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In stereochemistry, a stereocenter of a molecule is an atom (center), axis or plane that is the focus of stereoisomerism; that is, when having at least three different groups bound to the stereocenter, interchanging any two different groups creates a new stereoisomer. Stereocenters are also referred to as stereogenic centers. A stereocenter is geometrically defined as a point (location) in a molecule; a stereocenter is usually but not always a specific atom, often carbon. Stereocenters can exist on chiral or achiral molecules; stereocenters can contain single bonds or double bonds. The number of hypothetical stereoisomers can be predicted by using 2n, with n being the number of tetrahedral stereocenters; however, exceptions such as meso compounds can reduce the prediction to below the expected 2n. Chirality centers are a type of stereocenter with four different substituent groups; chirality centers are a specific subset of stereocenters because they can only have sp3 hybridization, meaning that they can only have single bonds. Stereocenters can exist on chiral or achiral molecules. They are defined as a location (point) within a molecule, rather than a particular atom, in which the interchanging of two groups creates a stereoisomer. A stereocenter can have either four different attachment groups, or three different attachment groups where one group is connected by a double bond. Since stereocenters can exist on achiral molecules, stereocenters can have either sp3 or sp2 hybridization. Stereoisomers are compounds that are identical in composition and connectivity but have a different spatial arrangement of atoms around the central atom. A molecule having multiple stereocenters will produce many possible stereoisomers. In compounds whose stereoisomerism is due to tetrahedral (sp3) stereogenic centers, the total number of hypothetically possible stereoisomers will not exceed 2n, where n is the number of tetrahedral stereocenters. However, this is an upper bound because molecules with symmetry frequently have fewer stereoisomers.

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Séances de cours associées (41)

Chiralité (chimie)

Le concept de la chiralité existe également dans d'autres domaines. En chimie, un composé est dit chiral (du grec χείρ : la main) s'il n'est pas superposable à son image dans un miroir plan. Il existe un certain nombre de raisons pour lesquelles une molécule peut être chirale : la présence d'un ou plusieurs centres asymétriques (sauf certaines conditions particulières de symétrie) ; une forme en hélice ; un plan de chiralité. Énantiomérie Si une molécule est chirale, elle possède au moins deux formes dites énantiomères qui se différencient par une configuration absolue opposée.

Centre stéréogène

Racemization

In chemistry, racemization is a conversion, by heat or by chemical reaction, of an optically active compound into a racemic (optically inactive) form. This creates a 1:1 molar ratio of enantiomers and is referred to as a racemic mixture (i.e. contain equal amount of (+) and (−) forms). Plus and minus forms are called Dextrorotation and levorotation. The D and L enantiomers are present in equal quantities, the resulting sample is described as a racemic mixture or a racemate.

CH-335: Asymmetric synthesis and retrosynthesis

La première partie du cours décrit les méthodes classiques de synthèse asymétrique. La seconde partie du cours traite des stratégies de rétrosynthèse basées sur l'approche par disconnection.

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Exploitation of Unconventional Electrophiles in Enantioselective Pd(0)-Catalyzed C-H Functionalizations

Daria Grosheva

Asymmetric metal-catalyzed C-H functionalization has enjoyed great success as a powerful strategy for the rapid construction of elaborate structures from simple precursors. For example, aryl (pseudo)halides have been extensively employed as electrophilic substrates in enantioselective Pd(0)-catalyzed syntheses of heterocycles. However, alternative substrates for C-H functionalizations are far less developed. This thesis focuses on the exploration of unconventional electrophilic partners for asymmetric Pd(0)-catalyzed C-H functionalizations, allowing access to relevant N-heterocyclic scaffolds. An enantioselective functionalization of readily accessible ketene aminal phosphates resulted in the formation of versatile isoindolines. A new class of bulky electron-rich phosphine ligands, designed explicitly for this transformation, enabled efficient functionalization at ambient temperature, resulting in high enantioselectivities of the desired products. Employing perfluoroalkyl imidoyl chlorides as electrophilic partners gave rise to previously inaccessible chiral 1H-isoindoles. The C-H functionalization strategy not only enabled efficient asymmetric construction of three-dimensional structures with functional exit vectors but also allowed the products to be additionally decorated with a perfluoroalkyl group and a quaternary stereogenic center.

EPFL2019

Construction of Quaternary Stereocenters by Palladium-Catalyzed Carbopalladation-Initiated Cascade Reactions

Jieping Zhu, Wangqing Kong, Yulin Li

The enantioselective synthesis of molecules containing quaternary stereocenters is a field of intense research interest and development. Among the known organic transformations, carbopalladation-initiated domino transformations constitutes a general method for the construction of compounds containing cyclic or spiro quaternary stereocenters. In this Minireview, recent achievements in palladium catalyzed domino Heck/C-H functionalizations and developments in enantioselective carbopalladation-initiated domino processes are summarized.

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Efficient Kinetic Resolution of Sulfur-Stereogenic Sulfoximines by Exploiting (CpRhIII)-Rh-X-Catalyzed C-H Functionalization

Nicolai Cramer, Marcus Brauns

Chiral sulfoximines with stereogenic sulfur atoms are promising motifs in drug discovery. We report an efficient method to access chiral sulfoximines through a C-H functionalization based kinetic resolution. A rhodium(III) complex equipped with a chiral Cp-x ligand selectively participates in conjunction with phthaloyl phenylalanine in the C-H activation of just one of the two sulfoximine enantiomers. The intermediate reacts with various diazo compounds, providing access to chiral 1,2-benzothiazines with synthetically valuable substitution patterns. Both sulfoximines and 1,2-benzothiazines were obtained in high yields and excellent enantioselectivity, with s-values of up to 200. The utility of the method is illustrated by the synthesis of the key intermediates of two pharmacologically relevant kinase inhibitors.

WILEY-V C H VERLAG GMBH2019

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