- OLEFINATION OF KETONES USING 1,1-DIMETALLOALKANES DERIVED FROM i-Bu2AlCH=CHR - Cl2TiCp2 SYSTEM
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The alkylidenation of ketone carbonyls using 1,1-dimetalloalkanes prepared by the reaction of 1-alkenyldiisobutylalanes with titanocene dichloride afforded the corresponding olefins in good yields.
- Yoshida, Tadao
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- Radical clock reactions under Pseudo-first-order conditions using catalytic quantities of dipnenyl diselenide. A 77Se- and 119Sn-NMR study of the reaction of tributylstannane and diphenyl diselenide
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A method for the trapping of alkyl radicals by constant, catalytic quantities of PhSeH as a clock reaction in radical kinetics is presented. PhSeH is introduced in the form of PhSeSePh and regenerated by slow addition of a stoichiometric quantity of Bu3SnH. Using this method the rate constant for cyclization of the 6,6-diphenyl-5-hexenyl radical was found to be 6.8 × 107 s-1 at 20 °C, in fair agreement with the literature value of 4 × 107 s-1. An extension of the method was used to determine the rate of quenching of the 2,3,4,6-tetra-O-acetoxy-1-glucosyl radical by PhSeH as 3.6 × 106 s-1 at 78°C. The reaction of Bu3nH and PhSeSePh was studied by a combination of 77Se- and 119Sn-NMR spectroscopy.
- Crich, David,Jiao, Xian-Yun,Yao, Qingwei,Harwood, John S.
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- Direct Deamination of Primary Amines via Isodiazene Intermediates
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We report here a reaction that selectively deaminates primary amines and anilines under mild conditions and with remarkable functional group tolerance including a range of pharmaceutical compounds, amino acids, amino sugars, and natural products. An anomeric amide reagent is uniquely capable of facilitating the reaction through the intermediacy of an unprecedented monosubstituted isodiazene intermediate. In addition to dramatically simplifying deamination compared to existing protocols, our approach enables strategic applications of iminium and amine-directed chemistries as traceless methods. Mechanistic and computational studies support the intermedicacy of a primary isodiazene which exhibits an unexpected divergence from previously studied secondary isodiazenes, leading to cage-escaping, free radical species that engage in a chain, hydrogen-atom transfer process involving aliphatic and diazenyl radical intermediates.
- Berger, Kathleen J.,Driscoll, Julia L.,Yuan, Mingbin,Dherange, Balu D.,Gutierrez, Osvaldo,Levin, Mark D.
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supporting information
p. 17366 - 17373
(2021/11/04)
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- Alkene homologation: via visible light promoted hydrophosphination using triphenylphosphonium triflate
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A hydrophosphination reaction of alkenes with triphenylphosphonium triflate under photocatalytic conditions is described. The reaction is promoted by naphthalene-fused N-acylbenzimidazole and is believed to proceed through intermediate formation of a phosphinyl radical cation. The resulting phosphonium salts are directly involved in the Wittig reaction leading to homologated alkenes.
- Levin, Vitalij V.,Dilman, Alexander D.
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supporting information
p. 749 - 752
(2021/02/03)
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- Conversion of Carbonyl Compounds to Olefins via Enolate Intermediate
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A general and efficient protocol to synthesize substituted olefins from carbonyl compounds via nickel catalyzed C—O activation of enolates was developed. Besides ketones, aldehydes were also suitable substrates for the presented catalytic system to produce di- or tri- substituted olefins. It is worth noting that this approach exhibited good tolerance to highly reactive tertiary alcohols, which could not survive in other reported routes for converting carbonyl compounds to olefins. This method also showed good regio- and stereo-selectivity for olefin products. Preliminary mechanistic studies indicated that the reaction was accomplished through nickel catalyzed C—O activation of enolates, thus offering helpful contribution to current enol chemistry.
- Cao, Zhi-Chao,Xu, Pei-Lin,Luo, Qin-Yu,Li, Xiao-Lei,Yu, Da-Gang,Fang, Huayi,Shi, Zhang-Jie
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supporting information
p. 781 - 785
(2019/06/24)
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- Ruthenium(II)-catalyzed olefination: Via carbonyl reductive cross-coupling
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Natural availability of carbonyl groups offers reductive carbonyl coupling tremendous synthetic potential for efficient olefin synthesis, yet the catalytic carbonyl cross-coupling remains largely elusive. We report herein such a reaction, mediated by hydrazine under ruthenium(ii) catalysis. This method enables facile and selective cross-couplings of two unsymmetrical carbonyl compounds in either an intermolecular or intramolecular fashion. Moreover, this chemistry accommodates a variety of substrates, proceeds under mild reaction conditions with good functional group tolerance, and generates stoichiometric benign byproducts. Importantly, the coexistence of KOtBu and bidentate phosphine dmpe is vital to this transformation.
- Wei, Wei,Dai, Xi-Jie,Wang, Haining,Li, Chenchen,Yang, Xiaobo,Li, Chao-Jun
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p. 8193 - 8197
(2017/11/27)
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- Hydropersulfides: H-Atom Transfer Agents Par Excellence
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Hydropersulfides (RSSH) are formed endogenously via the reaction of the gaseous biotransmitter hydrogen sulfide (H2S) and disulfides (RSSR) and/or sulfenic acids (RSOH). RSSH have been investigated for their ability to store H2S in vivo and as a line of defense against oxidative stress, from which it is clear that RSSH are much more reactive to two-electron oxidants than thiols. Herein we describe the results of our investigations into the H-atom transfer chemistry of RSSH, contrasting it with the well-known H-atom transfer chemistry of thiols. In fact, RSSH are excellent H-atom donors to alkyl (k ~ 5 × 108 M-1 s-1), alkoxyl (k ~ 1 × 109 M-1 s-1), peroxyl (k ~ 2 × 106 M-1 s-1), and thiyl (k > 1 × 1010 M-1 s-1) radicals, besting thiols by as little as 1 order and as much as 4 orders of magnitude. The inherently high reactivity of RSSH to H-atom transfer is based largely on thermodynamic factors; the weak RSS-H bond dissociation enthalpy (~70 kcal/mol) and the associated high stability of the perthiyl radical make the foregoing reactions exothermic by 15-34 kcal/mol. Of particular relevance in the context of oxidative stress is the reactivity of RSSH to peroxyl radicals, where favorable thermodynamics are bolstered by a secondary orbital interaction in the transition state of the formal H-atom transfer that drives the inherent reactivity of RSSH to match that of α-tocopherol (α-TOH), nature's premier radical-trapping antioxidant. Significantly, the reactivity of RSSH eclipses that of α-TOH in H-bond-accepting media because of their low H-bond acidity (α2H ~ 0.1). This affords RSSH a unique versatility compared to other highly reactive radical-trapping antioxidants (e.g., phenols, diarylamines, hydroxylamines, sulfenic acids), which tend to have high H-bond acidities. Moreover, the perthiyl radicals that result are highly persistent under autoxidation conditions and undergo very rapid dimerization (k = 5 × 109 M-1 s-1) in lieu of reacting with O2 or autoxidizable substrates.
- Chauvin, Jean-Philippe R.,Griesser, Markus,Pratt, Derek A.
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p. 6484 - 6493
(2017/09/12)
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- Unexpected and powerful effect of chlorobenzene in direct palladium-catalyzed cascade Sonogashira-hydroarylation reaction
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A ubiquitous accelerating effect of chlorobenzene (PhCl) was observed unexpectedly in the Pd-catalyzed cascade Sonogashira-hydroarylation reaction. This new type of carbon-carbon bond forming cross-coupling reaction was efficiently catalysed by Pd2(dba)3 in the presence of a catalytic amount of PhCl, which provides a facile and direct approach to the synthesis of trisubstituted olefins.
- Yu, Bo,Xu, Wei,Sun, Huaming,Yu, Binxun,Zhang, Guofang,Xu, Li-Wen,Zhang, Weiqiang,Gao, Ziwei
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p. 8351 - 8354
(2015/02/19)
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- Palladium-catalyzed hydrophenylation of alkynes with sodium tetraphenylborate under mild conditions
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(Chemical Equation Presented) In an aqueous solution of acetic acid, PdCl2(PPh3)2 showed high catalytic activity for the hydrophenylation of both terminal and internal alkynes with sodium tetraphenylborate (NaBPh4) under mild conditions, affording phenyl alkenes in moderate to excellent yields.
- Zeng, Hanxiang,Hua, Ruimao
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p. 558 - 562
(2008/09/17)
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- 3,5-Bis(trifluoromethyl)phenyl sulfones in the Julia-Kocienski olefination - Application to the synthesis of tri- and tetrasubstituted olefins
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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 yi
- Alonso, Diego A.,Fuensanta, Monica,Najera, Carmen
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p. 4747 - 4754
(2007/10/03)
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- (E)-α-Iodovinylstannanes as convenient precursors for stereoselective synthesis of trisubstituted alkenes
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Based on the different reactivities of iodo-groups and tributylstannyl groups, (E)-α-iodovinylstannanes can undergo sequential cross-coupling reactions in the presence of a palladium(0) catalyst to form two carbon-carbon bonds to the same olefinic carbon leading to trisubstituted alkenes stereoselectively.
- Cai, Mingzhong,Ye, Hongde,Zhao, Hong,Song, Caisheng
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p. 465 - 467
(2007/10/03)
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- A novel tandem [2 + 2] cycloaddition-Dieckmann condensation with ynolate anions. Efficient synthesis of substituted cycloalkenones and naphthalenes via formal [n + 1] cycloaddition
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A novel tandem [2 + 2] cycloaddition-Dieckmann condensation via ynolate anions is described. Ynolate anions are useful for the formation of reactive β-lactone enolates via a pathway not involving the enolization of the corresponding β-lactones. The [2 + 2] cycloaddition of ynolate anions with δ- or σ-keto esters, followed by Dieckmann condensation, gives bicyclic β-lactones, which are easily decarboxylated to produce synthetically useful 2,3-disubstituted cyclopentenones and cyclohexenones in one pot. This tandem reaction was applied to a novel, one-pot synthesis of highly substituted naphthalenes.
- Shindo,Sato,Shishido
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p. 7818 - 7824
(2007/10/03)
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- Adjusting the top end of the alkyl radical kinetic scale. Laser flash photolysis calibrations of fast radical clocks and rate constants for reactions of benzeneselenol
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Rate constants for 5-exo cyclizations of the 6,6-diphenyl-5-hexenyl radical (1a), the 1-methyl-6,6-diphenyl-5-hexenyl radical (1b), and the 1,1- dimethyl-6,6-diphenyl-5-hexenyl radical (1c) were measured by laser flash photolysis methods, and Arrhenius parameters for these cyclizations were determined. Relative rate constants for cyclizations of radicals 1 and reactions with benzeneselenol were determined by indirect kinetic methods, and the relative Arrhenius parameters for the competing reactions were combined with the parameters for the cyclization reactions to give absolute Arrhenius parameters for the PhSeH reactions. At 20 °C, PhSeH reacts with the 1°, 2°, and 3°radicals 1 with nearly the same rate constants, (1.2 ± 0.1) x 109 M-1 s-1. Absolute Arrhenius parameters for reactions of PhSH and t-BuSH with the primary alkyl radical 1a were calculated using literature values for the competition between cyclization of 1a and reactions with the appropriate thiol and the absolute values for cyclization of 1a determined in this work. The results suggest that rate constants for reactions of primary alkyl radicals with t-BuSH are about 20% smaller than those previously reported. In the case of PhSH, the results are in good agreement with one previously reported set of rate constants but about 35% smaller than another set of rate constants that was subsequently incorporated into fast alkyl radical kinetics. The rate constants for alkyl radical reactions calibrated by competition against reaction with PhSeH and PhSH apparently are 30-40% smaller than those previously reported, and the derived rate constants for the fast radical reactions should be adjusted. An especially noteworthy example is ring opening of the cyclopropylcarbinyl radical, the Arrhenius function for which was determined in part from PhSH trapping results. Using the adjusted rate constants for PhSH and recalculating the Arrhenius parameters for the cyclopropylcarbinyl radical ring opening gives log(k/s- 1) = (13.045 ± 0.10) (6.99 ± 0.09)/θ (kcal/mol, errors at 2σ); the rate constant at 20 °C of 6.7 x 107 s-1 is about 13% smaller than that previously calculated.
- Newcomb,Choi,Horner
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p. 1225 - 1231
(2007/10/03)
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- A hydride transfer reaction from salts of carbanions to activated olefins
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A novel reaction - a β-elimination of a hydride ion from carbanion salts RM (R = Li, MgBr) and R2N-Li+, and its transfer to tetra-substituted activated olefins of the type Ar2C=C(CN)CO2R (R = Me,Et), was studied. Yields of the reduced H--acceptor were used to follow the extent of the H--transfer reaction. A competing Michael addition reaction of RM to the activated olefin also took place. The effects of the solvation properties of the solvent, the reaction temperature, the positive counter-ion, and of various structural features of the H--donor and the H--acceptor, were studied. The structural factors associated with both reactants, played a critically significant role due to the bimolecularity of the reaction. A benzyl substituent at C(β) of RM, a methine-type β-carbon, or a small size of R of RM, resulted in a relatively high extent of the H--transfer reaction. It is suggested that the presently studied β-elimination of a hydride ion takes place by a bimolecular E2cB-type mechanism.
- Feit, Ben-Ami,Shapira, Sarit,Herbst, Amatzya
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p. 317 - 328
(2007/10/02)
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- Kinetic Studies of the Cyclization of the 6,6-Diphenyl-5-hexenyl Radical. A Test of the Accuracy of Rate Constants for Reactions of Hydrogen Transfer Agents
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Cyclization of the 6,6-diphenyl-5-hexenyl radical (1) to the diphenylcyclopentylcarbinyl radical (2) was studied by indirect and direct methods.Indirect kinetic studies were accomplished by the PTOC-thiol method using hydrogen atom transfer trapping from
- Ha, Chau,Horner, John H.,Newcomb, Martin,Varick, Thomas R.,Arnold, Bradley R.,Lusztyk, Janusz
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p. 1194 - 1198
(2007/10/02)
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- Reactions of Alkylmercurials with Heteroatom-Centered Acceptor Radicals
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The relative reactivities of alkylmercury halides toward PhS., PhSe., or I. decrease drastically from R = tert-butyl to R = sec-alkyl to R = n-butyl, indicative that R. is formed in the rate-determining step in the attack of these radicals upon RHgCl.The alkyl radicals thus formed will enter into chain reactions in which a heteroatom-centered radical (A.) is regenerated from substrates such as RS-SR, ArSe-SeAr, ArTe-TeAr, PhSe-SO2Ar, Cl-SO2Ph; ZCH=CHA (A = Cl, I, SPh, SO2Ph); or PhCCHA (A = I, SPh, SO2Ph). β-Styrenyl (PhCH=CHA, Ph2C=CHA) and β-phenethynyl (PhCCA) systems with A = I, Br, SO2Ph also enter into chain reactions with mercury(II) salts with the ligands PhS, PhSe, PhSO2, or (EtO)2PO.The relative reactivities of a series of reagents toward t-Bu. and of PhCH=CHA, Ph2C=CHA, and PhCCA toward c-C6H11. are reported as well as the regioselectivity of t-Bu. attack observed for 1,2-disubstituted ethylenes (ZCH=CHA) with Z and A from the group Ph, Cl, Br, I, SO2Ph, SPh, Bu3Sn.Reactions of (E)- and (Z)-PhCH=CHI or MeO2CCH=CHI with t-Bu. or c-C6H11. occurred in a regioselective and stereospecific (retention) manner.Reactions of (E)- and (Z)-ClCH=CHCl occurred in a nonstereospecific manner in which the E/Z product ratio increased with the bulk of the attacking radical.A similar effect on the E/Z product ratios was observed for (Z)-MeO2CCH=CHCl.
- Russell, Glen A.,Ngoviwatchai, Preecha,Tashtoush, Hasan I.,Pla-Dalmau, Anna,Khanna, Rajive K.
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p. 3530 - 3538
(2007/10/02)
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- Synthesis of Alkenes via Peterson Reaction
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The α-phenylthiosilanes (2) have been used to prepare the α-silyl anions (1) by reaction with lithium naphthalenide; subsequent condensation with a carbonyl compound gave the alkene (8) via the Peterson reaction.The α-phenylthiosilanes (2) were prepared from n,n-bis(phenylthio)acetals (4) by reaction with lithium naphthalenide and chlorotrimethylsilane.The n,n-bis(phenylthio)acetals (4) were obtained, in turn, from 1,1-bis(phenylthio)acetals (5) by anion formation with butyl-lithium-N,N,N',N'-tetramethylethylenediamine complex in hexane followed by reaction with an alkyl halide.The Peterson reaction was also used to prepare vinyl sulphides (9) and vinyl sulphones (13).
- Ager, David J.
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p. 183 - 194
(2007/10/02)
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- A NEW METHOD FOR PREPARING 1-PHENYLTHIO-1-TRIMETHYLSILYLALKANES: THE PREPARATION OF α-SILYLCARBANIONS AND OLEFINS.
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1-Phenylthio-1-trimethylsilylalkanes(1) are prepared in high yield from 1,1-bis(phenylthio)acetals(2) by reaction with lithium naphthalenide(3) followed by chlorotrimethylsilane. α-Silylcarbanions are formed from the alkanes(1) and lithium naphthalenide(3).Subsequent reaction with carbonyl compounds gave the olefins(4) via the Peterson reaction.
- Ager, David J.
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p. 2923 - 2926
(2007/10/02)
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