In this communication, we report an asymmetric Friedel−Crafts reaction of indoles with imines catalyzed by a bifunctional cinchona alkaloid catalyst. This is the first efficient organocatalytic ...asymmetric Friedel−Crafts reaction of indoles with imines. This reaction is operationally simple and, unprecedentedly, affords high enantioselectivity for a wide range of indoles and both aryl and alkyl imines. This establishes a direct, convergent, and versatile approach to optically active 3-indolyl methanamines, a structural motif embedded in numerous indole alkaloids and synthetic indole derivatives.
In this communication, we describe the development of the first highly enantioselective catalytic conjugate addition to vinyl sulfones. Promoted by readily accessible organocatalysts derived from ...C6‘−OH cinchona alkaloid derivatives and under mild, air- and moisture-tolerant conditions, conjugate additions of a wide range of α-cyanoacetates bearing either an α-aryl or an α-alkyl substituent to vinyl sulfones proceeded in excellent enantioselectivity and high yield. Consequently, this efficient and operationally simple enantioselective C−C bond forming conjugate addition provides a new and useful approach for the enantioselective construction of all-carbon quaternary stereocenters.
Objective On the fully automatic operation metro lines, there exists a gap between the platform screen door and the train, leading to the risk of clamping people and objects. In order to ensure train ...operation safety, a gap detection device must be installed. Method The current situation of the gap detection device application is briefly described, the working state of the laser gap detection device is mainly discussed, two interlocking modes of the laser gap detection device and the train operation are compared in order to access the safety loop of the train, and put forward some suggestions on the application of the anti-clamping safety device on the fully automatic operation metro lines. Result & Conclusion The signal system directly controls the start and shutdown of the gap detection device, and obtains the gap detecting state of the device. The laser gap detection device starts to work only after both the train door and the platform screen door are closed and locked, avoiding the extreme situation in wh
The development of highly enantioselective and general catalytic nitroaldol (Henry) reactions with ketones is a challenging yet desirable task in organic synthesis. In this communication, we report ...an asymmetric nitroaldol reaction with α-ketoesters catalyzed by a new C6‘−OH cinchona alkaloid catalyst. This is the first highly efficient organocatalytic asymmetric Henry reaction with ketones. This reaction is operationally simple and affords high enantioselectivity as well as good to excellent yield for a broad range of α-ketoesters.
The development of readily accessible bifunctional chiral catalysts is a desirable yet challenging goal in catalytic asymmetric synthesis. In this communication, we describe the development of a new ...class of readily accessible chiral bifunctional organic catalysts that could be derived in one or two steps in high yield from either quinidine or quinine. These catalysts have been shown to catalyze a highly enantioselective conjugate addition of methyl and ethyl malonates and β-ketoesters to a broad range of β-substituted nitroalkenes, an synthetically important C−C bond-forming reaction utilizing readily available starting materials. This new catalytic asymmetric reaction proceeds in 91−98% ee and 71−99% yield.
The reactions of 2-pyrones with electron-deficient dienophiles constitute a synthetically useful class of Diels−Alder reaction. By exploring cinchona alkaloid-derived organic molecules as acid−base ...bifunctional catalysts, we successfully developed the first highly enantioselective and diastereoselective catalytic Diels−Alder reaction with 2-pyrones. Furthermore, we demonstrated the possibility of using such catalysts to control the endo/exo selectivity in a Diels−Alder reaction.
Observation of the Λb0→Λϕ decay Ajaltouni, Z.; Alvarez Cartelle, P.; Alves, A.A. ...
Physics letters. B,
08/2016, Letnik:
759, Številka:
C
Journal Article
Recenzirano
Odprti dostop
The Λb0→Λϕ decay is observed using data corresponding to an integrated luminosity of 3.0 fb−1 recorded by the LHCb experiment. The decay proceeds at leading order via a b→ss‾s loop transition and is ...therefore sensitive to the possible presence of particles beyond the Standard Model. A first observation is reported with a significance of 5.9 standard deviations. The value of the branching fraction is measured to be (5.18±1.04±0.35−0.62+0.67)×10−6, where the first uncertainty is statistical, the second is systematic, and the third is related to external inputs. Triple-product asymmetries are measured to be consistent with zero.
A search for the decays of the Bc+ meson to pp¯π+ is performed for the first time using a data sample corresponding to an integrated luminosity of 3.0 fb−1 collected by the LHCb experiment in pp ...collisions at centre-of-mass energies of 7 and 8 TeV. No signal is found and an upper limit, at 95% confidence level, is set, fcfu×B(Bc+→pp‾π+)<3.6×10−8 in the kinematic region m(pp‾)<2.85 GeV/c2, pT(B)<20 GeV/c and 2.0<y(B)<4.5, where B is the branching fraction and fc (fu) is the fragmentation fraction of the b quark into a Bc+ (B+) meson.
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