Tandem Epoxide Research Articles

Synthesis of substituted pyrido-oxazepine-3-ols and benzo-oxazin-2-yl methanol via tandem epoxide opening and SNAr reaction

A general and catalyst-free protocol for the synthesis of pyrido-oxazepine-3-ols and benzo-oxazin-2-yl methanol via tandem epoxide opening followed by SNAr reactions is reported. Oxirane derived from tribromopyridine undergoes epoxide opening followed by the SNAr reaction, yielding seven-membered pyrido-oxazepine-3-ols. Predominantly 2-cyclized pyrido-oxazepine-3-ols observed in this reaction. Oxirane derived from tribromonitrobenzene undergoes epoxide opening followed by SNAr reaction to produce six-membered benzo-oxazin-2-yl methanol. When oxirane treated with primary amine, mainly 2-cyclized benzo-oxazin-2-yl methanol is formed. furthermore, treatment of oxirane with secondary amine result in regio-selective 4-cyclized benzo-oxazin-2-yl methanol, accompanied by de-alkylation. A plausible reaction mechanism is proposed for the synthesis of benzo-oxazin-2-yl methanol, which proceeds via epoxide opening followed by a Smiles rearrangement.

Mesoporous Fe-Doped Carbon Electrocatalysts with Highly Exposed Active Sites for Efficient Synthesis of Hydrogen Peroxide and Tandem Epoxidation of Propene

Mesoporous Fe-Doped Carbon Electrocatalysts with Highly Exposed Active Sites for Efficient Synthesis of Hydrogen Peroxide and Tandem Epoxidation of Propene

Selective Catalytic Epoxidation-Hydration of α-Pinene with Hydrogen Peroxide to Sobrerol by Durable Ammonium Phosphotungstate Immobilized on Imidazolized Activated Carbon.

It is presented that the activated carbon was carboxylated with hydrogen peroxide and then acylated with 2-methylimidazole to prepare the porous carbon support with a surface imidazolated modification. Through the adsorption of phosphotungstic acid on the fundamental site of an imidazolyl group and then adjusting the acid strength with the ammonia molecule, a catalytic carbon material immobilized with ammonium phosphotungstate (AC-COIMO-NH4PW) was obtained, which was used to catalyze a one-pot reaction of convenient α-pinene and hydrogen peroxide to sobrerol. The bifunctional active site originated from the dual property of ammonium phosphotungstate, as the oxidant and acid presenting a cooperatively catalytic performance, which effectively catalyzes the tandem epoxidation-isomerization-hydration of α-pinene to sobrerol, in which the solvent effect of catalysis simultaneously exists. The sobrerol selectivity was significantly improved after the acid strength weakening by ammonia. Monomolecular chemical bonding and anchoring of ammonium phosphotungstate at the basic site prevented the loss of the active catalytic species, and the recovered catalyst showed excellent catalytic stability in reuse. Using acetonitrile as the solvent at 40 °C for 4 h, the conversion of α-pinene could reach 90.6%, and the selectivity of sobrerol was 40.5%. The results of five cycles show that the catalyst presents excellent stability due to the tight immobilization of ammonium phosphotungstate bonding on the imidazolized activated carbon, based on which a catalytic-cycle mechanism is proposed for the tandem reaction.

Peroxidase-like biomimetic epoxidation and subsequent alcoholysis of olefins by Fe(III)tetrakis(4-sulphonatophenyl) porphyrin (Fe4SP) encapsulated in the metal-organic framework HKUST-1

The efficiency and diverse functionality of biological catalysts has inspired the synthetic design of systems to mimic the stabilizing and catalytic properties of enzyme substrate binding protein pockets. One such system is the Fe4SP@HKUST-1 metal organic framework (MOF) system, also known as MOMzyme-1, in which Fe(III)tetrakis(4-sulphonatophenyl)porphyrin (Fe4SP) is encapsulated within the cuboctahedral cavities of the HKUST-1 MOF. Within this system the Fe4SP heme active site is encapsulated in a pseudo protein pocket within the MOF. Here, the ability of the Fe4SP@HKUST-1 to catalyze the tandem epoxidation of olefins followed by selective alcoholysis is examined. It is observed that encapsulation of Fe4SP within the MOF framework significantly enhances the turnover number (TON) of peroxide-driven epoxidation of styrene while greatly reducing metalloporphyrin degradation and maintaining stereoisomer selectivity. The Fe4SP@HKUST-1 catalyzes both the olefin epoxidation and the subsequent ring opening through the addition of CH3OH. The epoxidation of styrene occurs through the hydrogen peroxide generated high valent Fe(IV) = O of the encapsulated Fe4SP while the corresponding ring opening and methanolysis takes place at the Cu metallo building blocks of the HKUST-1 framework. These results provide a framework through which to develop a more extensive library of bio-inspired heme-based MOF catalysts.

Triflic‐Acid‐Catalyzed Tandem Epoxide Rearrangement and Annulation with Alkynes: An Efficient Approach for Regioselective Synthesis of Naphthalenes

AbstractA facile triflic acid catalyzed method to synthesize 1‐arylnaphthalenes from one‐pot annulation reaction of arylepoxides and arylalkynes has been reported. The annulation reaction involves a successive epoxide to carbonyl rearrangement, electrophilic attack of carbonyl on arylalkyne followed by cyclization catalyzed by triflic acid. The present catalyst effects this transformation at room temperature itself.

Concise stereoselective and stereodivergent syntheses of (±)-melicolones A and B

The first total syntheses of the epimeric (±)-melicolones A and B, which are bioactive constituents isolated as racemates from the leaves of Melicope ptelefolia, were achieved in 12.3% combined overall yield. The divergent approach to these unusual natural products is remarkably concise and required a longest linear sequence of only nine steps (11 total steps) from commercially available starting materials. The significant synthetic challenge posed by the unique and densely functionalized polycyclic framework characteristic of the melicolones was addressed by a novel and highly regioselective (16:1) and diastereoselective (15:1) dipolar cycloaddition to deliver the oxabicycloheptane core. This pivotal reaction featured an innovative combination of an unsaturated vinylogous ester dipolarophile with a carbonyl ylide that was generated by an unusual cyclization of the carbonyl oxygen atom of an aliphatic aldehyde with a rhodium carbenoid. Stereoselective prenylation of the ketone enolate derived from this bicyclic core gave an intermediate that was processed via a one-pot O-demethylation cycloaldolization sequence to give the penultimate intermediate. The synthesis was completed by a bioinspired tandem epoxidation of the prenyl substituent followed by a regioselective, acid-catalyzed cyclization to deliver (±)-melicolones A and B. This approach may be applicable to the syntheses of other melicolones having a tetracyclic core.

Bifunctional Metal-Organic Layers for Tandem Catalytic Transformations Using Molecular Oxygen and Carbon Dioxide.

Tandem catalytic reactions improve atom- and step-economy over traditional synthesis but are limited by the incompatibility of the required catalysts. Herein, we report the design of bifunctional metal-organic layers (MOLs), HfOTf-Fe and HfOTf-Mn, consisting of triflate (OTf)-capped Hf6 secondary building units (SBUs) as strong Lewis acidic centers and metalated TPY ligands as metal active sites for tandem catalytic transformations using O2 and CO2 as coreactants. HfOTf-Fe effectively transforms hydrocarbons into cyanohydrins via tandem oxidation with O2 and silylcyanation whereas HfOTf-Mn converts styrenes into styrene carbonates via tandem epoxidation and CO2 insertion. Density functional theory calculations revealed the involvement of a high-spin FeIV (S = 2) center in the challenging oxidation of the sp3 C-H bond. This work highlights the potential of MOLs as a tunable platform to incorporate multiple catalysts for tandem transformations.

Total Syntheses of (±)-Melicolones A and B.

The first total syntheses of (±)-melicolones A and B, which have a unique and densely functionalized framework derived from a rearranged prenylated acetophenone, were accomplished in 12.3% combined overall yield. The concise and divergent synthesis of these two natural products, which were isolated in racemic form, was achieved in a longest linear sequence requiring only 9 steps (11 total steps) and 8 isolated intermediates using commercially available starting materials. This approach, which might enable access to all tetracyclic melicolones, features the highly regioselective (16:1) and diastereoselective (15:1) dipolar cycloaddition of a carbonyl ylide generated by the unusual cyclization of a rhodium carbene with the carbonyl oxygen atom of an aliphatic aldehyde. This cycloaddition proceeds with dominant steric control to give a highly functionalized oxabicycloheptane core. Stereoselective enolate alkylation led to a prenylated intermediate that underwent an intramolecular aldol reaction to give the penultimate tricyclic intermediate. Tandem epoxidation of the pendant prenyl group followed by a regioselective, acid-catalyzed cyclization delivered (±)-melicolones A and B.

Synthesis of fatty ketoesters by tandem epoxidation–rearrangement with heterogeneous catalysis

Fatty ketoesters are obtained from unsaturated fatty esters in a tandem two-step process with a combination of two heterogeneous catalysts, without intermediate purification and with maximum productivity of the catalysts through recycling and reuse.

Synthesis of (E)‐α,β‐Unsaturated Carbonyls via Silver‐Catalyzed Tandem Epoxide Rearrangement/Intermolecular Carbonyl‐ Heteroalkyne Metathesis

AbstractA regio‐ and stereoselective method for the synthesis of (E)‐α,β‐unsaturated carbonyls has been developed via a silver‐catalyzed tandem epoxide rearrangement/intermolecular carbonyl‐heteroalkyne metathesis. Various heteroalkynes including ynol ethers, ynamides, and thioalkynes work well for this transformation, leading to the production of (E)‐α,β‐unsaturated esters, amides, and thioesters in moderate to excellent yields with good functional group compatibility. It represents one of the rare examples of regio‐ and stereoselective intermolecular alkyne‐carbonyl metathesis (ACM).magnified image

ChemInform Abstract: Construction of Fused‐ and Spiro‐oxa‐[n.2.1] Skeletons by a Tandem Epoxide Rearrangement/Intramolecular [3 + 2] Cycloaddition of Cyclopropanes with Carbonyls.

A Lewis acid promoted tandem reaction of epoxide rearrangement and intramolecular [3+2] cycloaddition reaction of cyclopropanes with carbonyls formed by epoxide rearrangement in situ, which were obtained with difficulty by a general method, is reported. A wide variety of fused- and spiro-oxa-[n.2.1] skeletons could be efficiently constructed.

Construction of fused- and spiro-oxa-[n.2.1] skeletons by a tandem epoxide rearrangement/intramolecular [3+2] cycloaddition of cyclopropanes with carbonyls.

A Lewis acid promoted tandem reaction of epoxide rearrangement and intramolecular [3+2] cycloaddition reaction of cyclopropanes with carbonyls formed by epoxide rearrangement in situ, which were obtained with difficulty by a general method, is reported. A wide variety of fused- and spiro-oxa-[n.2.1] skeletons could be efficiently constructed.

ChemInform Abstract: Efficient Construction of Highly Substituted and Stereodefined cis‐Fused Lactones.

AbstractThe tandem epoxidation—ring opening of cyclic ene‐acetals, e.g. (I), (IX) or (XII), proceeds smoothly in the presence of NaBO3 to give 6α‐hydroxy‐bis‐acetal derivatives.

ChemInform Abstract: A Concise and Enantioselective Approach to Cyclobutanones by Tandem Asymmetric Epoxidation and Enantiospecific Ring Expansion of Cyclopropylidene Alcohols. An Enantiocontrolled Synthesis of (+)- and ( -)-α-Cuparenones.

A tandem Katsuli-Sharpless asymmetric epoxidation and enantiospecific ring expansion of 2-alkyl(or 2-aryl)-2-cyclopropylideneethanols (1a-i) afforded chiral 1-alkyl(or 1-aryl)-1-(hydroxymethyl)cyclobutanones (3a-i) in high yields and high enantiomeric excess. These compounds are potentially valuable synthons for the enantioselective creation of the quaternary carbons. Hence, this enabled us to accomplish a concise and enantioselective total synthesis of both (+)- and (-)-α-cuparenones

ChemInform Abstract: A Remarkable Substituent Effect on the Enantioselectivity of Tandem Asymmetric Epoxidation and Enantiospecific Ring Expansion of Cyclopropylidene Alcohols: A New Enantiocontrolled Synthesis of (-)- Debromoaplysin and (-)-Aplysin.

A remarkable substituent effect by the tert-butyldimethylsiloxy group on the enantioselectivity of the tandem asymmetric epoxidation and enantiospecific ring expansion of 2-[2-(tert-butyldimethylsiloxy)-4-methylphenyl]-2-cyclopropylideneethanol (18), affording (S)-(-)-2-[2-(tert-butyldimethylsiloxy)-4-methylphenyl]-2-hydroxymethylcyclobutanone (21) in high yield and high enantiomeric excess, was observed. This enabled us to accomplish a concise and highly enantioselective total synthesis of (-)-debromoaplysin (2) and (-)-aplysin (1), providing a new and general strategy for the enantioselective synthesis of biologically important substances having the dihydrobenzofuran framework

ChemInform Abstract: Ruthenium Porphyrin‐Catalyzed Aerobic Oxidation of Terminal Aryl Alkenes to Aldehydes by a Tandem Epoxidation—Isomerization Pathway.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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.

Ruthenium Porphyrin‐Catalyzed Aerobic Oxidation of Terminal Aryl Alkenes to Aldehydes by a Tandem Epoxidation–Isomerization Pathway

Catalytic oxidation of 1-alkenes to aldehydes by an epoxidation–isomerization pathway with air or dioxygen as terminal oxidant has been realized for bulky ruthenium(VI) porphyrin catalysts. For the new, recyclable catalyst [RuVI(tmttp)O2], product yields of up to 99 % and total turnover numbers of up to 1144 were obtained. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2008/z801500_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Ruthenium Porphyrin‐Catalyzed Aerobic Oxidation of Terminal Aryl Alkenes to Aldehydes by a Tandem Epoxidation–Isomerization Pathway

Die katalytische Oxidation von 1-Alkenen zu Aldehyden über eine Epoxidierung-Isomerisierung gelang mit Luft oder Disauerstoff als stöchiometrischem Oxidationsmittel in Gegenwart sperriger RuIV- oder RuVI-Porphyrin-Katalysatoren. Der wiederverwendbare Katalysator [RuVI(tmttp)O2] erreichte Produktausbeuten von 99 % bei Umsatzzahlen bis 1144. tmttp=1,3,5,7-Tetramethyl-2,4,6,8-tetraterphenylporphyrinato-Dianion.

ChemInform Abstract: A Novel Synthesis of γ‐Lactones by Tandem Epoxide Opening‐Cyclization Reaction Mediated by Samarium(II) Diiodide.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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.

A novel synthesis of γ-lactones by tandem epoxide opening-cyclization reaction mediated by samarium(II) diiodide

Various epoxy esters readily reacted with SmI 2 (2 equiv) in the presence of ethyl bromoacetate (1 equiv) and HMPA (6 equiv) under mild conditions (THF, −78 °C, 2 h, Ar) providing the corresponding γ-lactones via tandem epoxide opening-cyclization reaction in good to excellent yields.