‘Reductive ozonolysis’ via a new fragmentation of carbonyl oxides

This account describes the development of methodologies for ‘reductive’ ozonolysis, the direct ozonolytic conversion of alkenes into carbonyl groups without the intermediacy of 1,2,4-trioxolanes (ozonides). Ozonolysis of alkenes in the presence of DMSO produces a mixture of aldehyde and ozonide. The combination of DMSO and Et₃N results in improved yields of carbonyls but still leaves unacceptable levels of residual ozonides; similar results are obtained using secondary or tertiary amines in the absence of DMSO. The influence of amines is believed to result from conversion to the corresponding N-oxides; ozonolysis in the presence of amine N-oxides efficiently suppresses ozonide formation, generating high yields of aldehydes. The reactions with amine oxides are hypothesized to involve an unprecedented trapping of carbonyl oxides to generate a zwitterionic adduct, which fragments to produce the desired carbonyl group, an amine, and ¹O₂.     

Catalytic Intramolecular Palladium-Ene Reactions. Preliminay Communication

Pd(dba)₂[dba = dibenzylideneacetone]/PPh₃-or Pd(PPh₃)₄-catalyzed cyclizations of acetoxy-dienes 2 → 3 and 10 → 11 gave 1-vinyl-2-methylidene-subsituted cyclopentances and cyclohexanes in high yield, consistent with a palladium-ene/β-elimination mechanism ( D → E → F , Scheme 2). The efficient and highly stereoselective cyclizations 7 → 7 and 8 → 9 illustrate intramolecular allylpalladium insertions into 1,2-dialkyl-, trialkyl-, trialkyl-, and cyclic alkenes followed by elimination of the exocyclic β–H giving 1,2-divinylcyclopentanes. These new olefin insertions proceed faster in AcOH (compared to THF) and occur preferentially cis relative to the Pd ( 13 → 14 → 15 ).     

Synthesis of oximes,conversion to nitrile oxides and their subsequent 1,3-dipolar cycloaddition reactions under microwave irradiation and solvent-free reaction conditions

Aldoximes and ketoximes were readily synthesized from aldehydes and hydroxylamine hydrochloride on Al₂O₃ without solvent under microwave irradiation. At higher irradiation power, aldoximes dehydrated to nitriles and ketoximes rearranged to amides. Aldoximes reacted in a one-pot reaction with N-chlorosuccinimide and alkenes or alkynes over alumina under microwave irradiation to give isoxazolines or isoxazoles. © 1998 John Wiley & Sons, Inc. Heteroatom Chem 9:351–354, 1998     

Metal triflate catalyzed highly regio- and stereoselective 1,2-bromoazidation of alkenes using NBS and TMSN3 as the bromine and azide sources

Metal triflate catalyzed 1,2-bromoazidation of alkenes was performed using N-bromosuccinimide (NBS) and trimethylsilyl azide (TMSN₃) as the bromine and azide sources, respectively. Among the metal triflates, Zn(OTf)₂ was found to be the best catalyst. This catalytic process represents a highly regioselective, stereoselective and high yielding method for the synthesis of anti-1,2-bromoazides from a variety of alkenes including α,β-unsaturated carbonyl compounds.     

Radical promoted cyclizations of aromatic carbonyl compounds to benzopyrans using titanocene(III) chloride

Aromatic carbonyl compounds undergo smooth intramolecular radical cyclization with alkenes or alkynes using titanocene(III) chloride to furnish the corresponding benzopyrans. The radical initiator, Cp₂TiCl, was prepared in situ from commercially available titanocene dichloride (Cp₂TiCl₂) and zinc dust in THF under argon.     

FeCl3‐Catalyzed Ring‐Closing Carbonyl–Olefin Metathesis

Exploiting catalytic carbonyl–olefin metathesis is an ongoing challenge in organic synthesis. Reported herein is an FeCl₃‐catalyzed ring‐closing carbonyl–olefin metathesis. The protocol allows access to a range of carbo‐/heterocyclic alkenes with good efficiency and excellent trans diastereoselectivity. The methodology presents one of the rare examples of catalytic ring‐closing carbonyl–olefin metathesis. This process is proposed to take place by FeCl₃‐catalyzed oxetane formation followed by retro‐ring‐opening to deliver metathesis products.     

Formation yields of epoxides and O(3P) atoms from the gas-phase reactions of O3 with a series of alkenes

Reactions of ozone with propene, 1-butene, cis-2-butene, trans-2-butene, 2,3-dimethyl-2-butene, and 1,3-butadiene were carried out in N₂ and air diluent at atmospheric pressure and room temperature and, by monitoring the formation of the epoxides and/or a carbonyl compound formed from the reactions of O(³P) atoms with these alkenes, the formation yields of O(³P) atoms from the O₃ reactions were investigated. No evidence for O(³P) atom formation was obtained, and upper limits to O(³P) atom formation yields of <4% for propene, <5% for 1.3-butadiene, and <2% for the other four alkenes were derived. The reaction of O₃ with 1,3-butadiene led to the direct formation of 3,4-epoxy-1-butene in (2.3 ± 0.4)% yield. These data are in agreement with the majority of the literature data and show that O(³P) atom formation is not a significant pathway in O₃—alkene reactions, and that epoxide formation only occurs to any significant extent from conjugated dienes. © 1994 John Wiley & Sons, Inc.     

A Bis(silylenyl)pyridine Zero‐Valent Germanium Complex and Its Remarkable Reactivity

The synthesis, reactivity, and electronic structure of the unique germylone iron carbonyl complex [SiNSi]Ge⁰ →Fe(CO)₄ is reported. The compound was obtained in 49 % yield from the reaction of the bis(N‐heterocyclic silylenyl)pyridine pincer ligand SiNSi (1,6‐C₅NH₃‐[EtNSi(N^tBu)₂CPh]₂) with GeCl₂?(dioxane) to give the corresponding chlorogermyliumylidene chloride precursor [SiNSi]Ge^IICl⁺ Cl^? , which was further reduced with K₂Fe(CO)₄. Single‐crystal X‐ray diffraction analysis of [SiNSi]Ge →Fe(CO)₄ revealed that the Ge⁰ center adopts a trigonal‐pyramidal geometry with a Si‐Ge‐Si angle of 95.66(2)°. Remarkably, one of the Si^II donor atoms in the complex is five‐coordinated because of additional (pyridine)N→Si coordination. Unexpectedly, the reaction of [SiNSi]Ge →Fe(CO)₄ with GeCl₂?(dioxane) (one molar equivalent) yielded the first push–pull germylone–germylene donor–acceptor complex, [SiNSi]Ge →GeCl₂→Fe(CO)₄ through the insertion of GeCl₂ into the dative Ge⁰→Fe bond. The electronic features of the new compounds were investigated by DFT calculations.     

Iridium-catalyzed carbonyl group-directed oxidative coupling of arenes with alkenes

The iridium complex [Cp¹IrCl₂]₂ is a good catalyst for the directed oxidative coupling of arenes with alkenes; a wide range of carbonyl functionalities (NHCOR, CONH₂ and COR) can be employed as the directing group.     

Multi-wall carbon nanotube supported tungsten hexacarbonyl: an efficient and reusable catalyst for epoxidation of alkenes with hydrogen peroxide

Highly efficient epoxidation of alkenes with H₂O₂ catalyzed by tungsten hexacarbonyl supported on multi-wall carbon nanotubes (MWCNTs) modified with 1,2-diaminobenzene is reported. The prepared catalyst, [W(CO)₆@DAB-MWCNT], was characterized by elemental analysis, scanning electron microscopy, FT-IR, and diffuse reflectance UV-Vis spectroscopic methods. The prepared catalyst was applied as an efficient catalyst for green epoxidation of alkenes with hydrogen peroxide in CH₃CN. This heterogeneous metal carbonyl catalyst showed high stability and reusability in epoxidation without loss of its catalytic activity.     

A new ruthenium-catalyzed cyclopropanation of alkenes using propargylic acetates as a precursor of vinylcarbenoids

[RuCl₂(CO)₃]₂ catalyzes intermolecular cyclopropanation of various alkenes with propargylic acetates to give vinylcycloropanes in good yields. The key intermediate of this reaction is a vinylcarbene complex generated by nucleophilic attack of the carbonyl oxygen of the acetate to an internal carbon of alkyne activated by the ruthenium complex.     

Synthesis of nitrogen-containing heterocycles. 3. Formation and structure of new 1,2,4-triazole derivatives

Treatment of N(3)-[(2-cyano-2-ethoxycarbonyl)vinyl]amino-N(4),N(4)-dimethylaminomethylenehydrazones of aromatic carbonyl compounds with hot acetic acid resulted in the formation of symmetrical gem-bis-(3-dimethylamino-1,2,4-triazol-1-yl)methanes, (3-dimethylamino-1,2,4-triazol-1-yl)arylmethyl acetates, and (3-dimethylamino-1,2,4-triazol-1-yl)alkenes of a gem-diaryl type depending upon whether the carbonyl compound was aldehyde or ketone.     

Ruthenium-catalysed transfer hydrogenation reactions with dimethylamine borane

Dimethylamine-borane adduct has been used as the hydrogen source for the reduction of carbonyl compounds, imines, oximes, nitriles, nitroarenes and alkenes using [Ru(p-cymene)Cl₂]₂ as the catalyst.     

Direct C−C Double Bond Cleavage of Alkenes Enabled by Highly Dispersed Cobalt Catalyst and Hydroxylamine

The utilization of a single-atom catalyst to break C−C bonds merges the merits of homogeneous and heterogeneous catalysis and presents an intriguing pathway for obtaining high-value-added products. Herein, a mild, selective, and sustainable oxidative cleavage of alkene to form oxime ether or nitrile was achieved by using atomically dispersed cobalt catalyst and hydroxylamine. Diversified substrate patterns, including symmetrical and unsymmetrical alkenes, di- and tri-substituted alkenes, and late-stage functionalization of complex alkenes were demonstrated. The reaction was successfully scaled up and demonstrated good performance in recycling experiments. The hot filtration test, catalyst poisoning and radical scavenger experiment, time kinetics, and studies on the reaction intermediate collectively pointed to a radical mechanism with cobalt/acid/O₂ promoted C−C bond cleavage as the key step.     

Organic base catalyzed carbonyl allylation of methyl trifluoropyruvate with activated alkenes

The carbonyl allylation of methyl trifluoropyruvate (MeTFP) with activated alkenes has been investigated in detail using organic bases as catalysts. Organic bases, such as DMAP, Et₃N, DABCO, NMM, Et₂NH, and quinine, could deprotonate the allylic hydrogen of activated alkenes and furnish nucleophilic species to undergo the addition reaction with methyl trifluoropyruvate and afford versatile homoallylic alcohols with CF₃ group in excellent yields. The ¹⁹F NMR monitoring indicated that the isomerization induced by base gave two separable diastereoisomers in an equilibrium ratio of 1:3. The relative configuration of hydroxy and the neighboring alkyl group in the major diastereoisomer was determined as syn-configuration by X-ray diffraction analysis.     

Antibacterial activity of a triterpenoid saponin from the stems of Caesalpinia pulcherrima Linn.

A new compound 1 was isolated from the methanolic extract of the stems of the Caesalpinia pulcherrima Linn. along with a reported compound (2) 3-O-β-D-glucopyranosyl-(1→4)-β-D-xylopyranosyl-(1→3)-α-L-rhamnopyranosyl-(1→2)-α-L-arabinopyranosyl hederagenin 28-O-β-D-glucopyranosyl-(1→6)-β-D-glucopyranosyl ester. The new compound 1 has m.p. 272–274°C, m.f. C₄₆H₇₄O₁₇, [M]⁺ m/z 898. It was characterised as 3-O-β-D-glucopyranosyl-(1→4)-α-L-arabinopyranosyl hederagenin 28-O-β-D- xylopyranosyl ester by various colour reactions, chemical degradations and spectral analyses. Antibacterial activity of compound 1 was screened against various Gram-positive and Gram-negative bacteria and showed significant results.     

On the reactions of alkylsulfonyl and perfluoroalkylsulfonyl fluorides with hydroxylamines and hydrazines

Sulfonic acid chlorides react with hydroxylamine to form predominantly N-substituted products [1].Sulfonic acid fluorides react with hydroxylamine by formation of N-mesylhydroxylamine, hydrazinium(1+) and hydroxylammonium mesylate [2]. R_fSO₂F (R_f = C₄F₉, C₈F₁₇) reacting in the same way as CH₃SO₂F [3], the latter is considered to be a model compound for this kind of reactions.

The formation of the hydrazinium salt is explained by the occurrence of O-mesylhydroxylamine as intermediate. We conclude from the yields that sulfonic acid fluorides react with hydroxylamine to form predominantly O-substituted products.In order to prepare this O-derivative the reaction between O-(trimethylsilyl)hydroxylamine and mesylfluoride was carried out. Hydrazinium mesylate could be isolated also, which indicates the formation of the instable O-derivative.The reactions of methylhydrazines and silylated hydrazines with mesylfluoride lead to mesylated products as expected.     

N-Phenylselenosaccharin (NPSSac): a new electrophilic selenium-containing reagent

A new reagent N-phenylselenosaccharin (NPSSac) was simply prepared and used as a source of the electrophilic phenylselenyl group. This relatively stable new compound was able to react with a series of electron rich organic molecules like alkenes in the presence of external or internal nucleophiles, activated aromatic substrates, or enolizable carbonyl derivatives, under very mild experimental conditions.     

β-substituted alkyltin halides : I. Monoalkyltin trihalides: Synthetic,mechanistic and spectroscopic aspects

HSnCl₃(Et₂O)₂ reacts with a variety of α,β-unsaturated carbonyl compounds to give high yields of β-substituted organotin compounds. The hydrostannation proceeds under a wide variety of conditions. Temperatures between approximately ?30 and 120°C can be employed. Ethereal solvents can be used but are not essential, since monomer solvation of HSnCl₃ (M → HSnCl₃) can occur in non-ethereal media. Intramolecular carbonyl coordination to tin occurs in these β-substituted organotin compounds.     

A theoretical study of the reactions of carbonyl oxide with water in atmosphere: the role of water dimer

Carbonyl oxide is a well-known intermediate formed in gas-phase reactions of ozone with alkenes. Secondary reactions of carbonyl oxide are suggested to lead to the formation of HO, H₂O₂ and organic peroxides in the atmosphere. We performed a theoretical study of reactions of carbonyl oxide with water and a water dimer. Using CCSD(T)/6-311+G(2d,2p)//B3LYP/6-311+G(2d,2p) calculations we found that the most energetically favourable channel is the formation of hydroxymethyl hydroperoxide (HMHP) as the result of reactions of carbonyl oxide with the water dimer. The potential importance of water dimer reactions in the chemistry of the troposphere is discussed herein.