Acid-catalyzed rearrangement of aryl-substituted homobenzoquinone epoxides

The BF3-catalyzed reactions of diphenyl-substituted and endo-monophenyl-substituted homobenzoquinone epoxides proceeded through a regioselective oxirane ring opening followed by participation of a pi-aryl transannular cyclization to give the tricyclic diketo alcohols. The conformationally semirigid ethano-bridged diphenyl-substituted homologues also provided similar diketo alcohols and the subsequent ring-expanded cycloheptenedione (via a subsequent 1,2-acyl migration associated with cyclopropane ring opening), depending on the methyl-substitution pattern of the quinone frame. However, the exo-monophenyl-substituted and the rigid biphenyl-2,2'-diyl-substituted homobenzoquinone epoxides essentially remained unchanged.     

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.     

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.     

Kinetic evidence for remote pi-aryl participation in the BF3-catalyzed rearrangement of [2 + 2] photocycloadducts of diarylhomobenzoquinones with diphenylacetylene

[reaction: see text] The BF(3)-catalyzed rearrangement of cyclobutene-fused m- and p-substituted diarylhomobenzoquinones exclusively gave the keto-alcohols via a Wagner-Meerwein vinyl-anion migration followed by the annulation of a delta-located endo-aryl group. The Hammett treatments for the endo/exo substituent effects, as well as the kinetic solvent effects, indicated that this reaction proceeds through the concerted S(N)2-like mechanism involving a rate-determining endo-aryl-assisted transition state.     

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.     

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.     

Mechanistic insights into the opening of epoxides with trimethylsilyl cyanide - zinc iodide

-2,3-Epoxy-1,7,7-trimethylbicyclo[2.2.1]heptane reacted with trimethylsilyl cyanide in the presence of zinc iodide to produce a complex mixture of products. The major product, -7-trimethylsiloxy- -2,3,3-trimethyl- -2-isocyanobicyclo[2.2.1]heptane was obtained in 72% yield. In addition, eight other products were identified in yields ranging from 10% to 1%. All of the products could be rationalized on the basis of initial generation of a carbocationic intermediate.     

Graphene oxide as an acid catalyst for the room temperature ring opening of epoxides

The minute amount of hydrogen sulfate groups introduced into the graphene oxide (GO) obtained by Hummers oxidation of graphite renders this material as a highly efficient, recyclable acid catalyst for the ring opening of epoxides with methanol and other primary alcohols as nucleophile and solvent.     

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.     

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.     

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.     

Substituted alkenediols by alkylative double ring opening of dihydrofuran and dihydropyran epoxides

[reaction: see text]. Dihydrofuran and dihydropyran epoxides undergo alkylative double ring opening with organolithiums to provide a new route to substituted alkenediols.     

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.     

An efficient catalyst for ring opening of epoxides with phenol and thiophenol under solvent-free conditions

An efficient and rapid procedure for ring opening reaction of various epoxides with phenol and thiophenol derivatives was developed. The procedure can be obtained at room temperature under solvent-free condition in presence of (C₄H₁₂N₂)₂[BiCl₆]Cl·H₂O (1 mol %). This catalyst can be reused several times without significant loss of activity.     

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.     

Studies on nucleophilic ring opening of some epoxides in polar protic solvents—I

The epoxides of the type 4 undergo ring-opening with carbanions; without exception, the nucleophiles attack at C-1 in spite of the increased steric hindrance at the site (as in epoxides 4b and 4e having peri-substituents). Interaction of the epoxide 4b with the anion of diethyl methylmalonate in refluxing t-butanol afforded, besides other products, the novel cyclopropane carboxylic acid 12. What is more significant is that although the formation of the trans-lactone on the whole is favoured in the ring opening of epoxides 4, at least in two cases, 4b and 4c, there is considerable formation of cis-lactones, a result that remains unexplained. Attempted synthesis of the model cis-lactone 3c always resulted in the formation of a 1:1 mixture of the cis-3c and the trans-lactone 2a. The stereochemistries of the cis- and the trans-lactones described in this paper have been unambiguously established from the position of the 3a-proton signals of these γ-lactones in their NMR spectra.     

First total synthesis of cucurbitaxanthin A applying regioselective ring opening of tetrasubstituted epoxides

The synthesis of cucurbitaxanthin A 1 was accomplished via the C(15)-3,6-epoxides 7e and 7f prepared by regioselective ring opening of the 3-hydroxy-5,6-epoxides 6e and 6f.     

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.