Stereochemistry

Stereochemistry, a subdiscipline of chemistry, involves the study of the relative spatial arrangement of atoms that form the structure of molecules and their manipulation. The study of stereochemistry focuses on the relationships between stereoisomers, which by definition have the same molecular formula and sequence of bonded atoms (constitution), but differ in the geometric positioning of the atoms in space. For this reason, it is also known as 3D chemistry—the prefix "stereo-" means "three-dimensionality". Stereochemistry spans the entire spectrum of organic, inorganic, biological, physical and especially supramolecular chemistry. Stereochemistry includes methods for determining and describing these relationships; the effect on the physical or biological properties these relationships impart upon the molecules in question, and the manner in which these relationships influence the reactivity of the molecules in question (dynamic stereochemistry). History It was not until

Synthesis and structure-activity studies of well-defined nickel complexes as catalysts for cross coupling of alkyl electrophiles

Pablo Marcelo Perez Garcia

This dissertation is devoted to the development of well-defined nickel complexes as catalysts for cross coupling processes of alkyl electrophiles. In chapter one, we summarize recent cross coupling methodologies of alkyl electrophiles using nickel based catalysts. The description of each study includes the coupling conditions, the substrate scope and the mechanistic considerations. In chapter two, we report the development of high diastereoselective alkyl-alkyl Kumada coupling method for 1,3- and 1,4-substituted cyclohexyl halides and tetrahydropyrans using an amido bis(amine) nickel complex "Nickamine" as catalyst. The stereochemical properties of the starting materials and of the coupling products were determined by NMR techniques. The mechanistic investigations of the coupling provided evidence of a reversible activation of the alkyl halide. In chapter three, we present the synthesis of new bidentate amido â amine ligands derived from 2,5-dimethylpyrrolidine or Î±-methylbenzylamine. The ligands were used to synthesize well-defined bidentate nickel complexes by transmetallation from the corresponding lithium complexes. A complex having an Î±-methylbenzylamine derived ligand and 2,4-lutidine as co-ligand was an effective catalyst for the coupling of non-activated secondary iodides with alkyl Grignard reagents. An enantiomerically pure version of this complex was synthesized and no racemization was observed during the synthesis. The chiral complex showed no asymmetric induction capacity as a cross coupling catalyst. In chapter four, the synthesis of new amido bis(amine) pincer ligands derived from Î±-methylbenzylamine or pyrrolidine are described. The metallation of a NNN ligand derived from Î±-methylbenzylamine was not possible by transmetallation from the corresponding lithium complex or by oxidative addition from the corresponding chloroamine. A well-defined pincer nickel complex was synthesized by Li â Ni transmetallation using a NNN ligand having dimethyl amino and pyrolidine donors. Crystal structure analysis shows that the pyrrolidine donor is slightly less hindered. This complex is an effective catalyst for alkyl-alkyl and alkyl-aryl Kumada coupling of non-activated primary and secondary alkyl halides. The coupling process shows good functional group tolerance. This is the first time that a well-defined nickel pincer complex shows high catalytic activity for Kumada coupling reactions of sterically hindered alkyl substrates. In chapter 5, a well-defined nickel pincer complex bearing an alkyl amine donor is synthesized. The complex is able to catalyzed direct coupling of non-activated primary halides with terminal alkynes at room temperature. The catalysis has a good substrate scope and high functional group tolerance. Kinetic data suggest that the new pincer ligand is hemilabile, and the dissociation of the alkyl amine donor is the turnover-determining step of the catalysis. An intermediate Ni-alkynyl species has been isolated and structurally characterized. The reactivity of this species gives insight into the nature of the active species for the activation of alkyl halide.

EPFL2015

Chiral Phosphoric Acid-Catalyzed Enantioselective Three- Component Aza-Diels-Alder Reactions of Aminopyrroles and Aminopyrazoles

Thibaut Christian Courant, Jieping Zhu

A highly stereoselective three-component Povarov reaction, catalyzed by (R)- and (S)-BINOL hydrogen phosphate, was achieved for the first time with aminopyrroles and aminopyrazoles as 2-azadiene precursors. A variety of aldehydes, enecarbamates, amino-substituted azines participated in the reaction to afford the tetrahydropyrrolopyridines and tetrahydropyrazolopyridines in good yields with excellent diatereo- and enantioselectivities. A stereochemical model is proposed to account for the observed absolute stereochemistry.

Wiley-Blackwell2014

Synthesis and structure-activity studies of well-defined nickel complexes as catalysts for cross coupling of alkyl electrophiles

Pablo Marcelo Perez Garcia

EPFL2015

On the Deformation Chirality of Real Cubic Fourfolds

Synthesis and structure-activity studies of well-defined nickel complexes as catalysts for cross coupling of alkyl electrophiles

Chiral Phosphoric Acid-Catalyzed Enantioselective Three- Component Aza-Diels-Alder Reactions of Aminopyrroles and Aminopyrazoles

Chiral Phosphoric Acid-Catalyzed Enantioselective Three- Component Aza-Diels-Alder Reactions of Aminopyrroles and Aminopyrazoles

On the Deformation Chirality of Real Cubic Fourfolds

Synthesis and structure-activity studies of well-defined nickel complexes as catalysts for cross coupling of alkyl electrophiles