10066-31-6Relevant academic research and scientific papers
Wagner-Meerwein rearrangements in the gas phase: Anchimeric assistance to acid-induced dissociation of optically active phenylpropanols
Speranza, Maurizio,Filippi, Antonello
, p. 834 - 844 (1999)
The kinetics and the stereochemistry of Wagner-Meerwein rearrangements of O-protonated and O-methylated (S)-1-phenyl-2-propanol (1s(A)+; A=H or Me) and (S)-2-phenyl-1-propanol (2S(A)+; A=H or Me) have been investigated in the gas phase at 750 Torr and in the 25-140°C temperature range. The 1S(A) and 2S(A)+ intermediates were generated in the gas phase by reaction of the C(n)H5+(n=1, 2; A= H) and (CH3)2F+ ions (A - Me), formed by stationary γ radiolysis of bulk CH4 and CH3F, respectively, with the corresponding optically active alcohols. The results are consistent with unimolecular H2O loss from both 1s(H)+ and 2s(H); this is anchimerically assisted by all the groups adjacent to the leaving moiety. Anchimeric assistance appears much less efficient in both 1S(Me)+ and 2S(Me)+. Analysis of the activation parameters indicates that competing neighboring-group participation in C-O bond fission in 1s(H)+ and 2s(H) respond essentially to entropic rather than enthalpic factors. The stereochemical distribution of the reaction products allowed us to discern between backside and frontside phenyl-group participation in 1s(H+). The counterintuitive observation of a frontside Ph participation, with an activation energy 1.3±0.5 kcal mol-1 lower than that of the accompanying backside assistance, is attributed to conformational factors and to the stabilizing electrostatic interactions between the phenonium ion and the leaving H2O complex that is spatially allowed only in the frontside participation and forbidden in the backside one.
Ether-directed ortho-C-H olefination with a palladium(II)/monoprotected amino acid catalyst
Li, Gang,Leow, Dasheng,Wan, Li,Yu, Jin-Quan
supporting information, p. 1245 - 1247 (2013/03/13)
Weak coordination is powerful! A PdII-catalyzed olefination of ortho-C-H bonds of arenes directed by weakly coordinating ethers is developed by using monoprotected amino acid (MPAA) ligands. This finding provides a method for chemically modifying ethers, which are abundant in natural products and drug molecules. HFIP=hexafluoroisopropanol. Copyright
Highly efficient reduction of unactivated aryl and alkyl iodides by a ground-state neutral organic electron donor
Murphy, John A.,Khan, Tanweer A.,Zhou, Sheng-Ze,Thomson, Douglas W.,Mahesh, Mohan
, p. 1356 - 1360 (2007/10/03)
Electron-transfer reductions of unactivated aryl and alkyl iodides with a neutral ground-state organic molecule are reported. The reducing agent 1 is formed in two steps from N-methylbenzimidazole using very simple chemistry, and subsequent treatment of the iodoalkane or-arene with 1 affords cyclized products (see scheme).
Product studies and laser flash photolysis on alkyl radicals containing two different β-leaving groups are consonant with the formation of an olefin cation radical
Bales,Horner,Huang,Newcomb,Crich,Greenberg
, p. 3623 - 3629 (2007/10/03)
1-Bromo-2-methoxy-1-phenylpropan-2-yl (3) and 2-methoxy-1-phenyl-1-diphenylphosphatopropan-2-yl (4) were generated under continual photolysis from the respective PTOC precursors in a mixture of acetonitrile and methanol. The radicals undergo heterolytic fragmentation of the substituent in the β-position to generate the olefin cation radical (5). Z-2-Methoxy-1-phenylpropene (15) is the major product formed in the presence of 1,4-cyclohexadiene, and is believed to result from hydrogen atom transfer to the oxygen of the olefin cation radical, followed by deprotonation. Laser flash photolysis experiments indicate that reaction between 5 and 1,4-cyclohexadiene occurs with a rate constant of ～6 × 105 M-1 s-1. 2,2-Dimethoxy-1-phenylpropane (18) is observed as a minor product. Laser flash photolysis experiments place an upper limit on methanol trapping of 5 at k 3 M-1 s-1 and do not provide any evidence for the formation of reactive intermediates other than 5. The use of two PTOC precursors containing different leaving groups to generate a common olefin cation radical enables one to utilize product analysis to probe for the intermediacy of other reactive intermediates. The ratio of 15:18 is dependent upon hydrogen atom donor concentration, but is independent of the PTOC precursor. These observations are consistent with the proposal that both products result from trapping of 5 that is formed via heterolysis of 3 and 4.
Cross-interaction Constants as a Measure of the Transition State Structure. Part 11. Solvolyses of 1-Phenyl-2-propyl Benzenesulphonates
Lee, Ikchoon,Lee, Won Heui,Lee, Hai Whang,Lee, Byung Choon
, p. 785 - 791 (2007/10/02)
The solvolyses of 1-phenyl-2-propyl benzenesulphonates (PPBs) have been investigated in methanol-acetonitrile mixtures and in hexafluoropropan-2-ol (HFIP).The transition state structure has been discussed using various selectivity parameters, especially with the cross-interaction constants, ρYZ and λYZ, between substituents in the substrate (Y) and in the leaving group (Z).It has been found that the solvolysis proceeds by the solvent-assisted pathway, ks, in methanol, whereas in HFIP PPBs solvolyse via the aryl-assisted pathway, kΔ.The only exception was the p-MeO substituent, which deviates positively in methanol from the log ks vs. ? plot due to participation of the aryl-assisted path and negatively in HFIP from the log kΔ vs. ?(neophyl) plot due to deactivation by hydrogen bonding of the methoxy oxygen in the acidic solvent.The two distinctive high values of ρYZ provided evidence for the strongly bound transition states in the two processes, ks and kΔ, with a relatively low degree of bond breaking.
Photosensitized (electron transfer) carbon-carbon bond cleavage of radical cations: the 2-phenylethyl ether and acetal systems
Arnold, Donald R.,Lamont, Laurie J.
, p. 2119 - 2127 (2007/10/02)
The scope of the photosensitized (electron transfer) carbon-carbon bond cleavage involving radical cations has been defined for 2-phenylethyl ethers and acetals.The thresholds for reactivity of the monophenylethyl and gem-diphenylethyl derivatives are compared.While the radical cation of methyl 2,2-diphenylethyl ether (7) cleaves to give ultimately diphenylmethane (2) and dimethoxymethane (8), the radical cation of methyl 2-phenylethyl ether (9) was stable under these conditions.In contrast to the lack of reactivity of the radical cation of 9, the radical cations of methyl 2-phenyl-2-propyl ether (11), methyl 2-phenylcyclopentyl ether (13), and 2-phenylmethyl-1,3-dioxolane (16) cleave.Cleavage in the monophenylethyl series is limited to formation of a carbocation at least as stable as the secondary α-oxyalkyl or di-α-oxyalkyl.The basis for predicting this type of reactivity of radical cations is defined.The rate of carbon-carbon bond cleavage is increased the oxidation potential of the molecule, by decreasing the carbon-carbon bond strength, and (or) by decreasing the oxidation potential of that fragment that will become the carbocation.The results obtained from the reactions of 2-diphenylmethyl-1,3-dioxolane (14) and 2-phenylmethyl-1,3-dioxolane (16) cast doubt on the published oxidation potential for the 1,3-dioxolan-2-yl radical.Key words: photochemistry, radical cation, electron transfer, bond cleavage, radical.
Gas-Phase Acid-Induced Nucleophilic Displacement Reactions. 7. Structural and Stereochemical Evidence for the Existence and the Relative Stability of Alkylenebenzenium Ions in the Gas Phase
Fornarini, Simonetta,Sparapani, Cinzia,Speranza, Maurizio
, p. 34 - 41 (2007/10/02)
A comprehensive investigation on the existence and relative stability of gaseous 2,3-butylene- and 1,2-propylenebenzenium ions was carried out by establishing the structural features and the stereochemistry of acid-induced displacement by CH3OH on isomeric 3-phenylbutyl-2 onium and β-phenylpropyl onium intermediates.The latter were obtained in the gas phase from the reaction of radiolytically formed GA+ (GA+ = D3+, CnH5+ (n=1,2), i-C3H7+, and CH3FCH3+) acids with isomeric 3-phenyl-2-chlorobutanes and β-phenyl-Y-propanes (Y = Cl, OH).The analysis of the isomeric distribution of the neutral substitution products allows the establishment of extensive phenyl-group participation in the displacement process, occuring in competition with methyl and hydrogen 1,2-transfers.The participating ability of a phenyl moiety adjacent to the substitution center is found to depend essentially upon the configuration of the precursor and to be related to its gas-phase nucleophilicity.The occurence of relatively stable cyclic alkylenebenzenium ions as static intermediates in these displacement reactions is suggested by the particular isomeric and stereoisomeric distribution of the products and by its comparison with that obtained from open-chain isomeric ions.The results obtained from the present gas-phase experiments are discussed in the light of those from related gas-phase and solution studies.
CONVERSION OF ALKYL PHENYL SELENIDES AND SELENOXIDES INTO DIALKYL ETHERS. NUCLEOFUGACITY ENHANCEMENT OF THE PLENYLSELENINYL GROUP BY meta-CHLOROPERBENZOIC ACID IN ALCOHOLS
Tiecco, Marcello,Testaferri, Lorenzo,Tingoli, Marco,Chianelli, Donatella,Bartoli, Donatella
, p. 423 - 428 (2007/10/02)
The recently reported conversion of alkyl phenyl selenides into dialkyl ethers, promoted by MCPBA in alcohols, has been reinvestigated.It is concluded that the reactive intermediate does not derive from the selenones, as reported, but from the selenoxides.It is suggested that MCPBA adds to the selenoxide function to give an intermediate which easily gives rise to solvolysis; thus, the addition of MCPBA greatly enhances the nucleofugacity of the phenylseleninyl group.The synthesis and the reactivity of several 1-phenyl, 2-phenylseleninyl- and 1-phenyl-, 2-phenylselenonyl-ethanes are also described.
Oxidation of Alkyl Phenyl Selenides, Tellurides, and Telluroxides with meta-Chloroperbenzoic Acid for a Facile and Novel Transformation of C-Se and C-Te Bonds to C-O Bonds
Uemura, Sakae,Fukuzawa, Shin-ichi
, p. 471 - 480 (2007/10/02)
In sharp contrast to the well-known selenoxide elimination leading to olefins, the treatment of alkyl phenyl selenides (PhSeR) with an excess of meta-chloroperbenzoic acid (MCPBA; 2-5 equiv. to a selenide) in alcohol at room temperature affords the corresponding dialkyl ethers by the substitution of a phenylselenium (PhSe) moiety with an alkoxy group.A similar reaction proceeds by using alkyl phenyl tellurides (PhTeR) and telluroxides , a facile substitution of PhTe or PhTe(O) moiety by an alkoxy group being observed.Methanol is the most appropriate solvent for these oxidations and alkyl methyl ethers are formed in excellent yields.The reaction is accompanied by phenyl migration when applied to some selenides, tellurides, and telluroxides having a phenyl group at a vicinal position to the PhSe, PhTe, or PhTe(O) moiety.Application to the methoxyselenation and methoxytelluration products of cyclohexene and cycloheptene results in a ring-contraction to afford the dimethyl acetals of cyclopentane- and cyclohexane-carbaldehyde, respectively.In case of an allylic phenyl selenide, a sigmatropic rearrangement giving a rearranged allylic alcohol occurs in much preference to the substitution by the methoxy group.Other oxidizing agents than MCPBA such as NaIO4, H2O2, t-BuOOH, and ozone are generally ineffective under similar conditions.It is proposed that the reaction mainly takes place as follows.Alkyl phenyl selenone, alkyl phenyl tellurone, or the MCPBA addition product to them is formed as a reactive intermediate in which an alkyl C-Se or alkyl C-Te bond fission occurs heterolytically by a nucleophilic attack of alcohol, sometimes accompanied by a 1,2-shift of the β-substituent, i.e., phenyl migration and ring-contraction.
