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108 results on '"MARTIN, V. S."'

26. Stereoselective Intramolecular Nicholas Reaction Using Epoxides as Nucleophiles

Author

Crisostomo, F. R. P., Martin, T., and Martin, V. S.

Abstract

The intramolecular nucleophilic attack of the epoxides on the exo-Co2(CO)6-propargylic cations provided cyclic ethers in good yields. The use of substrates with stereochemically defined oxiranes provided polysubstituted tetrahydropyrans and oxepanes with a high degree of stereocontrol. The cyclization is sensitive to the nature of the protecting group used at the primary alcohol, the use of tert-butyl carbonates being highly effective in terms of regioselectivity and yields.

Published
2004

27. Iron(III)-Catalyzed Prins-Type Cyclization Using Homopropargylic Alcohol:  A Method for the Synthesis of 2-Alkyl-4-halo-5,6-dihydro-2H-pyrans

Author

Miranda, P. O., Diaz, D. D., Padron, J. I., Bermejo, J., and Martin, V. S.

Abstract

A new Prins-type cyclization between homopropargylic alcohol and aldehydes in the presence of FeX3 to obtain 2-alkyl-4-halo-5,6-dihydro-2H-pyrans in good yield is described. Osmium-catalyzed cis dihydroxylation provided direct access to trans-2-alkyl-3-hydroxy-tetrahydro-pyran-4-ones. Anhydrous ferric halides are also shown to be excellent catalysts for the standard Prins cyclization using homoallylic alcohol. Isolation of an intermediate acetal provides substantiation of a proposed mechanism.

Published
2003

30. γ-Lactone-Tethered Ring-Closing Metathesis. A Route to Enantiomerically Enriched γ-Lactones α,β-Fused to Medium-Sized Rings

Author

Rodriguez, C. M., Ravelo, J. L., and Martin, V. S.

Abstract

The stereoselective alkylation of α-(phenylsulfonyl)-β-[(methoxycarbonyl)methyl]-γ-lactones obtained by the base-induced cyclization of enantiomerically enriched α-[(phenylthio)acyl]-α,β-unsaturated esters and ring-closing olefin metathesis (RCM) are the basis of a new approach for gaining access to γ-lactones that are α,β-fused to medium-sized carbocycles and cyclic ethers.

Published
2004

31. Macrokinetic Processes in Porous Media (Fuel Cells)

Author

ARMY FOREIGN SCIENCE AND TECHNOLOGY CENTER CHARLOTTESVILLE VA, Chizmadzhev,Yu. A., Martin,V. S., Tarasevich,M. R., Chirkov,Yu. G., ARMY FOREIGN SCIENCE AND TECHNOLOGY CENTER CHARLOTTESVILLE VA, Chizmadzhev,Yu. A., Martin,V. S., Tarasevich,M. R., and Chirkov,Yu. G.

Abstract

The book deals with macrokinetic processes in porous media, particularly in porous catalysts of fuel cells. It presents a detailed exposure of the theory of porous gas-diffusion electrodes and investigates capillary phenomena in porous media, hydrodynamic mixing and related processes., Trans. of unidentified Russian nono., pub. by 'Nauka', Moscow, 1971 364p.

Published
1974

32. Double Cationic Propargylation:  From Linear to Polycyclic Ethers

Author

Diaz, D., Martin, T., and Martin, V. S.

Abstract

The trapping of cations generated from Co2(CO)6-bispropargylic alcohols provided diethers in good yield. The procedure is also valid when two vicinal acetylenes are present. The methodology can be applied to the synthesis of symmetrical or unsymmetrical linear or cyclic propargylic ethers. The use of substrates with a stereochemically defined secondary nucleophilic alcohol provided cyclic ethers with a high degree of stereocontrol.

Published
2001

33. Enantiocontrolled Synthesis of Trialkyl-Substituted Stereogenic Carbons. A General Route to cis-3,5-Dialkyl γ-Lactones

Author

Diaz, D. and Martin, V. S.

Abstract

Lewis acid treatment of tertiary Co2(CO)6-propargylic alcohols having a stereochemically defined benzyloxy group at the γ-benzyl position yielded after cobalt demetalation sec-dialkyl bishomopropargylic alcohols in good yields. The reaction is highly stereoselective and predictable, providing pure stereoisomers. The use of benzyl-α,α‘-d2 ethers permitted the stereoselective d-labeling of methines and methylenes. Very simple chemical manipulations provided a general methodology to obtain the enantiomers of 3,5-dialkyl-γ-lactones.

Published
2000

35. Stability indicating high performance liquid chromatography methods for 5-fluorouridine in aqueous solution

Author

Dorta, M. J., Munguía, O., Jose Fariña, Martin, V. S., and Llabrés, M.

Subjects
Solutions, Magnetic Resonance Spectroscopy, Drug Stability, Spectrophotometry, Ultraviolet, Uridine, Chromatography, High Pressure Liquid
Abstract

Two methods of reversed-phase high performance liquid chromatography (RP-HPLC) were used to detect and quantify the degradation of 5-fluorouridine (CAS 316-46-1, 5-FUR) in aqueous solution. The 1H-NMR technique was used for identifying the degradation products. Several assays were performed from different aqueous solutions of 5-FUR. The best results (optimal resolution, reproducibility and rapidity) were achieved by using Resolve C-18 as stationary phase and a mix (96:4) of 50 mmol/l ammonium dihydrogen phosphate (adjusted to pH 3.5 with phosphoric acid) and acetonitrile as mobile phase. Despite the 5-FUR hydrolysis to 5-fluorouracil (5-FU) and D-ribose under moderate conditions in unlikely, due to high stability of the nucleoside, these were the identified degradation products in assays carried out.

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