Rearrangement Of Epoxides Research Articles

Tris(pentafluorophenyl)boron as an Efficient Catalyst in the Stereoselective Rearrangement of Epoxides

Tris(pentafluorophenyl)boron as an Efficient Catalyst in the Stereoselective Rearrangement of Epoxides

ChemInform Abstract: A Convenient Procedure for Rearrangement of Epoxides by Use of Dimethylaluminum Catalysts.

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.

ChemInform Abstract: Epoxide Rearrangement. Part 16. Isomerization of Cyclooctene and Cyclododecene Oxides Catalyzed by Solid Acids and Bases.

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.

Synthesis of a chiral 2,6-bridged morpholine system: trans-6,7-diol derivatives of 8-oxa-3-azabicyclo[3.2.1]octane

The title compound 6, [1R-(6 endo, 7 exo)]-8-oxa-3-azabicyclo[3.2.1]octane-6,7-diol, was derived in nine steps from 1-amino-1-deoxy-D-glucitol 2. The key step was the acid catalyzed rearrangement of epoxide 3 to the 2,5- cis-disposed hydrofuran compound 5. Linkage of the 2,5-substituents, to form the bridged secondary amine 23, proceeded via mesylation of 6-OH and deprotection of 1-NH 2. Further O-debenzylation and (or) N-substitution afforded the aminodiol 6 and various N-alkylated derivatives. On basis of 1H NMR analysis the chair form was assigned to the bridged morpholine ring.

ChemInform Abstract: Lewis Acid‐Promoted Selective Rearrangement of Trisubstituted Epoxides to Aldehydes or Ketones.

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.

Alkyleisen‐ und Alkylcobalt‐Reagenzien, IX. Umlagerung aliphatischer terminaler Epoxide zu Methylketonen durch Eisenalkyl‐Reagenzien statt durch Co2(CO)8 oder Edelmetallkatalysatoren

Alkyliron and Alkylcobalt Reagents, IX[1]. — Rearrangement of Aliphatic Terminal Epoxides to Methyl Ketones by Iron Alkyl Reagents instead of Co2(CO)8 or Noble Metal CatalystsThe highly selective rearrangement of aliphatic terminal epoxides to methyl ketones, hitherto possible only with Co2(CO)8 or noble metal catalysts, occurs smoothly with Me4‐FeLi2, Me3FeLi, or the catalytic systems [RLi + 2.5 mol% FeCl3] (R = Me, Bu). This was demonstrated by the rearrangement of 1‐decene oxide (1) to 2‐decanone (2) (yield 80–81%; Table 1) and 6‐bromo‐1‐hexene oxide (5) to 6‐bromo‐2‐hexanone (6) (yield 78%, Me4FeLi2 applied only). The competition reaction of Me4FeLi2 with 1 and 2‐octanone (8) (mole ratio 0.5:1:1) led to 87% 2‐methyl‐2‐octanol (9) and not to the rearrangement 1 → 2. This indicates that Me4FeLi2 ‐ in contrast to the opposite behavior of organo cuprates ‐ reacts faster with ketones than with the aliphatic terminal epoxides. By treatment of 1 with methyl derivatives of MnII, CoII, and NiII or with Bu4FeLi2 (Table 2) other products (3, 4) besides 2 were formed. The rearrangement of 1 with Me4FeLi2 is assumed to start with an oxidative addition and yields 2 as its Li or Fe enolate (trapped with acetanhydride to give 64% of 20) after reductive elimination of CH4. The catalytic rearrangement of 1 with [MeLi + 0.25 mol% FeCl3] very probably occurs in an analogous manner with an super‐ate complex Me4FeLi2(MeLi)n as the active species and the Li enolate of 2 as end product (Scheme 4). The aromatic terminal epoxides styrene oxide and α‐methylstyrene oxide give various products in the reaction with Me4FeLi2 or Me3FeLi, including the deoxygenation products styrene and α‐methylstyrene. These products are exclusively formed on treatment of the epoxides with Me4MnLi2. (Prepared, hitherto in the literature not described compounds: 7 and 10–15.)

Lewis acid-promoted selective rearrangement of trisubstituted epoxides to aldehydes or ketones

Rearrangement of trisubstituted epoxides has been effected under the influence of various Lewis acids. Among these, methylaluminum bis(4-bromo-2,6-di- tert-butylphenoxide) (MABR) can be selectively rearranged from trisubstituted epoxides to aldehydes, while antimony pentafluoride is employable for selective rearrangement to ketones under mild conditions.

Synthesis of C-17-functionalized beyerane diterpenes. Synthesis of (–)-erythroxylol B, (–)-erythroxydiol A and (–)-benuol

The title compounds 1, 2 and 3 became accessible from an appropriately functionalized podocarpenone 4 in short sequences of operations, in which the key step involves the toluene-p-sulfonic acid-induced rearrangement of 13-epimeric epoxides 6 and 7.

Stereospecific construction of multiple contiguous quaternary carbons. Total synthesis of (±)-cis,anti,cis-1,8,12,12-tetramethyl-4-oxatricyclo[6.4.0.02,6]dodecan-3-ol, a thapsane isolated from Thapsia villosa var minor

The details of the first total synthesis of a natural thapsane 1g containing three contiguous quaternary carbon atoms, starting from cyclogeraniol (9) is described. The Claisen rearrangement of 9 with methoxyropene in the presence of a catalytic amount of propionic acid produced ketone 10. Rhodium acetate-catalyzed intramolecular cyclopropanation of α-diazo-β-keto ester 12, obtained from 10 via β-keto edter 8, furnished cyclopropyl keto ester 7. Lithium in liquid ammonia reductive cleavage of cyclopropyl compound 7 gave a 1:1 mixture of hydrindanone 6 and ketol 13. Wittig methylenation of 6 furnished ester 21. Epoxidation of 21, followed by BF 3 -OEt 2 catalyzed rearrangement of epoxide 23 afforded hemiacetal 25. Treatment of hemiacetal 25 with triethylsilane in trifluoroacetic acid furnished lactone 22, a degradation product of various thapsanes. Finally, DIBAH reduction of lactone 22 generated the thapsane 1g

Alkylative epoxide rearrangement. A stereospecific approach to chiral epoxide pheromones

The alkylative rearrangement of 1,2-epoxy-3-alkanol tosylates is applied to the synthesis of chiral epoxide pheromones. Attack at the terminal carbon atom of epoxy tosylates by lithioacetylenes and cyclization of the intermediate tosyloxy alcohols produces internal epoxides in high yield. The method is streospecific: threo-epoxy tosylates give cis-epoxides, and erythro-epoxy tosylates yield trans-epoxides. Several diastereomerically pure epoxides were prepared in high optical purity from chiral pool intermediates derived from sugars. Pheromone components prepared include (±)-cis-epoxyalkene 20 and both enantiomers of cis-epoxy diene 16, a female sex pheromone component of a number of lepidopteran species

ChemInform Abstract: Trityl Antimonate Catalyzed Sequential Reactions of Epoxides with Silylated Nucleophiles. Rearrangement of Epoxides and C‐C or C‐O Bond Forming Nucleophilic Reaction onto the Intermediate Carbonyl Compounds.

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.

Comparison of the electronic effect and the steric influence between the 1,1,2,2,2-pentamethyldisilanyl and the trimethylsilyl groups

A comparison of the electronic effects expressed by the Me 3SiMe 2Si-; and Me 3Si- groups towards carbocationic intermediates was made by study of acid-catalyzed rearrangements of decalin epoxides 3 and 4. Reaction of the Me 3SiMe 2Si-epoxide 3 with BF 3 · Et 2O in CH 2Cl 2 at -50°C gave four products: B-ring contracted spirocyclic alcohol 9 (21%), methyl-migrated decanol 12 (23%), A-ring contracted aldehyde 15 (21%), and fluorohydrin 17 (14%). Under the same conditions, Me 3Si-epoxide 4 afforded alcohol 9 (24%), decanol 12 (18%), aldehyde 16 (23%; cf. 15), and fluorohydrin 18 (13%; cf. 17). These results show that the Me 3SiMe 2Si- and Me 3Si- groups exerted electronic influence to the same extents on carbocations. In HMPA and THF at -78°C, reagent Me 3SiMe 2SiLi reacted with cross-conjugated dienone 19 in a 1,4 fashion from the less hindered side to give enone 20 (63%) as the only adduct. In comparison with Me 3SiLi, reagent Me 3SiMe 2SiLi possessed better stereoselectivity. In addition, the Me 3SiMe 2Si- moiety with α configuration in 24 was able to prevent m-chloroperbenzoic acid ( m-CPBA) from attacking from the same face during epoxidation, such that β-epoxide 3 was obtained in 59% yield exclusively.

Activation and metabolism of benz[ j]aceanthrylene-9,10-dihydrodiol, the precursor to bay-region metabolism of the genotoxic cyclopenta-PAH benz[ j]aceanthrylene

Benz[ j]aceanthrylene, a cyclopentafused polycyclic aromatic hydrocarbon produced in combustion emissions, possesses a bay region and an etheno bridge which may both contribute to the overall genotoxicity of the compound. In order to assess the role of activation at the bay region, the precursor epoxide benz[ j]aceanthrylene 9,10-oxide, its dehydration product 10-hydroxybenz[ j]aceanthrylene, the key dihydrodiol 9,10-dihydroxy-9,10-dihydrobenz[ j]aceanthrylene and the bay-region diol-epoxide 7,8- epoxy-9,10-dihydroxy-7,8,9,10-tetrahydrobenz[ j]aceanthrylene were evaluated in the bacterial histidine-reversion plate incorporation assay (Ames assay) with Salmonella typhimurium strain TA98. The diol-epoxide alone showed direct-acting mutagenicity (10 revertants per nmole), which was decreased by addition of exogenous metabolic activation (Aroclor 1254-treated rat-liver S9), whereas all the other compounds tested were activated by increasing concentrations of S9. The potency of the diol-epoxide was not sufficient to account for the activity of the parent compound. Identification by proton nuclear magnetic resonance and mass spectrometry of the major products of further metabolism by Aroclor 1254-treated rat-liver S9 of the bay region precursor dihydrodiol 9,10-dihydroxy-9,10- dihydrobenz[ j]aceanthrylene indicated that oxidation occurred predominantly at the etheno bridge, to give 9,10-dihydroxy-9,10-dihydrobenz[ j]aceanthrylene-2(1 H)-one, arising by (non-enzymic) rearrangement of the etheno bridge epoxide and the tetrol 1,2,9,10-tetrahydroxy-1,2,9,10-tetrahydrobenz[ j]acenthrylene. The bay region tetrol 7,8,9,10-tetrahydroxy-7,8,9,10-tetrahydrobenz[ j]aceanthrylene was observed, implying further bay-region metabolism; re-aromatization of the benzo ring to benz[ j]aceanthrylene-9,10-diol also occurred. Thus oxidation at the etheno bridge accounts for the majority of the activity of benz[ j]aceanthrylene and its derivatives when Aroclor 1254-treated rat-liver S9 is used for exogenous metabolic activation.

ChemInform Abstract: A Convenient Method for the Preparation of Ethers (III) from Epoxides ( I). Trityl Hexafluoroantimonate‐Catalyzed Sequential Reactions, Rearrangement, and Reductive Condensation of Epoxides.

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.

Trityl Antimonate-Catalyzed Sequential Reactions of Epoxides with Silylated Nucleophiles. Rearrangement of Epoxides and C–C or C–O Bond Forming Nucleophilic Reaction onto the Intermediate Carbonyl Compounds

Abstract In the presence of a catalytic amount of trityl hexafluoroantimonate, sequential reactions of epoxides with silylated nucleophiles, rearrangement of epoxides and C–C or C–O bond forming nucleophilic reaction onto the intermediate carbonyl compounds, proceed smoothly to afford the corresponding products in fairly good yields by one-pot procedure. Trityl hexafluoroantimonate (5 mol %) efficiently promotes the above plural sequential reactions.

ジメチルアルミニウム化合物を触媒とするエポキシ化合物の簡便な転位反応

The modified dimethylaluminum reagents such as tris(dimethylaluminum)aryloxide (3), dimethylaluminum 4-bromo-2, 6-di-t-butylphenoxide (7), dimethylaluminum 2, 6-di-t-buty14-methylphenoxide (8), and dimethylaluminum 4-bromo-2, 6-diphenylphenoxide (9) can be utilized as mild Lewis acidic catalysts for the selective rearrangement of epoxides to carbonyl compounds under mild conditions. Among these, the catalyst 3 is highly effective for epoxy silyl ether substrates, while 9 is useful for simple epoxides.

A reinvestigation of the reductive ring-opening of a 3-substituted exo-4,5-epoxytricyclo[5.2.1.02,6]dec-8-en-3α-ol to the corresponding 3,5-diol

Regio- and stereo-specific reduction of the exo-epoxy alcohol 5 with LiAID4 produced the 4α-D-trans-3,5-diol 7 and the 4β-D-trans-3,5-diol 8 in varying ratios, an indication that in spite of epoxide rearrangement between 5 and 6 direct epoxide ring-opening of 5 to afford the 3,5-diol 4 is the primary pathway.

A Facile Workup-Free Catalytic Rearrangement of Epoxides on Immobilized Organoaluminum Columns

Abstract The immobilized organoaluminum columns can be successfully utilized as a workup-free reactor for the catalytic rearrangement of various epoxides to carbonyl compounds.

ChemInform Abstract: A New Cyclization of Olefinic Epoxides by Modified Organoaluminum Reagents via Epoxide Rearrangement and Subsequent Intramolecular Ene Reaction.

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.

Phenylthio radical catalyzed rearrangement of acetoxyalkenyl epoxides to acetoxyalkenyl cyclopentanols

Exposure of cyclic acetoxyalkenyl exposides to a catalytic amount of PhS· initiates a tandem radical induced expoxide fragmentation-H· abstraction-cyclization process that results in a net isomerization to bicyclic enolacetates.