Meetings by month
Copper(I)-Catalyzed Asymmetric Monoborylation of 1,3-Dienes: Synthesis of Enantioenriched Cyclic Homoallyl- and Allylboronates
Yusuke Sasaki, Chongmin Zhong, Masaya Sawamura, and Hajime Ito
Copper(I)-catalyzed asymmetric monoborylation of 1,3-dienes has been developed. We describe the production of either optically active homoallyl- or allylboronates with high regio- and enantioselectivity (88−97% ee) through monoborylation of 1,3-dienes. The reaction with 1,3-cyclohexadiene derivatives afforded the corresponding enantioenriched homoallyboronates. By simply changing the reaction conditions, a drastic change of product preference between homoallyl- and allylboronates was found in the reaction of 1,3-cyclopentadiene and 1,3-cycloheptadiene.
Highly Enantioselective Titanium-Catalyzed Cyanation of Imines at Room Temperature
Abdul Majeed Seayad, Balamurugan Ramalingam, Kazuhiko Yoshinaga, Takushi Nagata, and Christina L. L. Chai
A highly active and enantioselective titanium-catalyzed cyanation of imines at room temperature is described. The catalyst used is a partially hydrolyzed titanium alkoxide (PHTA) precatalyst together with a readily available N-salicyl-β-aminoalcohol ligand. Up to 98% ee was obtained with quantitative yields in 15 min of reaction time using 5 mol % of the catalyst. Various N-protecting groups such as benzyl, benzhydryl, Boc, and PMP are tolerated.
Boopathy Gnanaprakasam, Jing Zhang, and David Milstein*
An excellent extension of work by D.Milstein and co from Israel on the use of Ruthenium complexes to synthesise aryl and aliphatic imines directly from alcohols and amines. Environmentally benign with H2 and water as the only by-products, however extensive reaction times are required.
Shoubhik Das, Daniele Addis, Shaolin Zhou, Kathrin Junge and Matthias Beller
A novel zinc-catalyzed reduction of tertiary amides was developed. This system shows remarkable chemoselectivity and substrate scope tolerating ester, ether, nitro, cyano, azo, and keto substituents.
Practical and Highly Selective Sulfur Ylide Mediated Asymmetric Epoxidations and Aziridinations Using an Inexpensive, Readily Available Chiral Sulfide. Applications to the Synthesis of Quinine and Quinidine
Ona Illa, Muhammad Arshad, Abel Ros, Eoghan M. McGarrigle and Varinder K. Aggarwal*
School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, United Kingdom
J. Am. Chem. Soc., Article ASAP
Science 18 December 2009:Vol. 326. no. 5960, p. 1662DOI: 10.1126/science.1180739
Regiodivergent Ring Opening of Chiral Aziridines
Bin Wu, Jon R. Parquette,* T. V. RajanBabu*
Kinetic resolution of strained three-membered rings has proven broadly useful for the generation of enantiopure organic intermediates. Herein we demonstrate a complementary approach whereby a single catalyst transforms a racemic mixture of aziridines to a pair of regioisomeric products, each in good yield with exceptionally high enantioselectivity. Specifically, the dimeric yttrium salen catalyst accelerates the ring opening of aliphatic aziridines by trimethylsilylazide, inducing nucleophilic attack at the primary position of one enantiomer and the secondary position of the other. Both rate and selectivity are highly sensitive to the catalyst structure.
Department of Chemistry, The Ohio State University, 100 West 18th Avenue, Columbus, OH 43210, USA.
Direct Conversion of Arylamines to Pinacol Boronates: A Metal-Free Borylation Process**
Fanyang Mo, Yubo Jiang, Di Qiu, Yan Zhang, and Jianbo Wang*
Leave the metal out: Arylboronates are produced in moderate to good yields by direct borylation of readily available aryl amines (see scheme). The reaction can be carried out under air at room temperature and transition-metal catalysis is not required. The boronate products can be used without purification in Suzuki-Miyaura cross-coupling reactions.
War of the Grignards: Battle Ground Fluorination Knochel only just missed out on the first publication describing fluorination of functionalised aryl Grignards Efficient Synthesis of Aryl Fluorides
Pazhamalai Anbarasan, Dr., Helfried Neumann, Dr., Matthias Beller, Prof.
Creating CF bonds: A novel electrophilic fluorination of aryl and heteroaryl Grignard reagents has been discovered and was used for the efficient synthesis of various aryl fluoride derivatives (see picture; THF=tetrahydrofuran).
Convenient Electrophilic Fluorination of Functionalized Aryl and Heteroaryl Magnesium Reagents
Shigeyuki Yamada, Dr., Andrei Gavryushin, Dr., Paul Knochel, Prof. Dr.
Give me an F: Electrophilic fluorination of various aromatic and heteroaromatic Grignard reagents is smoothly performed with (PhSO2)2NF as fluorinating agent in a 4:1 mixture of CH2Cl2/perfluorodecalin (see scheme). This solvent system allows minimization of most side reactions.
Jinkun Huang*, Johann Chan, Ying Chen, Christopher J. Borths, Kyle D. Baucom, Robert D. Larsen and Margaret M. Faul
Heteroarenes are important structural moieties in many chemical industry fields. A highly efficient Pd/Cu-catalyzed C−H arylation method for a range of heterocycles has been discovered. It was found that the key to the success of this transformation is a combination of a palladium catalyst and a well-defined copper cocatalyst. The efficiency and low loadings of catalyst (0.25 mol %) and cocatalyst (1 mol %) together with the mild reaction conditions demonstrate this method to be practically useful and mechanistically interesting.
Asymmetric Cooperative Catalysis of Strong Brønsted Acid–Promoted Reactions Using Chiral Ureas
Hao Xu, Stephan J. Zuend, Matthew G. Woll, Ye Tao, Eric N. Jacobsen*
Cationic organic intermediates participate in a wide variety of useful synthetic transformations, but their high reactivity can render selectivity in competing pathways difficult to control. Here, we describe a strategy for inducing enantioselectivity in reactions of protio-iminium ions, wherein a chiral catalyst interacts with the highly reactive intermediate through a network of noncovalent interactions. This interaction leads to an attenuation of the reactivity of the iminium ion and allows high enantioselectivity in cycloadditions with electron-rich alkenes (the Povarov reaction). A detailed experimental and computational analysis of this catalyst system has revealed the precise nature of the catalyst-substrate interactions and the likely basis for enantioinduction.
Novel thiourea-amine bifunctional catalysts for asymmetric conjugate addition of ketones/aldehydes to nitroalkenes: rational structural combination for high catalytic efficiency
Jia-Rong Chen, Yi-Ju Cao, You-Quan Zou, Fen Tan, Liang Fu, Xiao-Yu Zhu and Wen-Jing Xiao
A series of thiourea-amine bifunctional catalysts have been developed by a rational combination of prolines with cinchona alkaloids, which are connected by a thiourea motif. The catalyst 3a, prepared from L-proline and cinchonidine, was found to be a highly efficient catalyst for the conjugate addition of ketones/aldehydes to a wide range of nitroalkenes (up to 98/2 dr and 96% ee). The privileged cinchonidine backbone and the thiourea motif are essential to the reaction activity and enantioselectivity.
An Expedient Procedure for the Oxidative Cleavage of Olefinic Bonds with PhI(OAc)2, NMO, and Catalytic OsO4
K. C. Nicolaou*, Vikrant A. Adsool and Christopher R. H. Hale
PhI(OAc)2 in the presence of OsO4 (cat.) and 2,6-lutidine cleaves olefinic bonds to yield the corresponding carbonyl compounds, albeit, in some cases, with α-hydroxy ketones as byproduct. A more practical and clean protocol to effect oxidative cleavage of olefinic bonds involves NMO, OsO4(cat.), 2,6-lutidine, and PhI(OAc)2.
DOI : 10.1021/ol100290a
Radical Synthesis of Guanidines from N-Acyl Cyanamides
Marie-Hélène Larraufie, Cyril Ollivier, Dr., Louis Fensterbank, Prof. *, Max Malacria, Prof. *, Emmanuel Lacôte, Dr. *
Center stage: Additions of nitrogen-centered radicals to cyanamide compounds provided the first radical synthesis of aromatic polycyclic guanidine derivatives (see scheme). Modular assembly of the substrates allows for a rapid increase of the molecular complexity of scaffolds, which have potential applications for medicinal chemistry.
a-Functionalization of non-activated aliphatic amines: ruthenium-catalyzed alkynylations and alkylations
Irina Jovel, Saisuree Prateeptongkum, Ralf Jackstell, Nadine Vogl, Christoph Weckbecker and Matthias Beller
DHTP Ligands for the Highly Ortho-Selective, Palladium-Catalyzed Cross-Coupling of Dihaloarenes with Grignard Reagents: A Conformational Approach for Catalyst
Shunpei Ishikawa and Kei Manabe
Angew. Chem. Int. Ed. 2010, 49, 772-775
Traditionally, palladium mediated site-selective cross-coupling of dihaloarenes has been a challenge for synthetic chemists, particularly when differentiation of the reactive sites becomes difficult by steric or electronic factors. Apart from that, formation of competing and undesired doubly cross-coupled product poses further challenge.
In this paper, Manabe et al. presents DHTP (dihydroxyterphenylphosphine) ligands as a new class of ligands for palladium catalysed highly ortho-selective cross-coupling of Grignard reagent with dihaloarenes. The rationale behind the design of these ligands has been well presented with a number of examples involving cross-coupling of arylmagnesium bromide with 2,4-dibromophenol, 2,5-dibromophenol, 2,4-dibromoaniline, 1,6-dibromonaphth-1-ol, 2-chloro-4-bromophenol, affording ortho-cross coupled product exclusively in all cases. This remarkable ortho-selective cross-coupling can be achieved by employing as less than 1 mol% of Pd2(dba)3 and 2.4 mol% of the DHTP ligand at room temperature in about 2-5 h. It is expected that this ligand will soon find application in several metal catalysed site-selective cross-coupling reactions to build drug frameworks and synthetic intermediates.
Tandem β-Alkylation−α-Arylation of Amines by Carbolithiation and Rearrangement of N-Carbamoyl Enamines (Vinyl Ureas)
Jonathan Clayden*, Morgan Donnard, Julien Lefranc, Alberto Minassi and Daniel J. Tetlow
Organolithiums add in an umpolung fashion to the β-carbon of N-carbamoyl enamines (N-vinyl ureas). The reaction proceeds with syn diastereospecificity and provides urea-stabilized, configurationally defined organolithiums. Facilitated by coordinating solvents (THF or DMPU), these undergo intramolecular attack on an N′-aryl group, resulting in retentive arylation of the organolithium and hence overall addition of an alkyl or aryl group to both carbon atoms of the urea-substituted alkene. Facile deprotection in hot butanol permits the rapid, multicomponent construction of heavily substituted amines.
Preparation of functionalized organoaluminiums by direct insertion of aluminium to
Tobias Blumke, Yi-Hung Chen, Zhihua Peng and Paul Knochel*
Nature Chem., 2010, 2, 313-318
Unlike the preparation of organomagnesium compounds, organoaluminium compounds cannot be prepared by direct insertion of the aluminium metal to a organohalide starting materials or through aluminium-halogen exchange reaction. This has limited the scope of the utility of organoaluminium reagents for C-C bond formation reactions. In this paper, Knochel and co-workers addresses this problem by reporting an elegant preparation of organoaluminium reagents by direct insertion of commercially available aluminium metal into the aryl and alkenyl halides using stoichiometric quantities of LiCl and catalytic quantities of Lewis acids such as PbCl2, InCl3, BiCl3, TiCl4, SnCl2 along with TMS-Cl (3 mol%). These additives are necessary to activate the unreactive metal surface which contain oxides and hydroxides that passivates the metal for direct metal-halide insertion reactions. Addition of stoichiometric quantities of LiCl solubilises and removes the resulting organometallic species from the metal surface, thereby allowing a further insertion to occur on the clean metal surface.
The authors have demonstrated the utility of this protocol to generate a range of aryl and alkenyl organoaluminium reagents containing various functionalities. Further, these resulting new organoaluminium reagents undergo smooth Pd-catalysed cross-coupling and acylation reactions, as well as copper-catalysed allylic substitutions, affording various interesting products for pharmaceutical and material science applications.
Rh(I)-Catalyzed Olefin Hydroarylation with Electron-Deficient Perfluoroarenes
Zhong-Ming Sun, Jing Zhang, Rajith S. Manan and Pinjing Zhao*
Assisted by a partially aqueous media, a catalyst system of [Rh(cod)(OH)]2 and DPPBenzene ligand effectively promotes direct conjugate additions by perfluoroarenes. This formal C−H alkylation process represents a rare example of olefin hydroarylation with electron-deficient arenes. The catalyst system can be modified to selectively form the corresponding olefination products under anhydrous conditions.
Direct Asymmetric Aldol Reaction of 5H-Oxazol-4-ones with Aldehydes Catalyzed by Chiral Guanidines
A new chiral bicyclic guanidine-catalyzed direct catalytic aldol reaction of 5H-oxazol-4-ones with aldehydes has been developed. The present aldol reaction proceeds smoothly with high enantioselectivity using bicyclic guanidines bearing a hydroxy group at the appropriate position, and various combinations of 5H-oxazol-4-ones and aldehydes are applicable. The method provides synthetically useful α,β-dihydroxycarboxylates bearing a chiral quaternary stereogenic center at the α-carbon atom.
One-Pot Procedure for the Synthesis of Unsymmetrical Diarylalkynes
Ren Severin, Jessica Reimer and Sven Doye
Unsymmetrical diarylalkynes are accessible by a one-pot procedure from two different aryl halides and (trimethylsilyl)acetylene. The three-component coupling is initialized by a Pd/Cu-catalyzed Sonogashira coupling of an aryl halide with (trimethylsilyl)acetylene. After subsequent desilylation of the formed aryl(trimethylsilyl)acetylene with aqueous potassium hydroxide, a second Sonogashira coupling with an aryl iodide that does not require any additional Pd/Cu-catalyst gives access to an unsymmetrical diarylalkyne.
CuH-Catalyzed Enantioselective 1,2-Reductions of α,β-Unsaturated Ketones
Ralph Moser, Zarko V. Boskovic, Christopher S. Crowe and Bruce H. Lipshutz*
Department of Chemistry and Biochemistry, University of California, Santa Barbara, California 93106
The first study on a general technology for arriving at valued nonracemic allylic alcohols using asymmetric ligand-accelerated catalysis by copper hydride is described.
Ross M. Denton*, Jie An and Beatrice Adeniran
Chem. Commun., 2010, 46, 3025 - 3027, DOI: 10.1039/c002825h
A phosphine oxide-catalysed chlorination reaction of primary and secondary alcohols has been developed. This process represents the first triphenylphosphine oxide-catalysed alcohol chlorination under Appel conditions
Graduate School of Science and Technology, and Department of Applied Chemistry, Faculty of Engineering, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan
Directed lithiation of N-benzenesulfonyl-3-bromopyrrole (1) with LDA in THF at −78 °C generated C-2 lithio species 3 selectively. Reactions of 3 with reactive electrophiles produced the corresponding 2-functionalized pyrroles 4. On the other hand, quenching with less reactive electrophiles generated the corresponding 5-substituted pyrroles 5. The latter unusual functionalization at C-5 could be rationalized by dynamic equilibrium between C-2 and C-5 lithio species.
Adam R. Brown, Wen-Hsin Kuo and Eric N. Jacobsen
Publication Date (Web): June 22, 2010 (Communication)
Primary aminothiourea derivatives are shown to catalyze enantioselective alkylation of R-arylpriopionaldehdyes with diarylbromomethane. Evidence for a stepwise, SN1 mechanism in the substitution reaction induced by anion binding to the catalyst is provided by catalyst structure-activity studies, kinetic isotope effects, linear free-energy relationship studies, and competition experiments.
Hydroacylation of α,β-unsaturated esters via aerobic C–H activation
Vijay Chudasama, Richard J. Fitzmaurice & Stephen Caddick
Nature Chemistry, 2010, 2, 592–596 ; doi:10.1038/nchem.685
The development of methods for carbon–carbon bond formation under benign conditions is an ongoing challenge for the synthetic chemist. In recent years there has been considerable interest in using selective C–H activation as a direct route for generating reactive intermediates. This article describes the use of aldehyde auto-oxidation as a simple, clean and effective method for C–H activation, resulting in the generation of an acyl radical. This acyl radical can be used for carbon–carbon bond formation and the application of this method for the hydroacylation of α,β-unsaturated esters without the requirement of additional catalysts or reagents is described. This methodology generates unsymmetrical ketones, which have been shown to have broad use in organic synthesis.
Enantioselective Organo-SOMO Cascade Cycloadditions: A Rapid Approach to Molecular Complexity from Simple Aldehydes and Olefins
Nathan T. Jui, Esther C. Y. Lee and David W. C. MacMillan*
A highly selective, radical-mediated (4 + 2) coupling reaction of aldehydes and conjugated olefins has been achieved through asymmetric SOMO-catalysis. A radical-polar crossover mechanism is proposed wherein olefin addition to a transient enamine radical cation and oxidation of the resulting radical furnishes a cation which is vulnerable to nucleophilic addition. A range of aromatic aldehydes are shown to couple with styrenes and dienes to provide cyclic products with high chemical efficiency, regioselectivity, and stereoselectivity.
Unusual Reversal of Enantioselectivity in the Proline-Mediated α-Amination of Aldehydes Induced by Tertiary Amine Additives
Department of Chemistry and Department of Chemical Engineering, Imperial College London SW7 2AZ, U.K.
J. Am. Chem. Soc., 2010, 132 (22), pp 7598–7599
In this paper, the authors report an unsual reveral of enantioselectivity observed in the proline-mediated a-amination of aldehydes induced by tertiary amine additivies such as DBU. The mechanistic implications of these findings are discussed in detail with contending models for the enantiodifferentiating step in enamine catalysis.
Cooperative Catalytic Reactions Using Organocatalysts and Transition-Metal Catalysts: Enantioselective Propargylic Alkylation of Propargylic Alcohols with Aldehydes
Masahiro Ikeda, Yoshihiro Miyake, Dr., Yoshiaki Nishibayashi, Prof. Dr. *
The titled reaction proceeds in the presence of a thiolate-bridged diruthenium complex (2) and a secondary amine (1) to give the corresponding propargylic alkylated products in excellent yields as a mixture of two diastereoisomers, each with high enantioselectivity. The two catalysts activate propargylic alcohols and aldehydes, respectively, and cooperatively promote the enantioselective reaction.
Scheidt co-operative catalysis......well it's OK.
Cooperative catalysis by carbenes and Lewis acids in a highly stereoselective route to γ-lactams
Enzymes are a continuing source of inspiration for the design of new chemical reactions that proceed with efficiency, high selectivity and minimal waste. In many biochemical processes, different catalytic species, such as Lewis acids and bases, are involved in precisely orchestrated interactions to activate reactants simultaneously or sequentially. This type of ‘cooperative catalysis’, in which two or more catalytic cycles operate concurrently to achieve one overall transformation, has great potential in enhancing known reactivity and driving the development of new chemical reactions with high value. In this disclosure, a cooperative N-heterocyclic carbene/Lewis acid catalytic system promotes the addition of homoenolate equivalents to hydrazones, generating highly substituted γ-lactams in moderate to good yields and with high levels of diastereo- and enantioselectivity.
A General and Special Catalyst for Suzuki–Miyaura Coupling Processes
Angew. Chem. Int. Ed. 2010, 49, 5879-5883; DOI: 10.1002/anie.201002404
Wenjun Tang*, Andrew G. Capacci, Xudong Wei, Wenjie Li, Andre White, Nitinchandra D. Patel, Jolaine Savoie, Joe J. Gao, Sonia Rodriguez, Bo Qu, Nizar Haddad, Bruce Z. Lu, Dhileepkumar Krishnamurthy, Nathan K. Yee, Chris H. Senanayake
In this paper, Tang and co-workers report a new class of biaryl monophosphorus ligands (e.g. BI-DMIE) containing a 2,3-dihydrobenzo[d][1,3]oxaphosphole framework that are highly effective for the palladium-catalyzed Suzuki–Miyaura cross-coupling reactions of a wide range of substrates. Notable feature of this ligand is its remarkable ability to cross couple extremely hindered aryl boronic acids with hindered aryl chlorides and bromides and vice versa which otherwise could not be achieved by some of the efficient and widely used ligands at the present such as S-Phos, X-Phos, Ru-Phos, PCy3, PtBu3, etc. The ability to achieve this difficult transformation will make BI-DIME a more general ligand to construct tri-ortho-subsituted biaryls via Suzuki-Miyaura cross-coupling method.
Though this new ligand currently suffers from a long synthetic route, when commercialized will be widely used in the academic R&D laboratories, pharmaceutical, agro-chemical and allied industries. There is no doubt this paper will attract greater attention among chemists in the near future.
Dynamic Kinetic Resolution of Biaryl Atropisomers via Peptide-Catalysed Asymmetric Bromination
Jeffrey L. Gustafson, Daniel Lim, Scott J. Miller*
Science, 2010, 328, 1251-1255; DOI: 10.1126/science.1188403
Abstract: Despite the widespread use of axially chiral, or atropisomeric, biaryl ligands in modern synthesis and the occurrence of numerous natural products exhibiting axial chirality, few catalytic methods have emerged for the direct asymmetric preparation of this compound class. This paper reports a tripeptide-derived small-molecule catalyst for the dynamic kinetic resolution of racemic biaryl substrates. The reaction proceeds via an atropisomer-selective electrophilic aromatic substitution reaction using simple bromination reagents. The result is an enantioselective synthesis that delivers chiral nonracemic biaryl compounds with excellent optical purity and good isolated chemical yields (in most cases a >95:5 enantiomer ratio and isolated yields of 65 to 87%). A mechanistic model is advanced that accounts for the basis of selectivity observed.
Enantioselective Synthesis of (Z)-1,2-anti-2,5-anti-Triol Monosilyl Ethers Using a Cross-Metathesis Allylboration Sequence
SusAnn M. Winbush and William R. Roush
The enantioselective synthesis of (Z)-1,2-anti-2,5-anti-triol monosilyl ethers via a two-step sequence involving olefin cross-metathesis of β-alkoxyallylboronate and subsequent allylboration of the derived bisboryl intermediate provides triol monoethers with good to excellent diastereoselectivity.
Total Synthesis of the Marine Antibiotic Pestalone and its Surprisingly Facile Conversion into Pestalalactone and Pestalachloride A
Nikolay Slavov, Dr. Ján Cvengroš, Dr. Jörg-Martin Neudörfl, Prof. Dr. Hans-Günther Schmalz
Surprise, surprise! The total synthesis of the marine natural product pestalone, a highly substituted benzophenone with strong antibiotic acitivity, has provided insight into the surprising tendency of this and related molecules to undergo intramolecular Cannizzaro–Tishchenko-type reactions. Pestalone can be readily converted into pestalachloride A, a strongly antifungal metabolite isolated from an endophytic fungus, by simple treatment with ammonia at pH 8.
Tetraquinanes via [4 + 4] Photocycloaddition/Transannular Ring Closure
Peiling Chen, Patrick J. Carroll, and Scott McN. Sieburth*
Org. Lett., 2010, 12 (20), pp 4510–4512 http://dx.doi.org/10.1021/ol101802s
Intramolecular [4 + 4] photocycloaddition of a furan and a cyclopentane-annulated 2-pyridone yields a cyclooctadiene product with four new stereogenic centers. Transannular ring closure produces the 5−5−5−5 fused ring system of the crinipellins, including three contiguous quaternary carbons, with the correct absolute stereochemistry derived from (−)-carvone.
Synthesis of Programmable Tetra-ortho-Substituted Biaryl Compounds Using Diels−Alder Cycloadditions/Cycloreversions of Disubstituted Alkynyl Stannanes
J. Am. Chem. Soc., 2008, 130 (11), pp 3290–3291
Orthogonally functionalized, programmable biaryl templates have been synthesized utilizing aryl acetylenic stannanes and oxygenated dienes in a cycloaddition/cycloreversion strategy. Sequential functionalization of each of the four ortho positions has been demonstrated. Subsequent resolution of a representative anilino phenol has been accomplished. Additionally, a highly active anhydrous, boroxine-based Suzuki coupling protocol has been developed for conversion of unreactive aryl chlorides.
Efficient Synthesis of 1-Sulfonyl-1,2,3-triazoles
by Jessica Raushel and Valery V. Fokin
Department of Chemistry, The Scripps Research Institute
An efficient room-temperature method for the synthesis of 1-sulfonyl-1,2,3-triazoles from in situ generated copper(I) acetylides and sulfonyl azides is described. The copper(I) thiophene-2-carboxylate (CuTC) catalyst produces the title compounds under both nonbasic anhydrous and aqueous conditions in good yields.
A Mild and Efficient Palladium-Catalyzed Cyanation of Aryl Mesylates in Water or tBuOH/Water
Pui Yee Yeung, Dr. Chau Ming So, Prof. Dr. Chak Po Lau, Prof. Dr. Fuk Yee Kwong
Cool and compatible: Aryl mesylates and tosylates underwent palladium-catalyzed cyanation under mild, aqueous conditions at 65–80 °C (see scheme). In many cases, water could be used as the reaction medium without a cosolvent, and a variety of substituents R, such as keto, aldehyde, ester, free amine, and nitrile groups, remained intact during the transformation. Cy=cyclohexyl, Ms=methanesulfonyl, Ts=p-toluenesulfonyl.
General and Mild Preparation of 2-Aminopyridines
A general and facile one-pot amination procedure for the synthesis of 2-minopyridines from the corresponding pyridine-N-oxides is presented as a mild alternative to SNAr chemistry. A variety of amines and heterocyclic-N-oxides participate effectively in this transformation which uses the phosphonium salt, PyBroP, as a means of substrate activation.
A New Approach for Modification of Phenylalanine Peptides by Suzuki-Miyaura Coupling Reaction
Kotha et al, Bioorg. Med. Che. Lett., 2001, 11, 21, p2887
Abstract - For the first time, we have modified phenylalanine peptides by the Suzuki-Miyaura coupling reaction which may be useful in developing combinatorial libraries of peptidomimetics.
The selective, direct hydrogenation of amides to the corresponding alcohols and amines with cleavage of the C−N bond was discovered. The expected products of C−O cleavage are not formed (except as traces in the case of anilides). The reaction proceeds under mild pressure and neutral, homogeneous conditions using a dearomatized, bipyridyl-based PNN Ru(II) pincer complex as a catalyst. The postulated mechanism involves metal−ligand cooperation by aromatization−dearomatization of the heteroaromatic pincer core and does not involve hydrolytic cleavage of the amide. The simplicity, generality, and efficiency of this environmentally benign process make it attractive for the direct transformations of amides to alcohols and amines in good to excellent yields.
Electrophilic Aromatic Substitution of a BN Indole
Eric R. Abbey, Lev N. Zakharov and Shih-Yuan Liu
We report the first examples of a “BN-fused” indole, and we demonstrate that this new family of unnatural indole derivatives undergoes electrophilic aromatic substitution (EAS) reactions with the same regioselectivity as its organic analogue. Competition experiments reveal that N-t-Bu-BN-indole is more nucleophilic in EAS reactions than its carbonaceous counterpart. X-ray structural analysis between BN indole and classic indole highlights significant differences in bond distances, in particular for bonds associated with the boron atom.
Property and Reactivity of Fluoro(silyl)acetylenes
Masahiro Shiosaki, Masashi Unno, and Takeshi Hanamoto*
Fluoro(silyl)acetylenes and fluoro(stannyl)acetylenes underwent a radical addition reaction of THF to furnish
the corresponding fluorinated cyclic ethers in moderate to good yields. These intriguing addition reaction proved to proceed via a radical reaction mechanism.
A Chiral-Anion Generator: Application to Catalytic Desilylative Kinetic Resolution of Silyl-Protected Secondary Alcohols
Hailong Yan, Hyeong Bin Jang, Ji-Woong Lee, Hong Ki Kim, Soon Won Lee, Jung Woon Yang, Choong Eui Song*
Angew. Chem. Int. Ed., 2010, 49, 8915-8917.
Bis-Terminal Hydroxy Polyethers as All-Purpose, Multifunctional Organic Promoters: A Mechanistic Investigation and Applications
Ji Woong Lee, Hailong Yan, Hyeong Bin Jang, Hong Ki Kim, Sung-Woo Park, Sungyul Lee,* Dae Yoon Chi,* and Choong Eui Song*
Angew. Chem. Int. Ed. 2009, 48, 7683-7686
Achiral polyether derivatives have been shown to dramatically accelerate SN2 reactions by the simultaneous activation of both the nucleophile (KF) and electrophile (sulfonate; see picture). By using chiral variants as catalysts, the desilylative kinetic resolution of the silyl ethers of racemic secondary alcohols has been achieved. Density functional calculations provide detailed insight into the modes of action of this type of organic promoter.
Two Flavors of PEPPSI-IPr: Activation and Diffusion Control in a Single NHC-Ligated Pd Catalyst?
Authors: Igor Larrosa, Clara Somoza, Alexandre Banquy, and Stephen M. Goldup
Abnormal reactivity has been observed in Negishi, Suzuki-Miyaura, and Kumada-Tamao-Corriu cross-couplings in which PEPPSI-IPr (where PEPPSI stands for pyridine enhanced precatalyst preparation, stabilization, and initiation and IPr refers to the NHC ligand) is employed, implicating the presence of two distinct Pd0 species in the catalytic cycle. Polybrominated arenes and organometallic reagents react selectively to give the product of exhaustive polysubstitution regardless of the initial reaction stoichiometry. Competition experiments suggest that, after an initial activation controlled oxidative addition, reductive elimination produces an ultrareactive Pd0 species which consumes all remaining C-Br bonds in the molecule under diffusion control.
Copper(II)-Catalyzed meta-Selective Direct Arylation of alpha-Aryl Carbonyl Compounds
Angew. Chem. Int. Ed., 2010, 49, 1-5
Hung A. Duong, Ruth E. Gilligan, Michael L. Cooke, Robert J. Phipps, and Matthew J. Gaunt*
Keywords:arylation;CH functionalization;copper;hypervalent iodine;meta substitution
Strong competition: A method for the meta-selective arylation of the highly versatile α-aryl carbonyl motif using diaryliodonium salts is described. In this CuII-catalyzed process the remote carbonyl group is capable of overpowering even strongly para-directing functionalities to form the elusive meta-products (see scheme). Remarkably, the arylation process can also operate under metal-free conditions.