Ring Opening Of Meso-epoxides Research Articles

Heteroaromatic N-Oxides in Asymmetric Catalysis: A Review.

An increasing interest in the synthesis and use of optically active pyridine N-oxides as chiral controllers for asymmetric reactions has been observed in the last few years. Chiral heteroaromatic N-oxides can work as powerful electron-pair donors, providing suitable electronic environments in the transition state formed within the reaction. The nucleophilicity of the oxygen atom in N-oxides, coupled with a high affinity of silicon to oxygen, represent ideal properties for the development of synthetic methodology based on nucleophilic activation of organosilicon reagents. The application of chiral N-oxides as efficient organocatalysts in allylation, propargylation, allenylation, and ring-opening of meso-epoxides, as well as chiral ligands for metal complexes catalyzing Michael addition or nitroaldol reaction, can also be found in the literature. This review deals with stereoselective applications of N-oxides, and how the differentiating properties are correlated with their structure. It contains more recent results, covering approximately the last ten years. All the reported examples have been divided into five classes, according to the chirality elements present in their basic molecular frameworks.

Iron-Catalyzed Asymmetric Ring Opening of meso-Epoxides

Iron-Catalyzed Asymmetric Ring Opening of meso-Epoxides

ChemInform Abstract: Asymmetric Ring Opening of Meso Epoxides with TMSCN Catalyzed by (Pybox)lanthanoid Complexes.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Lewis Base Catalysts Containing Axial Chirality of Allenes

A series of optically active allene-containing phosphine oxides (like 3-5) were synthesized and investigated as Lewis base catalyst in the ring opening of meso-epoxides. In the presence of 0.1 to 2 mol% of catalyst 3, a set of meso-epoxides 1 can be efficiently opened by SiCl4 with high enantioselectivity providing the corresponding enantioenriched chlorohydrins 2 with up to 97:3 er, while ortho-substituted stilbenes showed no reactivity and aliphatic epoxides (linear or cyclic) proceeded with lower stereoselectivity.

Synthetic and Mechanistic Studies of Strained Heterocycle Opening Reactions Mediated by Zirconium(IV) Imido Complexes

The reactions of the bis(cyclopentadienyl)(tert-butylimido)zirconium complex (Cp(2)Zr=N-t-Bu)(THF) (1) with epoxides, aziridines, and episulfides were investigated. Heterocycles without accessible beta-hydrogens undergo insertion/protonation of the C-X bond to produce 1,2-amino alcohols (X = O) and 1,2-diamines (X = NR), whereas heterocycles with accessible beta-hydrogens undergo elimination/protonation to produce allylic alcohols (X = O) and allylic sulfides (X = S). Mechanistic investigations support a stepwise pathway with zwitterionic intermediates for the first reaction class and a concerted pathway for the second reaction class. Additionally, the feasibility of chirality transfer from the planar-chiral ebthi (ebthi = ethylenebis(tetrahydroindenyl)) ligand was demonstrated with a chiral analogue, (ebthi)-Zr=NAr(THF) (Ar = 2,6-dimethylphenyl), 2, through the diastereoselective ring opening of meso epoxides.

Coordination of CrIII(Salen) on Functionalised Silica for Asymmetric Ring Opening Reactions of Epoxides

The heterogeneous asymmetric ring opening (ARO) ofmeso-epoxides with trimethylsilylazide (TMSN3) catalysed by a Cr(salen) catalyst coordinated on an aminopropyl functionalised silica material combines good enantioselectivities with high conversions and suffers low leaching (<1%).

The First Example of Enantioselective Isocyanosilylation of meso Epoxides with TMSCN Catalyzed by Novel Chiral Organogallium and Indium Complexes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The first example of enantioselective isocyanosilylation of meso epoxides with TMSCN catalyzed by novel chiral organogallium and indium complexesElectronic supplementary information (ESI) available: Characterization data, chiral analysis and determination of absolute configuration. See http://www.rsc.org/suppdata/cc/b2/b212511k/

The desymmetrization ring opening of meso epoxides using trimethylsilyl cyanide catalyzed by organogallium and indium complexes with binaphthol monoether derivatives as chiral ligands gave beta-isocyanohydrins with moderate to excellent enantioselectivities of up to 95% ee.

On the Beneficial Effect of ortho-Methoxy Groups in the Asymmetric Ring Opening of meso Epoxides with Silicon Tetrachloride Catalyzed by Chiral ortho-Methoxyphenyldiazaphosphonamide Lewis Bases A Response to the correspondence by Professor Scott E. Denmark et al.3

On the Beneficial Effect of ortho-Methoxy Groups in the Asymmetric Ring Opening of meso Epoxides with Silicon Tetrachloride Catalyzed by Chiral ortho-Methoxyphenyldiazaphosphonamide Lewis Bases A Response to the correspondence by Professor Scott E. Denmark et al.3

On the Beneficial Effect of ortho-Methoxy Groups in the Asymmetric Ring Opening of meso Epoxides with Silicon Tetrachloride Catalyzed by Chiral ortho-Methoxyphenyldiazaphosphonamide Lewis Bases

We published in this journal a communication on the enantioselective opening of meso epoxides with silicon tetrachloride in the presence of a catalytic amount of chiral phosphonamides.1 In that paper we reported the asymmetric ring opening of cyclooctene oxide with SiCl4 in the presence of 10 mol % of chiral phophonamide base (R,R)-1 as a catalyst (Scheme 1). For this reaction, we described up to 83 % yield and enantiomeric excess higher than 99 %. This spectacular result attracted the attention of Professor Scott E. Denmark, who pioneered this research field,2 because it was found that cyclooctene oxide is one of the slowest acting epoxides in this catalytic system and produced the racemic chlorohydrin. However, Denmark et al. did not succeed in reproducing the results we disclosed and submitted a rebuttal to our paper.3 We were then contacted by the Editor and Prof. Denmark and prompted to elucidate the origin of such a striking discrepancy. At this stage, I asked my co-workers4 to check the experimental procedures and analytical conditions and to try to reproduce the described results. I was provided with experimental data and material that fully confirmed our original claims. On the basis of these results we sent a first answer to the rebuttal published in Angewandte Chemie, an answer that could not explain why our observation differed from Prof. Denmark's. One month later, we received a letter from the Editor who required further complementary analytical data and information. When I had these new data from my co-workers in hand, I noticed several inconsistencies with the analytical material they had previously provided. Therefore, I decided to reproduce personally and independently the whole experimental procedures from the very beginning. I was unable to observe the opening of cyclooctene oxide under the described conditions and to reproduce the analytical data (for example, NMR, retention times in chiral GPC and HPLC analyses) provided by my co-workers. Instead, I obtained results similar to those reported by Denmark et al. in their rebuttal.3 A cross-check undertaken by several colleagues led to identical results. To date, my co-workers4 have been unable to provide an appropriate scientific rationale for the non-reproducibility of the former results and analyses. Under these circumstances, although our communication presented several other meso epoxide openings with fair to high enantioselectivities, which require experimental verification, I wish to withdraw that communication.1 Other pieces of work based on related experimental results that were published elsewhere will also be withdrawn.5, 6

On the Beneficial Effect ofortho-Methoxy Groups in the Asymmetric Ring Opening ofmeso Epoxides with Silicon Tetrachloride Catalyzed by Chiralortho-Methoxyphenyldiazaphosphonamide Lewis Bases

On the Beneficial Effect ofortho-Methoxy Groups in the Asymmetric Ring Opening ofmeso Epoxides with Silicon Tetrachloride Catalyzed by Chiralortho-Methoxyphenyldiazaphosphonamide Lewis Bases

ChemInform Abstract: Beneficial Effect of ortho‐Methoxy Groups in the Asymmetric Ring Opening of meso Epoxides with Silicon Tetrachloride Catalyzed by Chiral ortho‐Methoxyphenyldiazaphosphonamide Lewis Bases. Response to the Communication by G. Buono et al.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Beneficial Effect ofortho-Methoxy Groups in the Asymmetric Ring Opening ofmeso Epoxides with Silicon Tetrachloride Catalyzed by Chiralortho-Methoxyphenyldiazaphosphonamide Lewis Bases Response to the Communication by G. Buono et al.

Die Eignung des chiralen Phosphonamids 1 als Katalysator für die enantioselektive Ringöffnung von meso-Epoxiden mit SiCl4 konnte in Denmarks Labor nicht bestätigt werden. Insbesondere bei der Ringöffnung von Cyclooctenoxid (siehe Schema) erhielten Denmark und Mitarbeiter vollkommen andere Ergebnisse (81–83 % zurückgewonnenes Epoxid und wenig, dazu nahezu racemisches Produkt) als Buono et al. (77 % Ausbeute und >99 % ee).

ChemInform Abstract: Beneficial Effect of ortho-Methoxy Groups in the Asymmetric Ring Opening of meso Epoxides with Silicon Tetrachloride Catalyzed by Chiral ortho-Methoxyphenyldiazaphosphonamide Lewis Bases.

ChemInform Abstract: Beneficial Effect of ortho-Methoxy Groups in the Asymmetric Ring Opening of meso Epoxides with Silicon Tetrachloride Catalyzed by Chiral ortho-Methoxyphenyldiazaphosphonamide Lewis Bases.

Asymmetric ring opening of meso epoxides with TMSCN catalyzed by (pybox)lanthanide complexes.

The asymmetric ring opening of meso epoxides with TMSCN is catalyzed by (pybox)YbCl3 complexes, yielding the beta-trimethylsilyloxy nitrile ring-opened products with good enantioselectivities (83-92% ee). The reaction exhibits a second-order kinetic dependence on catalyst concentration and a first-order dependence on epoxide concentration, consistent with a bimetallic pathway involving simultaneous activation of epoxide and cyanide.

Asymmetric Ring Opening of Meso Epoxides with Thiols: Enantiomeric Enrichment Using a Bifunctional Nucleophile

Asymmetric Ring Opening of Meso Epoxides with Thiols: Enantiomeric Enrichment Using a Bifunctional Nucleophile

Practical Synthesis of Enantiopure Cyclic 1,2-Amino Alcohols via Catalytic Asymmetric Ring Opening of Meso Epoxides

Practical Synthesis of Enantiopure Cyclic 1,2-Amino Alcohols via Catalytic Asymmetric Ring Opening of Meso Epoxides