6004-44-0Relevant articles and documents
Alkaloid-Catalyzed Enantioselective [3 + 2] Cycloaddition of Ketenes and Azomethine Imines
Mondal, Mukulesh,Wheeler, Kraig A.,Kerrigan, Nessan J.
, p. 4108 - 4111 (2016)
A new asymmetric synthesis of bicyclic pyrazolidinones through an alkaloid-catalyzed formal [3 + 2] cycloaddition of in situ generated ketenes and azomethine imines is described. The products were formed in good to excellent yields (52-99% for 17 examples), with good to excellent diastereoselectivity (dr 5:1 to 27:1 for 11 examples), and with excellent enantioselectivity in all cases (≥96% ee). This method represents the first unambiguous example of an enantioselective reaction between ketenes and a 1,3-dipole.
CeO2 Facet-Dependent Surface Reactive Intermediates and Activity during Ketonization of Propionic Acid
Guo, Yonghua,Qin, Yuyao,Liu, Huixian,Wang, Hua,Han, Jinyu,Zhu, Xinli,Ge, Qingfeng
, p. 2998 - 3012 (2022/03/03)
CeO2 rods, octahedrons, and cubes exposing well-defined (110), (111), and (100) surfaces, respectively, were synthesized and investigated for the catalytic ketonization of propionic acid. The intrinsic ketonization rates at 350 °C on the rods, octahedrons, and cubes are 54.3, 40.4, and 25.1 mmol·m-2·h-1, respectively, indicating that the (110) facet is the most active surface for ketonization. The reaction was tracked by both in situ infrared and mass spectroscopies under transient conditions, and the results showed that monodentate propionate, a minority surface species, is responsible for the formation of 3-pentanone. In contrast, bidentate propionate, a dominant species on all three surfaces, appears to a spectator for ketonization. Moreover, the ketonization activity can be correlated with relative concentration of monodentate propionate. A density functional theory study showed that the relative concentration of monodentate propionate (or the adsorption energy difference between monodentate and bidentate configurations) at high coverages is strongly dependent on the surface geometry. The stability of monodentate propionate on the (110) surface exposing both the O and Ce sites in the outermost layer with the well-separated Ce sites exhibits little dependence on the propionate coverage. In contrast, strong steric hindrance due to the top layer O atom and the closely packed Ce atoms in (111) destabilizes monodentate propionate significantly at high coverages. This study demonstrates that the surface geometrical structure of CeO2 can determine the abundance of the active monodentate propionate, which, in turn, will determine the catalytic activity of CeO2 for ketonization.
Generation of Reactive Ketenes under Flow Conditions through Zinc-Mediated Dehalogenation
Hafner, Andreas,Ley, Steven V.
supporting information, p. 1470 - 1474 (2015/06/30)
Herein, we describe the generation of highly reactive monoalkyl and phenyl ketenes by using a dehalogenation procedure under flow conditions. All ketenes were generated in good yields (determined by quenching with an appropriate aniline derivative) and showed high reactivity in the [2+2] cycloaddition with imines, resulting in the formation of a range of β-lactams at room temperature in less than 10 minutes. Furthermore, initial experiments were performed by using these reactive ketenes for the synthesis of β-lactams under flow conditions.
Decomposition of malonic anhydrides
Perrin, Charles L.,Flach, Agnes,Manalo, Marlon N.
experimental part, p. 9698 - 9707 (2012/07/14)
Malonic anhydrides decompose at or below room temperature, to form a ketene and carbon dioxide. Rate constants for the thermal decomposition of malonic, methylmalonic, and dimethylmalonic anhydrides were measured by NMR spectroscopy at various temperatures, and activation parameters were evaluated from the temperature dependence of the rate constants. Methylmalonic anhydride is the fastest, with the lowest δH?, and dimethylmalonic anhydride is the slowest. The nonlinear dependence on the number of methyl groups is discussed in terms of a concerted [2s + (2s + 2s)] or [2s + 2a] cycloreversion that proceeds via a twisted transition-state structure, supported by computations.
Promotion of asymmetric aza-claisen rearrangement of N-allylic carboxamides using excess base
Yoshizuka, Makoto,Nishii, Takeshi,Sasaki, Hiromi,Kitakado, Junko,Ishigaki, Noriko,Okugawa, Shinobu,Kaku, Hiroto,Horikawa, Mitsuyo,Inai, Makoto,Tsunoda, Tetsuto
scheme or table, p. 2967 - 2970 (2012/01/05)
The aza-Claisen rearrangement of the enolate of N-(Z)-crotyl-N-(S)- phenethylpropanamide did not proceed in the presence of 1.5 equivalents of LHMDS as a base. However, the use of a large excess of base (10 equiv) promoted the reaction to give N-(S)-phenethyl-anti-2,3-dimethylpent-4-enamide with good stereoselectivities (anti/syn = ca. 95:5). An excess of base stabilized the amide enolates and prevented the decomposition to the ketene to prompt the rearrangement of various carboxamides with good stereoselectivity. This reaction provided a new method for the construction of asymmetric quaternary carbon centers. Georg Thieme Verlag Stuttgart · New York.
Concerted wolff rearrangement in two simple acyclic diazocarbonyl compounds
Burdzinski, Gotard,Zhang, Yunlong,Wang, Jin,Platz, Matthew S.
experimental part, p. 13065 - 13068 (2011/02/28)
The photochemistry of two simple acyclic diazo carbonyl compounds, azibenzil and diazoacetone, were studied using the tools of ultrafast time-resolved spectroscopy. In the former case, UV-vis detection allows observation of an absorption band of singlet benzoylphenylcarbene, decaying with a 740 ± 150 ps time-constant in acetonitrile. IR detection shows that the ketene product of Wolff rearrangement (～2100 cm-1) is formed by two parallel pathways: a stepwise mechanism with carbene intermediacy with a slow rise time-constant of 660 ± 100 ps, and directly in the diazo excited state as confirmed by the immediate formation of an IR band of a nascent hot ketene species. Photolysis (270 nm) of diazoacetone in chloroform leads mainly to the ketene species through a concerted process, consistent with the predominance of the syn conformation in the diazoacetone electronic ground state and a zero quantum yield of the internal conversion process.
Catalytic, Asymmetric Preparation of Ketene Dimers from Acid Chlorides
Calter, Michael A.,Orr, Robert K.,Song, Wei
, p. 4745 - 4748 (2007/10/03)
(Matrix presented) The cinchona alkaloid-catalyzed dimerization of monosubstituted ketenes generated in situ from the reaction of acid chlorides and diisopropylethylamine yields ketene dimers in high yields and enantioselectivities. This reaction tolerates sterically demanding and functionally diverse substituents. Kinetic studies suggest that the rate-determining step for the reaction is the deprotonation of the acid chloride by the tertiary amine to form ketene and that the stereochemistry- forming step is addition of an ammonium enolate with ketene.
Tandem [4+2] cycloaddition versus electrocyclisation reactions of 1-aryl-2-phenyl-5-alkyl/aryl-1,3-diazapenta-1,3,4-trienes in aza-Wittig reactions of N′-aryl-N-(triphenylphosphoranlidene) benzenecarboximidamides with ketenes
Jayakumar,Kumar, Vipan,Mahajan, Mohinder P.
, p. 2235 - 2237 (2007/10/03)
1-Aryl-2-phenyl-5-alkyl/aryl-1,3-diazapenta-1,3,4-triene 3 generated in situ aza-Wittig reactions of N′-aryl-N-(triphenylphosphoranylidene)carboximidamides 1 which are shown to undergo selective [4+2] cycloaddition and electrocyclisation reactions leading to the formation of novel pyrimidinone derivatives 5 and quinazoline derivatives 7 with monosubstituted ketenes and diphenylketene, respectively.
Gas-phase kinetics of elimination reactions of pentane-2,4-dione derivatives. Part II. Thermolysis of derivatives and analogues of 3-phenylhydrazonopentane-2,4-dione
Al-Awadi,Elnagdi,Al-Awadhi,El-Dusouqui
, p. 457 - 462 (2007/10/03)
Six analogues and derivatives (1-6) of 3-phenylhydrazonopentane-2,4-dione (7) were subjected to gas-phase thermolysis. The Arrhenius log A (s-1) and Ea (kJ mol-1) of the analogues (1-5) are, respectively: 10.42 and 140.8 for 1-cyano-1-phenyl-hydrazonopropanone (1), 11.19 and 135.4 for 1-cyano-1-(p-nitrophenylhydrazono)-propanone (2), 10.68 and 144.9 for 1-cyano-1-(p-methoxyphenylhydrazono)propanone (3), 11.76 and 137.8 for 1-cyano-3-phenyl-1-phenylhydrazonopropanone (4), and 11.29 and 145.9 for 1-cyano-1-phenylhydrazonobutanone (5). The corresponding values for ethyl 3-oxo-2-phenylhydrazonobutanoate (6) are 11.90 s-1 and 143.3 kJ mol-1. The rates of reaction at 600 K are compared with those of the title diketone (7) and of pentane-2,4-dione (8) and rationalized in terms of a plausible elimination pathway involving a semiconcerted six-membered transition state.
