTf2). The two approaches gave satisfactory results to access this otherwise elusive alkynylation process, which furnishes 4-bromo-substituted alkynes and tolerates various functional groups.
- Rubial, Belén,Ballesteros, Alfredo,González, José M.
-
supporting information
p. 6194 - 6198
(2018/07/31)
-
- Insertion of carbenoids into X-H bonds catalyzed by the cyclobutadiene rhodium complexes
-
The cyclobutadiene rhodium complex [(C4Et4)RhCl]2 (generated from [(C4Et4)Rh(p-xylene)]PF6 and BnNEt3Cl) catalyzes the reaction of methyl α-diazophenylacetate with RnX
- Loskutova, Natalia L.,Shvydkiy, Nikita V.,Nelyubina, Yulia V.,Perekalin, Dmitry S.
-
-
- Silica-supported HClO4 promotes catalytic solvent- and metal-free O-H insertion reactions with diazo compounds
-
Solvent-free O-H insertion reactions in the presence of diazo carbonyl compounds were carried-out in very mild conditions. Unlike the traditional metal-catalysed version, employing rhodium acetate dimer, this method uses eco-friendly silica-supported HClO4 as the catalyst. Only 0.3 mol% of this Br?nsted acid catalyst, that can also be recycled several times, is necessary to guarantee very good yields (up to 97%) in the O-H insertion reactions. Reaction set-up is simple and permitted the preparation of forty-three α-hydroxy and α-alkoxy esters/ketones in just 1 h and at room temperature.
- Gallo, Rafael Douglas C.,Burtoloso, Antonio C. B.
-
p. 4547 - 4556
(2018/10/17)
-
- Mg(OMe)2 promoted allylic isomerization of γ-hydroxy-α,β-alkenoic esters to synthesize γ-ketone esters
-
This work concerns the Mg(OMe)2 promoted allylic isomerization of γ-hydroxy-α,β-alkenoic esters with TMEDA as an additive. The isomerization proceeded under mild conditions and afforded γ-keto esters in high yield (up to 96%) within 2 h. Both (Z)- and (E)-γ-hydroxy-α,β-alkenoic esters were tolerated under the reaction conditions. This transformation involves the in situ formation of a dienolate intermediate from the easily accessible γ-hydroxy-α,β-alkenoic ester. The in situ generated dienolate can react with benzaldehyde and undergo a practical, useful tandem allylic isomerization-Aldol reaction to afford more functionalized compounds.
- Lai, Luhao,Li, A-Ni,Zhou, Jiawei,Guo, Yarong,Lin, Li,Chen, Wei,Wang, Rui
-
supporting information
p. 2185 - 2190
(2017/03/17)
-
- Sensing remote chirality: Stereochemical determination of β-, γ-, and δ-chiral carboxylic acids
-
Determining the absolute stereochemisty of small molecules bearing remote nonfunctionalizable stereocenters is a challenging task. Presented is a solution in which appropriately substituted bis(porphyrin) tweezers are used. Complexation of a suitably derivatized β-, γ-, or δ-chiral carboxylic acid to the tweezer induces a predictable helicity of the bis(porphyrin), which is detected as a bisignate Cotton Effect (ECCD). The sign of the ECCD curve is correlated with the absolute stereochemistry of the substrate based on the derived working mnemonics in a predictable manner.
- Tanasova, Marina,Anyika, Mercy,Borhan, Babak
-
supporting information
p. 4274 - 4278
(2015/04/14)
-
- Rh(iii)-catalyzed and alcohol-involved carbenoid C-H insertion into N-phenoxyacetamides using α-diazomalonates
-
Here we report a new and mild Rh(iii)-catalyzed and alcohol-involved carbenoid C-H insertion into N-phenoxyacetamides using α-diazomalonates. This reaction provided a straightforward way for installing both an α-quaternary carbon center and a free-OH moiety into the phenyl ring, thus giving access to useful 2-(2-hydroxyphenyl)-2-alkoxymalonates with good substrate/functional group tolerance. This journal is
- Zhou, Jie,Shi, Jingjing,Liu, Xuelei,Jia, Jinlong,Song, Huacan,Xu, H. Eric,Yi, Wei
-
p. 5868 - 5871
(2015/03/30)
-
- Rapid access to α-alkoxy and α-amino acid derivatives through safe continuous-flow generation of diazoesters
-
Microreactors: A highly efficient continuous-flow process has been developed for the synthesis of diazoesters from arylsulfonylhydrazones by means of in-flow Bamford-Stevens reactions. Furthermore, a range of α-alkoxy and α-amino acid derivatives have bee
- Bartrum, Hannah E.,Blakemore, David C.,Moody, Christopher J.,Hayes, Christopher J.
-
supporting information; experimental part
p. 9586 - 9589
(2011/10/08)
-
- Kinetic resolution of (R,S)-pyrazolides containing substituents in the leaving pyrazole for increased lipase enantioselectivity
-
With hydrolysis of (R,S)-azolides in water-saturated methyl tert-butyl ether (MTBE) via Candida antarctica lipase B (CALB) as the model system, (R,S)-pyrazolides containing a leaving 3-, 4- or 3,4-substituted-pyrazole moiety are selected as the best substrates for preparing various optically pure carboxylic acids containing an α-chiral center. Great improvements of enzyme activity for the (R)-enantiomers with excellent enantioselectivity (VR/VS > 100) are obtainable, if (R,S)-pyrazolides containing a leaving 3- or 3,4-substituted-pyrazole moiety are employed for the hydrolysis or alcoholysis by methanol in anhydrous MTBE. A detailed kinetic analysis for (R,S)-N-2-phenylpropionylpyrazoles indicates that a bulky 3-substituent such as 3-(3-bromophenyl) or 3-(2-pyridyl) in the leaving pyrazole moiety has profound effects on decreasing the nucleophilic attack and proton transfer of catalytic serine for the slow-reacting enantiomer in anhydrous MTBE, as well as that and substrate affinity for both enantiomers in water-saturated MTBE. The resolution platform is also successfully applied to the hydrolysis of (R,S)-pyrazolides in water-saturated cyclohexane via Candida rugosa lipase (Lipase MY) having opposite enantioselectivity to CALB.
- Wang, Pei-Yun,Wu, Chia-Hui,Ciou, Jyun-Fen,Wu, An-Chi,Tsai, Shau-Wei
-
experimental part
p. 113 - 119
(2011/02/21)
-
- Chiral induction by Cinchona alkaloids in the rhodium(II) catalyzed O-H insertion reaction
-
Cinchona alkaloids are effective additives for enantioselective O-H insertion of α-phenyldiazoacetate and water by rhodium(II) complexes. Addition of silica gel promotes O-H insertion in the reaction rate and the reaction proceeds smoothly at less than the freezing point of water, e.g., -10°C, and provided mandelate in up to 50% ee. The results reported here are the highest asymmetric inductions obtained to date for O-H insertions via a Rh-carbenoid.
- Saito, Hiroaki,Iwai, Ryo,Uchiyama, Taketo,Miyake, Muneharu,Miyairi, Shinichi
-
scheme or table
p. 872 - 874
(2010/09/04)
-
- An improved bouveault-blanc ester reduction with stabilized alkali metals
-
Significantly improved Bouveault-Blanc conditions for ester reduction have been developed using sodium in silica gel (Na-SG), a free-flowing powder that can be easily handled in the open atmosphere. Primary alcohols were prepared in excellent yield from a variety of aliphatic esters under mild reaction conditions. The chemistry presented here is far safer than the classic Bouveault-Blanc reduction and is competitive with more modern hydride reduction methods.
- Bodnar, Brian S.,Vogt, Paul F.
-
supporting information; experimental part
p. 2598 - 2600
(2009/08/07)
-
- Chiral N-heterocyclic carbene ligands for asymmetric catalytic oxindole synthesis
-
The Pd-catalysed asymmetric intramolecular α-arylation of amide enolates containing heteroatom substituents gives chiral 3-alkoxy or 3-aminooxindoles in high yield and with enantioselectivities up to 97% ee when a new chiral N-heterocyclic carbene ligand is used. The Royal Society of Chemistry.
- Jia, Yi-Xia,Hillgren, J. Mikael,Watson, Emma L.,Marsden, Stephen P.,Kuendig, E. Peter
-
supporting information; scheme or table
p. 4040 - 4042
(2009/03/11)
-
- Copper(I{cyrillic, ukrainian}) hexafluorophosphate: a dual functional catalyst for three-component reactions of methyl phenyldiazoacetate with alcohols and aldehydes or α-ketoesters
-
Oxonium ylides in situ generated from methyl phenyldiazoacetate and alcohols in the presence of CuPF6(CH3CN)4 underwent an aldol-type reaction with aldehydes or α-ketoesters in a convergent, three-component fashion to give α-alkoxyl-β-hydroxyl acid derivatives in good yields.
- Yue, Yongli,Guo, Xin,Chen, Zhiyong,Yang, Liping,Hu, Wenhao
-
scheme or table
p. 6862 - 6865
(2009/04/07)
-
- New boron(III)-catalyzed amide and ester condensation reactions
-
In 1996, we reported that benzeneboronic acids bearing electron-withdrawing groups at the meta- or para-position are highly effective catalysts for the amide condensation reaction in less-polar solvents. In this paper, we report that N-alkyl-4-boronopyridinium halides are more effective catalysts than the previous ones in more polar solvents. N-Alkyl-4-boronopyridinium halides are effective not only for amide condensation between equimolar mixtures of carboxylic acids and amines but also for the esterification of α-hydroxycarboxylic acids in alcohol solvents. Furthermore, perchlorocatecholborane is more effective than areneboronic acids for the amide condensation of sterically demanding carboxylic acids. In addition, Lewis acid-assisted Br?nsted acid (LBA), which is prepared from a 1:2 M mixture of boric acid and tetrachlorocatechol, is effective for the Ritter reaction from alcohols and nitriles to amides.
- Maki, Toshikatsu,Ishihara, Kazuaki,Yamamoto, Hisashi
-
p. 8645 - 8657
(2008/02/08)
-
- Lewis acid-mediated highly regioselective SN2-type ring-opening of 2-Aryl-N-tosylazetidines and aziridines by alcohols
-
(Chemical Equation Presented) Lewis acid-mediated highly regioselective SN2-type ring-opening of 2-aryl-N-tosylazetidines with alcohols to afford various 1,3-amino ethers in excellent yields with good enantiomeric excess is described. Similar S
- Ghorai, Manas K.,Das, Kalpataru,Shukla, Dipti
-
p. 5859 - 5862
(2008/02/09)
-
- Efficient trapping of oxonium ylides with imines: A highly diastereoselective three-component reaction for the synthesis of β-amino-α-hydroxyesters with quaternary stereocenters
-
(Chemical Equation Presented) In one huge stride: The single-step construction of polyfunctionalized compounds with a quaternary stereocenter is possible through a highly diastereoselective multicomponent reaction of phenyldiazoacetates, alcohols, and imi
- Huang, Haoxi,Guo, Xin,Hu, Wenhao
-
p. 1337 - 1339
(2008/03/28)
-
- Highly chemoselective methylation and esterification reactions with dimethyl carbonate in the presence of NaY faujasite. The case of mercaptophenols, mercaptobenzoic acids, and carboxylic acids bearing OH substituents
-
In the presence of NaY faujasite, the reactions of dimethyl carbonate (DMC) with several ambident nucleophiles such as o- and p-mercaptophenols (1a,b), o- and p-mercaptobenzoic acids (2a,b), o- and p-hydroxybenzoic acids (3a,b), mandelic and phenyllactic acids (4, 5), have been explored under batch conditions. Highly chemoselective reactions can be performed: at 150 °C, compounds 1 and 2 undergo only a S-methylation reaction, without affecting OH and CO2H groups; at 165 °C, acids 3-5 form the corresponding methyl esters, while both their aromatic and aliphatic OH substituents are fully preserved from methylation and/or transesterification processes. Typical selectivities are of 90-98% and isolated yields of products (S-methyl derivatives and methyl esters, respectively) are in the range of 85-96%. A comparative study with K2CO3 as a catalyst is also reported. Although the base (K2CO3) turns out to be more active than the zeolite, the chemoselectivity is elusive: compounds 2a,b undergo simultaneous S-methylation and esterification reactions, and acids 3-5 yield complex mixtures of products of O-methylation, O-methoxycarbonylation, and esterification of their OH and CO2H groups, respectively. Overall, the combined use of a nontoxic reagent/solvent (DMC) and a safe promoter (NaY) imparts a genuine ecofriendly nature to the investigated synthesis.
- Selva, Maurizio,Tundo, Pietro
-
p. 1464 - 1470
(2007/10/03)
-
- Bulky diarylammonium arenesulfonates as mild and extremely active dehydrative ester condensation catalysts
-
More environmentally benign alternatives to current chemical processes, especially large-scale, fundamental reactions like ester condensations, are highly desirable for many reactions. Bulky diarylammonium pentafluorobenzenesulfonates and tosylates serve as extremely active dehydration catalysts for the ester condensation reaction of carboxylic acids with equimolar amounts of sterically demanding alcohols and acid-sensitive alcohols. Typically, the esterification reaction is performed in heptane by heating at 80°C in the presence of 1 mol% of the catalyst without removing water. Esterification with primary alcohols proceeds without solvents even at room temperature. Furthermore, 4-(N-mesitylamino)polystyrene resin-bound pentafluorobenzenesulfonate can be recycled more than 10 times without a loss of activity.
- Sakakura, Akira,Nakagawa, Shoko,Ishihara, Kazuaki
-
p. 422 - 433
(2007/10/03)
-
- Enantioselective homoallyl-cyclopropanation of dibenzylideneacetone by modified allylindium halide reagents-rapid access to enantioenriched 1-styryl-norcarene
-
Dibenzylideneacetone (8) reacts with in situ-generated allylindium halide reagents to yield the product of a homoallyl-cyclopropanation reaction: 2-(3″-butenyl)-1,1-bis[(E)-2′-phenylethenyl]cyclopropane (9), which proceeds via step-wise cleavage of the C{double bond, long}O bond and delivery of two allyl fragments from the reagent. A range of enantiomerically enriched ligands have been tested as stoichiometric asymmetric modifiers for this process. Enantiopure compounds such as cinchona alkaloids, ephedra, aminoalcohols and tartaric acid derivatives, which have proven of utility as asymmetric modifiers for the indium-mediated allylation of aldehydes and ketones, were very inefficient in the process 8→9. However, mandelic acid derivatives, in particular mandelates, were found to be of significant potential. The absolute stereochemistry of the cyclopropane 9 has been determined by degradation to 1,1-dicarboxymethyl-2-butylcyclopropane, converging with an independent enantioselective synthesis starting from hexene. Under optimised conditions, viz. using allylindium iodide reagents and working-up with aqueous Na2SO3 to avoid iodine-mediated polymerisation, (S)-9 can be generated in 86% yield and with (S)-methyl mandelate as modifier useful enantiopurity (94/6 er) was observed. The cyclopropane product ((S)-9) undergoes RCM using standard conditions to afford a norcarene unit ((1S,6S)-1-(E)-2′-(phenylethenyl)-bicyclo[4.1.0]hept-2-ene) without loss of enantiopurity.
- Lloyd-Jones, Guy C.,Wall, Philip D.,Slaughter, Jennifer L.,Parker, Alexandra J.,Laffan, David P.
-
p. 11402 - 11412
(2007/10/03)
-
- Regioselective synthesis of optically active (pyrazolyl)pyridines with adjacent quaternary carbon stereocenter: Chiral N,N-donating ligands
-
Novel optically active 2-(pyrazol-1-yl)pyridines have been prepared using resolved the O-methyl ether of atrolactic acid as a source of the adjacent quaternary carbon stereocenter. Different regioisomers were formed selectively in the reaction of 2-hydraz
- Kowalczyk, Rafa?,Skarzewski, Jacek
-
p. 623 - 628
(2007/10/03)
-
- The first asymmetric catalytic halo aldol reaction of β-iodo allenoates with aldehydes by using chiral salen catalyst
-
The first asymmetric catalytic halo aldol reaction of β-iodo allenoates with aldehydes was established. The reaction was successfully achieved by using (R,R)-SalenAlCl as the chiral catalyst and LiI as an additive at 0°C in dichloromethane. Moderate to good yields and up to 62% ee were obtained. The new system showed a good substrate scope in which both aromatic aldehydes and aliphatic aldehydes can be employed. The reaction provided the first catalytic and enantioselective approach to chiral β-iodo Baylis-Hillman ester adducts.
- Chen, Dianjun,Guo, Li,Kotti, S. R. S. Saibabu,Li, Guigen
-
p. 1757 - 1762
(2007/10/03)
-
- Synthesis of esters by selective methanolysis of the trifluoromethyl group
-
The trifluoromethyl group of certain compounds containing one or two trifluoromethyl groups can be converted to the carbomethoxy group by treatment with sodium methoxide followed by aqueous acidic work-up. α-Trifluoromethyl esters can be obtained by selective methanolysis of the 1,1,1,3,3,3-hexafluoroisopropyl group in some cases. The structural requirements for the transformation are delineated, and a mechanistic study confirms the proposed mechanism, a dehydrofluorination-addition-elimination process.
- Ramig, Keith,Englander, Miriam,Kallashi, Florida,Livchits, Lilia,Zhou, Jessica
-
p. 7731 - 7734
(2007/10/03)
-
- The asymmetric catalytic aldol reaction of allenolates with aldehydes using N-fluoroacyl oxazaborolidine as the catalyst
-
matrix presented The asymmetric catalytic aldol reaction of silyl allenolates with aldehydes has been achieved by using N-C3F7CO oxazaborolidine as the catalyst. The fluoroacyl group of the catalyst was found to be crucial for control of enantioselectivity. The reaction provides the first enantioselective approach to β-halo Baylis-Hillman-type adducts.
- Li, Guigen,Wei, Han-Xun,Phelps, Brian S.,Purkiss, David W.,Kim, Sun Hee
-
p. 823 - 826
(2007/10/03)
-
- Enantioselective protonation of silyl enol ethers and ketene disilyl acetals with Lewis acid-assisted chiral Bronsted acids: Reaction scope and mechanistic insights
-
Enantioselective protonation is a potent and efficient way to construct chiral carbons. Here we report details of the reaction using Lewis acid-assisted chiral Bronsted acids (chiral LBAs). The 1:1 coordinate complex of tin tetrachloride and optically active binaphthol ((R)- or (S)-BINOL) can directly protonate various silyl enol ethers and ketene disilyl acetals to give the corresponding α-aryl ketones and α-arylcarboxylic acids, respectively, with high enantiomeric excesses (up to 98% ee). A catalytic version of enantioselective protonation has also been achieved using stoichiometric amounts of 2,6-dimethylphenol and catalytic amounts of monomethyl ether of optically active BINOL in the presence of tin tetrachloride. This protonation is also effective for producing α-halocarbonyl compounds (up to 91% ee). DFT calculations on the B3LYP/LANL2DZ level show that the conformational structure of the chiral LBA and the orientation of activated proton on (R)-BINOLs are important for understanding the absolute stereochemistry of the products.
- Nakamura, Shingo,Kaneeda, Masanobu,Ishihara, Kazuaki,Yamamoto, Hisashi
-
p. 8120 - 8130
(2007/10/03)
-
- Enantioselective carboxylation of α-methoxybenzyllithium generated via asymmetric lithiation with a t-BuLi/chiral bis(oxazoline) complex
-
Treatment of benzyl methyl ether with a t-BuLi/chiral bis(oxazoline) complex followed by carboxylation is shown to afford α-methoxy phenylacetic acid in high % ee (up to 95%). The asymmetric induction was proved to occur at the post-lithiation step.
- Komine, Nobuyuki,Wang, Lan-Fang,Tomooka, Katsuhiko,Nakai, Takeshi
-
p. 6809 - 6812
(2007/10/03)
-
- Almond oxynitrilase-catalyzed transformation of aldehydes is strongly influenced by naphthyl and alkoxy substituents
-
Different α- and β-substituted aldehydes have been submitted to the catalytic action of almond oxynitrilase (PaHNL), in order to explore the influence of a stereocenter already present in the substrate on the selectivity of this enzyme. The results indicate that naphthyl and alkoxy substituents in the α- and also in the β-position to the aldehyde group significantly influence the stereochemical outcome of the PaHNL-catalyzed transformation.
- Roda, Gabriella,Riva, Sergio,Danieli, Bruno
-
p. 3939 - 3949
(2007/10/03)
-
- Cesium promoted O-alkylation of alcohols for the efficient ether synthesis
-
Efficient Williamson type O-alkylation of alcohols was developed using cesium bases in the presence of tetrabutylammonium iodide (TBAI) and molecular sieves. Various substrates including unreactive primary and secondary alcohols were converted smoothly to
- Dueno,Chu,Kim,Kyung Woon Jung
-
p. 1843 - 1846
(2007/10/03)
-
- Methyltrioxorhenium supported on silica tethered with polyethers as catalyst for the epoxidation of alkenes with hydrogen peroxide
-
Methyltrioxorhenium has been supported on silica functionalized with polyether tethers; in the absence of an organic solvent, this catalytic assembly catalysed the epoxidation of alkenes with 30% aqueous H2O2 in high selectivity compared to the ring opening products observed in homogeneous media.
- Neumann, Ronny,Wang, Tie-Jun
-
p. 1915 - 1916
(2007/10/03)
-
- Hypervalent iodine oxidation of trimethylsilyl ketene acetals: A convenient route to α-methoxylation of esters and lactones
-
Hypervalent iodine oxidation of trimethylsilyl ketene acetals of esters and lactones using iodosobenzene in methanol affords the corresponding α- methoxylated carbonyl compounds in good yields.
- Moriarty, Robert M.,Rani, Neena,Condeiu, Cristian,Duncan, Michael P.,Prakash, Om
-
p. 3273 - 3277
(2007/10/03)
-
- New chiral rhodium(II) carboxylates and their use as catalysts in carbenoid transformations
-
New chiral dirhodium(II) carboxylates 11-15 have been prepared from the half phthalate esters 6-8 and the pyrroles 9 and 10, and their use as catalysts for the decomposition of diazocarbonyl compounds 16 and 18 investigated.
- Ferris, Leigh,Haigh, David,Moody, Christopher J.
-
p. 107 - 110
(2007/10/02)
-
- Enantioselective Allylic Substitution Catalyzed by Chiral palladium Complexes: Catalyst Structure and Possible Mechanism of Enantioselection
-
Allylpalladium complexes with chiral bis(dihydrooxazole) ligands were studied as catalysts for the enantioselective allylic substitution reaction of rac-1,3-diphenylprop-2-enyl acetate (rac-5) with the anion of dimethyl malonate (Scheme 1).Using enantiome
- Matt, Peter von,Lloyd-Jones, Guy C.,Minidis, Alexander B. E.,Pfaltz, Andreas,Macko, Ludwig,et al.
-
p. 265 - 284
(2007/10/02)
-
- The Chemistry of 5-Oxodihydroisoxales. XI; The Photolysis of 3-Hydroxy-4-phenylisoxazol-5(2H)-ones (Phenyldisic Acids)
-
3-Hydroxy-2-methyl-4-phenylisoxazol-5(2H)-one, 3-hydroxy-2,4-diphenylisoxazol-5(2H)-one and phenyldisic acid have been photolysed at 254 nm in hydroxylic solvents.By comparision of the respective products with those obtained from 3-methoxy-4-phenylisoxazo
- Prager, Rolf H.,Smith, Jason A.
-
p. 217 - 226
(2007/10/02)
-
- Spectroscopy and photochemistry of phenylacetic acid esters and related substrates. The stereoelectronic dependence of the aryl/carboxyl bichromophore interaction
-
The 254-nm-initiated Norrish Type II photofragmentation of the ethoxyethyl esters of a series of phenylacetic acids (1b-4b) has been studied in order to further elaborate the aryl/ester interaction that is photochemically and photophysically evident in these systems. The ethoxyethyl ester of benzonorbornene-1-carboxylic acid (5) has also been prepared and studied, as has a rigid tricyclic lactone (6) which places the chromophores in an optimal stereoelectronic relationship for interaction. The experimental work is accompanied by Hartree-Fock (HF), Natural Bond Orbital (NBO), and Configuration Interaction with Single Excitations (CIS) calculations on the methyl esters of phenylacetic acid (1a) and α-methoxyphenylacetic acid (4a). The calculations confirm extensive through-space (TS) and through-bond (TB) interactions between the aryl and ester π* orbitals but fail to provide conformational or electronic arguments to explain the unusually high reactivity of the α-methoxy series.
- Kasper,Nash,Morrison
-
p. 2792 - 2798
(2007/10/02)
-
- Palladium-catalysed Arylation of α-Methoxyketene Methyl Silyl Acetals
-
Methyl α-methoxyarylacetates 3 have been synthesized by the palladium-catalysed reaction of iodobenzenes 1 with α-methoxyketene methyl silyl acetals 2.The diastereoselective and enantioselective synthesis of the arylacetates has also been examined.
- Sakamoto, Takao,Kondo, Yoshinori,Masumoto, Kaoru,Yamanaka, Hiroshi
-
p. 235 - 236
(2007/10/02)
-
- Photolysis of Phenyldisic Acids: Evidence for Unique Product Formation from Discrete Tautomers
-
3-Hydroxy-2-methyl-4-phenylisoxazol-5(2H)-one exists as four tautomers, two of which are isolated and characterised; photolysis in methanol leads to formation of products identified as arising uniquely from three of the tautomers, and the 2-phenyl analogue and phenyldisic acid undergo similar photochemical reactions.
- Prager, Rolf H.,Smith, Jason A.
-
p. 1805 - 1806
(2007/10/02)
-
- Asymmetric Induction in the Diels-Alder Reactions of α-Hydroxy Acyl Nitrones
-
The hydroxamic acids 7, derived from a series of α-hydroxy acids 5, have been oxidised with periodate to form transient, chiral acyl nitroso compounds 8, which were trapped in situ with cyclopentadiene and cyclohex-1,3-diene to give mixtures of diastereoi
- Kirby, Gordon W.,Nazeer, Muhammad
-
p. 1397 - 1402
(2007/10/02)
-
- Electrochemical methoxylation of arylacetates
-
Electrochemical methoxylation at the active methylene group of phenylacetates and 1-naphthaleneacetate was conducted successfully at room temperature, in methanol containing potassium iodide as an electron carrier and sodium methoxide as a base and a methoxylating agent. Along with the mono-methoxylated products, dimethoxy, hydroxy, and oxo derivatives as well as the dimers (succinates) were produced as by-products.
- Kato,Suzuki,Shimamura,Nozawa,Kawai,Nakajima
-
p. 1037 - 1038
(2007/10/02)
-
- Applications of Optically Active Aryl Cyanohydrins in the Synthesis of α-Hydroxy Aldehydes, α-Hydroxy Ketones and β-Hydroxy Amines
-
Cyanohydrins, prepared in high optical purity from aryl aldehydes, have been converted into α-hydroxy aldehydes, α-hydroxy ketones and β-hydroxy amines without any racemization and frequently with good stereoselectivity for the erythro-diastereoisomer (>90percent) at the newly introduced stereogenic centre.
- Jackson, W. Roy,Jacobs, Howard A.,Jayatilake, Gamini S.,Matthews, Barry R.,Watson, Keith G.
-
p. 2045 - 2062
(2007/10/02)
-
- Hypervalent Iodine Oxidation of Aryl Methyl Ketones: A Convenient Route to Methyl α-Methoxyarylacetates
-
Hypervalent iodine oxidation of aryl methyl ketones using two equivalents of iodosobenzene diacetate leads to 1,2-aryl migration followed by solvohyperiodination to yield the corresponding methyl α-methoxyarylacetates.
- Singh, Om V.
-
p. 3055 - 3058
(2007/10/02)
-
- Photolysis of 1,1,1-Triphenyl-2-alkenes and Methyl Triphenylacetate
-
Upon UV irradiation in methanol 1,1,1-triphenyl-2-alkene or methyl triphenylacetate underwent two kinds of α,α-elimination of two phenyl groups and phenyl-alkenyl groups or phenyl-methoxycarbonyl groups to give biphenyl, 1-phenylalkene or methyl benzoate, and two kinds of correspondending carbene intermediates, which inserted into the O-H bond of methanol to afford two kinds of methyl ethers, respectively.
- Shi, Min,Okamoto, Yoshiki,Takamuku, Setsuo
-
p. 1079 - 1082
(2007/10/02)
-
- Photolysis of Triphenylacetic Acid and Its Methyl Ester: A Novel Photochemical Generation of Carbene Intermediates
-
The photolysis of methyl triphenylacetate in methanol gave biphenyl, methyl α-methoxyphenylacetate, methyl benzoate, and methoxydiphenylmethane.The formation of these products suggests that two types of α,α-elimination take place: One is the elimination of two phenyl groups leaving Ph-C-CO2Me (type a), and the other is the elimination of the phenyl and methoxycarbonyl groups generating Ph2C: (type b).Only type a elimination was efficiently quenched by oxygen.
- Shi, Min,Okamoto, Yoshiki,Takamuku, Setsuo
-
p. 3345 - 3347
(2007/10/02)
-
- Electrochemical Hydroxylation, Methoxylation, and Hydroxymethylation of Active Methine Compounds
-
Hydroxylation, methoxylation, or hydroxymethylation at the active methine group of phenylmalonate, benzylmalonate and diphenylacetate were achieved by anodic oxidation.
- Kawabata, Jin-ichi,Nozawa, Koohei,Kawai, Ken-ichi,Nakajima, Shoichi
-
p. 181 - 183
(2007/10/02)
-