Stojan Stavber - Academia.edu (original) (raw)
Papers by Stojan Stavber
ChemInform, Feb 10, 2004
Halogenation Halogenation O 0235 Use of a Fluorous Bridge for Diffusion Controlled Uptake of Mole... more Halogenation Halogenation O 0235 Use of a Fluorous Bridge for Diffusion Controlled Uptake of Molecular Chlorine in Chlorine Addition to Alkenes.-Fluorous solvent is used for passive transport of molecular chlorine from one side of the U-tube to the other, where addition of chlorine to alkenes is quantitative and diffusion controlled.-(ISKRA*,
ChemInform, Jul 21, 2009
The visible-light-induced transformation of toluenes with N-bromosuccinimide (NBS) under solvent-... more The visible-light-induced transformation of toluenes with N-bromosuccinimide (NBS) under solvent-free reaction conditions (SFRC) was studied. The reaction took place in spite of the very restricted molecular motion; toluenes could be regioselectively converted to benzyl bromides. Selective radical-chain reactions with NBS were carried out in liquid/liquid and in solid/solid systems; furthermore, reactions could be performed in the presence of air. The radical scavenger TEMPO (¼ 2,2,6,6tetramethylpiperidin-1-yloxy) completely suppressed the side-chain bromination of toluenes with NBS under SFRC. Electron-withdrawing groups decreased the reactivity of the toluenes, and the Hammett reaction constant 1 þ ¼ À 1.7 indicated involvement of polar radical intermediates with electrophilic character.
Advances in organic synthesis, Oct 28, 2021
Journal of Polymer Science Part A, Sep 15, 1996
Crosslinked chloromethylated polystyrene (1) and crosslinked copoly(styrene-p-nitrophenylacrylate... more Crosslinked chloromethylated polystyrene (1) and crosslinked copoly(styrene-p-nitrophenylacrylate) (3) readily reacted with 1,l-dimethylhydrazine, but the course of the reaction is strongly dependent on the structure of the backbone. Monofunctionalization was observed with chloromethylated polystyrene (1) giving the l,l,l-dimethylhydrazinium chloride derivative (2), while high degree of additional crosslinking took place with crosslinked copoly(styrene-p-nitrophenylacrylate) (3), and additional crosslinking was also observed in functionalization with N-aminopiperidine and N-aminomorpholine. The additional crosslinking suggested a higher backbone mobility in acrylate beads (3) compared to chloromethylated polystyrene (1). The type of transformation and the degree of additional crosslinking also depended on the starting crosslinking of copoly(styrene-p-nitrophenylacrylate) (3; 3a. 2% DVB; 3b, 4% DVB; 3c, 10% DVB). Replacement of p-nitrophenol groups in copoly(styrene-p-nitrophenylacrylate) (3) with hydrazino units resulted in enhanced swelling abilities of the hydrazine derivatives (4, 5, 6) in methanol, dimethylformamide, and chloroform, while formation of the hydrazinium chloride derivative (2) from chloromethylated polystyrene (1) caused enhancement of swelling in methanol but diminished it in toluene. The degree of crosslinking of copoly(styrene-p-nitrophenylacrylate) (3) also influenced the swelling abilities of 3 and its hydrazino derivatives, being higher with 2% crosslinked resins and lower with 4% and 10% crosslinked resins.
Pure and Applied Chemistry, Jan 8, 2018
CC bond formation is one of the most fundamental approaches toward molecular diversity in organic... more CC bond formation is one of the most fundamental approaches toward molecular diversity in organic synthesis. In pursuit of environmentally friendlier chemical approaches to organic chemistry, we present a new metal-free method for direct dehydrative cross-coupling of alcohols and alkenes using molecular iodine as a Lewis acid catalyst under solvent-free reaction conditions. The reaction is atom-economical, tolerant to air and allows simple synthetic procedure, furnishing C sp 3-C sp 2 coupling products with yields up to 97 %. The method has proved efficient for coupling of secondary benzyl alcohols with phenyl-substituted alkenes.
Organic Letters, May 9, 2006
Ketones and 30% aq H 2 O 2 were obtained from commercial sources and were used as received. Silic... more Ketones and 30% aq H 2 O 2 were obtained from commercial sources and were used as received. Silica gel 60 (70-230 mesh ASTM) was used for column chromatography. 1 H and 13 C spectra were obtained with TMS and CDCl 3 as internal standards on a 300 MHz spectrometer. Standard KBr pellet procedures were used to obtain IR spectra of solids, while a film of neat material was used for liquid products. Absorptions are reported in cm-1 (ν max). Active oxygen content was determined by iodometric titration. 1 Caution. Although we have encountered no difficulties in working with these peroxides, routine precautions (shields, fume hoods, avoidance of transition metal salts) should be observed whenever possible, as organic peroxides are potentially hazardous compounds. Reaction procedure for synthesis of 4-tert-Butyl-1-methoxy-cyclohexyl-hydroperoxide 3: To the solution of 0.1 mmol of I 2 (25.4 mg) and 4 mmol of 30% aq H 2 O 2 (0.45 mL) in 2 mL of methanol, 1 mmol (154 mg) of 4-t-Bu-cyclohexanone 1 was added and solution stirred at room temperature for 24 hours. The mixture was then poured into water, products were extracted by dichloromethane, organic phase was dried over Na 2 SO 4 and solvent was partly evaporated under reduced pressure (cca. 20 mmHg). The product was separated from iodine and starting substrate by column chromatography on SiO 2. Elution with ethyl acetatedichloromethane (1: 9) yielded 141 mg (70%) of monoperoxy ketal 3 as a 3: 2 mixture of diastereomers.
Journal of Fluorine Chemistry, Feb 1, 1987
ChemInform, Aug 4, 2010
The Regioselectivity in the Fluorination of Dibenzofuran, Diphenylether and Biphenyl with N-F Typ... more The Regioselectivity in the Fluorination of Dibenzofuran, Diphenylether and Biphenyl with N-F Type of Reagents.-The regioselectivity depends on the structure of educt and slightly on the used fluoro reagent. Dibenzofuran gives predominantly the 2-fluoro derivative (III). Fluorination of biphenyl and anisole results in preferred formation of the ortho-products, while starting from diphenylether the para-product is mainly obtained.
ChemInform, May 19, 2009
www.cheminform.wiley-vch.de Halogenation O 0235 Iodination of Organic Compounds with Elemental Io... more www.cheminform.wiley-vch.de Halogenation O 0235 Iodination of Organic Compounds with Elemental Iodine in the Presence of Hydrogen Peroxide in Ionic Liquid Media.-The influence of oxidant, reagent ratio and hydrophilicity/hydrophobicity of ionic liquid on the iodination reaction of various substrates is studied. Methoxybenzenes (I) are iodinated at the aromatic ring, while alkyl aryl ketones (III) and (V) are iodinated at the α-alkyl position. Interestingly, the iodination of methoxybenzenes (Ia) and (Ib) proceeds with excellent atom economy probably via an ionic mechanism. In this case, the hydroperoxide reagent UHP is proposed to act as activator of iodination system and as regenerator of iodine. For the other substrates, hydroperoxide reagent only activates the iodination system, thus decreasing atom economy. Reusability of the solvent depends on the mechanism of iodination of the substrates.-(
ChemInform, Mar 20, 2007
Dehydration O 0336 Iodine-Induced Transformations of Alcohols under Solvent-Free Conditions.-It i... more Dehydration O 0336 Iodine-Induced Transformations of Alcohols under Solvent-Free Conditions.-It is demonstrated that iodine is an efficient catalyst for the dehydration or etherification of alcohols under solvent-free conditions. Interestingly, dehydration of 2-phenyl-propen-2-ol (IX) produces an olefin which directly undergoes dimerization and Friedel-Crafts cyclization to yield the indanone (X).-(STAVBER, G.; ZUPAN, M.;
ChemInform, Jul 14, 2009
www.cheminform.wiley-vch.de Halogenation O 0235 Micellar System Mediated Direct Fluorination of K... more www.cheminform.wiley-vch.de Halogenation O 0235 Micellar System Mediated Direct Fluorination of Ketones in Water.-Optimized reaction conditions A) are developed for the selective monofluorination of acyclic and cyclic ketones without prior activation or the use of an acid catalyst. In some cases, the amount of SDS has to be increased for better yields.-(STAVBER, G.; ZUPAN, M.;
ChemInform, Sep 22, 2009
The transformation of acid hydrazides to primary amides is of certain relevance for the organic s... more The transformation of acid hydrazides to primary amides is of certain relevance for the organic synthesis of complex molecules. While existing methods require harsh reaction conditions, we present an electrochemical approach in which monoacylhydrazines are reduced to primary amides in 40-90% yield in a divided electrochemical cell with a tin cathode. This method proved superior to reduction by sodium/mercury or lithium/biphenyl in terms of yield and practicability. Most importantly, the new method is distinguished by its tolerance of aryl halogen and olefinic groups.
ChemInform, Nov 24, 2011
One of the most powerful approaches for the formation of simple and complex chiral molecules is t... more One of the most powerful approaches for the formation of simple and complex chiral molecules is the metal-catalysed asymmetric allylic alkylation. This reaction has been broadly studied with a great variety of substrates and nucleophiles under different reaction conditions and it has promoted the synthesis of new chiral ligands to be evaluated as asymmetric inductors. Although the mechanism as well as the active species equilibria are known, the performance of the catalytic system depends on the fine tuning of factors such as type of substrate, nucleophile nature, reaction medium, catalytic precursor and type of ligand used. Particularly interesting are chiral phosphines which have proved to be effective asymmetric inductors in several such reactions. The present review covers the application of phosphine-donor ligands in Pd-catalysed asymmetric allylic alkylation in the last decade.
Tetrahedron, Jul 1, 2009
Scheme 1. Properties and common functions of ILs.
Catalysts, Nov 11, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY
ChemInform, Feb 10, 2004
Halogenation Halogenation O 0235 Use of a Fluorous Bridge for Diffusion Controlled Uptake of Mole... more Halogenation Halogenation O 0235 Use of a Fluorous Bridge for Diffusion Controlled Uptake of Molecular Chlorine in Chlorine Addition to Alkenes.-Fluorous solvent is used for passive transport of molecular chlorine from one side of the U-tube to the other, where addition of chlorine to alkenes is quantitative and diffusion controlled.-(ISKRA*,
ChemInform, Jul 21, 2009
The visible-light-induced transformation of toluenes with N-bromosuccinimide (NBS) under solvent-... more The visible-light-induced transformation of toluenes with N-bromosuccinimide (NBS) under solvent-free reaction conditions (SFRC) was studied. The reaction took place in spite of the very restricted molecular motion; toluenes could be regioselectively converted to benzyl bromides. Selective radical-chain reactions with NBS were carried out in liquid/liquid and in solid/solid systems; furthermore, reactions could be performed in the presence of air. The radical scavenger TEMPO (¼ 2,2,6,6tetramethylpiperidin-1-yloxy) completely suppressed the side-chain bromination of toluenes with NBS under SFRC. Electron-withdrawing groups decreased the reactivity of the toluenes, and the Hammett reaction constant 1 þ ¼ À 1.7 indicated involvement of polar radical intermediates with electrophilic character.
Advances in organic synthesis, Oct 28, 2021
Journal of Polymer Science Part A, Sep 15, 1996
Crosslinked chloromethylated polystyrene (1) and crosslinked copoly(styrene-p-nitrophenylacrylate... more Crosslinked chloromethylated polystyrene (1) and crosslinked copoly(styrene-p-nitrophenylacrylate) (3) readily reacted with 1,l-dimethylhydrazine, but the course of the reaction is strongly dependent on the structure of the backbone. Monofunctionalization was observed with chloromethylated polystyrene (1) giving the l,l,l-dimethylhydrazinium chloride derivative (2), while high degree of additional crosslinking took place with crosslinked copoly(styrene-p-nitrophenylacrylate) (3), and additional crosslinking was also observed in functionalization with N-aminopiperidine and N-aminomorpholine. The additional crosslinking suggested a higher backbone mobility in acrylate beads (3) compared to chloromethylated polystyrene (1). The type of transformation and the degree of additional crosslinking also depended on the starting crosslinking of copoly(styrene-p-nitrophenylacrylate) (3; 3a. 2% DVB; 3b, 4% DVB; 3c, 10% DVB). Replacement of p-nitrophenol groups in copoly(styrene-p-nitrophenylacrylate) (3) with hydrazino units resulted in enhanced swelling abilities of the hydrazine derivatives (4, 5, 6) in methanol, dimethylformamide, and chloroform, while formation of the hydrazinium chloride derivative (2) from chloromethylated polystyrene (1) caused enhancement of swelling in methanol but diminished it in toluene. The degree of crosslinking of copoly(styrene-p-nitrophenylacrylate) (3) also influenced the swelling abilities of 3 and its hydrazino derivatives, being higher with 2% crosslinked resins and lower with 4% and 10% crosslinked resins.
Pure and Applied Chemistry, Jan 8, 2018
CC bond formation is one of the most fundamental approaches toward molecular diversity in organic... more CC bond formation is one of the most fundamental approaches toward molecular diversity in organic synthesis. In pursuit of environmentally friendlier chemical approaches to organic chemistry, we present a new metal-free method for direct dehydrative cross-coupling of alcohols and alkenes using molecular iodine as a Lewis acid catalyst under solvent-free reaction conditions. The reaction is atom-economical, tolerant to air and allows simple synthetic procedure, furnishing C sp 3-C sp 2 coupling products with yields up to 97 %. The method has proved efficient for coupling of secondary benzyl alcohols with phenyl-substituted alkenes.
Organic Letters, May 9, 2006
Ketones and 30% aq H 2 O 2 were obtained from commercial sources and were used as received. Silic... more Ketones and 30% aq H 2 O 2 were obtained from commercial sources and were used as received. Silica gel 60 (70-230 mesh ASTM) was used for column chromatography. 1 H and 13 C spectra were obtained with TMS and CDCl 3 as internal standards on a 300 MHz spectrometer. Standard KBr pellet procedures were used to obtain IR spectra of solids, while a film of neat material was used for liquid products. Absorptions are reported in cm-1 (ν max). Active oxygen content was determined by iodometric titration. 1 Caution. Although we have encountered no difficulties in working with these peroxides, routine precautions (shields, fume hoods, avoidance of transition metal salts) should be observed whenever possible, as organic peroxides are potentially hazardous compounds. Reaction procedure for synthesis of 4-tert-Butyl-1-methoxy-cyclohexyl-hydroperoxide 3: To the solution of 0.1 mmol of I 2 (25.4 mg) and 4 mmol of 30% aq H 2 O 2 (0.45 mL) in 2 mL of methanol, 1 mmol (154 mg) of 4-t-Bu-cyclohexanone 1 was added and solution stirred at room temperature for 24 hours. The mixture was then poured into water, products were extracted by dichloromethane, organic phase was dried over Na 2 SO 4 and solvent was partly evaporated under reduced pressure (cca. 20 mmHg). The product was separated from iodine and starting substrate by column chromatography on SiO 2. Elution with ethyl acetatedichloromethane (1: 9) yielded 141 mg (70%) of monoperoxy ketal 3 as a 3: 2 mixture of diastereomers.
Journal of Fluorine Chemistry, Feb 1, 1987
ChemInform, Aug 4, 2010
The Regioselectivity in the Fluorination of Dibenzofuran, Diphenylether and Biphenyl with N-F Typ... more The Regioselectivity in the Fluorination of Dibenzofuran, Diphenylether and Biphenyl with N-F Type of Reagents.-The regioselectivity depends on the structure of educt and slightly on the used fluoro reagent. Dibenzofuran gives predominantly the 2-fluoro derivative (III). Fluorination of biphenyl and anisole results in preferred formation of the ortho-products, while starting from diphenylether the para-product is mainly obtained.
ChemInform, May 19, 2009
www.cheminform.wiley-vch.de Halogenation O 0235 Iodination of Organic Compounds with Elemental Io... more www.cheminform.wiley-vch.de Halogenation O 0235 Iodination of Organic Compounds with Elemental Iodine in the Presence of Hydrogen Peroxide in Ionic Liquid Media.-The influence of oxidant, reagent ratio and hydrophilicity/hydrophobicity of ionic liquid on the iodination reaction of various substrates is studied. Methoxybenzenes (I) are iodinated at the aromatic ring, while alkyl aryl ketones (III) and (V) are iodinated at the α-alkyl position. Interestingly, the iodination of methoxybenzenes (Ia) and (Ib) proceeds with excellent atom economy probably via an ionic mechanism. In this case, the hydroperoxide reagent UHP is proposed to act as activator of iodination system and as regenerator of iodine. For the other substrates, hydroperoxide reagent only activates the iodination system, thus decreasing atom economy. Reusability of the solvent depends on the mechanism of iodination of the substrates.-(
ChemInform, Mar 20, 2007
Dehydration O 0336 Iodine-Induced Transformations of Alcohols under Solvent-Free Conditions.-It i... more Dehydration O 0336 Iodine-Induced Transformations of Alcohols under Solvent-Free Conditions.-It is demonstrated that iodine is an efficient catalyst for the dehydration or etherification of alcohols under solvent-free conditions. Interestingly, dehydration of 2-phenyl-propen-2-ol (IX) produces an olefin which directly undergoes dimerization and Friedel-Crafts cyclization to yield the indanone (X).-(STAVBER, G.; ZUPAN, M.;
ChemInform, Jul 14, 2009
www.cheminform.wiley-vch.de Halogenation O 0235 Micellar System Mediated Direct Fluorination of K... more www.cheminform.wiley-vch.de Halogenation O 0235 Micellar System Mediated Direct Fluorination of Ketones in Water.-Optimized reaction conditions A) are developed for the selective monofluorination of acyclic and cyclic ketones without prior activation or the use of an acid catalyst. In some cases, the amount of SDS has to be increased for better yields.-(STAVBER, G.; ZUPAN, M.;
ChemInform, Sep 22, 2009
The transformation of acid hydrazides to primary amides is of certain relevance for the organic s... more The transformation of acid hydrazides to primary amides is of certain relevance for the organic synthesis of complex molecules. While existing methods require harsh reaction conditions, we present an electrochemical approach in which monoacylhydrazines are reduced to primary amides in 40-90% yield in a divided electrochemical cell with a tin cathode. This method proved superior to reduction by sodium/mercury or lithium/biphenyl in terms of yield and practicability. Most importantly, the new method is distinguished by its tolerance of aryl halogen and olefinic groups.
ChemInform, Nov 24, 2011
One of the most powerful approaches for the formation of simple and complex chiral molecules is t... more One of the most powerful approaches for the formation of simple and complex chiral molecules is the metal-catalysed asymmetric allylic alkylation. This reaction has been broadly studied with a great variety of substrates and nucleophiles under different reaction conditions and it has promoted the synthesis of new chiral ligands to be evaluated as asymmetric inductors. Although the mechanism as well as the active species equilibria are known, the performance of the catalytic system depends on the fine tuning of factors such as type of substrate, nucleophile nature, reaction medium, catalytic precursor and type of ligand used. Particularly interesting are chiral phosphines which have proved to be effective asymmetric inductors in several such reactions. The present review covers the application of phosphine-donor ligands in Pd-catalysed asymmetric allylic alkylation in the last decade.
Tetrahedron, Jul 1, 2009
Scheme 1. Properties and common functions of ILs.
Catalysts, Nov 11, 2022
This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY