Papers by Cristobal Lopez
Organic Letters, 2004
Melting points are uncorrected. Mass spectra were determined at an ionizing voltage of 70 eV. Unl... more Melting points are uncorrected. Mass spectra were determined at an ionizing voltage of 70 eV. Unless otherwise noted, all reactions were performed in flamedried glassware under an atmosphere of dry argon. The microwave reactor and reaction vessels were purchased from CEM Corporation. All solids were recrystallized from ethyl acetate/hexane for analytical data. General Procedure for the Free Radical Cyclization of Bromo Substituted Hexahydro-indol-2-ones. In a 35 mL reaction tube were placed (1-methyl-2oxo-cyclohexyl)-acetic acid 1 (2.0 mmol), the appropriate amine (2.2 mmol), and xylene (5 mL). The tube was sealed and heated in an oil bath at 160°C for 1 h. The cyclization reaction was also carried out using a microwave reactor at 100 Watts, 160 °C for 10 min. The reaction mixture was allowed to cool to rt and the resulting hexahydroindolinone was purified by flash silica gel chromatography. A solution containing the appropriate hexahydroindolinone (5.0 mmol) in CH 2 Cl 2 (50 mL) was cooled in an ice bath. Bromine (0.25 mL, 5.0 mmol) was slowly added via a syringe and, after the color disappeared, the mixture was stirred for an additional 5 min. Triethylamine (2.1 mL, 15.0 mmol) was then added in one portion and the mixture was allowed to stir at rt for 10 min, and was then washed with water. The organic phase was separated, dried over MgSO 4 , filtered, and concentrated under reduced pressure. The crude product was purified by flash silica gel chromatography. To a solution of the appropriate bromo enamide (0.7 mmol) in benzene (70 mL) was added Bu 3 SnH (1.1 mmol) and AIBN (0.07 mmol). The mixture was heated at reflux for 12 h and the solvent was removed under reduced pressure. The crude product was purified by flash silica gel chromatography. 1-Allyl-7-bromo-3a-methyl-1,3,3a,4,5,6-hexahydro-indol-2-one (7). A sample of 1-allyl-3a-methyl-1,3,3a,4,5,6-hexahydro-indol-2-one (6) was prepared in 96%
Chemistry: A European Journal, Oct 9, 2017
Chemistry – A European Journal, 2019
The development of efficient and stable red and near‐IR emitting materials under hard radiation d... more The development of efficient and stable red and near‐IR emitting materials under hard radiation doses and/or prolonged times is a sought‐after task due to their widespread applications in optoelectronics and biophotonics. To this aim, novel symmetric all‐BODIPY‐triads, ‐pentads, and ‐hexads have been designed and synthesized as light‐harvesting arrays. These photonic materials are spectrally active in the 655–730 nm region and display high molar absorption across UV–visible region. Furthermore, they provide, to the best of our knowledge, the highest lasing efficiency (up to 68 %) and the highest photostability (tolerance >1300 GJ mol−1) in the near‐IR spectral region ever recorded under drastic pumping conditions. Additionally, the modular synthetic strategy to access the cassettes allows the systematic study of their photonic behavior related to structural factors. Collectively, the outstanding behavior of these multichromophoric photonic materials provides the keystone for engi...
Tetrahedron Letters, 1990
... Stereoselective access to bis-annulated pyranosides. Alberto A. Ghini , Catherine Bumouf , J.... more ... Stereoselective access to bis-annulated pyranosides. Alberto A. Ghini , Catherine Bumouf , J. Cristobal Lopez , * , Alain Olesker and Gabor Lukacs , *. ... Alberto A. Ghini, Catherine Bumouf, J. Cristobal Lopez*, Alain Olesker and Gabor Lukacs*. ...
Recent Trends in Carbohydrate Chemistry, 2020
The complexation of alkynes to form dicobalt hexacarbonyl derivatives facilitates the formation, ... more The complexation of alkynes to form dicobalt hexacarbonyl derivatives facilitates the formation, under acid catalysis, of highly stabilized propargylic cations whose reaction with nucleophiles to form propargylic compounds, currently known as the Nicholas reaction, has found ample use in organic synthesis. This transformation has shown to be particularly useful when applied to carbohydrate derivatives. In this chapter, we provide a brief overview on this subject pioneered by early contributions from Isobe's research group. Thus, carbohydrate-derived dicobalt hexacarbonyl complexes have been used in the epimerization of C-alkynyl glycosides, pyranose ring-opening nucleophile trapping reactions, pyranose ring-opening ring-recyclization leading to medium-sized oxacycles, glycosylation strategies, C-glycosylation and pyranose to carbocycle transformations among others. Finally, contributions from our research group focusing on the synthetic applications of Ferrier-Nicholas cations are also presented.
Frontiers in Chemistry, 2019
Herein we describe the synthesis, computationally assisted spectroscopy, and lasing properties of... more Herein we describe the synthesis, computationally assisted spectroscopy, and lasing properties of a new library of symmetric bridged bis-BODIPYs that differ in the nature of the spacer. Access to a series of BODIPY dimers is straightforward through synthetic modifications of the pending ortho-hydroxymethyl group of readily available C-8 (meso) ortho-hydroxymethyl phenyl BODIPYs. In this way, we have carried out the first systematic study of the photonic behavior of symmetric bridged bis-BODIPYs, which is effectively modulated by the length and/or stereoelectronic properties of the spacer unit. The designed bis-BODIPYs display bright fluorescence and laser emission in non-polar media. The fluorescence response is governed by the induction of a non-emissive intramolecular charge transfer (ICT) process, which is significantly enhanced in polar media. The effectiveness of the fluorescence quenching and also the prevailing charge transfer mechanism (from the spacer itself or between the BODIPY units) rely directly on the electron-releasing ability of the spacer. Moreover, the linker moiety can also promote intramolecular excitonic interactions, leading to excimer-like emission characterized by new spectral bands and the lengthening of lifetimes. The substantial influence of the bridging moiety on the emission behavior of these BODIPY dyads and their solvent-sensitivity highlight the intricate molecular dynamics upon excitation in multichromophoric systems. In this regard, the present work represents a breakthrough in the complex relationship between the molecular structure of the chromophores and their photophysical signatures, thus providing key guidelines for rationalizing the design of tailored bis-BODIPYs with potential advanced applications.
The Journal of organic chemistry, Jan 27, 2016
O-Ethylation of phthalides with Meerwein's reagent followed by reaction of the ensuing salts ... more O-Ethylation of phthalides with Meerwein's reagent followed by reaction of the ensuing salts with pyrrole, results in the formation of 5-alkoxy-5-phenyl dipyrromethane derivatives, which function as ready precursors of ortho-substituted 8-aryl BODIPY derivatives by reaction with borontrifluoride etherate, an overall process that can be carried out in a one-pot operation.
Tetrahedron, 1993
Three new processes for the obtention of pyranosidic dienes type B, and D and homologated conjuga... more Three new processes for the obtention of pyranosidic dienes type B, and D and homologated conjugated enals A, have been designed in the context of the preparation of useful chiral building blocks from monosaccharides. Addition of vinylmagnesium bromide ...
Journal of Biological Chemistry, 2003
Chemistry – A European Journal, 2020
A series of fluorescent boron‐dipyrromethene (BODIPY, 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene)... more A series of fluorescent boron‐dipyrromethene (BODIPY, 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene) dyes have been designed to participate, as aglycons, in synthetic oligosaccharide protocols. As such, they served a dual purpose: first, by being incorporated at the beginning of the process (at the reducing‐end of the growing saccharide moiety), they can function as fluorescent glycosyl tags, facilitating the detection and purification of the desired glycosidic intermediates, and secondly, the presence of these chromophores on the ensuing compounds grants access to fluorescently labeled saccharides. In this context, a sought‐after feature of the fluorescent dyes has been their chemical robustness. Accordingly, some BODIPY derivatives described in this work can withstand the reaction conditions commonly employed in the chemical synthesis of saccharides; namely, glycosylation and protecting‐group manipulations. Regarding their photophysical properties, the BODIPY‐labeled saccharides obta...
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 29, 2017
Herein we describe the synthesis, and computationally-aided photophysical characterization, of a ... more Herein we describe the synthesis, and computationally-aided photophysical characterization, of a new set of urea-bridged bis-BODIPY derivatives. These new dyads are efficiently obtained by a one-pot tandem Staudinger/Aza-Wittig ureation protocol, from easily accessible meso-phenyl ortho-azidomethyl BODIPYs. These symmetric bis-BODIPYs outstand by a high absorption probability and excellent fluorescence and laser emission in less polar media. Nevertheless, this emission ability decreases in more polar media, which is ascribed to a light-induced charge transfer from the urea spacer to the dipyrrin core, a process that can be modulated by appropriate changes in the substitution pattern of the BODIPY core. Furthermore, this ureation protocol can also be employed for the direct conjugation of our BODIPY-azides to amine-containing compounds, thus providing access to fluorescent non-symmetric ureas.
Pure and Applied Chemistry, 2014
Pyranosidic allylic (Ferrier) cations that share dicobalt hexacarbonyl propargyl (Nicholas) stabi... more Pyranosidic allylic (Ferrier) cations that share dicobalt hexacarbonyl propargyl (Nicholas) stabilization at C-1, can be easily generated by treatment of hexacarbonyldicobalt alkynyl glycals with BF3·OEt2, and display a remarkable reactivity leading to a variety of products. The substituent at O-6 in these glycals plays a pivotal role in directing the outcome of the transformations. Accordingly, 6-O-benzyl or 6-O-allyl groups cause a series of transformations resulting in the stereoselective formation of oxepanes through a process that involves an initial hydride transfer step from the allyl or benzyl substituent to the Ferrier–Nicholas cation. On the contrary, 6-OH derivatives undergo an overall ring contraction to branched tetrahydrofuran derivatives. 6-O-Silyl derivatives, in the presence of heteroaryl nucleophiles, were transformed into C-3 branched bis-C-C-glycosides, containing two of such molecules.
Molecules, 2021
A convergent synthetic route to a tetrasaccharide related to PI-88, which allows the incorporatio... more A convergent synthetic route to a tetrasaccharide related to PI-88, which allows the incorporation of a fluorescent BODIPY-label at the reducing-end, has been developed. The strategy, which features the use of 1,2-methyl orthoesters (MeOEs) as glycosyl donors, illustrates the usefulness of suitably-designed BODIPY dyes as glycosyl labels in synthetic strategies towards fluorescently-tagged oligosaccharides.
The Journal of Organic Chemistry, 2021
Novel, linker-free, BODIPY-carbohydrate derivatives containing sugar residues at positions C2 and... more Novel, linker-free, BODIPY-carbohydrate derivatives containing sugar residues at positions C2 and C6 are efficiently obtained by, hitherto unreported, Ferrier-type C-glycosylation of 8aryl-1,3,5,7-tetramethyl BODIPYs with commercially available tri-Oacetyl-D-glucal followed by saponification. This transformation, which involves the electrophilic aromatic substitution (S E Ar) of the dipyrrin framework with an allylic oxocarbenium ion, provides easy access to BODIPY-carbohydrate hybrids with excellent photophysical properties and a weaker tendency to aggregate in concentrated water solutions.
Molecules, 2015
Unsaturated carbohydrate derivatives are useful intermediates in synthetic transformations leadin... more Unsaturated carbohydrate derivatives are useful intermediates in synthetic transformations leading to a variety of compounds. The aim of this review is to highlight the rich chemistry of ∆-2,3 unsaturated pyranosides, emphasizing the variety of transformations that have been carried out in these substrates during the last decade.
Organic Letters
Carbohydrates U 0500 Formation and Reactivity of Novel Pyranosidic Nicholas Oxocarbenium Ions: Ac... more Carbohydrates U 0500 Formation and Reactivity of Novel Pyranosidic Nicholas Oxocarbenium Ions: Access to C-Ketosides and Branched-Chain C-Ketosides.-The title ions are generated via dicobalt hexacarbonyl propargyl complexes prepared from alkynyl ketoses. They react with a variety of nucleophiles in the presence of BF3•Et2O to give C-ketosides (III), branched-chain C-ketosides (V) or branched-chain C-glycals (VII) depending on the nucleophile and the carbohydrate starting material.-(GOMEZ*, A. M.;
Organic Letters, 2002
General. All reactions were performed in dry flasks fitted with a glass stopper or rubber septa u... more General. All reactions were performed in dry flasks fitted with a glass stopper or rubber septa under a positive pressure of argon. Air-and moisture-sensitive liquids and solutions were transferred via syringe or stainless steel cannula. Flash column chromatography was performed employing 230-400 mesh silica gel. Thin-layer chromatography was conducted in Kieselgel 60 F 254 (Merck). Detection was first by UV (254 nm) then charring with a solution of phosphomolybdic acid in ethanol. Anhydrous MgSO 4 or Na 2 SO 4 was used to dry the organic solutions during work-ups, and the removal of the solvents was done under vacuum with a rotoevaporator. Unless otherwise noted, materials were obtained from commercially available sources and used without further purification. Solvents were dried and purified using standard methods. 1 H and-13 CNMR spectra were recorded in CDCl 3 at 200 or 300 and 50 or 75 MHz respectively. Chemical shifts are expressed in parts per million (δ scale) downfield from tetramethylsilane and are referenced to residual protium in the NMR solvent (CHCl 3 : δ 7.25). Proton NMR (1 H NMR) are presented in the following order: multiplicity (s, singlet; d, doublet; t, triplet; q, quartet and m, multiplet), coupling constants in Hertz, and integration. General Procedure for the Ozonation of Vinylstannanes. Method A. A solution of the corresponding olefin in MeOH (20 mL/mmol) at-78 o C was bubbled through with ozone for 15 min, after which oxygen was bubbled through the solution for 5 minutes. Next, the mixture was treated with borane-methyl sulfide complex (BMS) (2.5 mmol/mmol) and allowed to warm to room temperature over 2h. After stirring for 1h, the solvent was removed and the residue submitted to acetylation (Ac 2 O, pyr) when indicated. General Procedure for the Reaction of Vinylstannanes with Ozone as shown in Table 2. A solution of the corresponding olefin in the appropriate solvent (20 mL/mmol) at-78 o C was bubbled through with ozone until TLC showed complete consumption of the starting compound, after which oxygen was bubbled through the solution for 5 minutes. The solution was warmed at room temperature for the time indicated in Table 2. Next, the mixture was cooled at-78 o C and treated with BMS (2.5 mmol/mmol) and then allowed to warm to room temperature over 2h. After stirring for 1h, the solvent was removed and the residue submitted, when indicated, to acetylation (Ac 2 O, pyr). One-pot syntheses of 1,2-diols from alkynes by hydrostannylation followed by ozonation and reductive work-up. A solution of the alkyne in MeOH (5 mL/mmol) was cooled at-78 o C and treated with Bu 3 SnH (1.3 mmol/mmol) and Et 3 B (0.1 mmol/mmol). The reaction mixture was stirred until TLC showed complete consumption of the starting compound. Next, at-78 o C ozone was bubbled into the mixture for 15 min after which oxygen was bubbled through the solution for 5 minutes. Next, the mixture was cooled at-78 o C and treated with BMS complex (2.5
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Papers by Cristobal Lopez