- Regioselective Annulation of Aryl Sulfonamides with Allenes through Cobalt-Promoted C-H Functionalization
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The development of an efficient method for the construction of biologically relevant sultams is described, which represents the first case of cobalt-promoted C-H/N-H functionalization of sulfonamides with allenes. This newly developed annulation reaction demonstrated good functional group tolerance and excellent regioselectivity. Both terminal monosubstituted allenes and internal disubstituted allenes can be employed to give the desired sultams in good yields. This strategy can be successfully used to build a unique sultam library with novel structural diversity.
- Lan, Tianlong,Wang, Liguo,Rao, Yu
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- Rates of Base-Catalyzed Hydrogen Exchange of Terminal Acetylenes in Aqueous Solution. Absence of Resonance Interaction
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Rates of detritiation of 13 monosubstituted acetylenes labeled at the acetylenic hydrogen position were measured in aqueous amine buffer solution at 25 deg C, and hydroxide ion catalytic coefficients were evaluated.These rate constants, plus a few additional values from the literature, give a good correlation against inductive or field substituent constants: log(kHO-/M-1s-1) = 1.46+/-0.12 + (8.00+/-0.50)?I.This correlation is not improved by addition of resonance substituted constants, and the coefficients of the resonance term in two different dual parameter (resonance plus field) treatments of the data are in fact zero.
- Kresge, A. J.,Powell, M. F.
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- Synthesis of polysubstituted stereodefined olefins via the reactivity of sp2 organo-gem-bismetallics
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We describe a new synthetically useful procedure for the stereoselective synthesis of polysubstituted olefins via the reaction of sp2 organometallics with different electrophiles.
- Creton, Isabelle,Marek, Ilane,Normant, Jean F.
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- Rhodium-Catalyzed Cyclization of Terminal and Internal Allenols: An Atom Economic and Highly Stereoselective Access Towards Tetrahydropyrans
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A comprehensive study of a diastereoselective Rh-catalyzed cyclization of terminal and internal allenols is reported. The methodology allows the atom economic and highly syn-selective access to synthetically important 2,4-disubstituted and 2,4,6-trisubstituted tetrahydropyrans (THP). Furthermore, its utility and versatility are demonstrated by a great functional-group compatibility and the enantioselective total synthesis of (?)-centrolobine.
- Breit, Bernhard,Schmidt, Johannes P.
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- A Convergent, Stereoselective Route to Trisubstituted Alkenyl Boronates
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A modular, stereoselective route to trisubstituted (Z)-alkenyl (MIDA)boronates is described, consisting of the radical addition-fragmentation of dithiocarbonates to 2-(MIDA)boronyl-3-(2′-fluoro-pyridyl-6′-oxy)-alkenes. The bulky (MIDA)boronate ensures a highly stereoselective fragmentation that is enhanced by the poor stabilization of the radical adjacent to the tetravalent boron atom. The vinyl boronate precursors are prepared from propargyl alcohols by copper-catalyzed regioselective protoboration of their fluoropyridoxy derivatives, with the fluoropyridine acting as an internal directing group.
- Michalland, Jean,Zard, Samir Z.
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supporting information
p. 8018 - 8022
(2021/10/30)
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- Ester Synthesis in Water: Mycobacterium smegmatis Acyl Transferase for Kinetic Resolutions
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The acyl transferase from Mycobacterium smegmatis (MsAcT) catalyses transesterification reactions in aqueous media because of its hydrophobic active site. Aliphatic cyanohydrin and alkyne esters can be synthesised in water with excellent and strikingly opposite enantioselectivity [(R);E>37 and (S);E>100, respectively]. When using this enzyme, the undesired hydrolysis of the acyl donor is an important factor to take into account. Finally, the choice of acyl donor can significantly influence the obtained enantiomeric excesses. (Figure presented.).
- de Leeuw, Nicolas,Torrelo, Guzman,Bisterfeld, Carolin,Resch, Verena,Mestrom, Luuk,Straulino, Emanuele,van der Weel, Laura,Hanefeld, Ulf
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p. 242 - 249
(2017/11/16)
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- Some special features of hydroalumination-iodination of alkyne-1,4-diols
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Hydroalumination-iodination of alkyne-1,4-diols of different structure showed that with increasing number of substituents at the C-OH group the amount of β-iodo-substituted products with respect to this group increased. In the case of symmetric secondary 1,4-diols the reaction results in a 1: 1 mixture of stereoisomeric iodoalkenediols, and in the case of phenyl substituents the reaction proceeds regio- and stereoselectively to give an alkenediol iodine atom in the β-position to phenyl group.
- Gharibyan,Makaryan,Hovhannisyan,Kinoyan,Chobanyan
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p. 457 - 464
(2014/05/20)
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- New and efficient synthesis of 1,3-dienylphosphonates by palladium-catalyzed substitution of propargylic esters to diethyl phosphite
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An efficient route to the synthesis of 1,3-dienylphosphonates (1) has been developed for the first time by the substitution of propargylic esters (2) to the diethyl phosphite (3) nucleophile in the presence of Pd2 (dba) 3 · CHCl3 (2 mol %) and 2,2′- bis(diphenylphosphino)-1,1′-binaphthyl (4 mol%). Both the alkyl and aryl 1,3-dienylphosphonates can be prepared from this transformation. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications to view the free supplemental file.
- Liu, Xiao-Ning,Guo, Wei-Lei,Hou, Chuan-Jin,Hu, Xiang-Ping
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supporting information
p. 2622 - 2626
(2013/07/26)
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- A novel Ireland-Claisen rearrangement/Diels-Alder tandem reaction of propargylic acrylates with acyclic dienophiles
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A novel DABCO-catalyzed Ireland-Claisen rearrangement/Diels-Alder tandem reaction of propargylic acrylates 3 with dienophiles 4 was developed in the presence of an excess TMSCl and DBU with 1% hydroquinone as polymerization inhibitor in acetonitrile at refluxing temperature under air. This protocol gave cyclic α,β-unsaturated carboxylic acids 5 with complete regioselectivity.
- Li, Yun-Xia,Sheng, Yi-Lin,Zhang, Bi-Song
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p. 137 - 139
(2013/06/26)
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- The substrate spectrum of the inverting sec-alkylsulfatase Pisa1
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The substrate spectrum of the inverting alkylsulfatase Pisa1 was investigated using a range of sec-alkyl sulfate esters bearing aromatic, olefinic and acetylenic moieties. Perfect enantioselectivities were obtained for substrates bearing groups of different size adjacent to the sulfate ester moiety. Insufficient selectivities could be doubled by using dimethyl sulfoxide (DMSO) as co-solvent. Hydrolytically unstable benzylic sulfate esters could be sufficiently stabilised by introduction of electron-withdrawing substituents. Overall, Pisa1 appears to be a very useful inverting alkylsulfatase for the deracemisation of rac-sec-alcohols via enzymatic hydrolysis of their corresponding sulfate esters, which furnishes homochiral products possessing the 'anti-Kazlauskas' configuration. Copyright
- Schober, Markus,Knaus, Tanja,Toesch, Michael,MacHeroux, Peter,Wagner, Ulrike,Faber, Kurt
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p. 1737 - 1742
(2012/07/31)
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- Copper-catalyzed enantioselective propargylic amination of nonaromatic propargylic esters with amines
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Chemical equations presented. The enantioselective propargylic amination of propargylic pentafluorobenzoates bearing an alkyl group at the propargylic position with amines in the presence of catalytic amounts of a copper complex and an optically active diphosphine such as BINAP has been found to give the corresponding propargylic amines in good yields with high enantioselectivity.
- Yoshida, Akiko,Hattori, Gaku,Miyake, Yoshihiro,Nishibayashi, Yoshiaki
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supporting information; experimental part
p. 2460 - 2463
(2011/07/09)
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- First stereoselective total synthesis of (-)-stagonolide A
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The first stereoselective total synthesis of the nonenolide (-)-stagonolide A is described. Olefin metathesis and epoxide opening reaction are the key steps involved.
- Srihari, Pabbaraja,Kumaraswamy, Boyapelly,Rao, Gokada Maheswara,Yadav, Jhillu Singh
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experimental part
p. 106 - 111
(2010/04/06)
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- Catalytic asymmetric synthesis of allylic thiol derivatives
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(Chemical Equation Presented) The palladium(II) complex [(Rp, S)-COP-Cl]2 and its enantiomer catalyze the rearrangement of linear prochiral O-allyl carbamothioates under mild conditions to provide branched S-allyl carbamothioates in high yield
- Overman, Larry E.,Roberts, Scott W.,Sneddon, Helen F.
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supporting information; experimental part
p. 1485 - 1488
(2009/04/12)
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- Substrate-dependent stereochemical course of the (Z)-13-desaturation catalyzed by the processionary moth multifunctional desaturase
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The stereochemical course of the Δ13 desaturation involved in the biosynthesis of Thaumetopoea pityocampa sex pheromone was studied using stereotopically labeled and tagged palmitic acids as metabolic probes. In the synthetic pathway, a functionalized acetylene common synthon was used for introducing the four deuterium tags. Further coupling of the tetradeuterated synthon to the appropriated alkynol and a double chemoenzymatic strategy to resolve the alcohol functionality allowed one to obtain the enantiomerically enriched probes used in the mechanistic studies. Mass spectrometric analyses of extracts from tissues cultured with each probe revealed that removal of the C13 and C14 hydrogens in 11-hexadecynoate and (Z)-11-hexadecenoate are pro-(R)- and pro-(S)-specific syn-dehydrogenation processes, respectively. This finding constitutes the first example in the literature of an enzymatic (Z)-desaturation exhibiting a substrate-dependent stereochemical course.
- Abad, Jose-Luis,Camps, Francisco,Fabrias, Gemma
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p. 15007 - 15012
(2008/09/18)
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- Catalytic asymmetric synthesis of allylic aryl ethers
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(Chemical Equation Presented) The reaction of trichloroacetimidate derivatives of (Z)-2-alken-1-ols with phenol nucleophiles in the presence of the palladium(II) catalyst [COP-OAc]2 provides 3-aryloxy-1-alkenes in high yields and high enantiomeric purity (typically 63-90% yield and 90-97% ee). The reaction is exemplified by 20 examples. The method employs 1 mol % of the commercially available catalysts (S)- or (R)-[COPOAc]2, produces the branched isomer with unprecedented regioselectivity, and is compatible with the presence of base-labile functionality in either reactant.
- Kirsch, Stefan F.,Overman, Larry E.,White, Nicole S.
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p. 911 - 913
(2007/10/03)
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- Synthesis of azide-alkyne fragments for 'click' chemical applications; formation of oligomers from orthogonally protected trialkylsilyl-propargyl azides and propargyl alcohols
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A series of orthogonally protected 1,4-disubstituted-1,2,3-triazoles were prepared from the corresponding alkynols and trialkylsilyl-propargyl azides via 1,3-dipolar cycloaddition. These cycloadducts were selectively deprotected and extended in a stepwise fashion via further 'click' reactions to form oligomeric peptidomimetic compounds. This methodology gives access to triazole-based peptidomimetics in a controlled fashion and lays the foundation for a fragment-based approach to drug discovery.
- Montagnat, Oliver D.,Lessene, Guillaume,Hughes, Andrew B.
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p. 6971 - 6974
(2007/10/03)
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- Studies on the Cu(I)-catalyzed regioselective anti-carbometallation of secondary terminal propargylic alcohols
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A highly regioselective Cu(I)-catalyzed anti-carbometallation of secondary terminal propargylic alcohols with 1° alkyl or aryl Grignard reagents affording 2-substituted allylic alcohols was developed. By using this method, optically active allylic alcohols can be prepared from the optically active propargylic alcohols without obvious loss of the enantiopurity. The cyclic organometallic intermediate formed may undergo an iodination or a Pd(0)-catalyzed coupling reaction to afford stereo-defined allylic alcohols.
- Lu, Zhan,Ma, Shengming
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p. 2655 - 2660
(2007/10/03)
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- Rearrangements and stereomutations of metallacycles derived from allenes and imidozirconium complexes
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The mechanisms of the rearrangements and Stereoinversion of azametallacyclobutenes generated via [2+2] cycloaddition of allenes and imidozirconium complexes have been studied. Metallacycles derived from allenes bearing β-hydrogen atoms racemize at room temperature by reversible β-hydride elimination, a process which is also responsible for their eventual conversion to monoazadiene complexes. Metallacycles derived from diarylallenes racemize by reversible thermal bond homolysis at 95°C; racemization of these metallacycles is also catalyzed by mild oxidants.
- Michael, Forrest E.,Duncan, Andrew P.,Sweeney, Zachary K.,Bergman, Robert G.
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p. 1752 - 1764
(2007/10/03)
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- Mechanisms of allene stereoinversion by imidozirconium complexes
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The zirconium-mediated stereoinversion of allenes has been investigated by studying the stereochemical behavior of metallacycles derived from [2+2] cycloaddition of enantioenriched allenes with chiral and achiral imidozirconocene complexes. Relative rates of metallacycle racemization were measured by circular dichroism, and intermediates in the selective stereoinversion of diphenylallene with a chiral imidozirconium complex were observed by NMR spectroscopy. Metallacycles derived from dialkylallenes are proposed to racemize via reversible β-hydride elimination. Stereoinversion of diarylallene-derived metallacycles proceeds much more slowly and is thought to proceed through an η4-azatrimethylenemethane transition state. Copyright
- Michael, Forrest E.,Duncan, Andrew P.,Sweeney, Zachary K.,Bergman, Robert G.
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p. 7184 - 7185
(2007/10/03)
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- The effect of catechin derivatives on the enantioselectivity of lipase-catalyzed hydrolyses of alkynol benzoate esters
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Polyphenols, such as (+)-catechin and pyrogallol could be used to enhance stereochemical control in the lipase-catalyzed hydrolysis of alkynol benzoate esters, leading to increased enantioselectivities in the kinetic resolution of alkynols with lipase Amano AH.
- Nakamura, Kaoru,Takenaka, Keishi
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p. 415 - 422
(2007/10/03)
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- Stereoselective synthesis of pamamycin-607
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A macrodiolide antibiotic pamamycin-607 was synthesized by joining two hydroxy acid components. Three cis-2, 5-disubstituted tetrahydrofuran rings in the molecule were stereoselectively prepared by radical cyclization reactions of β-alkoxyvinyl ketone intermediates and a β-alkoxymethacrylate substrate. The key step of the synthesis is characterized by the predominant threo product formation in the radical cyclization reaction of a β-alkoxymethacrylate intermediate.
- Jeong, Eun Jeong,Kang, Eun Joo,Sung, Lee Taek,Hong, Sung Kil,Lee, Eun
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p. 14655 - 14662
(2007/10/03)
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- Mutation of cysteine-295 to alanine in secondary alcohol dehydrogenase from thermoanaerobacter ethanolicus affects the enantioselectivity and substrate specificity of ketone reductions
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The mutation of Cys-295 to alanine in Thermoanaerobacter ethanolicus secondary alcohol dehycrogenase (SADH) was performed to give C295A SADH, on the basis of molecular modeling studies utilizing the X-ray crystal structure coordinates of the highly homologous T. brockii secondary alcohol dehydrogenase (YKF.PDB). This mutant SADH has activity for 2-propanol comparable to wild-type SADH. However, the C295A mutation was found to cause a significant shift of enantioselectivity toward the (S)-configuration in the reduction of some ethynylketones to the corresponding chiral propargyl alcohols. This result confirms our prediction that Cys-295 is part of a small alkyl group binding pocket whose size determines the binding orientation of ketone substrates, and, hence, the stereochemical configuration of the product alcohol. Furthermore, C295A SADH has much higher actifity towards t-butyl and some α-branched ketones than does wild-type SADH. The C295A mutation does not affect the thioester reductase activity of SADH. The broader substrate specificity and altered stereoselectivity for C295A SADH make it a potentially useful tool for asymmetric reductions. Copyright
- Heiss, Christian,Laivenieks, Maris,Zeikus,Phillips, Robert S.
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p. 1659 - 1666
(2007/10/03)
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- Enantioselective synthesis of both enantiomers of various propargylic alcohols by use of two oxidoreductases
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The oxidoreductases Lactobacillus brevis alcohol dehydrogenase (LBADH) and Candida parapsilosis carbonyl reductase (CPCR) are suitable catalysts for the reduction of ketones to afford enantiopure sec. alcohols. A broad variety of alkynones (1, 3, and 5) are accepted as substrates and the corresponding propargylic alcohols (2, 4, and 6) are obtained in good yield and excellent enantiomeric excess. By changing the steric demand of the substituents the ee values can be adjusted and even the configurations of the products can be altered.
- Schubert, Thomas,Hummel, Werner,Kula, Maria-Regina,Mueller, Michael
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p. 4181 - 4187
(2007/10/03)
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- Stereoselective synthesis of β-ketoesters from prop-2-yn-1-ols
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The activation of allylic prop-2-yn-1-ols by the [Ru(μ-O2CH)(CO)2(PPh3)]2 catalyst in the presence of carboxylic acids leads to unsaturated β-ketoesters in one step. The utilization of optically active prop-2-yn-1-ols provides a new stereoselective access to optically active β-ketoesters with retention of configuration at the propargylic carbon.
- Darcel, Christophe,Bruneau, Christian,Dixneuf, Pierre H.,Roberts, Stanley M.
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p. 9241 - 9252
(2007/10/03)
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- HYDRATION TRIMERIZATION OF ACETYLENE IN SUPERBASIC MEDIA III. VINYLATION OF ACETYLENIC ALCOHOLS AS INTERMEDIATE STAGE
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It was confirmed that the hydration-trimerization of acetylene to 2-vinyloxy-1,3-butadiene in superbasic media takes place by a stepwise mechanism, involving the initial formation of acetaldehyde, its ethynylation, vinylation of the acetylenic alcohol, and prototropic acetyl-allene-1,3-diene rearrangements.A method was developed for the direct vinylation of primary and secondary acetylenic alcohols in the potassium hydroxide-DMSO system, leading to 3-vinyloxy-1-alkynes and 3-vinyloxy-1,2-alkadienes with overall yields of 45-87percent .
- Tarasova, O. A.,Trofimov, B. A.,Afonin, A. V.,Sinegovskaya, L. M.,Kalinina, N. A.,Amosova, S. V.
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p. 1018 - 1025
(2007/10/02)
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- Synthesis of optically active alkynyl alcohols and α-hydroxy esters by microbial asymmetric hydrolysis of the corresponding acetates
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Asymmetric hydrolysis of the acetates of racemic alkynyl alcohols and α-hydroxy esters by Bacillus subtilis var. Niger afforded optically active acetates and alcohols in 7-90% optical purities. The both enantiomers of optically pure mandelie acid were prepared by this microbial method.
- Mori, Kenji,Akao, Hiroko
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