Meetings by month
The Fluorine-Iminium Ion Gauche Effect: Proof of Principle and Application to Asymmetric Organocatalysis.
The first publication from the new Gilmour group at ETH, Zurich. It describes the exploitation of the gauche effect when fluorine is positioned alpha to an electronegative atom. The effect is used to impart greater rigidity on an iminium ion involved in the organocatalytic assymmetric epoxidation of a,b-unsaturated aldehydes. The extra rigidity leads to higher ee's and the effect will surely have wider implications in the vast and active field of secondary amine organocatalysis.
Trifunctional organocatalyst-promoted counterion catalysis for fast and enantioselective aza-Moritaâ€“Baylisâ€“Hillman reactions at ambient temperature
J-M, Garnier and F, Liu, Org. Biomol. Chem., 2009,Â 7, 1272 - 1275
Cu(I)-Catalyzed C-H a-Amination of Aryl
Ketones: Direct Synthesis of Imidazolinones
J. Org. Chem.ASAP Article
This paper describes an Î±-amination process of aryl ketones using CuCl as catalyst and di-tert-butyldiaziridinone as the nitrogen source. A variety of imidazolinone derivatives are prepared in moderate yields under mild conditions. A possible catalytic cycle is proposed for this reaction.
Enantioselective Robinson-Type Annulation Reaction Catalyzed by Chiral Phosphoric Acids
Angewandte Chemie Int. Ed.Â (Early view)
I chose this paper because it demonstrated an interesting application of a bifunctional chiral phosphoric acid in enantioselective organocatalysisÂ via hydrogen bonding.
Yo Yo's paper
Metalâˆ’BrÃ¸nsted Acid Cooperative Catalysis for Asymmetric Reductive Amination
Direct reductive amination of a wide range of ketones has been accomplished by the cooperative catalysis of an Ir(III)-diamine complex and a chiral phosphoric acid or its conjugate base.
Versatile Pd(OTf)2Â·2H2O-Catalyzed ortho-Fluorination Using NMP as a Promote
Xisheng Wang, Tian-Sheng Mei, and Jin-Quan Yu
J. Am. Chem. Soc., Article ASAP â€¢ DOI: 10.1021/ja901352k
The authors have developed a new protocol for efficient ortho-fluorination using Pd(OTf)2 Â·2H2O as the catalyst, N-fluoro-2,4,6- trimethylpyridinium triflate as the F+ source, and NMP as the crucial promoter. The triflamide directing group can be readily displaced bya wide range of heteroatom and carbon nucleophiles, thereby affording this fluorination protocol excellent versatility for synthetic applications.
Ruthenium-Catalyzed Oxidation of Alcohols into Amides
The synthesis of secondary amides from primary alcohols and amines has been developed using commercially available [Ru(p-cymene)Cl2]2 with bis(diphenylphosphino)butane (dppb) as the catalyst.
Xinbo Wang, Bo Zhang and David Zhigang Wang*
An intriguing paper which claims that NaH is an effective oxidation promoter. A series of benzylic alcohol oxidations are performed and the results seem surprising taking into account the usual reactivity of NaH. The authors claim that NaH is directly involved in the oxidation process and the fact that, NaH can be recovered at the end of the reaction, there is the suggestion that the reaction is catalytic. The article was picked up almost immediately on Paul Doherty's Totally Synthetic blog and has since become the most commented thread in the site's history. It's caused quite a stir.
Metal-Catalyzed Carboxylation of Organometallic Reagents with Carbon Dioxide
Arkaitz Correa, Dr. and Rubén Martín, Dr
Angew.Chem.Int.Ed, 2009, 48, 2-6
An easy to read overview of key publications and recent developments in the metal-catalysed carboxylation of organometallic reagents
Thio FCMA Intermediates as Strong Acyl Donors: A General Solution to the Formation of Complex Amide Bonds
Yu Rao,† Xuechen Li,† and Samuel J. Danishefsky*,†,‡
Novel methodology for the formation of amide bonds under neutral conditions is described. Evidence is presented that the active acyl donors are thio FCMA intermediates, generated from the reactions of thioacids with isonitriles.
Plagiarizing Proteins: Enhancing Efficiency in Asymmetric Hydrogen-Bonding Catalysis through Positive Cooperativity
Christopher R. Jones , G. Dan Panto, Dr. , Angus J. Morrison, Dr. , Martin D. Smith, Dr.
Conformationally well-defined thiourea catalysts, like that shown, stabilized by intramolecular hydrogen bonds demonstrate cooperative ligand-receptor binding. This conformation leads to significantly enhanced catalytic efficiency, resulting in higher turnover rates and lower catalyst loading whilst maintaining high enantioselectivity in a model reaction.
Exploring the Positional Attachment of Glycopeptide/bold beta-lactam Heterodimers
Daniel D Long, James B Aggen†, Jason Chinn, Seok-Ki Choi, Burton G Christensen, Paul R Fatheree, David Green††, Sharath S Hegde, J Kevin Judice†, Koné Kaniga†††, Kevin M Krause, Michael Leadbetter, Martin S Linsell†, Daniel G Marquess, Edmund J Moran, Matthew B Nodwell, John L Pace††††, Sean G Trapp and S Derek Turne
Theravance, Inc., 901 Gateway Blvd., South San Francisco, CA 94080, USA
Further investigations towards novel glycopeptide/-lactam heterodimers are reported. Employing a multivalent approach to drug discovery, vancomycin and cephalosporin synthons, 4, 2, 5 and 10, 18, 25 respectively, were chemically linked to yield heterodimer antibiotics. These novel compounds were designed to inhibit Grampositive bacterial cell wall biosynthesis by simultaneously targeting the principal cellular targets of both glycopeptides and -lactams. The positional attachment of both the vancomycin and the cephalosporin central cores has been explored and the SAR is reported. This novel class of bifunctional antibiotics 2836 all displayed remarkable potency against a wide range of Gram-positive organisms, including methicillin-resistant Staphylococcus aureus (MRSA). A subset of compounds, 29, 31 and 35 demonstrated excellent bactericidal activity against MRSA (ATCC 33591) and 31 and 35 also exhibited superb in vivo efficacy in a mouse model of MRSA infection. As a result of this work compound 35 was selected as a clinical candidate, TD-1792.
Bing Li's paper
Chiral Guanidinium Salt Catalyzed Enantioselective Phospha-Mannich Reactions
Xiao Fu, Wei-Tian Loh, Yan Zhang, Tao Chen, Dr., Ting Ma, Hongjun Liu, Jianmin Wang, Choon-Hong Tan, Prof.
Guanidinium catalyst 1HBArF4 (ArF=3,5-CF3C6H3, Bn=benzyl, Ts=4-toluenesulfonyl) was obtained in a single step from a commercially available diamine. By using this catalyst an asymmetric phospha-Mannich reaction has been developed, involving secondary phosphine oxides and H-phosphinates as the P nucleophile. A series of enantiomerically enriched -amino phosphine oxides (2), -amino phosphinate, and H-phosphinates containing P-chiral center were prepared.
Efficient Enantioselective Synthesis of Optically Active Diols by Asymmetric Hydrogenation with Modular Chiral Metal Catalysts
Renat Kadyrov, Dr., René M. Koenigs, Dipl.-Chem., Claus Brinkmann, Dipl.-Chem., David Voigtlaender, Dr., Magnus Rueping, Prof. Dr.
AbstractValuable vicinal 1,2-diols can be prepared with high enantioselectivity by the asymmetric ruthenium-catalyzed hydrogenation of aryl- and alkyl-substituted -hydroxy ketones (see scheme). The ligands, which are distinguished by their modular construction, display excellent enantioface differentiation
Iridium-Catalyzed Regio- and Enantioselective N-Allylation of Indoles
Levi M. Stanley and John F. Hartwig
Angew. Chem. Int. Ed., 2009, 48, 1-5
Iridium is blind to C: Highly regio- and enantioselective, iridium-catalyzed N-allylations of indoles, which complement the more common reactivity of indoles as carbon nucleophiles, have been developed (see scheme). These reactions form highly enantioenriched N-allylindoles, which are readily transformed into enantioenriched 3-(1H-indol-1-yl)-N-methyl-3-aryl propan-1-amines, dihydropyrrolo[1,2-a]indoles, and indol-1-yl propanoic acids.
Xinhui Feng and Jaesook Yun
Chem. Commun., 2009 DOI: 10.1039/b914207
Asymmetric β-boronation of α,β-unsaturated carbonyl compounds promoted by chiral rhodium-bisoxazolinylphenyl catalysts.
Chem. Commun., 2009 DOI: 10.1039/b915759j
Comparison of two papers both of which give methods for the enantioselective boration of α,β-unsaturated carbonyl compounds. One paper studies cyclic compounds with the use of a copper catalyst, and the other acyclic compounds with a rhodium catalyst.
Dongbing Zhao, Ningjie Wu, Shuai Zhang, Peihua Xi, Xiaoyu Su, Jingbo Lan, Jingsong YouDOI: 10.1002/anie.200903923
Interesting synthesis of phenols from aryl iodides using a copper catalyst in comparison of the use of palladium catalysed conditions.
Formal [4 + 2] Cycloaddition of Donor−Acceptor Cyclobutanes and Aldehydes: Stereoselective Access to Substituted Tetrahydropyrans
Andrew T. Parsons and Jeffrey S. Johnson
A highly diastereoselective synthesis of 2,6-cis-disubstituted tetrahydropyrans (THPs) via Lewis acid-catalyzed formal [4 + 2] cycloaddition of donor−acceptor cyclobutanes and aldehydes has been developed. THP products are formed in up to 96% yield and 99:1 diastereoselectivity. Aromatic, cinnamyl, and aliphatic aldehydes are competent dipolarophiles in this system. This methodology was extended to a [[2 + 2] + 2] cycloaddition of 4-methoxystyrene, dimethyl methylidene malonate, and an aldehyde to furnish THPs directly without prior isolation of the cyclobutane.
J. Am. Chem. Soc., Article ASAP
Synthesis of Pyridines and Pyrazines Using an Intramolecular Hydroamination-Based Reaction Sequence (p NA)
Toni Rizk, Eric J.-F. Bilodeau, André M. BeaucheminDOI: 10.1002/anie.200903922
Various pyridines and pyrazines can be efficiently accessed from simple acyclic precursors using an intramolecular hydroamination/isomerization/aromatization sequence (see scheme). p-Toluenesulfonic acid (2 mol %) is used to catalyze this novel alkyne annulation, in which the oxime group allows for a subsequent redox-neutral aromatization step to occur.
Rajeev S. Menon, Alison D. Findlay, Alex C. Bissember and Martin G. Banwell
Operationally simple Au(I)-catalyzed intramolecular hydroarylation (IMHA) reactions of terminal alkynes that proceed in high yield and under very mild conditions are described. These processes involve low catalyst loadings, mild reaction temperatures, and short reaction times, require no cocatalysts or additives, and allow for the generation of a number of important heterocyclic motifs from readily accessible starting materials.
Efficient Chiral N-Heterocyclic Carbene/Copper(I)-Catalyzed Asymmetric Allylic Arylation with Aryl Grignard Reagents
by Khalid B. Selim, Dr., Yasumasa Matsumoto, Dr., Ken-ichi Yamada, Dr., Kiyoshi Tomioka, Prof. Dr.
The title reaction was achieved in a highly regioselective manner using aryl Grignard reagents with monodentate chiral N-heterocyclic carbene-copper(I) catalyst to give diarylvinylmethanes with excellent enantiomeric excess in excellent yield
Eleanor E. Maciver, Sam Thompson, Dr., Martin D. Smith, Dr. *
How to close a ring: An approach to catalytic asymmetric 6 electrocyclization leads to a highly enantioselective process that was used in the synthesis of chiral indolines (see scheme). Treatment of N-aryl imines under phase transfer conditions in the presence of N-benzyl cinchonidinium chloride generates a delocalized 2-aza-pentadienyl anion system that cyclizes in up to 99 % yield and 98 % ee
Anne Boussonnière, Fabrice Dénès, Dr., Jacques Lebreton, Prof.
An efficient procedure for radical cyclization of alpha-bromo esters is reported. Reduction of the esters by DIBAL-H at low temperature gives aluminum acetals, which are cyclized in the presence of nBu3SnH and Et3B (see scheme). These one-pot conditions lead to polysubstituted gamma-lactols in high yields, and the mildness of the reaction conditions allows the preparation of acid-sensitive derivatives.
Angew. Chem. Int. Ed. 2009, 48, 3322-3325
Siti Nurhanna Riduan, Yugen Zhang, Dr., Jackie Y. Ying, Prof.
The authors of this paper report an elegant protocol of utilising a stable N-heterocyclic carbene (NHC) organocatalyst for activation and reduction of carbondioxide (CO2) to methanol under very mild conditions. In contrast to the traditional transition metal-catalysed methods, NHC organocatalyst exhibits excellent turnover number (TON) and turnover frequency (TOF) of 1840 and 25.5 h-1 respectively for conversion of CO2 to methanol at ambient conditions.
The authors have taken substantial effort to identify the reaction intermediates involved in the catalytic cycle using sophisticated NMR spectroscopic experiments and have mapped the complete mechanism of the process.
One of the drawbacks in this process is the utilisation of expensive hydrosilanes as reducing reagents. However, the authors conclude in this paper that their ongoing research is focussed on using cheaper alternative hydride sources. Nevertheless, this protocol offers remarkable scope for new discoveries in chemical CO2 activation and fixation under metal-free conditions along with a possible hope for cheaper production of sustainable form of fuel in the era of global warming.
Comments posted by Mahesh
Nickel-Catalyzed Regioselective Carbomagnesation of Methylenecyclopropanes through a Site-Selective Carbon–Carbon Bond Cleavage
Jun Terao,* Masahiro Tomita, Surya Prakash Singh, and Nobuaki Kambe*
MCP's are reacted with vinyl and aryl Grignard reagents in the presence of a nickel catalyst to afford vinyl- and aryl-magnesation products through a selective C-C bond cleaveage.
Ang. Chem. Int. Ed., Early View.
Rhenium- and Manganese-Catalyzed Synthesis of Aromatic Compounds from 1,3-Dicarbonyl Compounds and Alkynes
Takai et al. have succeeded in the development of three approaches to the synthesis of aromatic compounds from 1,3-dicarbonyl compounds and alkynes. The first approach is a manganese-catalyzed [2+2+2] cycloaddition between 1,3-dicarbonyl compounds, which have no substituents at the active methylene moiety, and terminal alkynes. This reaction proceeds with high regioselectivity when aryl acetylenes are employed as the alkyne component. The second approach is a rhenium- or manganese-catalyzed formal [2+1+2+1] cycloaddition between β-keto esters and two kinds of alkynes. In this reaction, the aromatic compounds are obtained by the following reaction sequence: (1) insertion of the first alkyne into a carbon−carbon single bond of a β-keto ester, (2) formation of 2-pyranones via intramolecular cyclization with the elimination of ethanol, and (3) Diels−Alder reaction between the formed 2-pyranone and the second alkyne. This reaction provides multisubstituted aromatic compounds in a regioselective manner. The third approach is a rhenium-catalyzed formal [2+2+1+1] cycloaddition reaction from two 1,3-diketones and one alkyne. In this reaction, the aromatic skeleton is constructed from three carbons of the first 1,3-diketone, two carbons of the alkyne, and one carbon of the second 1,3-diketone.