Eli Rochlin | Jerusalem College of Technology (original) (raw)
Papers by Eli Rochlin
The Journal of Organic Chemistry, Mar 1, 2003
2-(m-Methoxymesityl)-1,2-dimesitylethenol (3a) isomerizes in the absence of a catalyst in solutio... more 2-(m-Methoxymesityl)-1,2-dimesitylethenol (3a) isomerizes in the absence of a catalyst in solution to a 1.0:0.9 E/Z (3a/3b) equilibrium mixture. In CDCl 3 , the isomerization is first order in 3a within a run, but the plot of the rate constant k obs vs the changing [3a] 0 in different runs is a half-parabola, indicating self-catalysis by more than one enol molecule. At 0.09 M enol, the isotope effect k 3a / k 3a-OD) 2.1. In the presence of 0.025-0.25 M pyridine-d 5 , the k obs vs [pyridine-d 5 ] plot displays a bell-shaped profile. The change in the shape of the OH signals of the 3a/3b mixture at 295-430 K in C 6 D 5 NO 2 was followed by DNMR. The four signals of the diastereomeric 3a/3b mixture observed at 330 K coalesce at 350 K with barriers of 18.3 and 18.4 kcal mol-1 due to the diastereomerization of the vinyl propellers. The resulting two signals observed at >360 K further coalesce at 425 K with a barrier of 22.9 kcal mol-1 due either to oxygen-to-oxygen proton exchange or to E/Z isomerization. The estimated upper limit for the rate of proton exchange of k ex e (2-4) × 10 3 M-1 s-1 at 425 K between the enol molecules is sufficiently slow to be a rate-controlling step in the isomerization. A process in which several enol molecules catalyze the isomerization is suggested, and several mechanistic routes are analyzed.
The Journal of Organic Chemistry, Feb 1, 2003
Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylet... more Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylethenol (2), 1-[9'-(2'-fluoroanthryl)]-2,2-dimesitylethenol (3), and 1-[9'-(2'-fluoroanthryl)]-2,2- dimesitylvinyl acetate (4) were synthesized and their DNMR behavior in C6D5NO2 was studied. 3 and 4 were resolved on an amylose tris(3,5-dimethylphenylcarbamate) HPLC column to their enantiomers. Acetate 4 racemizes slowly in solution with DeltaG(e)(++), DeltaH(e)(++), and DeltaS(e)(++) values of 26.2, 27.6 kcal mol(-)(1), and 4.3 eu, respectively, as expected for a rotational betabeta'-2-ring flip process in a vinyl propeller and the racemization is unaffected by added TFA, Et3N, and EtOD. Although 3 racemizes almost 350 times faster, the racemization is catalyzed by TFA and shows bell-shape catalysis by Et3N and a KIE in a partially deuteriated solvent. From this and the DNMR data, it is concluded that 3 does not racemize via a rotational betabeta'-2-ring flip. Five nonflip routes are discussed for the racemization of 3, and it is concluded that only the one initiated by protonation at C1 does not contradict the experimental data. By analogy with the E/Z isomerization of the structurally related 2-(m-methoxymesityl)-1,2-dimesitylethenol 17, it is suggested that in the absence of added catalyst one or more enol molecule(s) catalyze the enantiomerization of another one. Only partial resolution was achieved for 2 and from the similarity of its behavior with that of 3, it is suggested that it racemizes by the same mechanism.
J Org Chem, 2003
Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylet... more Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylethenol (2), 1-[9'-(2'-fluoroanthryl)]-2,2-dimesitylethenol (3), and 1-[9'-(2'-fluoroanthryl)]-2,2- dimesitylvinyl acetate (4) were synthesized and their DNMR behavior in C6D5NO2 was studied. 3 and 4 were resolved on an amylose tris(3,5-dimethylphenylcarbamate) HPLC column to their enantiomers. Acetate 4 racemizes slowly in solution with DeltaG(e)(++), DeltaH(e)(++), and DeltaS(e)(++) values of 26.2, 27.6 kcal mol(-)(1), and 4.3 eu, respectively, as expected for a rotational betabeta'-2-ring flip process in a vinyl propeller and the racemization is unaffected by added TFA, Et3N, and EtOD. Although 3 racemizes almost 350 times faster, the racemization is catalyzed by TFA and shows bell-shape catalysis by Et3N and a KIE in a partially deuteriated solvent. From this and the DNMR data, it is concluded that 3 does not racemize via a rotational betabeta'-2-ring flip. Five nonflip routes are discussed for the racemization of 3, and it is concluded that only the one initiated by protonation at C1 does not contradict the experimental data. By analogy with the E/Z isomerization of the structurally related 2-(m-methoxymesityl)-1,2-dimesitylethenol 17, it is suggested that in the absence of added catalyst one or more enol molecule(s) catalyze the enantiomerization of another one. Only partial resolution was achieved for 2 and from the similarity of its behavior with that of 3, it is suggested that it racemizes by the same mechanism.
Vaccine, 2006
We recently showed that lipid assemblies comprised of a novel polycationic sphingolipid (ceramide... more We recently showed that lipid assemblies comprised of a novel polycationic sphingolipid (ceramide carbamoyl-spermine, CCS) are an effective adjuvant/carrier when complexed with cholesterol (CCS/C) for influenza and other vaccines administered parenterally and intranasally (i.n.) in mice. Here we expand these studies to ferrets, an established model of influenza infection. We also address the question of why the CCS/C-based liposomal vaccine (also known as VaxiSome™) in mice is superior to vaccines based on liposomes of other lipid compositions (neutral, anionic or cationic). Ferrets immunized i.n. with CCS/C-influenza vaccine produced significantly higher hemagglutination inhibition (HI) antibody titers compared to ferrets immunized intramuscularly with the unadjuvanted influenza vaccine, indicating that the CCS/C-based vaccine is very immunogenic. Furthermore, the i.n. adjuvanted vaccine was shown to significantly reduce the severity of influenza virus infection in ferrets following homologous viral challenge as determined by weight loss, temperature rise and viral titer. No adverse reactions were observed. Pharmacokinetic and biodistribution studies following i.n. administration in mice of CCS/C-based vaccine showed that both the lipids and antigens are retained in the nose and lung for at least 24h, and it appears that this retention correlates with the superior immunogenicity elicited by the adjuvanted vaccine formulation. The CCS lipid also increases production of cytokines (mainly IFN gamma, IL-2 and IL-12) and co-stimulatory molecules' expression, which might further explain the robust adjuvantation of this liposome-based vaccine.
Pure and Applied Chemistry, 2000
Two new aspects of the chemistry of simple bulky-aryl substituted enols are described. (i) The re... more Two new aspects of the chemistry of simple bulky-aryl substituted enols are described. (i) The reactions of amines such as Me2NH, morpholine piperidine, or pyrrolidine with ditipyl ketene (tipyl = Tip = 2,4,6-tri-isopropyl-phenyl) generate the enol of the amide Tip2C=C(OH)NR1R2 which is observed and characterized by NMR spectra. The addition reaction is reversible. Further tautomerization of the enol to the stable conformer of the amide is relatively slow and involves an additional NMR observable intermediate which is presumably the kinetically controlled unstable conformer of the amide. (ii) Di-and tri-bulky arylvinyl alcohols and their derivatives such as the ethers or acetates are chiral, having a propeller conformation. The enantiomerizations of triarylethenols usually proceed by a three ring flip, and the rotational barriers are mostly too low for resolution of stereoisomers. In the Mes2C=C(OH)(2-X-9-anthryl) system where X = F, OMe, the a-ring lacks a C2 symmetry and enantiomerization barriers in which this ring passes through the molecular plane are higher. Resolution on an optically active column is achieved when X = F, but fast enantiomerization then takes place. This is probably due to an E-Z enol interconversion which was observed in other systems.
Journal of The American Chemical Society, 1993
... Enol Equilibria of 2,2-Dimesityl-1 -R-ethenols' Irina Eventova, Ella B. Nadler, Elimelec... more ... Enol Equilibria of 2,2-Dimesityl-1 -R-ethenols' Irina Eventova, Ella B. Nadler, Elimelech Rochlin, Joseph Frey, and Zvi Rappoport* ... (IO) O'Neill, P.; Hegarty, AF J. Chem. Soc., Chem. Commun. 1987, 744. ... 1992, 57, 1940. (1 5) Clarke, L. F.; Hegarty, F. A.; ONeill, P. J. Org. Chem. ...
Pure and Applied Chemistry, 1997
Two new aspects of the chemistry of simple bulky-aryl substituted enols are described. (i) The re... more Two new aspects of the chemistry of simple bulky-aryl substituted enols are described. (i) The reactions of amines such as Me2NH, morpholine piperidine, or pyrrolidine with ditipyl ketene (tipyl = Tip = 2,4,6-tri-isopropyl-phenyl) generate the enol of the amide Tip2C=C(OH)NR1R2 which is observed and characterized by NMR spectra. The addition reaction is reversible. Further tautomerization of the enol to the stable conformer of the amide is relatively slow and involves an additional NMR observable intermediate which is presumably the kinetically controlled unstable conformer of the amide. (ii) Di-and tri-bulky arylvinyl alcohols and their derivatives such as the ethers or acetates are chiral, having a propeller conformation. The enantiomerizations of triarylethenols usually proceed by a three ring flip, and the rotational barriers are mostly too low for resolution of stereoisomers. In the Mes2C=C(OH)(2-X-9-anthryl) system where X = F, OMe, the a-ring lacks a C2 symmetry and enantiomerization barriers in which this ring passes through the molecular plane are higher. Resolution on an optically active column is achieved when X = F, but fast enantiomerization then takes place. This is probably due to an E-Z enol interconversion which was observed in other systems.
Journal of Organic Chemistry, 2003
E)-2-(m-Methoxymesityl)-1,2-dimesitylethenol (3a) isomerizes in the absence of a catalyst in solu... more E)-2-(m-Methoxymesityl)-1,2-dimesitylethenol (3a) isomerizes in the absence of a catalyst in solution to a 1.0:0.9 E/Z (3a/3b) equilibrium mixture. In CDCl 3 , the isomerization is first order in 3a within a run, but the plot of the rate constant k obs vs the changing [3a] 0 in different runs is a half-parabola, indicating self-catalysis by more than one enol molecule. At 0.09 M enol, the isotope effect k 3a / k 3a-OD ) 2.1. In the presence of 0.025-0.25 M pyridine-d 5 , the k obs vs [pyridine-d 5 ] plot displays a bell-shaped profile. The change in the shape of the OH signals of the 3a/3b mixture at 295-430 K in C 6 D 5 NO 2 was followed by DNMR. The four signals of the diastereomeric 3a/3b mixture observed at 330 K coalesce at 350 K with barriers of 18.3 and 18.4 kcal mol -1 due to the diastereomerization of the vinyl propellers. The resulting two signals observed at >360 K further coalesce at 425 K with a barrier of 22.9 kcal mol -1 due either to oxygen-to-oxygen proton exchange or to E/Z isomerization. The estimated upper limit for the rate of proton exchange of k ex e (2-4) × 10 3 M -1 s -1 at 425 K between the enol molecules is sufficiently slow to be a rate-controlling step in the isomerization. A process in which several enol molecules catalyze the isomerization is suggested, and several mechanistic routes are analyzed.
Journal of Organic Chemistry, 1999
The vinyl propellers (E)-and (Z)-2-m-methoxymesityl-1,2-dimesitylvinyl acetates (3c and 3d) were ... more The vinyl propellers (E)-and (Z)-2-m-methoxymesityl-1,2-dimesitylvinyl acetates (3c and 3d) were prepared and their geometries assigned. The stereoisomerization barriers of the trimesityl vinyl acetate system were determined by DNMR and by enantioselective LC resolution and polarimetric monitoring of the behavior of the two diastereomeric racemates of 3c and 3d. Combined with data for trimesitylvinyl-OAc 3a and its 1-m-methoxymesityl analogue 3b, the following order of barriers ∆G q is obtained: R -2-ring flip > R ′-2-ring flip > ′-2-ring flip > R ′-3-ring flip (the threshold enantiomerization barrier). This order which differs from the previously found orders for trimesitylvinyl-X, X ) H, OPr-i was rationalized and discussed.
Journal of Organic Chemistry, 1994
... Elimelech Rochlin and Zvi Rappoport* Department of Organic Chemistry, The Hebrew University, ... more ... Elimelech Rochlin and Zvi Rappoport* Department of Organic Chemistry, The Hebrew University, Jerusalem 91904, Israel Received April 4, 1994" E-and Z-(m-methoxymesityl)-1,2-dimesitylethenols ... 3a bond led A 3aQ 3 e leb angle cze 3c angle, deg angle, deg angle, deg ...
Journal of Organic Chemistry, 2003
Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylet... more Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylethenol (2), 1-[9'-(2'-fluoroanthryl)]-2,2-dimesitylethenol (3), and 1-[9'-(2'-fluoroanthryl)]-2,2- dimesitylvinyl acetate (4) were synthesized and their DNMR behavior in C6D5NO2 was studied. 3 and 4 were resolved on an amylose tris(3,5-dimethylphenylcarbamate) HPLC column to their enantiomers. Acetate 4 racemizes slowly in solution with DeltaG(e)(++), DeltaH(e)(++), and DeltaS(e)(++) values of 26.2, 27.6 kcal mol(-)(1), and 4.3 eu, respectively, as expected for a rotational betabeta'-2-ring flip process in a vinyl propeller and the racemization is unaffected by added TFA, Et3N, and EtOD. Although 3 racemizes almost 350 times faster, the racemization is catalyzed by TFA and shows bell-shape catalysis by Et3N and a KIE in a partially deuteriated solvent. From this and the DNMR data, it is concluded that 3 does not racemize via a rotational betabeta'-2-ring flip. Five nonflip routes are discussed for the racemization of 3, and it is concluded that only the one initiated by protonation at C1 does not contradict the experimental data. By analogy with the E/Z isomerization of the structurally related 2-(m-methoxymesityl)-1,2-dimesitylethenol 17, it is suggested that in the absence of added catalyst one or more enol molecule(s) catalyze the enantiomerization of another one. Only partial resolution was achieved for 2 and from the similarity of its behavior with that of 3, it is suggested that it racemizes by the same mechanism.
The Journal of Organic Chemistry, Mar 1, 2003
2-(m-Methoxymesityl)-1,2-dimesitylethenol (3a) isomerizes in the absence of a catalyst in solutio... more 2-(m-Methoxymesityl)-1,2-dimesitylethenol (3a) isomerizes in the absence of a catalyst in solution to a 1.0:0.9 E/Z (3a/3b) equilibrium mixture. In CDCl 3 , the isomerization is first order in 3a within a run, but the plot of the rate constant k obs vs the changing [3a] 0 in different runs is a half-parabola, indicating self-catalysis by more than one enol molecule. At 0.09 M enol, the isotope effect k 3a / k 3a-OD) 2.1. In the presence of 0.025-0.25 M pyridine-d 5 , the k obs vs [pyridine-d 5 ] plot displays a bell-shaped profile. The change in the shape of the OH signals of the 3a/3b mixture at 295-430 K in C 6 D 5 NO 2 was followed by DNMR. The four signals of the diastereomeric 3a/3b mixture observed at 330 K coalesce at 350 K with barriers of 18.3 and 18.4 kcal mol-1 due to the diastereomerization of the vinyl propellers. The resulting two signals observed at >360 K further coalesce at 425 K with a barrier of 22.9 kcal mol-1 due either to oxygen-to-oxygen proton exchange or to E/Z isomerization. The estimated upper limit for the rate of proton exchange of k ex e (2-4) × 10 3 M-1 s-1 at 425 K between the enol molecules is sufficiently slow to be a rate-controlling step in the isomerization. A process in which several enol molecules catalyze the isomerization is suggested, and several mechanistic routes are analyzed.
The Journal of Organic Chemistry, Feb 1, 2003
Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylet... more Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylethenol (2), 1-[9'-(2'-fluoroanthryl)]-2,2-dimesitylethenol (3), and 1-[9'-(2'-fluoroanthryl)]-2,2- dimesitylvinyl acetate (4) were synthesized and their DNMR behavior in C6D5NO2 was studied. 3 and 4 were resolved on an amylose tris(3,5-dimethylphenylcarbamate) HPLC column to their enantiomers. Acetate 4 racemizes slowly in solution with DeltaG(e)(++), DeltaH(e)(++), and DeltaS(e)(++) values of 26.2, 27.6 kcal mol(-)(1), and 4.3 eu, respectively, as expected for a rotational betabeta'-2-ring flip process in a vinyl propeller and the racemization is unaffected by added TFA, Et3N, and EtOD. Although 3 racemizes almost 350 times faster, the racemization is catalyzed by TFA and shows bell-shape catalysis by Et3N and a KIE in a partially deuteriated solvent. From this and the DNMR data, it is concluded that 3 does not racemize via a rotational betabeta'-2-ring flip. Five nonflip routes are discussed for the racemization of 3, and it is concluded that only the one initiated by protonation at C1 does not contradict the experimental data. By analogy with the E/Z isomerization of the structurally related 2-(m-methoxymesityl)-1,2-dimesitylethenol 17, it is suggested that in the absence of added catalyst one or more enol molecule(s) catalyze the enantiomerization of another one. Only partial resolution was achieved for 2 and from the similarity of its behavior with that of 3, it is suggested that it racemizes by the same mechanism.
J Org Chem, 2003
Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylet... more Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylethenol (2), 1-[9'-(2'-fluoroanthryl)]-2,2-dimesitylethenol (3), and 1-[9'-(2'-fluoroanthryl)]-2,2- dimesitylvinyl acetate (4) were synthesized and their DNMR behavior in C6D5NO2 was studied. 3 and 4 were resolved on an amylose tris(3,5-dimethylphenylcarbamate) HPLC column to their enantiomers. Acetate 4 racemizes slowly in solution with DeltaG(e)(++), DeltaH(e)(++), and DeltaS(e)(++) values of 26.2, 27.6 kcal mol(-)(1), and 4.3 eu, respectively, as expected for a rotational betabeta'-2-ring flip process in a vinyl propeller and the racemization is unaffected by added TFA, Et3N, and EtOD. Although 3 racemizes almost 350 times faster, the racemization is catalyzed by TFA and shows bell-shape catalysis by Et3N and a KIE in a partially deuteriated solvent. From this and the DNMR data, it is concluded that 3 does not racemize via a rotational betabeta'-2-ring flip. Five nonflip routes are discussed for the racemization of 3, and it is concluded that only the one initiated by protonation at C1 does not contradict the experimental data. By analogy with the E/Z isomerization of the structurally related 2-(m-methoxymesityl)-1,2-dimesitylethenol 17, it is suggested that in the absence of added catalyst one or more enol molecule(s) catalyze the enantiomerization of another one. Only partial resolution was achieved for 2 and from the similarity of its behavior with that of 3, it is suggested that it racemizes by the same mechanism.
Vaccine, 2006
We recently showed that lipid assemblies comprised of a novel polycationic sphingolipid (ceramide... more We recently showed that lipid assemblies comprised of a novel polycationic sphingolipid (ceramide carbamoyl-spermine, CCS) are an effective adjuvant/carrier when complexed with cholesterol (CCS/C) for influenza and other vaccines administered parenterally and intranasally (i.n.) in mice. Here we expand these studies to ferrets, an established model of influenza infection. We also address the question of why the CCS/C-based liposomal vaccine (also known as VaxiSome™) in mice is superior to vaccines based on liposomes of other lipid compositions (neutral, anionic or cationic). Ferrets immunized i.n. with CCS/C-influenza vaccine produced significantly higher hemagglutination inhibition (HI) antibody titers compared to ferrets immunized intramuscularly with the unadjuvanted influenza vaccine, indicating that the CCS/C-based vaccine is very immunogenic. Furthermore, the i.n. adjuvanted vaccine was shown to significantly reduce the severity of influenza virus infection in ferrets following homologous viral challenge as determined by weight loss, temperature rise and viral titer. No adverse reactions were observed. Pharmacokinetic and biodistribution studies following i.n. administration in mice of CCS/C-based vaccine showed that both the lipids and antigens are retained in the nose and lung for at least 24h, and it appears that this retention correlates with the superior immunogenicity elicited by the adjuvanted vaccine formulation. The CCS lipid also increases production of cytokines (mainly IFN gamma, IL-2 and IL-12) and co-stimulatory molecules' expression, which might further explain the robust adjuvantation of this liposome-based vaccine.
Pure and Applied Chemistry, 2000
Two new aspects of the chemistry of simple bulky-aryl substituted enols are described. (i) The re... more Two new aspects of the chemistry of simple bulky-aryl substituted enols are described. (i) The reactions of amines such as Me2NH, morpholine piperidine, or pyrrolidine with ditipyl ketene (tipyl = Tip = 2,4,6-tri-isopropyl-phenyl) generate the enol of the amide Tip2C=C(OH)NR1R2 which is observed and characterized by NMR spectra. The addition reaction is reversible. Further tautomerization of the enol to the stable conformer of the amide is relatively slow and involves an additional NMR observable intermediate which is presumably the kinetically controlled unstable conformer of the amide. (ii) Di-and tri-bulky arylvinyl alcohols and their derivatives such as the ethers or acetates are chiral, having a propeller conformation. The enantiomerizations of triarylethenols usually proceed by a three ring flip, and the rotational barriers are mostly too low for resolution of stereoisomers. In the Mes2C=C(OH)(2-X-9-anthryl) system where X = F, OMe, the a-ring lacks a C2 symmetry and enantiomerization barriers in which this ring passes through the molecular plane are higher. Resolution on an optically active column is achieved when X = F, but fast enantiomerization then takes place. This is probably due to an E-Z enol interconversion which was observed in other systems.
Journal of The American Chemical Society, 1993
... Enol Equilibria of 2,2-Dimesityl-1 -R-ethenols' Irina Eventova, Ella B. Nadler, Elimelec... more ... Enol Equilibria of 2,2-Dimesityl-1 -R-ethenols' Irina Eventova, Ella B. Nadler, Elimelech Rochlin, Joseph Frey, and Zvi Rappoport* ... (IO) O'Neill, P.; Hegarty, AF J. Chem. Soc., Chem. Commun. 1987, 744. ... 1992, 57, 1940. (1 5) Clarke, L. F.; Hegarty, F. A.; ONeill, P. J. Org. Chem. ...
Pure and Applied Chemistry, 1997
Two new aspects of the chemistry of simple bulky-aryl substituted enols are described. (i) The re... more Two new aspects of the chemistry of simple bulky-aryl substituted enols are described. (i) The reactions of amines such as Me2NH, morpholine piperidine, or pyrrolidine with ditipyl ketene (tipyl = Tip = 2,4,6-tri-isopropyl-phenyl) generate the enol of the amide Tip2C=C(OH)NR1R2 which is observed and characterized by NMR spectra. The addition reaction is reversible. Further tautomerization of the enol to the stable conformer of the amide is relatively slow and involves an additional NMR observable intermediate which is presumably the kinetically controlled unstable conformer of the amide. (ii) Di-and tri-bulky arylvinyl alcohols and their derivatives such as the ethers or acetates are chiral, having a propeller conformation. The enantiomerizations of triarylethenols usually proceed by a three ring flip, and the rotational barriers are mostly too low for resolution of stereoisomers. In the Mes2C=C(OH)(2-X-9-anthryl) system where X = F, OMe, the a-ring lacks a C2 symmetry and enantiomerization barriers in which this ring passes through the molecular plane are higher. Resolution on an optically active column is achieved when X = F, but fast enantiomerization then takes place. This is probably due to an E-Z enol interconversion which was observed in other systems.
Journal of Organic Chemistry, 2003
E)-2-(m-Methoxymesityl)-1,2-dimesitylethenol (3a) isomerizes in the absence of a catalyst in solu... more E)-2-(m-Methoxymesityl)-1,2-dimesitylethenol (3a) isomerizes in the absence of a catalyst in solution to a 1.0:0.9 E/Z (3a/3b) equilibrium mixture. In CDCl 3 , the isomerization is first order in 3a within a run, but the plot of the rate constant k obs vs the changing [3a] 0 in different runs is a half-parabola, indicating self-catalysis by more than one enol molecule. At 0.09 M enol, the isotope effect k 3a / k 3a-OD ) 2.1. In the presence of 0.025-0.25 M pyridine-d 5 , the k obs vs [pyridine-d 5 ] plot displays a bell-shaped profile. The change in the shape of the OH signals of the 3a/3b mixture at 295-430 K in C 6 D 5 NO 2 was followed by DNMR. The four signals of the diastereomeric 3a/3b mixture observed at 330 K coalesce at 350 K with barriers of 18.3 and 18.4 kcal mol -1 due to the diastereomerization of the vinyl propellers. The resulting two signals observed at >360 K further coalesce at 425 K with a barrier of 22.9 kcal mol -1 due either to oxygen-to-oxygen proton exchange or to E/Z isomerization. The estimated upper limit for the rate of proton exchange of k ex e (2-4) × 10 3 M -1 s -1 at 425 K between the enol molecules is sufficiently slow to be a rate-controlling step in the isomerization. A process in which several enol molecules catalyze the isomerization is suggested, and several mechanistic routes are analyzed.
Journal of Organic Chemistry, 1999
The vinyl propellers (E)-and (Z)-2-m-methoxymesityl-1,2-dimesitylvinyl acetates (3c and 3d) were ... more The vinyl propellers (E)-and (Z)-2-m-methoxymesityl-1,2-dimesitylvinyl acetates (3c and 3d) were prepared and their geometries assigned. The stereoisomerization barriers of the trimesityl vinyl acetate system were determined by DNMR and by enantioselective LC resolution and polarimetric monitoring of the behavior of the two diastereomeric racemates of 3c and 3d. Combined with data for trimesitylvinyl-OAc 3a and its 1-m-methoxymesityl analogue 3b, the following order of barriers ∆G q is obtained: R -2-ring flip > R ′-2-ring flip > ′-2-ring flip > R ′-3-ring flip (the threshold enantiomerization barrier). This order which differs from the previously found orders for trimesitylvinyl-X, X ) H, OPr-i was rationalized and discussed.
Journal of Organic Chemistry, 1994
... Elimelech Rochlin and Zvi Rappoport* Department of Organic Chemistry, The Hebrew University, ... more ... Elimelech Rochlin and Zvi Rappoport* Department of Organic Chemistry, The Hebrew University, Jerusalem 91904, Israel Received April 4, 1994" E-and Z-(m-methoxymesityl)-1,2-dimesitylethenols ... 3a bond led A 3aQ 3 e leb angle cze 3c angle, deg angle, deg angle, deg ...
Journal of Organic Chemistry, 2003
Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylet... more Chiral 1-[9'-(2'-methoxyanthryl)]-2,2-dimesitylethenol (2), 1-[9'-(2'-fluoroanthryl)]-2,2-dimesitylethenol (3), and 1-[9'-(2'-fluoroanthryl)]-2,2- dimesitylvinyl acetate (4) were synthesized and their DNMR behavior in C6D5NO2 was studied. 3 and 4 were resolved on an amylose tris(3,5-dimethylphenylcarbamate) HPLC column to their enantiomers. Acetate 4 racemizes slowly in solution with DeltaG(e)(++), DeltaH(e)(++), and DeltaS(e)(++) values of 26.2, 27.6 kcal mol(-)(1), and 4.3 eu, respectively, as expected for a rotational betabeta'-2-ring flip process in a vinyl propeller and the racemization is unaffected by added TFA, Et3N, and EtOD. Although 3 racemizes almost 350 times faster, the racemization is catalyzed by TFA and shows bell-shape catalysis by Et3N and a KIE in a partially deuteriated solvent. From this and the DNMR data, it is concluded that 3 does not racemize via a rotational betabeta'-2-ring flip. Five nonflip routes are discussed for the racemization of 3, and it is concluded that only the one initiated by protonation at C1 does not contradict the experimental data. By analogy with the E/Z isomerization of the structurally related 2-(m-methoxymesityl)-1,2-dimesitylethenol 17, it is suggested that in the absence of added catalyst one or more enol molecule(s) catalyze the enantiomerization of another one. Only partial resolution was achieved for 2 and from the similarity of its behavior with that of 3, it is suggested that it racemizes by the same mechanism.