Presence Of Chiral Diamine Research Articles

Cooperative Titanocene and Phosphine Catalysis: Accelerated C–X Activation for the Generation of Reactive Organometallics

The study presented herein describes a reductive transmetalation approach toward the generation of Grignard and organozinc reagents mediated by a titanocene catalyst. This method enables the metalation of functionalized substrates without loss of functional group compatibility. Allyl zinc reagents and allyl, vinyl, and alkyl Grignard reagents were generated in situ and used in the addition to carbonyl substrates to provide the corresponding carbinols in yields up to 99%. It was discovered that phosphine ligands effectively accelerate the reductive transmetalation event to enable the metalation of C-X bonds at temperatures as low as -40 °C. Performing the reactions in the presence of chiral diamines and amino alcohols led to the enantioselective allylation of aldehydes.

Configurationally Labile LithiatedO-Benzyl Carbamates: Application in Asymmetric Synthesis and Quantum Chemical Investigations on the Equilibrium of Diastereomers

The title compounds were generated by deprotonation of different benzyl-type carbamates with sec-butyllithium in the presence of chiral diamines (-)-sparteine or diisopropyl and di-tert-butyl bis(oxazoline)s. These lithiated species exhibit configurational lability at -78 degrees C. In the case of the chiral di-tert-butyl bis(oxazoline), the equilibrium of the epimeric complexes can be used synthetically to obtain highly enantioenriched secondary benzyl carbamates. The enantiodetermining step was proven to be a dynamic thermodynamic resolution. The absolute configurations of the products were determined, and the stereochemical pathways of selected substitution reactions were thus elucidated. High-level quantum chemical investigations were performed to gain insight into the experimentally investigated system. To obtain an accuracy for the energy difference (delta deltaH) between two epimeric complexes of about 0.5 kcal mol(-1) as well as the correct sign, a theoretical procedure was established. It included geometry optimization at the dispersion-corrected DFT level, computation of zero-point vibrational energies, and single-point SCS-MP2 energy calculations with large atomic-orbital basis sets.

Enantioselective synthesis of chiral sulfinates using chiral diamines

The reaction of p-toluenesulfinyl chloride with alcohols in the presence of chiral diamines was examined. Chiral sulfinates were obtained in good yields with enantioselectivity up to 76% ee.

Stereoselective Intermolecular Carbolithiation of Open-Chain and Cyclic 1-Aryl-1-alkenyl N,N-Diisopropylcarbamates Coupled with Electrophilic Substitution. Observation of p-Carboxylation in a Benzyllithium Derivative

1-Aryl-1-alkenyl N,N-diisopropylcarbamates (1) are obtained from alkyl aryl ketones and N,N-diisopropylcarbamoyl chloride (CbCl) by heating with excess pyridine. These undergo facile syn-carbolithiation by alkyllithium/diamine and produce configurationally stable lithiated benzyl carbamates, which have been trapped with different electrophiles. If the reaction is carried out in the presence of chiral diamines, such as (-)-sparteine or (-)-α-isosparteine, moderate enantiofacial differentiation is observed.

Poly-NAP as Ligand for the Asymmetric Hydrogenation of Ketones

A new heterogeneous catalytic system is described incorporating the BINAP structure as coordinating agent. In the presence of chiral diamines as auxiliaries, this ligand is efficient for the ruthenium catalyzed asymmetric hydrogenation of acetophenone (e.e. 68%) and can be reused several times without loss of selectivity and activity. The best e.e. (96%) is obtained for the reduction of 1′-acetonaphthone.

Enantioselective ortho lithiation of tricarbonyl(masked phenol and aniline)chromium complexes

Tricarbonyl(η 6-phenylcarbamate)chromium complexes were lithiated in the presence of chiral diamine followed by quenching with electrophiles to afford optically active ( o-substituted phenylcarbamate)chromium complexes up to 82% ee.

ChemInform Abstract: EFFICIENT ASYMMETRIC INDUCTION VIA COORDINATION OF CHIRAL DIAMINE TO TIN(II) ENOLATE: A HIGHLY ENANTIOSELECTIVE SYNTHESIS OF 2‐SUBSTITUTED MALATES

AbstractIn Gegenwart des chiralen Diamins (II) reagiert das in situ erzeugte Zinn‐enolat des Acetyl‐thiazolidinthions (I) mit den α‐Ketoestern (III) in hoher optischer Ausbeute zu den aldolartigen Produkten (IV).