The Experts below are selected from a list of 657 Experts worldwide ranked by ideXlab platform
Barbara Zajc - One of the best experts on this subject based on the ideXlab platform.
-
Regiospecifically Fluorinated Polycyclic Aromatic Hydrocarbons via Julia–Kocienski Olefination and Oxidative Photocyclization. Effect of Fluorine Atom Substitution on Molecular Shape
Journal of Organic Chemistry, 2016Co-Authors: Shaibal Banerjee, Saikat Sinha, Padmanava Pradhan, Alessio Caruso, Daniel Liebowitz, Damon A. Parrish, Miriam Rossi, Barbara ZajcAbstract:A modular synthesis of regiospecifically fluorinated polycyclic aromatic hydrocarbons (PAHs) is described. 1,2-Diarylfluoroalkenes, synthesized via Julia–Kocienski Olefination (70–99% yields), were converted to isomeric 5- and 6-fluorobenzo[c]phenanthrene, 5-and 6-fluorochrysene, and 9- and 10-benzo[g]chrysene (66–83% yields) by oxidative photocyclization. Photocyclization to 6-fluorochrysene proceeded more slowly than conversion of 1-styrylnaphthalene to chrysene. Higher fluoroalkene dilution led to a more rapid cyclization. Therefore, photocyclizations were performed at higher dilutions. To evaluate the effect of fluorine atom on molecular shapes, X-ray data for 5- and 6-fluorobenzo[c]phenanthrene, 6-fluorochrysene, 9- and 10-fluorobenzo[g]chrysene, and unfluorinated chrysene as well as benzo[g]chrysene were obtained and compared. The fluorine atom caused a small deviation from planarity in the chrysene series and decreased nonplanarity in the benzo[c]phenanthrene derivatives, but its influence was most...
-
Synthesis of Regiospecifically Fluorinated Conjugated Dienamides
Molecules, 2014Co-Authors: Mohammad Ziaul Islam Chowdhury, Shaibal Banerjee, Samir Kumar Mandal, Barbara ZajcAbstract:Modular synthesis of regiospecifically fluorinated 2,4-diene Weinreb amides, with defined stereochemistry at both double bonds, was achieved via two sequential Julia-Kocienski Olefinations. In the first step, a Z-a-fluorovinyl Weinreb amide unit with a benzothiazolylsulfanyl substituent at the allylic position was assembled. This was achieved via condensation of two primary building blocks, namely 2-(benzo[d]thiazol-2-ylsulfonyl)-2-fluoro-N-methoxy-N-methylacetamide (a Julia-Kocienski Olefination reagent) and 2-(benzo[d]thiazol-2-ylthio)acetaldehyde (a bifunctional building block). This condensation was highly Z-selective and proceeded in a good 76% yield. Oxidation of benzothiazolylsulfanyl moiety furnished a second-generation Julia-Kocienski Olefination reagent, which was used for the introduction of the second olefinic linkage via DBU-mediated condensations with aldehydes, to give (2Z,4E/Z)-dienamides in 50%–74% yield. Although Olefinations were 4Z-selective, (2Z,4E/Z)-2-fluoro-2,4-dienamides could be readily isomerized to the corresponding 5-substituted (2Z,4E)-2-fluoro-N-methoxy-N-methylpenta-2,4-dienamides in the presence of catalytic iodine.
-
Facile Synthesis of 4‐Vinyl‐ and 4‐Fluorovinyl‐1,2,3‐triazoles via Bifunctional “Click‐Olefination” Reagents.
ChemInform, 2011Co-Authors: Rakesh Kumar, Padmanava Pradhan, Barbara ZajcAbstract:Title compounds are readily obtained by a copper-catalyzed click triazole synthesis and a subsequent Julia—Kocienski Olefination of sulfones (V) and (XII).
-
Facile synthesis of 4-vinyl- and 4-fluorovinyl-1,2,3-triazoles via bifunctional “click-Olefination” reagents
Chemical Communications, 2011Co-Authors: Rakesh Kumar, Padmanava Pradhan, Barbara ZajcAbstract:Modular synthesis of vinyl and fluorovinyl triazoles can be achieved from bifunctional propargyl and fluoropropargyl sulfones by Cu-catalyzed azide–alkyne ligation and Julia–Kocienski Olefination. Competitive click reactions of the protio and fluoropropargyl sulfones show higher reactivity of the latter, and a preliminary DFT analysis was performed.
-
Synthesis of Fluoroolefins via Julia-Kocienski Olefination
Synthesis, 2010Co-Authors: Barbara Zajc, Rakesh KumarAbstract:The Julia-Kocienski Olefination provides a versatile platformfor the synthesis of fluorovinyl compounds. This review describesour efforts as well as those of others in the synthesis of variousfluorinated aryl and heteroaryl sulfones and their utility as Olefinationreagents for the modular assembly of fluoroalkenes. Where data isavailable, the influence of the fluorine atom on the reactivityof the Olefination reagents and the stereochemical outcome of theOlefination are described. 1 Introduction 2 Synthesis of Fluorostilbene-like and Fluorostyrene-like Derivatives 3 Synthesis of Fluoroalkylidenes 3.1 Benzothiazole-Based Reagents 3.2 Phenyltetrazole-Based Reagents 4 Synthesis of Functionalized Fluoroolefins 4.1 α-Fluoroacrylates 4.1.1 Benzothiazole- and Phenyltetrazole-Based Reagents 4.1.2 Bis(trifluoromethyl)phenyl-Based Reagents 4.2 α-Fluoroacrylonitriles 4.3 α-Fluorovinyl Phenyl Sulfones 4.4 α-Fluorovinyl Weinreb Amides 4.4.1 Bis(trifluoromethyl)phenyl-Based Reagent 4.4.2 Benzothiazole-Based Reagent 4.5 α-Fluoroenones 5 Synthesis of 1,1-Difluoroalkenes 6 Mechanism of Julia-Kocienski Olefination 7 Miscellaneous Syntheses of Heteroaryl-Derived FluorinatedSulfides and Sulfones 8 Conclusions
Carmen Nájera - One of the best experts on this subject based on the ideXlab platform.
-
3,5‐Bis(trifluoromethyl)phenyl Sulfones for the Highly Stereoselective Julia–Kocienski Synthesis of α,β‐Unsaturated Esters and Weinreb Amides
European Journal of Organic Chemistry, 2008Co-Authors: Diego A. Alonso, Mónica Fuensanta, Enrique Gómez-bengoa, Carmen NájeraAbstract:The 3,5-bis(trifluoromethyl)phenyl (BTFP) sulfones tert-butyl α-(BTFPsulfonyl)acetate (4) and Weinreb α-(BTFPsulfonyl)acetamide (5) have successfully been employed in the Julia–Kocienski Olefination of aldehydes with K2CO3 as the base at 120 °C in DMF under solid/liquid phase-transfer catalysis conditions to afford α,β-unsaturated esters and Weinreb amides, respectively. The corresponding products were obtained in good yields and with high E stereoselectivities (E/Z up to >99:1), especially in the case of the amides. A detailed computational study of the Julia–Kocienski Olefination with BTFP sulfone 4 was carried out and confirmed the existence of an equilibrium in the initial addition of the sulfone enolate to the aldehyde and, in contrast to other proposed mechanisms, a non-concerted final elimination of SO2 and 3,5-bis(trifluoromethyl)phenoxide. A plausible explanation for the high E diastereoselectivity observed in the reaction has been suggested based on kinetic considerations at spirocyclic TS2 and thermodynamic factors during the elimination after TS2. ESI-MS studies carried out during the Olefination reaction of benzaldehyde with BTFP sulfone 4 were used to characterize the sulfone enolate and the intermediate assumed for the reaction mechanism. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
-
3,5‐Bis(trifluoromethyl)phenyl Sulfones in the Julia–Kocienski Olefination – Application to the Synthesis of Tri‐ and Tetrasubstituted Olefins
European Journal of Organic Chemistry, 2006Co-Authors: Diego A. Alonso, Mónica Fuensanta, Carmen NájeraAbstract:3,5-Bis(trifluoromethyl)phenyl (BTFP) sulfones 8a–d are successfully employed in the modified Julia Olefination reaction with carbonyl compounds employing phosphazene base P4-tBu at room temp. in THF, affording tri- and tetrasubstituted olefins in good yields. The Julia–Kocienski Olefination between primary alkyl BTFP sulfones 8a,b and aromatic and aliphatic ketones affords the corresponding trisubstituted alkenes in good yields and low stereoselectivities. On the other hand, higher yields and stereoselectivities are obtained in the synthesis of trisubstituted olefins through the other approach, the coupling of secondary alkyl BTFP sulfones 8c,d with aliphatic, aromatic and α,β-unsaturated aldehydes. For the first time, tetrasubstituted olefins are synthesized by means of the Julia–Kocienski protocol when the isopropyl BTFP sulfone 8c reacts with aliphatic and aromatic ketones, employing P4-tBu as base at THF reflux. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
-
3,5-bis(trifluoromethyl)phenyl sulfones in the direct Julia-Kocienski Olefination.
Journal of Organic Chemistry, 2005Co-Authors: Diego A. Alonso, Mónica Fuensanta, Carmen Nájera, Montserrat VareaAbstract:3,5-Bis(trifluoromethyl)phenyl (BTFP) sulfones 7 have been employed in the Julia−Kocienski Olefination reaction with carbonyl compounds. Sulfones 7 are readily prepared in high yields (64−97%) from commercially available 3,5-bis(trifluoromethyl)thiophenol through an alkylation/oxidation two-step sequence. The stability of metalated BTFP sulfones has been studied and compared with heteroaryl benzothiazol-2-yl (BT), 1-phenyl-1H-tetrazol-5-yl (PT), and 1-tert-butyl-1H-tetrazol-5-yl (TBT) sulfones 9−11 under different reaction conditions. The Julia−Kocienski Olefination between alkyl BTFP sulfones 7 and a wide variety of aldehydes affords the corresponding 1,2-disubstituted alkenes and dienes in good yields and stereoselectivities. This one-pot protocol can be performed using KOH at room temperature or the phosphazene bases P2-Et and P4-t-Bu at −78 °C or rt and has been successfully used in a high-yielding and stereoselective synthesis of various methoxylated stilbenes such as trimethylated resveratrol. These...
-
3,5-Bis(trifluoromethyl)phenyl sulfones in the modified julia Olefination: application to the synthesis of resveratrol
Tetrahedron Letters, 2004Co-Authors: Diego A. Alonso, Carmen Nájera, Montserrat VareaAbstract:Abstract The reaction between carbanions derived from alkyl 3,5-bis(trifluoromethyl)phenyl sulfones and aldehydes, affords with good yields and stereoselectivities the corresponding 1,2-disubstituted alkenes through the Julia–Kocienski Olefination reaction. This one-pot protocol can be performed using KOH at room temperature or the phosphazene base P4- t -Bu at −78 °C, and has been successfully used in a high yielding and stereoselective synthesis of various stilbenes such as resveratrol.
Diego A. Alonso - One of the best experts on this subject based on the ideXlab platform.
-
3,5‐Bis(trifluoromethyl)phenyl Sulfones for the Highly Stereoselective Julia–Kocienski Synthesis of α,β‐Unsaturated Esters and Weinreb Amides
European Journal of Organic Chemistry, 2008Co-Authors: Diego A. Alonso, Mónica Fuensanta, Enrique Gómez-bengoa, Carmen NájeraAbstract:The 3,5-bis(trifluoromethyl)phenyl (BTFP) sulfones tert-butyl α-(BTFPsulfonyl)acetate (4) and Weinreb α-(BTFPsulfonyl)acetamide (5) have successfully been employed in the Julia–Kocienski Olefination of aldehydes with K2CO3 as the base at 120 °C in DMF under solid/liquid phase-transfer catalysis conditions to afford α,β-unsaturated esters and Weinreb amides, respectively. The corresponding products were obtained in good yields and with high E stereoselectivities (E/Z up to >99:1), especially in the case of the amides. A detailed computational study of the Julia–Kocienski Olefination with BTFP sulfone 4 was carried out and confirmed the existence of an equilibrium in the initial addition of the sulfone enolate to the aldehyde and, in contrast to other proposed mechanisms, a non-concerted final elimination of SO2 and 3,5-bis(trifluoromethyl)phenoxide. A plausible explanation for the high E diastereoselectivity observed in the reaction has been suggested based on kinetic considerations at spirocyclic TS2 and thermodynamic factors during the elimination after TS2. ESI-MS studies carried out during the Olefination reaction of benzaldehyde with BTFP sulfone 4 were used to characterize the sulfone enolate and the intermediate assumed for the reaction mechanism. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
-
3,5‐Bis(trifluoromethyl)phenyl Sulfones in the Julia–Kocienski Olefination – Application to the Synthesis of Tri‐ and Tetrasubstituted Olefins
European Journal of Organic Chemistry, 2006Co-Authors: Diego A. Alonso, Mónica Fuensanta, Carmen NájeraAbstract:3,5-Bis(trifluoromethyl)phenyl (BTFP) sulfones 8a–d are successfully employed in the modified Julia Olefination reaction with carbonyl compounds employing phosphazene base P4-tBu at room temp. in THF, affording tri- and tetrasubstituted olefins in good yields. The Julia–Kocienski Olefination between primary alkyl BTFP sulfones 8a,b and aromatic and aliphatic ketones affords the corresponding trisubstituted alkenes in good yields and low stereoselectivities. On the other hand, higher yields and stereoselectivities are obtained in the synthesis of trisubstituted olefins through the other approach, the coupling of secondary alkyl BTFP sulfones 8c,d with aliphatic, aromatic and α,β-unsaturated aldehydes. For the first time, tetrasubstituted olefins are synthesized by means of the Julia–Kocienski protocol when the isopropyl BTFP sulfone 8c reacts with aliphatic and aromatic ketones, employing P4-tBu as base at THF reflux. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
-
3,5-bis(trifluoromethyl)phenyl sulfones in the direct Julia-Kocienski Olefination.
Journal of Organic Chemistry, 2005Co-Authors: Diego A. Alonso, Mónica Fuensanta, Carmen Nájera, Montserrat VareaAbstract:3,5-Bis(trifluoromethyl)phenyl (BTFP) sulfones 7 have been employed in the Julia−Kocienski Olefination reaction with carbonyl compounds. Sulfones 7 are readily prepared in high yields (64−97%) from commercially available 3,5-bis(trifluoromethyl)thiophenol through an alkylation/oxidation two-step sequence. The stability of metalated BTFP sulfones has been studied and compared with heteroaryl benzothiazol-2-yl (BT), 1-phenyl-1H-tetrazol-5-yl (PT), and 1-tert-butyl-1H-tetrazol-5-yl (TBT) sulfones 9−11 under different reaction conditions. The Julia−Kocienski Olefination between alkyl BTFP sulfones 7 and a wide variety of aldehydes affords the corresponding 1,2-disubstituted alkenes and dienes in good yields and stereoselectivities. This one-pot protocol can be performed using KOH at room temperature or the phosphazene bases P2-Et and P4-t-Bu at −78 °C or rt and has been successfully used in a high-yielding and stereoselective synthesis of various methoxylated stilbenes such as trimethylated resveratrol. These...
-
3,5-Bis(trifluoromethyl)phenyl sulfones in the modified julia Olefination: application to the synthesis of resveratrol
Tetrahedron Letters, 2004Co-Authors: Diego A. Alonso, Carmen Nájera, Montserrat VareaAbstract:Abstract The reaction between carbanions derived from alkyl 3,5-bis(trifluoromethyl)phenyl sulfones and aldehydes, affords with good yields and stereoselectivities the corresponding 1,2-disubstituted alkenes through the Julia–Kocienski Olefination reaction. This one-pot protocol can be performed using KOH at room temperature or the phosphazene base P4- t -Bu at −78 °C, and has been successfully used in a high yielding and stereoselective synthesis of various stilbenes such as resveratrol.
Rakesh Kumar - One of the best experts on this subject based on the ideXlab platform.
-
Facile Synthesis of 4‐Vinyl‐ and 4‐Fluorovinyl‐1,2,3‐triazoles via Bifunctional “Click‐Olefination” Reagents.
ChemInform, 2011Co-Authors: Rakesh Kumar, Padmanava Pradhan, Barbara ZajcAbstract:Title compounds are readily obtained by a copper-catalyzed click triazole synthesis and a subsequent Julia—Kocienski Olefination of sulfones (V) and (XII).
-
Facile synthesis of 4-vinyl- and 4-fluorovinyl-1,2,3-triazoles via bifunctional “click-Olefination” reagents
Chemical Communications, 2011Co-Authors: Rakesh Kumar, Padmanava Pradhan, Barbara ZajcAbstract:Modular synthesis of vinyl and fluorovinyl triazoles can be achieved from bifunctional propargyl and fluoropropargyl sulfones by Cu-catalyzed azide–alkyne ligation and Julia–Kocienski Olefination. Competitive click reactions of the protio and fluoropropargyl sulfones show higher reactivity of the latter, and a preliminary DFT analysis was performed.
-
Synthesis of Fluoroolefins via Julia-Kocienski Olefination
Synthesis, 2010Co-Authors: Barbara Zajc, Rakesh KumarAbstract:The Julia-Kocienski Olefination provides a versatile platformfor the synthesis of fluorovinyl compounds. This review describesour efforts as well as those of others in the synthesis of variousfluorinated aryl and heteroaryl sulfones and their utility as Olefinationreagents for the modular assembly of fluoroalkenes. Where data isavailable, the influence of the fluorine atom on the reactivityof the Olefination reagents and the stereochemical outcome of theOlefination are described. 1 Introduction 2 Synthesis of Fluorostilbene-like and Fluorostyrene-like Derivatives 3 Synthesis of Fluoroalkylidenes 3.1 Benzothiazole-Based Reagents 3.2 Phenyltetrazole-Based Reagents 4 Synthesis of Functionalized Fluoroolefins 4.1 α-Fluoroacrylates 4.1.1 Benzothiazole- and Phenyltetrazole-Based Reagents 4.1.2 Bis(trifluoromethyl)phenyl-Based Reagents 4.2 α-Fluoroacrylonitriles 4.3 α-Fluorovinyl Phenyl Sulfones 4.4 α-Fluorovinyl Weinreb Amides 4.4.1 Bis(trifluoromethyl)phenyl-Based Reagent 4.4.2 Benzothiazole-Based Reagent 4.5 α-Fluoroenones 5 Synthesis of 1,1-Difluoroalkenes 6 Mechanism of Julia-Kocienski Olefination 7 Miscellaneous Syntheses of Heteroaryl-Derived FluorinatedSulfides and Sulfones 8 Conclusions
Montserrat Varea - One of the best experts on this subject based on the ideXlab platform.
-
3,5-bis(trifluoromethyl)phenyl sulfones in the direct Julia-Kocienski Olefination.
Journal of Organic Chemistry, 2005Co-Authors: Diego A. Alonso, Mónica Fuensanta, Carmen Nájera, Montserrat VareaAbstract:3,5-Bis(trifluoromethyl)phenyl (BTFP) sulfones 7 have been employed in the Julia−Kocienski Olefination reaction with carbonyl compounds. Sulfones 7 are readily prepared in high yields (64−97%) from commercially available 3,5-bis(trifluoromethyl)thiophenol through an alkylation/oxidation two-step sequence. The stability of metalated BTFP sulfones has been studied and compared with heteroaryl benzothiazol-2-yl (BT), 1-phenyl-1H-tetrazol-5-yl (PT), and 1-tert-butyl-1H-tetrazol-5-yl (TBT) sulfones 9−11 under different reaction conditions. The Julia−Kocienski Olefination between alkyl BTFP sulfones 7 and a wide variety of aldehydes affords the corresponding 1,2-disubstituted alkenes and dienes in good yields and stereoselectivities. This one-pot protocol can be performed using KOH at room temperature or the phosphazene bases P2-Et and P4-t-Bu at −78 °C or rt and has been successfully used in a high-yielding and stereoselective synthesis of various methoxylated stilbenes such as trimethylated resveratrol. These...
-
3,5-Bis(trifluoromethyl)phenyl sulfones in the modified julia Olefination: application to the synthesis of resveratrol
Tetrahedron Letters, 2004Co-Authors: Diego A. Alonso, Carmen Nájera, Montserrat VareaAbstract:Abstract The reaction between carbanions derived from alkyl 3,5-bis(trifluoromethyl)phenyl sulfones and aldehydes, affords with good yields and stereoselectivities the corresponding 1,2-disubstituted alkenes through the Julia–Kocienski Olefination reaction. This one-pot protocol can be performed using KOH at room temperature or the phosphazene base P4- t -Bu at −78 °C, and has been successfully used in a high yielding and stereoselective synthesis of various stilbenes such as resveratrol.
