Rearrangement Of Epoxides Research Articles

A novel approach for construction of the naturally occurring dihydroagarofuran sesquiterpene skeleton

A general and efficient approach for the synthesis of a kind of dihydrofuran sesquiterpenes extensively present in the Celastraceae family of plants has been developed by a series of transformations from santonin. The key creative and versatile steps involve the strategic acid-catalyzed double-bond shifting affording 6 , the novel base-promoted epoxide rearrangement of 7 generating two key functions (the C5OH and the Δ 7,11 double bond) and the stereoselective construction of a tetrahydrofuran moiety without particularly controlling the stereochemistry of C7. In particular, this approach can introduce any number of hydroxyls at the required positions for synthesis of many natural dihydroagarofuran sesquiterpenes.

A facile and efficient method for the rearrangement of aryl-substituted epoxides to aldehydes and ketones using bismuth triflate

Aryl-substituted epoxides undergo smooth rearrangement in the presence of 0.01–0.1 mol% Bi(OTf) 3· xH 2O. The rearrangement is regioselective with aryl-substituted epoxides, and products arise from cleavage of the benzylic CO bond. The highly catalytic nature of this method coupled with the fact that the reagent is relatively non-toxic, easy to handle and inexpensive make it an attractive alternative to more corrosive and toxic Lewis acids, such as BF 3·Et 2O, currently used to effect epoxide rearrangements.

ChemInform Abstract: Effect of BF3×Et2O Reagent on the Base‐Promoted Rearrangements of Epoxides Attached to Eight‐Membered Rings.

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Rearrangements of Neoclovene Epoxides in Acidic Media

Rearrangements of neoclovene epoxides in the presence of a solid superacid ZrO2/SO42- and in formic acid were investigated. In the latter case a ketone was obtained with a previously unknown carbon skeleton. The most probable pathway of its formation was derived from calculations by molecular mechanics and quantum-chemical methods.

Rearrangements of Epoxides of Some Acyclic Terpenoids in Acidic Media

2,3-Epoxygeraniol undergoes dissimilar rearrangements in contact with liquid superacids at low temperature or on solid superacids at room temperature due to different location of the arising cationic center depending on the superacid character. 2,3-Epoxynerol, 6,7-epoxycitronellol, and 6,7-geranyl acetate on ZrO2SO42- afford the corresponding ketones via epoxy ring opening followed by 1,2-hydride shift. With 6,7-geranyl acetate 7-oxanobornane formed as a minor product. The mode of generation of the cationic center (either the olefin protonation or the epoxy ring opening) affects the rearrangement direction at similar conditions.

Isolation, identification, synthesis, and bioefficacy of female Diacrisia obliqua (Arctiidae) sex pheromone blend. An Indian agricultural pest

Diacrisia obliqua is a polyphagous pest especially on oil seed crops. Adult female sex pheromone blend consists of five pheromone components, which include (3Z,6Z)-cis-9,10-epoxyl,3,6-henicosatriene and (3Z,6Z)-cis-9,10-epoxy3,6-henicosadiene. Synthesis of these enantiomers was achieved through alkylative epoxide rearrangement and stereoselective Wittig olefination reactions as key steps. Bioefficacy experiments both at laboratory and minifield were very positive.

ChemInform Abstract: Diastereoselective Epoxide Rearrangements Using Lithium Amide Bases: First Stereocontrolled Synthesis of 4-Deoxyconduritols.

Two novel and completely diastereoselective lithium amide-mediated rearrangements of diprotected 4,5-dihydroxycyclohexene oxides and their use in the synthesis of 4-deoxyconduritols are described.

ChemInform Abstract: High Valence Vanadium Complex Promoted Selective Rearrangement of Epoxides to Aldehydes or Ketones.

High valence vanadium complexes induce the selective ring opening of epoxides. The monosubstituted epoxides are isomerized with complete regioselectivity each forming a single carbonyl compound exclusively. Likewise a highly regioselective isomerization of 1,1-disubstituted or 1,1,2-trisubstituted epoxides was observed in all reactions.

Ring Contraction Through Epoxide Rearrangement: A Formal Synthesis of Capsorubin

An eight-step synthesis of the cyclopentane keto-alcohol 2, which has previously been converted in one step into the carotenoid pigment capsorubin (1), is described. The key step in our synthesis is a stereospecific epoxide rearrangement with ring contraction, thus producing the cyclopentane ring from an epoxide of a cyclohexene.

Indium Metal and Its Halides in Organic Synthesis

This review highlights the applications of indium metal and indium(III) halides in organic synthesis with particular reference to regio-, stereo-, and chemoselectivity. Indium-mediated reactions include the regioselective allylation of alkynes, the stereoselective debromination of vic-aryl-substituted dibromides, the homocoupling of alkyl/aryl halides, and the reduction of α-halocarbonyl compounds. Indium trichloride has been used as a Lewis acid catalyst in epoxide rearrangements, in the synthesis of α-amino phosphonates, and in the construction of the quinoline system. Indium triiodide has proven to be a very efficient catalyst for transesterification processes.

Allylic Alcohols via Catalytic Asymmetric Epoxide Rearrangement

Optically active allylic alcohols can be prepared via rearrangement of epoxides using chiral lithium amides, but other than for a small subset of meso-epoxides, insufficient reactivity and enantios...

Regioselective intramolecular oxidation of phenols and anisoles by dioxiranes generated in situ

A novel method for regioselective oxidation of phenols and anisoles has been developed in which dioxiranes, generated in situ from ketones and Oxone, oxidize phenol derivatives in an intramolecular fashion. A series of ketones with electron-withdrawing groups, such as CF(3), COOMe, and CH(2)Cl, were attached to phenols, anisoles, or aryl rings via a C(2) or C(3) methylene linker. In a homogeneous solvent system of CH(3)CN and H(2)O, oxidation of phenol derivatives 1-10 afforded spiro 2-hydroxydienones in 24-55% yields regardless of the presence of other substituents (ortho Me, meta Me or Br) on the aryl ring and the length of the linker. Experimental evidences were provided to support the mechanism that involves a regioselective pi bond epoxidation of aryl rings followed by epoxide rearrangement and hemiketal formation.

Further studies on the synthesis of 24(S),25-epoxycholesterol. A new, efficient preparation of desmosterol.

Efforts to improve the synthesis of 24(S),25-epoxycholesterol (1) from stigmasterol (3) have included identification of 6 alpha-hydroxy-i-steroid 11 as a byproduct from the ozonolysis of 9 and an attempt to effect conversion of sulfone 14 to diol 18 via Payne rearrangement and nucleophilic trapping of epoxide 25, which led instead to 27 and 28 (97% yield). A more efficient synthesis of 1 was achieved via coupling of cuprate 21 with allylic acetate 31 to give 73% of 16, in the most efficient conversion yet of a C22 intermediate to desmosterol (5) or its acetate 6.

Bismuth(III) oxide perchlorate promoted rearrangement of epoxides to aldehydes and ketones

Aryl-substituted epoxides and aliphatic epoxides with a tertiary epoxide carbon undergo smooth rearrangement in the presence of 10–50 mol% bismuth(III) oxide perchlorate, BiOClO 4·×H 2O, to give carbonyl compounds. The rearrangement is regioselective with aryl substituted epoxides and a single carbonyl compound arising from cleavage of benzylic C–O bond is formed. BiOClO 4·×H 2O is relatively non-toxic, insensitive to air and inexpensive, making this catalyst an attractive alternative to more corrosive and toxic Lewis acids such as BF 3·Et 2O or InCl 3 currently used to effect epoxide rearrangements.

Structural and solvent effects on the mechanism of base-induced rearrangement of epoxides to allylic alcohols

A combined experimental and computational study is presented which explores the influence of structure and solvent on the base-catalyzed isomerization of cyclopentene- and cyclohexene oxides. Cyclohexene oxide is known to rearrange via a syn beta-elimination in nonpolar solvents. Cyclopentene oxide instead undergoes alpha-elimination to a carbenoid intermediate in nonpolar solvents due to the unusual acidity of the alpha-proton, not because of an unfavorable conformation. In HMPA, cyclopentene oxide undergoes beta-elimination. To explore the origins of this mechanistic change, deuterium-labeled cis-4-tert-butylcyclohexene oxide was rearranged in HMPA and was found to react via anti beta-elimination, as presumably do cyclopentene oxide and other epoxides.

Zinc bromide as catalyst for the stereoselective construction of quaternary carbon: improved synthesis of diastereomerically enriched spirocyclic diols

Zinc bromide (ZnBr2) has proved to be a facile and efficient catalyst for the stereoselective semipinacol rearrangement of α-hydroxy epoxides at room temperature. Of note are the presence in the product of two adjacent chiral carbon centers, particularly the creation of a stereoselective quaternary center, and the efficient synthesis of β-hydroxy ketones, including some with naturally occurring spiroalkane skeletons. As an example of its application, important diastereomerically enriched spirocyclic diol ligands have been synthesized conveniently via this rearrangement followed by reduction of the spirocyclic β-hydroxy ketones obtained with appropriate hydride reagents.

Iron(III)picolinate-induced oxygenation and subsequent rearrangement of triterpenoid derivatives with hydrogen peroxide.

The reaction of oleanane triterpenoid 1b with a FeIII(PA; picolinate)3/H2O2/MeCN system (reagent system A), a simple model system for mono-oxygenase, gave the 11 alpha-hydroxyl derivative 3 as major product, along with 11-oxo derivative 4 and 12-oxo derivative 6. The reaction of lupane triterpenoid 2b with reagent system A gave only oxidative rearrangement compounds, (20R)-aldehyde 8 and (20S)-aldehyde 9 were epimeric isomers. Then, we have found that iron(III) picolinate complex, FeIII(PA)3 is efficient in effecting the rearrangement of triterpenoid epoxides 5 and 7 into the corresponding carbonyl compounds, 6, 8 and 9 with 1,2-shift of the hydride.

Effect of BF3·Et2O reagent on the base-promoted rearrangements of epoxides attached to eight-membered rings

Cyclooctene oxide 1, cycloocta-1,3-diene oxide 4, and cycloocta-1,5-diene oxide 7 react with organolithium reagents by nucleophilic opening or α- or β-deprotonation. The addition of BF3·Et2O affects the course of the reaction, and also strongly accelerates it. If (−)-sparteine is present, a moderate to high asymmetric induction is obtained.

Exploring the Chemistry of 3-Substituted 2-Azanorbornyls in Asymmetric Catalysis

This account summarizes our recent achievements in asymmetric catalysis using 3-substituted 2-azanorbornyl based ligands. Using this structural unit in ligand synthesis offers several advantages over the analogous proline chemistry, such as equal availability of both enantiomers and increased rigidity of the catalysts. The reactions so far performed with good results, include the copper-catalyzed allylic acyloxylation, zinc mediated alkylation of imines, the base-catalyzed rearrangement of epoxides, and the ruthenium-catalyzed transfer hydrogenation. Other reactions where the results are less satisfactory are described are the oxazaborolidine catalyzed borane reduction of ketones, and the copper-catalyzed 1,4-addition of alkyl Grignard reagents to α,β-unsaturated ketones. In the last part of the article, some intriguing ring-opening reactions are described, leading to synthetically very interesting structural units such as α-aminoacids and cycloalkyl amines.

High valence vanadium complex promoted selective rearrangement of epoxides to aldehydes or ketones

High valence vanadium complexes induce the selective ring opening of epoxides. The monosubstituted epoxides are isomerized with complete regioselectivity each forming a single carbonyl compound exclusively. Likewise a highly regioselective isomerization of 1,1-disubstituted or 1,1,2-trisubstituted epoxides was observed in all reactions.