Excited biradical states in oxirane ring opening

The mechanism of oxirane ring opening was studied by ab initio [RHF, ROHF, GVB/DH, RHF/SBK(p, d)] calculations. The strained structure of oxiranes and their complexes with aliphatic alcohols and amines is characterized by low-lying biradical states whose thermal population leads to the ring opening. The examined oxirane ring opening reacitons have low activation energy (<10 kcal mol-¹) and are catalyzed by labile hydrogen atoms in hydroxy and amino groups of the reaction complex.     

Studies of rhodium-catalyzed ring opening of vinyl epoxides

The stereoselective 6-endo mode cyclization of vinyl epoxides has been achieved by the use of a catalytic amount of [Rh(CO)₂Cl]₂ affording six-membered heterocycle systems, such as piperidines and tetrahydropyrans. The scope and limitations of the reaction are discussed.     

Enantioselectivity of epoxide hydrolase catalysed oxirane ring opening: a 3D QSAR study

A 3D QSAR analysis (quantitative structure activity relationships) of a set of 2,2-disubstituted epoxides, substrates for epoxide hydrolases originating from four different organisms, was conducted by CoMFA (comparative molecular field analysis) and CoMSIA (comparative molecular similarity indices analysis), with respect to the enantioselective ring opening to the corresponding vicinal diol. Structural variations of the substrates include alkyl chains of different lengths, unsaturated moieties ((E)- and (Z)-alkenyl, alkinyl, aryl) and electronegative groups (ether oxygens, halogen atoms) at different locations within the 2-substituent group. Generally, all four organisms, namely Rhodococcus ruber NCIMB 11216, Rhodococcus ruber DSM 43338, Rhodococcus ruber DSM 44540 and Rhodococcus ruber DSM 44539, preferentially react with the (S)-enantiomer of the epoxide. Enantioselectivities (enantiomeric ratio, lnE values) show a rather large variation, ranging from almost no (lnE<1) to nearly complete selectivity (lnE>5.3). In addition, the response of the epoxide hydrolases stemming from the four organisms towards structural modifications of the substrate is different. Models for the enantioselectivity (enantiomeric ratio, ln E values) obtained by CoMFA and CoMSIA are of different but reasonable predictive power, e.g., q² _CV=0.701 and r²=0.937 for the CoMFA model of Rhodococcus ruber DSM 43338. Enantiomeric ratios for the test molecules can be well predicted. Plots of steric and electrostatic CoMFA (CoMSIA) fields allow conclusions to be drawn for the choice of the most suitable organism for a specific type of substrate.     

New reactivity of the uranyl ion: ring opening polymerisation of epoxides

The uranyl aryloxide, [UO(2)(OAr)(2)(THF)(2)], and uranyl chloride, [UO(2)Cl(2)(THF)(3)] or [UO(2)Cl(2)(THF)(2)](2) act as pre-catalysts for the ring opening polymerization of propylene oxide and cyclohexene oxide. Coordination of the monomers has been investigated using (1)H EXSY spectroscopy and kinetic and thermodynamic parameters reported. NMR analyses of the polymers suggest a bimetallic mechanism for the polymerization.     

Solvent-free direct regioselective ring opening of epoxides with imidazoles

The reaction of different epoxides with commercially available imidazole at 60 °C leads to the formation of the corresponding 1-(β-hydroxyalkyl)imidazoles in a regioselective manner. When the reaction is applied to a chiral epoxide [(R)-styrene oxide], the expected chiral alcohol is isolated with the same enantiomeric excess. The use of benzimidazole as the heterocyclic component in the same process also allows the simple preparation of the corresponding 1-(β-hydroxyalkyl)benzimidazoles.     

Carbonylative ring opening of terminal epoxides at atmospheric pressure

The carbonylative opening of terminal epoxides under mild conditions has been developed using Co2(CO)8 as the catalyst. Under 1 atm of carbon monoxide and at room temperature in methanol, propylene oxide is converted to methyl 3-hydroxybutanoate in up to 89% yield. This transformation is general for many terminal epoxides bearing alkyl, alkenyl, aryl, alkoxy, chloromethyl, phthalimido, and acetal functional groups. The opening takes place without epimerization at the secondary stereocenter.     

Demonstration of a phosphazirconocene as a catalyst for the ring opening of epoxides with TMSCl

[reaction: see text] In this study, it was demonstrated for the first time that a phosphazirconocene catalyzes the ring opening of epoxides with TMSCl. This reactivity leads to a facile preparation of chlorohydrins. The late transition metal Fe analogue was found to catalyze the reaction at rates and stereoselectivity comparable to those of the Zr complex.     

Recent trends in ring opening of epoxides by amines as nucleophiles

β-Amino alcohols are versatile intermediates in the synthesis of various biologically potent compounds, which can also be achieved by ring opening of epoxides by amines. In the present review, focus has been placed on the ring opening of epoxides with amines under a variety of reaction parameters reported during 2011–2015. All the factors that resulted in excellent yields and high regioselectivity, are environmentally benign, and use mild conditions have been discussed in detail. In addition, the applications of these methods in the synthesis of biologically active compounds such as β-blockers have also been described.     

Aluminium triflate: a remarkable Lewis acid catalyst for the ring opening of epoxides by alcohols

Al(OTf)3 was found to be an extremely effective catalyst (at ppm levels) for ring opening reactions of epoxides using a range of alcohols.     

Regioselective ring opening in epoxides under the action of amines in water medium

Amino(bis-amino)derivatives of 2-propanol were synthesized by ring opening in epoxides under the action of amines in water medium using environmentally safe methods. The structure of the compounds obtained was established by elemental analysis and the IR, ¹H and ¹³C NMR spectroscopy. It was found that these substances are effective bactericides. They suppress the growth of the sulfate-reducing bacteria and exhibit high anticorrosive properties.     

Highly selective ring opening of epoxides with silicon tetrafluoride: Preparation of fluorohydrins

Regio-, stereo-, and chemoselective transformation of epoxides into fluorohydrins with silicon tetrafluoride is described.     

Antimony(III) chloride-catalyzed ring opening of epoxides with anilines

A mild and convenient ring opening of epoxides with aniline and its derivatives takes place at room temperature in the presence of antimony trichloride as catalyst to afford the corresponding β-amino alcohols in good yields.     

Rhodium-catalyzed ring opening of vinyl epoxides with alcohols and aromatic amines

[Rh(CO)(2)Cl](2) is an effective catalyst for the ring opening of vinyl epoxides with alcohols and aromatic amines under neutral conditions at room temperature. The reaction occurs with excellent diastereo- and regioselectivity (>20:1) giving the trans-1,2-amino alcohols or alkoxy alcohols for a wide range of substrates. The regio- and stereochemistry of these reactions is complementary to that typically obtained with palladium-catalyzed ring openings of vinyl epoxides.     

Photoenolization-induced oxirane ring opening in 2,5-dimethylbenzoyl oxiranes to form pharmaceutically promising indanone derivatives

Irradiation of 2,5-dimethylbenzoyl oxiranes results in a relatively efficient and high-yielding formation of β-hydroxy functionalized indanones that structurally resemble biologically active pterosines. Nanosecond laser flash photolysis and quantum-chemical calculations based on density functional theory provided evidence that this photochemical transformation proceeds primarily via a photoenolization mechanism. Our study revealed considerable complexity of the mechanism and that structural modifications can significantly alter the reaction pathway and yield different products. The scope of this photochemical transformation for the synthesis of some pharmaceutically important compounds was investigated.     

Lanthanides as lewis-acid catalysts in aldol addition,cyanohydrin-forming and oxirane ring opening reactions

Lanthanide trichlorides (Ln = La,Ce,Sm) and Eu(fod)₃ catalyze the aldol addition of silyl enol ethers to aldehydes, the addition of trimethylsilyl cyanide to aldehydes and ketones as well as thesynthesis of β-cyanosilyl ethers.     

Electrocremical procedure directed to the selective ring opening of epoxides to allylic alcohols

A transformation of epoxides $\text{2}$ into allylic alcohols $\text{1}$ was achieved by an electrogenerated acid-catalysis in a ClCH₂CH₂Cl - TsONa - TsONEt₄ -Pt system.     

Mechanistic evidence for remote pi-aryl participation in acid-catalyzed ring opening of homobenzoquinone epoxides

The acid-induced reaction of bis(p-chlorophenyl)homobenzoquinone epoxide gave the dual ipso/ortho intramolecular S(E)2-Ar products associated with pi-aryl participated oxirane ring opening, whereas bis(p-tolyl)- and diphenyl-substituted homologues provided only the ortho products.     

TiCp2Cl-catalyzed living radical polymerization of styrene initiated by oxirane radical ring opening

Epoxides and paramagnetic early transition metal complexes are introduced as two new classes of initiators and catalysts, respectively, for living radical polymerizations. Thus, Ti(III)Cp2Cl synthesized in situ from the reduction of TiCp2Cl2 with Zn catalyzes the radical ring opening of oxiranes to initiate the radical polymerization of styrene. A linear dependence of molecular weight on conversion, low polydispersity, and reinitiation of the polymerization in the presence of fresh monomer indicates that the polymerization is living and that it most likely occurs by the reversible endcapping of the macroradical with Ti(III). Moreover, epoxides provide convenient access to alcohol chain ends, suitable for further transformations.     

Synthesis of nitrophenyl-substituted 1,3-thiazoline-2-thiones by oxirane ring opening with several dithiocarbamates

Thiazolo-2(3H)-thiones have been prepared by the reaction of triethylamine dithiocarbamates and 4-nitrophenyloxirane via formation of intermediate 2-hydroxy-2-(4-nitrophenyl)ethyldithiocarbamates with simultaneous dehydrogenation of the thiazolidine ring to a thiazoline. It was found that both the basicity of the starting amines and the temperature influenced the course of the reaction.     

Sulfamic acid catalyzed ring opening of epoxides with amines under solvent-free conditions

Sulfamic acid (SA) catalyses the nucleophilic opening of epoxide rings by amines leading to the efficient synthesis of ß-amino alcohols. The reaction works well with aromatic and aliphatic amines in short reaction times and in the absence of solvent. Exclusive trans stereoselectivity is observed for the ring opening of cyclohexene oxide. This method exhibits excellent regioselectivity for preferential nucleophilic attack at the less hindered position during the reaction with unsymmetrical epoxides.