628-16-0Relevant academic research and scientific papers
The Synthesis of Chiral Allyl Carbamates via Merger of Photoredox and Nickel Catalysis
Garbacz, Mateusz,Stecko, Sebastian
supporting information, p. 3213 - 3222 (2020/07/06)
A mild, and versatile, organophotoredox/Ni-mediated protocol was developed for the direct preparation of diverse, enantioenriched allyl carbamates. The reported approach represents a significant departure from classical step-by-step synthesis of allyl carbamates. This dual photoredox/Ni based strategy offers unrivalled capacity for convergent unification of readily available alkyl halides and chiral carbamates derived from 1-bromo-alken-3-ols with high chemoselectivity and efficiency. The reported photoredox/Ni catalyzed cross-coupling reaction is not limited to carbamates, but also to other O-derivatives such as esters, ethers, acetals, carbonates or silyl ethers. To demonstrate the utility of the reported protocol, the resulting allyl carbamates were transformed into functionalized non-racemic allylamines through a sigmatropic rearrangement reaction in enantiospecific manner. This approach allowed for synthesis of enantiomeric allylamines by a simple control of the geometry of a double bond of allyl carbamates. (Figure presented.).
Removal of water - a factor influencing the synthesis of alkynes in a phase-transfer catalyzed β-elimination reaction
Zakrzewski,Huras,Sas,Zelechowski,Bombinska
, p. 1051 - 1057 (2008/09/21)
Acetylene derivatives 4 were synthesized from the corresponding vicinal bromo compounds 2 in the phase-transfer catalyzed hydrogen bromide β-elimination reaction using solid potassium hydroxide as a base, xylene as a solvent, and a phase-transfer catalyst. The yields of the synthesized acetylene derivatives 4 were substantially improved when water formed in the process had been removed.
Pressure and Temperature Effects on Product Channels of the Propargyl (HC≡CCH2) Combination Reaction and the Formation of the First Ring
Howe, Pui-Teng,Fahr, Askar
, p. 9603 - 9610 (2007/10/03)
The mechanism for formation of aromatic and polyaromatic hydrocarbons and soot in combustion processes is still far from being well understood. The formation of the first aromatic ring, particularly benzene, is thought to be a critical step in soot formation mechanisms and has been the subject of continuing interest. Experimental results on the nature and the relative yields of the final products of the propargyl combination, C3H3 + C3H3 → C6H6 (1) were presented. Propargyl radicals, for most experiments, were generated by the 248 nm excimer laser photolysis of propargyl bromide. Five isomeric C6H6 final products were detected including 1,5-hexadiyne, fulvene, dimethylenecyclobutene, and benzene. The formation of dimethylenecyclobutene and benzene from the propargyl combination reaction was significantly more efficient than previously predicted. The relative yield of fulvene was less than those of dimethylenecyclobutene and benzene.
Kinetics and products of the self-reaction of propargyl radicals
Shafir, Eugene V.,Slagle, Irene R.,Knyazev, Vadim D.
, p. 8893 - 8903 (2007/10/03)
The kinetics and product branching of the self-reaction of propargyl radicals, C3H3 + C3H3 → products (1), have been studied as functions of temperature. Rate constants of reaction 1 were obtained in direct real-time experiments by laser photolysis/photoionization mass spectrometry over the temperature interval 500-1000 K and at a bath gas density of (3-6) × 1016 molecules cm-3. Propargyl radicals were produced by the 248 nm laser photolysis of oxalyl chloride ((CCIO)2) followed by a fast conversion of the produced chlorine atoms into propargyl radicals and HCl via the reaction with propyne. No active species other than C3H3 were present in the system during the kinetics of C3H3 decay. The values of the rate constant of reaction 1 were determined from the [C3H3] temporal profiles. The rate constants of reaction 1 decrease from (3.30 ± 0.35) × 10-11 cm3 molecule-1 s-1 at 500 K to (2.74 ± 0.43) × 10-11 cm3 molecule-1 s-1 at 700 K and to (1.20 ± 0.14) × 10-11 cm3 molecule-1 s-1 at 1000 K. The value obtained at 1000 K is likely to be influenced by falloff effects and secondary reactions initiated by the H + C6H5 products of reaction 1. The rate constants of reaction 1 determined in the current study at elevated temperatures correlate well with the room temperature value of ～4 × 10-11 cm3 molecule-1 s-1 obtained in several earlier studies. Combination of the results of the current work with those of earlier room temperature investigations results in the following temperature dependence of the high-pressure-limit rate constant of reaction 1: k1∞ = 4.49 × 10-9T-0.75 exp(-128 K/T) cm3 molecule-1 s-1 (295-700 K). Product channels of reaction 1 were studied using final product analysis by gas chromatography/mass spectrometry in the 500-1100 K temperature interval. Several C6H6 isomers were detected as products of the self-reaction of propargyl radicals: 1,5-hexadiyne, fulvene, benzene, and two unknown species identified in the text as unknown 1 and unknown 2. The distribution of products depends on the temperature. At lower temperatures, 1,5-hexadiyne, unknown 1, and benzene were observed. The fraction of benzene increases with temperature; it becomes the major product at 900 K and above. Fulvene and unknown 2 were observed in minor amounts in the 900-1100 K range. The product analysis provides evidence for the appearance of the reaction channel 1b (C6H5 + H) at high temperatures: formation of C8H6 and C9H8 was observed and attributed to the fast reaction of the phenyl radical with the excess of propyne present in the reactor.
Enantioselective total synthesis of (+)-testudinariol A using a new nickel-catalyzed allenyl aldehyde cyclization
Amarasinghe, Kande K. D.,Montgomery, John
, p. 9366 - 9367 (2007/10/03)
An enantioselective total synthesis of (+)-testudinariol A was completed. A new nickel-catalyzed allenyl aldehyde cyclization was developed in the approach. In addition, an asymmetric anti aldol reaction and a two-directional oxocarbenium ion/vinyl silane condensation were employed as key steps. Copyright
Kinetics and products of propargyl (C3H3) radical self-reactions and propargyl-methyl cross-combination reactions
Fahr, Askar,Nayak, Akshaya
, p. 118 - 124 (2007/10/03)
Propargyl and methyl radicals were produced through the 193-nm excimer laser photolysis of mixtures of C3H3Cl/He and CH3N2CH3/He, respectively. Gas chromatographic and mass spectrometric (GC/MS) product analyses were employed to characterize and quantify the major reaction products. The rate constants for propargyl radical self-reactions and propargyl-methyl cross-combination reactions were determined through kinetic modeling and comparative rate determination methods. The major products of the propargyl radical combination reaction, at room temperature and total pressure of about 6.7 kPa (50 Torr) consisted of three C6H6 isomers. The rate constant determination in the propargyl-methyl mixed radical system yielded a value of (4.0±0.4)×10-11 cm3 molecule-1 s-1 for propargyl radical combination reactions and a rate constant of (1.5±0.3)×10-10 cm3 molecule-1 s-1 for propargyl-methyl cross-combination reactions. The products of the methyl-propargyl cross-combination reactions were two isomers of C4H6, 1-butyne (about 60%) and 1,2-butadiene (about 40%).
Magnesium Adducts of Substituted Anthracenes - Preparation and Properties
Bogdanovic, Borislav,Janke, Nikolaus,Kinzelmann, Hans-Georg,Seevogel, Klaus,Treber, Joachim
, p. 1529 - 1535 (2007/10/02)
2-Methyl-, 1,4-dimethyl-, 9-methyl-, 9-ethyl-, 9,10-dimethyl-, and 9-phenylanthracene (1a-f) react with magnesium in THF at room temperature to afford the corresponding substituted magnesium anthracenes 2a-f. 9,10-Diphenylanthracene (1g), however, reacts with magnesium under the same conditions to produce the deep-blue magnesium bis(9,10-diphenylanthracenide) * 6 THF (4g).Upon heating to 60 deg C in THF, 4g reversibly dissociates to give magnesium 9,10-diphenylanthracene * 3 THF (2g) and 1g, while prolonged heating at 60 deg C causes decomposition of 2g to active magnesium (Mg*) and 1g.In THF 2a-c, e, and f exhibit temperature-dependent equilibria with 1a-c, e, and f and magnesium.Compared with magnesium anthracene * 3 THF (2), these equilibria are strongly shifted toward substituted anthracenes and magnesium, and only at 0 deg C high conversions are achieved.The magnesium exchange between 2 and the substituted anthracenes 1a, b, and f in THF has been experimentally verified. 2a, e, and f react with organic halides in the same way as 2, however, in the case of allyl, propargyl, and benzyl chloride the yields of Grignard compounds are lower than for 2; with bromobenzene, the tendency for the radical transfer reaction is stronger than for 2.Magnesium 9,10-dimethylanthracene (2e) reacts with ethyl acetate to give the bicyclic tertiary alcohol 9 by an intramolecular C-C coupling reaction.
Formation of C6H6 Isomers by Recombination of Propynyl in the System Sodium Vapour/Propynylhalide
Alkemade, U.,Homann, K. H.
, p. 19 - 34 (2007/10/02)
2-Propynyl radicals (C3H3) were generated from the respective chloride or bromide by the reaction Na + C3H3X -> C3H3 + NaX in a low-pressure flow reactor fed by multislit-diffusion burner.The temperature range was 623 to 673 K and total pressures of 300 and 600 Pa were applied.Analyses were performed by nozzle beam/mass spectrometry and by gas chromatography/mass spectrometry.The rate constants of the primary reactions were determined as k(Na + C3H3Cl) = 1.6E13 and k(Na + C3H3Br) = 7.8E13 cm3 mol-1 s-1, independent of temperature within the above range.The overall recombination rate constant of 2-propynyl was found to be 3.4E13 cm3 mol-1 s-1.The recombination products of propynyl were 1,5-hexadiyne, 1,2-hexadien-5-yne and 1,2,4,5-hexatetraene.Besides these direct products also 1,3-hexadien-5-yne and benzene were detected in relatively high yields which decreased with increasing pressure.A reaction mechanism via a propynyl-cyclopropene intermediate by which the chemically activated primary recombination products can rearrange to benzene and 1,3-hexadien-5-yne is discussed. - Keywords: Reaction kinetics / Hydrocarbon radicals / Sodium reactions / Benzene formation
Allylic and Propargylic Substitution Reactions Involving Radicals Generated from Alkylmercury Halides
Russell, Glen A.,Ngoviwatchai, Preecha,Wu, Yuh Wern
, p. 4921 - 4927 (2007/10/02)
Addition of alkyl radicals to allyl or propargyl derivatives forms adduct radicals which can undergo β-elimination with substituents such as halogen, PhS, PhSO2, Bu3Sn, or HgCl to form the alkyl-substituted propene or allene and an eliminated radical which regenerates the alkyl radical by displacement from an alkylmercurial.With β-oxy substituents, such as O2CR, OP(O)(OEt)2, O3SAr, OPh, OSiMe3, or OH, the adduct radicals can displace the alkyl radical from the alkylmercurial to yield β-substituted alkylmercurials which spontaneously, or in the presence of nucleophiles, undergo an elimination reaction to yield the alkene or allene.Relative reactivities toward tert-butyl radical attack, such as k(allyl chloride)/k(propargyl chloride) = ca. 10, have been determined.A similar relative reactivity is observed in reaction with (t-Bu)2CuLi implicating attack by free tert-butyl radicals.With allyl or propargyl iodide, radical attack leads to iodine atom abstraction.Reaction of propargyl iodide with t-BuHgCl/hν, (t-Bu)2CuLi, or (t-Bu)3ZnLi leads to a mixture of hydrocarbons in which tert-butylallene is present in only trace amounts.Benzene is an important reaction product which seems to be formed via the cyclodimerization of two "propargyl" (C3H3.) radicals.
