نتایج جستجو برای: desymmetrization

تعداد نتایج: 310  

Journal: :Journal of the American Chemical Society 2008
Ngoc T Vo Robert D M Pace Fionn O'Hara Matthew J Gaunt

The inherent reactivity and functionality stored within aromatic systems provide numerous possibilities for the synthesis of 3-D organic structures via dearomatization processes.1,2 Under oxidizing conditions, the dearomatization of orthoand para-substituted phenols forms cyclohexadienones,3 and these products have found widespread use in the chemical synthesis of natural products.4 Additionall...

2007
S. Denisov L. Morales-Molina S. Flach P. Hänggi

We study the quantum version of a tilting and flashing Hamiltonian ratchet, consisting of a periodic potential and a time-periodic driving field. The system dynamics is governed by a Floquet evolution matrix bearing the symmetry of the corresponding Hamiltonian. The dc-current appears due to the desymmetrization of Floquet eigenstates, which become transporting when all the relevant symmetries ...

2015
Depeng Zhao Thomas M. Neubauer Ben L. Feringa

Chirality plays a fundamental role in biology and chemistry and the precise control of chirality in a catalytic conversion is a key to modern synthesis most prominently seen in the production of pharmaceuticals. In enantioselective metal-based catalysis, access to each product enantiomer is commonly achieved through ligand design with chiral bisphosphines being widely applied as privileged liga...

2017
Michela Milan Massimo Bietti Miquel Costas

Monosubstituted cycloalkanes undergo regio- and enantioselective aliphatic C-H oxidation with H2O2 catalyzed by biologically inspired manganese catalysts. The reaction furnishes the corresponding ketones resulting from oxidation at C3 and C4 methylenic sites (K3 and K4, respectively) leading to a chiral desymmetrization that proceeds with remarkable enantioselectivity (64% ee) but modest regios...

2009
Kristin Williams Fiori Angela L. A. Puchlopek Scott J. Miller

While Nature excels at performing selective modifications of complex polyfunctional molecules through the use of tailoring enzymes, synthetic chemistry has lagged behind in this regard. In prior work, we have applied a biomimetic approach to this problem, developing small peptides to achieve various group transfer reactions on polyol substrates with high enantio- or regioselectivity. The utilit...

2014
Quanxuan Zhang Hong Ren Gregory L. Baker

A new simple and practical protocol for scalable synthesis of a novel library of propargylated and PEGylated α-hydroxy acids toward the preparation of "clickable" polylactides was described. The overall synthesis starting from readily available propargyl alcohol, bromoacetaldehyde diethyl acetal, and OEGs or PEGs was developed as a convenient procedure with low cost and no need of column chroma...

Journal: :Nature chemistry 2010
Aldo Peschiulli Barbara Procuranti Cornelius J O' Connor Stephen J Connon

Kinetic resolution is an important method for the separation of racemates into their component enantiomers. Thiols are precursors to a variety of organosulfur compounds, with high utility in both chemistry and chemical biology, yet there is a surprising dearth of methodologies for their direct and efficient catalytic kinetic resolution. Here, we demonstrate an organocatalytic process involving ...

Journal: :Physical review. E, Statistical, nonlinear, and soft matter physics 2001
S Denisov S Flach

Recent symmetry considerations [Flach et al., Phys. Rev. Lett. 84, 2358 (2000)] have shown that dc currents may be generated in the stochastic layer of a system describing the motion of a particle in a one-dimensional potential in the presence of an ac time-periodic drive. In this paper we explain the dynamical origin of this current. We show that the dc current is induced by the presence and d...

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