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Biomedical subjects

Stephen L Buchwald

Publications and source records attributed to Stephen L Buchwald.

At least 37 records · Page 2Linked to original sources
PubMed2005

Catalysts for Suzuki-Miyaura coupling processes: scope and studies of the effect of ligand structure.

Suzuki-Miyaura coupling reactions of aryl and heteroaryl halides with aryl-, heteroaryl- and vinylboronic acids proceed in very good to excellent yield with the use of 2-(2',6'-dimethoxybiphenyl)dicyclohexylphosphine, SPhos (1). This ligand confers unprecedented activity for these processes, allowing reactions to be performed at low catalyst levels, to prepare extremely hindered biaryls and to be carried out, in general, for reactions of aryl chlorides at room temperature. Additionally, structural studies of various 1.Pd complexes are presented along with computational data that help elucidate the efficacy that 1 imparts on Suzuki-Miyaura coupling processes. Moreover, a comparison of the reactions with 1 and with 2-(2',4',6'-triisopropylbiphenyl)diphenylphosphine (2) is presented that is informative in determining the relative importance of ligand bulk and electron-donating ability in the high activity of catalysts derived from ligands of this type. Further, when the aryl bromide becomes too hindered, an interesting C-H bond functionalization-cross-coupling sequence intervenes to provide product in high yield.

Boronic Acids↗
PubMed2005

The role of chelating diamine ligands in the goldberg reaction: a kinetic study on the copper-catalyzed amidation of aryl iodides.

The mechanistic details of the Cu-catalyzed amidation of aryl iodides are presented. The kinetic data suggest that the diamine ligand prevents multiple ligation of the amide. The formation of an amidocuprate species external to the catalytic cycle helped to rationalize the dependence on diamine concentration and the inverse dependence on amide concentration at low diamine concentrations. The intermediacy of a Cu(I) amidate was established through both its chemical and kinetic competency.

Amides↗
PubMed2004

One-pot sequential Cu-catalyzed reduction and Pd-catalyzed arylation of silyl enol ethers.

[reaction: see text] Enantiomerically enriched beta-substituted diphenylsilyl enol ethers, which can be prepared from Cu-catalyzed asymmetric conjugate reduction, are utilized in the Pd-catalyzed arylation of various aryl bromides. This new method provides a simple route to alpha-arylated cycloalkanones with excellent levels of enantiomeric and diastereomeric purity. The isolation of the intermediate, diphenylsilyl enol ethers is not necessary; the procedure can be carried out in one-pot.

Alkylation↗
PubMed2004

An extremely active catalyst for the Negishi cross-coupling reaction.

A new catalyst system for the Pd-catalyzed cross-coupling of organozinc reagents with aryl halides (Negishi coupling) has been developed. This system permits efficient preparation of hindered biaryls (tri- and tetra-ortho-substituted), functions effectively at low levels of catalyst, and tolerates a wide range of functional groups and heterocyclic substrates. A systematic study of ligand structure was performed and was correlated with catalyst activity.

Biphenyl Compounds↗
PubMed2004

Copper-diamine-catalyzed N-arylation of pyrroles, pyrazoles, indazoles, imidazoles, and triazoles.

This paper details the copper-catalyzed N-arylation of pi-excessive nitrogen heterocycles. The coupling of either aryl iodides or aryl bromides with common nitrogen heterocycles (pyrroles, pyrazoles, indazoles, imidazoles, and triazoles) was successfully performed in good yield with catalysts derived from diamine ligands and CuI. General conditions were found that tolerate functional groups such as aldehydes, ketones, alcohols, primary amines, and nitriles on the aryl halide or heterocycle. Hindered aryl halides or heterocycles were also found to be suitable substrates using the conditions reported herein.

Catalysis↗
PubMed2004

Efficient catalyst for the Suzuki-Miyaura coupling of potassium aryl trifluoroborates with aryl chlorides.

Palladium-catalyzed Suzuki-Miyaura cross-coupling reactions of aryl- and heteroaryl chlorides with potassium aryl- and heteroaryltrifluoroborates have been accomplished with the supporting ligand S-Phos in good to excellent yield. Hindered biaryls and substrates containing a variety of functional groups can be prepared. Suzuki-Miyaura couplings of a 3-pyridyl boron-based nucleophile with aryl- and heteroaryl chlorides proceed in good to very good yield. [reaction: see text]

Borates↗
PubMed2004

Palladium-catalyzed regioselective hydrodebromination of dibromoindoles: application to the enantioselective synthesis of indolodioxane U86192A.

A novel approach to the selective preparation of 4-bromoindoles was developed via Pd(OAc)(2)/rac-BINAP catalytic reactions. A variety of 4,6-dibromoindoles were transformed to 4-bromoindoles with high regioselectivity. This methodology, along with C-N and C-O bond-forming reactions developed in our laboratory, was applied to the enantioselective synthesis of indolodioxane U86192A, an antihypertensive agent.

Antihypertensive Agents↗
PubMed2004

Copper-catalyzed asymmetric conjugate reduction as a route to novel beta-azaheterocyclic acid derivatives.

A chiral copper-hydride catalyst for the asymmetric conjugate reduction of alpha,beta-unsaturated carbonyl compounds has been used for the reduction of substrates containing beta-nitrogen substituents. A new set of reaction conditions has allowed for a variety of beta-azaheterocyclic acid derivatives to be synthesized in excellent yields and with high degrees of enantioselectivity. In addition, the effect that the nature of the nitrogen substituent has on the rate of the conjugate reduction reaction has been explored.

Acids↗
PubMed2004

Synthesis of medium ring nitrogen heterocycles via a tandem copper-catalyzed C-N bond formation-ring-expansion process.

A simple method for the preparation of medium ring heterocycles (7-, 8-, 9-, and 10-membered) has been developed. The process employs a Cu-catalyzed coupling of a beta-lactam with an aryl bromide or iodide followed by intramolecular attack of a pendant amino group. In some instances, the intermediate beta-lactam is observable but can be converted to the aza-heterocycle by catalysis. Acetic acid was found to be superior to transition metal complexes as a catalyst for this ring-expansion process.

Amines↗
PubMed2003

Palladium-catalyzed amination of aryl nonaflates.

The first detailed study of the palladium-catalyzed amination of aryl nonaflates is reported. Use of ligands 2-4 and 6 allows for the catalytic amination of electron-rich and -neutral aryl nonaflates with both primary and secondary amines. With use of Xantphos 5, the catalytic amination of a variety of functionalized aryl nonaflates resulted in excellent yields of anilines; even 2-carboxymethyl aryl nonaflate is effectively coupled with a primary alkylamine. Moderate yields were obtained when coupling halo-aryl nonaflates with a variety of amines, where in most cases the aryl nonaflate reacted in preference to the aryl halide. Overall, aryl nonaflates are an effective alternative to triflates in palladium-catalyzed C-N bond-forming processes due to their increased stability under the reaction conditions.

Alkylation↗
PubMed2003

Insights into the origin of high activity and stability of catalysts derived from bulky, electron-rich monophosphinobiaryl ligands in the Pd-catalyzed C-N bond formation.

A comparative kinetic examination of catalyst systems based on several monophosphinobiaryl ligands is reported. The bulk of the phosphine ligand controls the catalytic activity and the rate of catalyst activation with the catalyst based on 2-dicyclohexylphosphino-2',4',6'-triisopropylbiphenyl providing the greatest activity and fastest activation. In the case where catalyst activation is slow (i.e., use of the smaller ligands such as 2-dicyclohexylphosphino-2'-methylbiphenyl in combination with Pd(OAc)2) stirring the amine with the catalyst/base mixture prior to the commencement of the reaction increases the reaction rate along with the rate of catalyst activation. Kinetic isotope effects established that the catalyst activation process occurs through a beta-hydride elimination pathway.

Amines↗
PubMed2003

Synthesis of substituted oxindoles from alpha-chloroacetanilides via palladium-catalyzed C[bond]H functionalization.

A novel method for the synthesis of oxindoles is described. In the presence of catalytic palladium acetate and 2-(di-tert-butylphosphino)biphenyl, alpha-chloroacetanilides are converted to oxindoles in good to excellent yields with high functional group compatibility using triethylamine as a stoichiometric base. The cyclization is highly regioselective, obviating the need for prefunctionalized arenes. Plausible mechanistic pathways for the reaction are discussed.

Acetanilides↗
PubMed2003

Copper-catalyzed coupling of amides and carbamates with vinyl halides.

[reaction: see text] A general and efficient copper-catalyzed method for the amidation of vinyl bromides and iodides has been developed. This protocol uses a combination of 5 mol % copper iodide and 20 mol % N,N'-dimethyl ethylenediamine. Substrates bearing ester, silyl ether, and amino groups were successfully coupled under the reaction conditions. The double bond geometry of the vinyl halides was retained under the reaction conditions.

Amides↗
PubMed2003

The first general palladium catalyst for the Suzuki-Miyaura and carbonyl enolate coupling of aryl arenesulfonates.

The first general method for the palladium-catalyzed Suzuki-Miyaura and carbonyl enolate coupling of unactivated aryl arenesulfonates was developed utilizing XPhos, 1, and Pd(OAc)2. This is of significant interest because aryl tosylates and aryl benzenesulfonates are more easily handled and considerably less expensive than aryl triflates. This catalyst system effects the coupling of a variety of aryl, heteroaryl, and extremely hindered arylboronic acids with different aryl tosylates, under mild conditions. The same catalyst was employed in the first carbonyl enolate coupling of aryl arensulfonates.

Benzenesulfonates↗
PubMed2003

Catalytic enantioselective conjugate reduction of lactones and lactams.

A dramatic acceleration of the enantioselective copper-catalyzed conjugate reduction of alpha,beta-unsaturated lactones, lactams, and esters is reported upon addition of alcohol additives. Good to excellent yields and enantioselectivities were realized using a catalyst generated in situ from CuCl(2).H(2)O, t-BuONa, p-tol-BINAP, and PMHS, and this methodology was applied to the synthesis of (-)-Paroxetine.

Alcohols↗