Nelu Grinberg | Technical University of Iasi (original) (raw)

Papers by Nelu Grinberg

Research paper thumbnail of Prediction of the Lipophilicity of Some Plant Growth Stimulators by RP‐TLC and Relationship Between Slope and Intercept of TLC Equations

Journal of Liquid Chromatography & Related Technologies, 2007

... of the lipophilicity of some plant growth-stimulating amido esters of ethanolamine using reve... more ... of the lipophilicity of some plant growth-stimulating amido esters of ethanolamine using reversed-phase thin-layer chromatography Simion Gocan*, Florin Irimie, Gabriela Cimpan Analytical ... Vigh, J. Varga-Puchony, J. Hlavay and E. PappHites, 1. Chromatogr., 236 (1982) 51. ...

Research paper thumbnail of A LIPOPHILICITY STUDY FOR SOME 2-HYDRAZINOTHIAZOLIC DERIVATIVES WITH ANTIFUNGAL ACTIVITY BY REVERSED PHASE THIN LAYER CHROMATOGRAPHY

Journal of Liquid Chromatography & Related Technologies, 1999

... 100101641 Gabriela Cîmpan a * , Cristina Bota b , Mioara Coman b , Nelu Grinberg c & Simi... more ... 100101641 Gabriela Cîmpan a * , Cristina Bota b , Mioara Coman b , Nelu Grinberg c & Simion Gocan a pages 29-40. ... 1986. J. Chromatogr., 373: 191–225. [CrossRef], [PubMed], [Web of Science ®]; 5. Danielsson, LG and Zhang, Yu-Hui. 1996. Trends Anal. Chem., 15: 188–196. ...

Research paper thumbnail of Enantiomeric Separation of trans‐2‐Aminocyclohexanol on a Crown Ether Stationary Phase Using Evaporative Light Scattering Detection

Journal of Liquid Chromatography & Related Technologies, 2003

... DOI: 10.1081/JLC-120017180 S. Chen a * , H. Yuan a , N. Grinberg a , A. Dovletoglou a &am... more ... DOI: 10.1081/JLC-120017180 S. Chen a * , H. Yuan a , N. Grinberg a , A. Dovletoglou a & G. Bicker a pages 425-442. Available online: 24 ... 22]22. Shinbo, T., Yamaguchi, T., Nishimura, K. and Suguira, M. 1987. J. Chromatogr. , 405 ...

Research paper thumbnail of Mechanistic Aspects of Chiral Discrimination on Modified Cellulose

Analytical Chemistry, 1997

The immobilization of the globular protein ␣-1-acid glycoprotein (AGP) onto silica gel led to the... more The immobilization of the globular protein ␣-1-acid glycoprotein (AGP) onto silica gel led to the commercial availability of an AGP column, which has a high enantioselectivity. The enantioselectivity of AGP columns has been demonstrated in numerous applications. Due to potential AGP structural changes occurring upon its immobilization, the interaction between particular pairs of enantiomers and the stationary phase is very difficult to assess. Therefore, in this paper we report a mechanistic study that probes the nature of these types of interactions. As model ligands, we employed two LTD 4 antagonists (L-708, 738, MK0476, and their enantiomers) which have a rigid backbone consisting of a conjugated aromatic region and a side chain which is terminated with a carboxylic functional group. The difference between the two compounds is a two-fluorine versus one-chlorine substituent in the aromatic region of the molecule. To study the interaction between the two homologues and the AGP stationary phase, several parameters were varied, including pH, ionic strength, organic modifier, and temperature. van't Hoff plots were constructed and found to be nonlinear. They could, however, be divided into two linear regions, one from 0°C to ∼30°C, and another from 39°C to 50°C. The region at lower temperature implied that the separation was entropy-dominated while the separation at higher temperature was enthalpically driven. The transition from the entropic to the enthalpically driven separation region suggested that bound AGP undergoes a conformational change. Fluorescence spectroscopy performed on the AGP stationary phase found evidence for a limited conformational transition at a similar temperature, consistent with this hypothesis.

Research paper thumbnail of Separation of Organophosphonates by Ion Chromatography with Indirect Photometric Detection

Journal of Liquid Chromatography & Related Technologies, 1994

An ion chromatographic method which utilizes lithium trimesate to separate three diphosphonate dr... more An ion chromatographic method which utilizes lithium trimesate to separate three diphosphonate drugs and two process related organophosphonates is described. The lack of a chromophore on the five species and the high absorptivity of the trimesate anion at 254 nm allows for facile detection using indirect photometry. The effects of mobile phase concentration on the capacity factor of the species

Research paper thumbnail of MECHANISTIC ASPECTS OF CHIRAL DISCRIMINATION ON A MOLECULAR IMPRINTED POLYMER PHASE

Journal of Liquid Chromatography & Related Technologies, 1999

... a , Nicholas H. Snow b * , Nelu Grinberg * & Louis Crocker pages 183-204. ... 694: 3 [Cro... more ... a , Nicholas H. Snow b * , Nelu Grinberg * & Louis Crocker pages 183-204. ... 694: 3 [CrossRef], [Web of Science ®] View all references This approach has been used to produce polymers selective for a host of compounds including sugars,[5]5. Wulff, G. and Vesper, W. 1978. ...

Research paper thumbnail of Enantiomeric separation of underivatized α-methyl-α-amino acids by high-performance liquid chromatography

Journal of Chromatography A, 1985

a-Methyl-cl-amino acids (a-Me-M) are present in various biological sys-tem++, amongst others, as ... more a-Methyl-cl-amino acids (a-Me-M) are present in various biological sys-tem++, amongst others, as constituents of peptide antibiotics. Also, they are of importance in the study of the origin of life and the determination of their enantiomeric composition in meteorites4~s, in which they have been detected (e.g., the Murchison), is of particular interest.

Research paper thumbnail of Evaluation of the Origins of the Selectivity of Polymers Imprinted with a HIV Protease Inhibitor using Infrared Spectroscopy and High Performance Liquid Chromatography

Enantiomer, 2002

This work investigates the origins of enantioselectivity of polymers imprinted with the HIV prote... more This work investigates the origins of enantioselectivity of polymers imprinted with the HIV protease inhibitor, Indinavir. For the preparation of imprints of the drug, the critical interactions between the functional monomer, methacrylic acid, and Indinavir were characterized by infrared (IR) spectroscopy to explore the optimum functional monomer concentration for the polymerization. It was shown that a polymer with high selectivity and minimum non-selective binding for Indinavir was obtained when prepared with enough functional monomer to hydrogen bond with all of the functional groups of the drug without using an excess of monomer. This observation is explained in terms of a balance that is achieved in the monomer-template equilibrium during the polymerization that yields a polymer with highly selective sites and minimal non-selective sites. This paper further demonstrates that IR spectroscopy can be a valuable tool in the design and syntheses of molecular imprinted polymers.

Research paper thumbnail of Enantiomeric separation of dansyl amino acids using MECC with a ligand exchange mechanism

Journal of Microcolumn Separations, 1996

Enantiomeric separation of 11 dansyl amino acids is reported using micellar electrokinetic capill... more Enantiomeric separation of 11 dansyl amino acids is reported using micellar electrokinetic capillary chromatography. The chiral phase consisted of a copper complex of N , N-di-decyl-D-alanine dissolved in the running buffer. Several factors affecting the separation were studied. The partitioning of the copper complex between the micelles and the buffer interface was investigated, and an attempt to describe the mechanism of separation is presented. o 1996 John Wiley & Sons, Inc.

Research paper thumbnail of Epimerization Reaction of a Substituted Vinylcyclopropane Catalyzed by Ruthenium Carbenes: Mechanistic Analysis

Journal of Organic Chemistry, 2006

A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction... more A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction rate strongly depends on the presence of ruthenium ligands in solution. When the first-generation Grubbs catalyst is employed, a 5.3:1 equilibrium ratio of epimers is established quickly, but when a first-generation Hoveyda catalyst is employed, epimerization is observed only if an additional phosphine or nitrogen ligand is added. NMR and kinetic studies suggest that the isomerization reaction occurs through the intermediacy of a ruthenacyclopentene. The observation suggests that cyclopropylmethylidene ruthenium carbenes of synthetic utility may be accessible via ruthenacyclopentenes obtained via other routes.

Research paper thumbnail of Novel, Tunable, and Efficient Chiral Bisdihydrobenzooxaphosphole Ligands for Asymmetric Hydrogenation

Organic Letters, 2010

A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands ... more A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands (BIBOPs) were developed for rhodium-catalyzed hydrogenations of various functionalized olefins such as alpha-arylenamides, alpha-(acylamino)acrylic acid derivatives, beta-(acylamino)acrylates, and dimethyl itaconate with excellent enantioselectivities (up to 99% ee) and reactivities (up to 2000 TON).

Research paper thumbnail of Epimerization Reaction of a Substituted Vinylcyclopropane Catalyzed by Ruthenium Carbenes: Mechanistic Analysis

Journal of Organic Chemistry, 2006

A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction... more A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction rate strongly depends on the presence of ruthenium ligands in solution. When the first-generation Grubbs catalyst is employed, a 5.3:1 equilibrium ratio of epimers is established quickly, but when a first-generation Hoveyda catalyst is employed, epimerization is observed only if an additional phosphine or nitrogen ligand is added. NMR and kinetic studies suggest that the isomerization reaction occurs through the intermediacy of a ruthenacyclopentene. The observation suggests that cyclopropylmethylidene ruthenium carbenes of synthetic utility may be accessible via ruthenacyclopentenes obtained via other routes.

Research paper thumbnail of Novel, Tunable, and Efficient Chiral Bisdihydrobenzooxaphosphole Ligands for Asymmetric Hydrogenation

Organic Letters, 2010

A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands ... more A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands (BIBOPs) were developed for rhodium-catalyzed hydrogenations of various functionalized olefins such as alpha-arylenamides, alpha-(acylamino)acrylic acid derivatives, beta-(acylamino)acrylates, and dimethyl itaconate with excellent enantioselectivities (up to 99% ee) and reactivities (up to 2000 TON).

Research paper thumbnail of Epimerization Reaction of a Substituted Vinylcyclopropane Catalyzed by Ruthenium Carbenes: Mechanistic Analysis

Journal of Organic Chemistry, 2006

A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction... more A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction rate strongly depends on the presence of ruthenium ligands in solution. When the first-generation Grubbs catalyst is employed, a 5.3:1 equilibrium ratio of epimers is established quickly, but when a first-generation Hoveyda catalyst is employed, epimerization is observed only if an additional phosphine or nitrogen ligand is added. NMR and kinetic studies suggest that the isomerization reaction occurs through the intermediacy of a ruthenacyclopentene. The observation suggests that cyclopropylmethylidene ruthenium carbenes of synthetic utility may be accessible via ruthenacyclopentenes obtained via other routes.

Research paper thumbnail of Novel, Tunable, and Efficient Chiral Bisdihydrobenzooxaphosphole Ligands for Asymmetric Hydrogenation

Organic Letters, 2010

A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands ... more A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands (BIBOPs) were developed for rhodium-catalyzed hydrogenations of various functionalized olefins such as alpha-arylenamides, alpha-(acylamino)acrylic acid derivatives, beta-(acylamino)acrylates, and dimethyl itaconate with excellent enantioselectivities (up to 99% ee) and reactivities (up to 2000 TON).

Research paper thumbnail of A Superior Method for the Reduction of Secondary Phosphine Oxides

Organic Letters, 2005

A Superior Method for the Reduction of Secondary Phosphine Oxides. -Diaryl, arylalkyl, and dialky... more A Superior Method for the Reduction of Secondary Phosphine Oxides. -Diaryl, arylalkyl, and dialkyl secondary phosphine oxides are readily reduced by neutral organoaluminums iBu2AlH or iBu3Al to give the corresponding secondary phosphines in high yields and purities. Several functionalities such as amide, aryl iodide, and ether are preserved under the reaction conditions. Even electron-rich and sterically hindered phosphine oxides are reduced in a few hours at 50-70 °C, and some of the phosphine oxides are reduced at cryogenic temperatures. - (BUSACCA*, C. A.; et al.; Org. Lett. 7 (2005) 19, 4277-4280; Dep. Chem. Dev., Boehringer Ingelheim Pharm. Inc., Ridgefield, CT 06877, USA; Eng.) -Klein 04-172

Research paper thumbnail of Ambient Temperature Hydrophosphination of Internal, Unactivated Alkynes and Allenyl Phosphineoxides with Phosphine Borane Complexes

Organic Letters, 2009

Phosphine boranes have been found to hydrophosphinate internal, unactivated alkynes at room tempe... more Phosphine boranes have been found to hydrophosphinate internal, unactivated alkynes at room temperature under basic conditions without the need for catalysts or radical initiators. The use of air-sensitive secondary phosphines is avoided in this facile process. Broad scope in both the phosphine borane and alkyne partners leads to excellent diversity in the phosphine products. Asymmetric hydrogenation of these species then provides one of the shortest possible routes to chiral monodentate phosphines. Hydrophosphination of allenyl phosphine oxides under similar conditions followed by hydrogenation of the exomethylene moiety yields a wide variety of bis-phosphine derivatives.

Research paper thumbnail of Palladium-catalyzed aminocarbonylation of heteroaryl halides using di- tert-butylphosphinoferrocene

Tetrahedron Letters, 2009

Pd-catalyzed aminocarbonylation of heteroaryl halides, using monodentate ligand di-tert-butylphos... more Pd-catalyzed aminocarbonylation of heteroaryl halides, using monodentate ligand di-tert-butylphosphinoferrocene tetrafluoroborate is reported. Good to high yields were obtained with chiral amines on a variety of substrates including 2-bromo heteroaryls.

Research paper thumbnail of An improved method of amide synthesis using acyl chlorides

Tetrahedron Letters, 2009

a b s t r a c t A simple, mild and highly efficient condition for amide synthesis from acyl chlor... more a b s t r a c t A simple, mild and highly efficient condition for amide synthesis from acyl chlorides has been developed to minimize hydrolysis, racemization and other side reactions. This method should expand capabilities in the peptide coupling area.

Research paper thumbnail of Asymmetric Hydrogenation of Unsaturated Ureas with the BIPI Ligands

Organic Letters, 2008

Asymmetric hydrogenation of unsaturated urea esters with the BIPI Ligands has been examined. Opti... more Asymmetric hydrogenation of unsaturated urea esters with the BIPI Ligands has been examined. Optimization of the P−N ligand structure has led to the development of chiral rhodium catalysts capable of producing the targets with >99% ee. The critical phosphine borane S N Ar reaction needed for ligand synthesis has been optimized to give the adducts in high yield at ambient temperature with no racemization. An extremely concise, economical, and scalable sequence to these important new ligands for catalysis of asymmetric hydrogenation has been developed.

Research paper thumbnail of Prediction of the Lipophilicity of Some Plant Growth Stimulators by RP‐TLC and Relationship Between Slope and Intercept of TLC Equations

Journal of Liquid Chromatography & Related Technologies, 2007

... of the lipophilicity of some plant growth-stimulating amido esters of ethanolamine using reve... more ... of the lipophilicity of some plant growth-stimulating amido esters of ethanolamine using reversed-phase thin-layer chromatography Simion Gocan*, Florin Irimie, Gabriela Cimpan Analytical ... Vigh, J. Varga-Puchony, J. Hlavay and E. PappHites, 1. Chromatogr., 236 (1982) 51. ...

Research paper thumbnail of A LIPOPHILICITY STUDY FOR SOME 2-HYDRAZINOTHIAZOLIC DERIVATIVES WITH ANTIFUNGAL ACTIVITY BY REVERSED PHASE THIN LAYER CHROMATOGRAPHY

Journal of Liquid Chromatography & Related Technologies, 1999

... 100101641 Gabriela Cîmpan a * , Cristina Bota b , Mioara Coman b , Nelu Grinberg c & Simi... more ... 100101641 Gabriela Cîmpan a * , Cristina Bota b , Mioara Coman b , Nelu Grinberg c & Simion Gocan a pages 29-40. ... 1986. J. Chromatogr., 373: 191–225. [CrossRef], [PubMed], [Web of Science ®]; 5. Danielsson, LG and Zhang, Yu-Hui. 1996. Trends Anal. Chem., 15: 188–196. ...

Research paper thumbnail of Enantiomeric Separation of trans‐2‐Aminocyclohexanol on a Crown Ether Stationary Phase Using Evaporative Light Scattering Detection

Journal of Liquid Chromatography & Related Technologies, 2003

... DOI: 10.1081/JLC-120017180 S. Chen a * , H. Yuan a , N. Grinberg a , A. Dovletoglou a &am... more ... DOI: 10.1081/JLC-120017180 S. Chen a * , H. Yuan a , N. Grinberg a , A. Dovletoglou a & G. Bicker a pages 425-442. Available online: 24 ... 22]22. Shinbo, T., Yamaguchi, T., Nishimura, K. and Suguira, M. 1987. J. Chromatogr. , 405 ...

Research paper thumbnail of Mechanistic Aspects of Chiral Discrimination on Modified Cellulose

Analytical Chemistry, 1997

The immobilization of the globular protein ␣-1-acid glycoprotein (AGP) onto silica gel led to the... more The immobilization of the globular protein ␣-1-acid glycoprotein (AGP) onto silica gel led to the commercial availability of an AGP column, which has a high enantioselectivity. The enantioselectivity of AGP columns has been demonstrated in numerous applications. Due to potential AGP structural changes occurring upon its immobilization, the interaction between particular pairs of enantiomers and the stationary phase is very difficult to assess. Therefore, in this paper we report a mechanistic study that probes the nature of these types of interactions. As model ligands, we employed two LTD 4 antagonists (L-708, 738, MK0476, and their enantiomers) which have a rigid backbone consisting of a conjugated aromatic region and a side chain which is terminated with a carboxylic functional group. The difference between the two compounds is a two-fluorine versus one-chlorine substituent in the aromatic region of the molecule. To study the interaction between the two homologues and the AGP stationary phase, several parameters were varied, including pH, ionic strength, organic modifier, and temperature. van't Hoff plots were constructed and found to be nonlinear. They could, however, be divided into two linear regions, one from 0°C to ∼30°C, and another from 39°C to 50°C. The region at lower temperature implied that the separation was entropy-dominated while the separation at higher temperature was enthalpically driven. The transition from the entropic to the enthalpically driven separation region suggested that bound AGP undergoes a conformational change. Fluorescence spectroscopy performed on the AGP stationary phase found evidence for a limited conformational transition at a similar temperature, consistent with this hypothesis.

Research paper thumbnail of Separation of Organophosphonates by Ion Chromatography with Indirect Photometric Detection

Journal of Liquid Chromatography & Related Technologies, 1994

An ion chromatographic method which utilizes lithium trimesate to separate three diphosphonate dr... more An ion chromatographic method which utilizes lithium trimesate to separate three diphosphonate drugs and two process related organophosphonates is described. The lack of a chromophore on the five species and the high absorptivity of the trimesate anion at 254 nm allows for facile detection using indirect photometry. The effects of mobile phase concentration on the capacity factor of the species

Research paper thumbnail of MECHANISTIC ASPECTS OF CHIRAL DISCRIMINATION ON A MOLECULAR IMPRINTED POLYMER PHASE

Journal of Liquid Chromatography & Related Technologies, 1999

... a , Nicholas H. Snow b * , Nelu Grinberg * & Louis Crocker pages 183-204. ... 694: 3 [Cro... more ... a , Nicholas H. Snow b * , Nelu Grinberg * & Louis Crocker pages 183-204. ... 694: 3 [CrossRef], [Web of Science ®] View all references This approach has been used to produce polymers selective for a host of compounds including sugars,[5]5. Wulff, G. and Vesper, W. 1978. ...

Research paper thumbnail of Enantiomeric separation of underivatized α-methyl-α-amino acids by high-performance liquid chromatography

Journal of Chromatography A, 1985

a-Methyl-cl-amino acids (a-Me-M) are present in various biological sys-tem++, amongst others, as ... more a-Methyl-cl-amino acids (a-Me-M) are present in various biological sys-tem++, amongst others, as constituents of peptide antibiotics. Also, they are of importance in the study of the origin of life and the determination of their enantiomeric composition in meteorites4~s, in which they have been detected (e.g., the Murchison), is of particular interest.

Research paper thumbnail of Evaluation of the Origins of the Selectivity of Polymers Imprinted with a HIV Protease Inhibitor using Infrared Spectroscopy and High Performance Liquid Chromatography

Enantiomer, 2002

This work investigates the origins of enantioselectivity of polymers imprinted with the HIV prote... more This work investigates the origins of enantioselectivity of polymers imprinted with the HIV protease inhibitor, Indinavir. For the preparation of imprints of the drug, the critical interactions between the functional monomer, methacrylic acid, and Indinavir were characterized by infrared (IR) spectroscopy to explore the optimum functional monomer concentration for the polymerization. It was shown that a polymer with high selectivity and minimum non-selective binding for Indinavir was obtained when prepared with enough functional monomer to hydrogen bond with all of the functional groups of the drug without using an excess of monomer. This observation is explained in terms of a balance that is achieved in the monomer-template equilibrium during the polymerization that yields a polymer with highly selective sites and minimal non-selective sites. This paper further demonstrates that IR spectroscopy can be a valuable tool in the design and syntheses of molecular imprinted polymers.

Research paper thumbnail of Enantiomeric separation of dansyl amino acids using MECC with a ligand exchange mechanism

Journal of Microcolumn Separations, 1996

Enantiomeric separation of 11 dansyl amino acids is reported using micellar electrokinetic capill... more Enantiomeric separation of 11 dansyl amino acids is reported using micellar electrokinetic capillary chromatography. The chiral phase consisted of a copper complex of N , N-di-decyl-D-alanine dissolved in the running buffer. Several factors affecting the separation were studied. The partitioning of the copper complex between the micelles and the buffer interface was investigated, and an attempt to describe the mechanism of separation is presented. o 1996 John Wiley & Sons, Inc.

Research paper thumbnail of Epimerization Reaction of a Substituted Vinylcyclopropane Catalyzed by Ruthenium Carbenes: Mechanistic Analysis

Journal of Organic Chemistry, 2006

A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction... more A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction rate strongly depends on the presence of ruthenium ligands in solution. When the first-generation Grubbs catalyst is employed, a 5.3:1 equilibrium ratio of epimers is established quickly, but when a first-generation Hoveyda catalyst is employed, epimerization is observed only if an additional phosphine or nitrogen ligand is added. NMR and kinetic studies suggest that the isomerization reaction occurs through the intermediacy of a ruthenacyclopentene. The observation suggests that cyclopropylmethylidene ruthenium carbenes of synthetic utility may be accessible via ruthenacyclopentenes obtained via other routes.

Research paper thumbnail of Novel, Tunable, and Efficient Chiral Bisdihydrobenzooxaphosphole Ligands for Asymmetric Hydrogenation

Organic Letters, 2010

A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands ... more A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands (BIBOPs) were developed for rhodium-catalyzed hydrogenations of various functionalized olefins such as alpha-arylenamides, alpha-(acylamino)acrylic acid derivatives, beta-(acylamino)acrylates, and dimethyl itaconate with excellent enantioselectivities (up to 99% ee) and reactivities (up to 2000 TON).

Research paper thumbnail of Epimerization Reaction of a Substituted Vinylcyclopropane Catalyzed by Ruthenium Carbenes: Mechanistic Analysis

Journal of Organic Chemistry, 2006

A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction... more A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction rate strongly depends on the presence of ruthenium ligands in solution. When the first-generation Grubbs catalyst is employed, a 5.3:1 equilibrium ratio of epimers is established quickly, but when a first-generation Hoveyda catalyst is employed, epimerization is observed only if an additional phosphine or nitrogen ligand is added. NMR and kinetic studies suggest that the isomerization reaction occurs through the intermediacy of a ruthenacyclopentene. The observation suggests that cyclopropylmethylidene ruthenium carbenes of synthetic utility may be accessible via ruthenacyclopentenes obtained via other routes.

Research paper thumbnail of Novel, Tunable, and Efficient Chiral Bisdihydrobenzooxaphosphole Ligands for Asymmetric Hydrogenation

Organic Letters, 2010

A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands ... more A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands (BIBOPs) were developed for rhodium-catalyzed hydrogenations of various functionalized olefins such as alpha-arylenamides, alpha-(acylamino)acrylic acid derivatives, beta-(acylamino)acrylates, and dimethyl itaconate with excellent enantioselectivities (up to 99% ee) and reactivities (up to 2000 TON).

Research paper thumbnail of Epimerization Reaction of a Substituted Vinylcyclopropane Catalyzed by Ruthenium Carbenes: Mechanistic Analysis

Journal of Organic Chemistry, 2006

A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction... more A novel ruthenium carbene-catalyzed epimerization of vinylcyclopropanes is reported. The reaction rate strongly depends on the presence of ruthenium ligands in solution. When the first-generation Grubbs catalyst is employed, a 5.3:1 equilibrium ratio of epimers is established quickly, but when a first-generation Hoveyda catalyst is employed, epimerization is observed only if an additional phosphine or nitrogen ligand is added. NMR and kinetic studies suggest that the isomerization reaction occurs through the intermediacy of a ruthenacyclopentene. The observation suggests that cyclopropylmethylidene ruthenium carbenes of synthetic utility may be accessible via ruthenacyclopentenes obtained via other routes.

Research paper thumbnail of Novel, Tunable, and Efficient Chiral Bisdihydrobenzooxaphosphole Ligands for Asymmetric Hydrogenation

Organic Letters, 2010

A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands ... more A series of novel, efficient, air-stable, and tunable chiral bisdihydrobenzooxaphosphole ligands (BIBOPs) were developed for rhodium-catalyzed hydrogenations of various functionalized olefins such as alpha-arylenamides, alpha-(acylamino)acrylic acid derivatives, beta-(acylamino)acrylates, and dimethyl itaconate with excellent enantioselectivities (up to 99% ee) and reactivities (up to 2000 TON).

Research paper thumbnail of A Superior Method for the Reduction of Secondary Phosphine Oxides

Organic Letters, 2005

A Superior Method for the Reduction of Secondary Phosphine Oxides. -Diaryl, arylalkyl, and dialky... more A Superior Method for the Reduction of Secondary Phosphine Oxides. -Diaryl, arylalkyl, and dialkyl secondary phosphine oxides are readily reduced by neutral organoaluminums iBu2AlH or iBu3Al to give the corresponding secondary phosphines in high yields and purities. Several functionalities such as amide, aryl iodide, and ether are preserved under the reaction conditions. Even electron-rich and sterically hindered phosphine oxides are reduced in a few hours at 50-70 °C, and some of the phosphine oxides are reduced at cryogenic temperatures. - (BUSACCA*, C. A.; et al.; Org. Lett. 7 (2005) 19, 4277-4280; Dep. Chem. Dev., Boehringer Ingelheim Pharm. Inc., Ridgefield, CT 06877, USA; Eng.) -Klein 04-172

Research paper thumbnail of Ambient Temperature Hydrophosphination of Internal, Unactivated Alkynes and Allenyl Phosphineoxides with Phosphine Borane Complexes

Organic Letters, 2009

Phosphine boranes have been found to hydrophosphinate internal, unactivated alkynes at room tempe... more Phosphine boranes have been found to hydrophosphinate internal, unactivated alkynes at room temperature under basic conditions without the need for catalysts or radical initiators. The use of air-sensitive secondary phosphines is avoided in this facile process. Broad scope in both the phosphine borane and alkyne partners leads to excellent diversity in the phosphine products. Asymmetric hydrogenation of these species then provides one of the shortest possible routes to chiral monodentate phosphines. Hydrophosphination of allenyl phosphine oxides under similar conditions followed by hydrogenation of the exomethylene moiety yields a wide variety of bis-phosphine derivatives.

Research paper thumbnail of Palladium-catalyzed aminocarbonylation of heteroaryl halides using di- tert-butylphosphinoferrocene

Tetrahedron Letters, 2009

Pd-catalyzed aminocarbonylation of heteroaryl halides, using monodentate ligand di-tert-butylphos... more Pd-catalyzed aminocarbonylation of heteroaryl halides, using monodentate ligand di-tert-butylphosphinoferrocene tetrafluoroborate is reported. Good to high yields were obtained with chiral amines on a variety of substrates including 2-bromo heteroaryls.

Research paper thumbnail of An improved method of amide synthesis using acyl chlorides

Tetrahedron Letters, 2009

a b s t r a c t A simple, mild and highly efficient condition for amide synthesis from acyl chlor... more a b s t r a c t A simple, mild and highly efficient condition for amide synthesis from acyl chlorides has been developed to minimize hydrolysis, racemization and other side reactions. This method should expand capabilities in the peptide coupling area.

Research paper thumbnail of Asymmetric Hydrogenation of Unsaturated Ureas with the BIPI Ligands

Organic Letters, 2008

Asymmetric hydrogenation of unsaturated urea esters with the BIPI Ligands has been examined. Opti... more Asymmetric hydrogenation of unsaturated urea esters with the BIPI Ligands has been examined. Optimization of the P−N ligand structure has led to the development of chiral rhodium catalysts capable of producing the targets with >99% ee. The critical phosphine borane S N Ar reaction needed for ligand synthesis has been optimized to give the adducts in high yield at ambient temperature with no racemization. An extremely concise, economical, and scalable sequence to these important new ligands for catalysis of asymmetric hydrogenation has been developed.