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Relevant academic research and scientific papers

Enantioselective ring opening of meso-epoxides with tetrachlorosilane catalyzed by chiral bipyridine N,N′-dioxide derivatives

An enantioselective ring opening of meso-epoxides with tetrachlorosilane in the presence of diisopropylethylamine exploiting chiral bipyridine N,N′-dioxides as catalysts affords the corresponding chlorohydrins in high enantioselectivities of up to 90% ee.

New development in the enantioselective ring opening of meso-epoxides by various chloride ion silicon sources catalyzed by an o-methoxyaryldiazaphosphonamide Lewis base

New developments in the enantioselective ring opening of meso-epoxides catalyzed by a chiral Lewis base have been achieved using various chloride ion silicon sources. Thus, the use of TMSCl led to enantioselectivities varying from 6 to 98% ee depending on

Atropisomeric chiral dienes in asymmetric catalysis: C2- symmetric (Z,Z)-2,3-Bis[1-(diphenylphosphinyl)ethylidene]tetralin as a highly active lewis base organocatalyst

Diene catalysts with a twist: The title C2-symmetric tetralin-fused 1,3-butadiene derivative is atropisomeric and can be resolved into the two helical enantiomers. The optically pure compound showed excellent enantioselectivity as well as unusu

3,3′-Bithiophene-Based Chiral Bisphosphine Oxides as Organocatalysts in Silicon-Derived Lewis Acid Mediated Reactions

This account summarizes the development of new biheteroaromatic chiral bisphosphine oxides. 3,3′-Bithiophene-based phosphine oxides (BITIOPOs) have been successfully used as organocatalysts to promote Lewis base catalyzed, Lewis acid mediated stereoselective transformations. These highly electron-rich compounds, in combination with trichorosilyl derivatives (allyltrichlorosilane and silicon tetrachloride), generate hypervalent silicon species that act as chiral Lewis acids in highly diastereo- and enantioselective organic reactions. Several relevant examples related to these applications are discussed in detail. 1 Introduction 2 The BITIOPO Family 3 Enantioselective Opening of Epoxides 4 Enantioselective Allylation of Aldehydes 5 Stereoselective Direct (Double) Aldol-Type Reaction with Ketones 6 Stereoselective Direct Aldol-Type Reaction with Ester Derivatives 7 Conclusions.

Enantioselective Ring Opening of meso-Epoxides with Silicon Tetrachloride Catalyzed by Pyridine N-Oxides Fused with the Bicyclo[3.3.1]nonane Framework

The synthesis of new chiral Lewis basic organocatalysts that contain pyridine N-oxide moieties fused with the bicyclo[3.3.1]nonane framework is reported. The obtained pyridine N-oxides were employed as catalysts in the enantioselective ring opening of meso-epoxides with silicon tetrachloride. Derivative 1b endowed with two 2,4-diaryl-substituted pyridine N-oxide moieties proved to be a particularly effective catalyst for desymmetrization of norbornene oxide 16i to furnish Wagner-Meerwein rearrangement product 20i in unprecedented 96 % ee. Difunctional congener 3, which is striped of the 4-aryl substituents, exhibited moderate to high levels of asymmetric induction (47-88 % ee) with alicyclic epoxide substrates. Chiral Lewis basic catalysts with pyridine N-oxide moieties fused with a bicyclo[3.3.1]nonane framework were used in the enantioselective ring opening of meso-epoxides. 2,4-Diaryl-substituted N-oxide exhibited excellent asymmetric induction with norbornene oxide (96 % ee), whereas less-substituted congener was most effective with alicyclic epoxide substrates (47-88 % ee).

Rhodium-catalyzed direct coupling of biaryl pyridine derivatives with internal alkynes

Axially chiral biaryls were synthesized by an isoquinoline or 2-pyridine-directed Rh(iii)-catalyzed dual C-H cleavage and coupling with internal alkynes in good to excellent yields. Oxidation of isoquinoline derivatives with m-CPBA furnished their corresponding N-oxides, which could be utilized as Lewis base catalysts in asymmetric reactions. This journal is the Partner Organisations 2014.

Conformationally rigid chiral bicyclic skeleton-tethered bipyridine N,N'-dioxide as organocatalyst: Asymmetric ring opening of meso-epoxides

The conformationally rigid chiral bicyclic skeleton tethered bipyridine NN'-dioxide (-)-9 has been designed, synthesized and examined as an organocatalyst in the enantioselective ring opening of meso-epoxides using tetrachlorosilane (SiCl4). The catalyst (-)-9 is found to exhibit good enantioselectivity for substituted cis-stilbene epoxides; whereas, the saturated cyclic meso-epoxides display a moderate enantioselectivity. At -30 °C in chloroform, the catalyst (-)-9 with 0.5 mol % loading generated the chlorohydrins in up to 97 % yield with up to 93 % ee. The possible creation of transient axial chiral environment around hypervalent silicon species due to the presence of conformationally rigid chiral bicyclic skeleton tethered bipyridine N,N'-dioxide may be responsible for such enantioselectivity observed in the desymmetrization of meso-epoxides.

Facile synthesis of chiral 1,2-chlorohydrins via the ring-opening of meso-epoxides catalyzed by chiral phosphine oxides

The facile synthesis of chiral 1,2-chlorohydrins via the enantioselective ring-opening of meso-epoxides with silicon tetrachloride in the presence of a chiral phosphine oxide was accomplished. The chiral 1,2-chlorohydrins were also obtained from the corresponding cis-alkenes in one-pot without significant loss in the selectivity, thereby permitting easy access to the 1,2-chlorohydrins from cis-alkenes with good yields and enantioselectivities.

Design, validation, and implementation of a rapid-injection NMR system

A Rapid Injection NMR (RINMR) apparatus has been designed and constructed to allow the observation of fast chemical reactions in real time by NMR spectroscopy. The instrument was designed to allow the rapid (2 s) injection and mixing of a metered volume

Allenes in asymmetric catalysis: Asymmetric ring opening of meso-epoxides catalyzed by allene-containing phosphine oxides

(Chemical Equation Presented) Unsymmetrically substituted allenes (1,2-dienes) are inherently chiral and can be prepared in optically pure form. Nonetheless, to date the allene framework has not been incorporated into ligands for asymmetric catalysis. Since allenes project functionality differently than either tetrahedral carbon or chiral biaryls, they may create complementary chiral environments. This study demonstrates that optically active, C 2-symmetric allene-containing bisphosphine oxides can catalyze the addition of SiCl4 to meso-epoxides with high enantioselectivity. The epoxide opening likely involves generation of a Lewis acidic, cationic (bisphosphine oxide)SiCl3 complex. The fact that high asymmetric induction is observed suggests that allenes may represent a new platform for the development of ligands and catalysts for asymmetric synthesis.