Oxime O-methyl Ethers Research Articles

A New Route to α-Carbolines Based on 6π-Electrocyclization of Indole-3-alkenyl Oximes

Indoles are converted into α-carbolines in four steps by acylation at C-3, Boc-protection, olefination of the resulting 3-indolyl aldehydes or ketones to give N-Boc-3-indolyl alkenyl oxime O-methyl ethers, which upon heating to 240 °C under microwave irradiation undergo loss of the Boc-group, and 6π-electrocyclization to α-carbolines, following aromatization by loss of methanol (11 examples, 30–90% yield).

Phenylacetaldehyde O-Methyloxime: A Volatile Compound Produced by Grapefruit Leaves Infected with the Citrus Canker Pathogen, Xanthomonas axonopodis pv. citri

An aldehyde oxime O-methyl ether, phenylacetaldehyde O-methyloxime, was detected using solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS) in the headspace above grapefruit leaves infected with Xanthomonas axonopodis pv. citri, the causal agent of citrus bacterial canker disease (CBCD). This disease is a major phytosanitary concern, and an eradication campaign against it is currently underway in Florida. Phenylacetaldehyde O-methyloxime has been reported to be produced by other plants and fragrant flowers, but it was not observed in the headspace above uninfected grapefruit leaves, the pathogenic bacterium X. axonopodis pv. citri itself, or grapefruit leaves infected with another closely related bacterial pathogen, X. axonopodis pv. citrumelo, which causes citrus bacterial spot, a disease of no phytosanitary significance. It was also not detected from CBCD infected fruits, including orange, lemon, grapefruit, and lime. We conclude that phenylacetaldehyde O-methyloxime may potentially be used to identify CBCD infestations. However, more intensive studies will be required to fully evaluate the potential of phenylacetaldehyde O-methyloxime as a diagnostic compound for CBCD. Using SPME and GC-MS to measure phenylacetaldehyde O-methyloxime may provide an easy and feasible tool to complement current methods used to detect X. axonopodis pv. citri in environmental samples.

One-Way and Two-Way Geometrical Isomerizations of 1, 1-Diarylketone Oxime O-Methyl Ethers Induced by Photosensitized Electron Transfer

Under an oxygen atmosphere, the E and Z isomer ratio of N-methoxy-4-methoxyphenyl-4'-methylphenylmethanimine (one of the title compounds; initially, ⌈E⌉/⌈Z⌉ = 1/1) reached to 4/96 upon irradiation (> 360 nm) of 9, 10-dicyanoanthracene (DCA) as a photosensitizer in acetonitrile. Key intermediate is presumed to be a putative distonic radical cation which is a unique one having a spatially separate radical and ionic centers on the molecular framework. The whole scenario of the reaction was supported by molecular orbital calculations. An excited singlet state of DCA generated by light absorption was quenched by oxime ethers to give the DCA anion radical and radical cations of E- and Z-oxime ethers. Then the subsequent single electron transfer from the DCA anion radical to molecular oxygen generates superoxide anion radical, which reacted with distonic radical cations of E- and Z-oxime ethers bya ⌈supra + antara⌉ manner. Geometry selection occurs at a stage of just making a new bond between nitrogen and oxygen terminals in the ensuing peroxyaminy1-1,4-diradical. The final oxime ether is afforded by releasing molecular oxygen without successful single bond formation. Instead, ring closure to azadioxetane gives rise to formation of byproducts, benzophenones and methyl nitrite, by decomposion of it in a metathesis fashion.

Conceptually new low-calcemic oxime analogues of the hormone 1 alpha,25-dihydroxyvitamin D(3): synthesis and biological testing.

New chemical entities 16-ene-25-ketone 2b and the corresponding oxime 3b and oxime ether 4b, analogues of natural calcitriol (1), were rationally designed and synthesized on a milligram scale. Chemical introduction of the oxime ether functionality in analogue 4b was successful via direct oximation of an intact vitamin D conjugated triene system. Even though all three analogues are at least as antiproliferative in vitro as calcitriol (1) even at physiologically relevant low nanomolar concentrations, only side chain ketone 2b is more transcriptionally potent than calcitriol (1). Although oxime O-methyl ether 4b lacks the traditional side chain hydrogen bond-donating OH group of the natural hormone and lacks also the oxime-NOH group of analogue 3b, surprisingly, oxime ether 4b retains 20% of the transcriptional potency of natural calcitriol (1). In terms of in vivo toxicity (hypercalcemia), ketone 2b is strongly calcemic in rats, whereas oxime 3b and oxime ether 4b are considerably less calcemic (i.e., safer) than calcitriol (1).

Design and synthesis of chemiluminescent substrates with high luminescent efficiency in an aqueous system: 5-tert-butyl-4,4-dimethyl-2,6,7-trioxabicyclo[3.2.0]heptanes bearing a 3-hydroxy-4-(1-iminoethyl)phenyl moiety at the 1-position.

A CIEEL-active dioxetane bearing a 4-acetyl-3-hydroxyphenyl moiety has very recently been found to emit light effectively, even in an aqueous system, albeit with a very slow CIEEL decay rate. As an attempt to improve the CIEEL decay rate of this type of dioxetane, three dioxetanes, in which a carbonyl in the 4-acetyl-3-hydroxyphenyl moiety was modified into an oxime, oxime O-methyl ether, or semicarbazone, were synthesized. These three dioxetanes decomposed to emit light far more rapidly than the parent 4-acetyl-3-hydroxyphenyl-substituted dioxetane. Among them, a dioxetane bearing a 3-hydroxy-4-(1-methoxyiminoethyl) phenyl, namely an oxime O-methyl ether derivative, gave high chemiluminescent efficiency. As for a semicarbazone derivative, decrease of the chemiluminescent yield was minimal, even in an aqueous system.

Curious oxygen effect on photosensitized electron-transfer reactions of benzophenone oxime O-methyl ethers: one-way photoisomerization of an iminic double bond

Under an oxygen atmosphere, the E and Z isomer ratio of N-methoxy-4-methoxyphenyl-4′-methylphenylmethanimine (initially, [ E]/[ Z]=1/1) reached 4/96 upon irradiation (>360 nm) of 9,10-dicyanoanthracene (DCA) as a photosensitizer in acetonitrile.

Gas phase chemistry of nitrogen containing negative ions: deprotonated nitromethane, acetone oxime, and acetone oxime o-methyl ether

The ion [CH 2NO 2] − is a weak base, a poor nucleophile and a weak oxidising agent. It is unable to oxidise COS but does react with CS 2 by the reaction [CH 2NO 2] − + CS 2 → CS 2O −· + [CH 2NO] ·. Deprotonated acetone oxime [Me 2CNO] − is a moderate gas phase oxidising agent reacting with COS, CS 2 and SO 2 to yield CO 2S −·, CS 2O −· and SO −· 3 respectively. Δ H ∘ acid of (CH 3) 2CNOMe is bracketted at 1560±15 kJ mol −1; the deprotonated species forms addition complexes with CO 2, CS 2, COS and SO 2.

Pyrolysis of Aryl Azides. IX. Azomethines as Weak Neighboring Groups

The following rates of pyrolysis (relative to azidobenzene at 120°) have been measured in decalin solution: 2-azidobenzaldehyde, 28.8; 2-azidobenzylideneaniline, 59.5; 2-azidobenzaldehyde phenylhydrazone, 8.9; 2-azidobenzaldehyde oxime O-methyl ether, 1.3;2-azidoacetophenone oxime O-methyl ether, 23.4; 2-azidobenzophenone phenylhydrazone, 9.7. It is argued that these relative rates are largely determined by the extent to which the ortho substituent is in the reactive conformation for an electrocyclic process. Indazoles substituted on N2 are isolated from pyrolysis of those azides with ortho-azomethine substituents.

Stereoselective synthesis of trans-2-aryl-3-(2-pyridyl)aziridines from an α-silyl carbanion

Five para-substituted benzaldehyde oxime O-methyl ethers (3)[Ar = phenyl, p-chlorophenyl, p-tolyl, p-methoxyphenyl, p-(N,N-dimethylamino)phenyl] reacted with 2-(trimethylsilylmethyl)pyridine (1) in the presence of lithium di-isopropylamide (LDA) in tetrahydrofuran to give the corresponding trans-2-aryl-3-(2-pyridyl)aziridines (4) in high yield (80, 85, 60, 58; and 74%, respectively), with small amounts of (Z)-1-amino-1-aryl-2-(2-pyridyl)ethenes (5), and N′,N′-di-isopropylbenzamidines (7) as by-products. The yields of compounds (4) and (5) and their ratio [(4) : (5)] were considerably influenced by experimental conditions (especially molar ratio and the addition method, of the reactants). When treated with LDA, compounds (3) were quantitatively converted into benzonitriles, which reacted, with anion (2) to give enamines (5) after elimination of a trimethylsilyl group from the corresponding N-trimeihylsilyl derivatives, or with additional LDA to give the benzamidine (7); aziridines (4) were not transformed into enamines (5) by the action of LDA. On the basis of these results, a reaction mechanism has been discussed for the formation of compounds (4).

Photochemistry of the carbon–nitrogen double bond. Part 1. Carbon–nitrogen vs. carbon–carbon double bond isomerisation in the photochemistry of α,β-unsaturated oxime ethers: the benzylideneacetone oxime O-methyl ether system

The syntheses of the four benzylideneacetone oxime O-methyl ether isomers (2)–(5) are described. Direct or sensitised irradiation of the E,E-isomer (2) or Z,E-isomer (3) leads to equilibration of all four isomers by a combination of rapid carbon–nitrogen double bond isomerisation and slower carbon–carbon double bond isomerisation. A previous investigation of the photochemistry of the E,E-isomer (2) had reported only carbon–carbon double bond isomerisation.

The Reactions of Singlet NH Radicals with Methyl and Ethyl Alcohols in the Liquid Phase

Abstract The reactions of the singlet NH(a1Δ) radicals with alcohols were studied by the photolyses of hydrogen azide in liquid methyl and ethyl alcohols at the temperature of Dry Ice–methyl alcohol and at 0 °C. The main products were nitrogen, ammonia, and oxime ethers; acetaldehyde oxime O-ethyl ether from ethyl alcohol and formaldehyde oxime O-methyl ether from methyl alcohol. The relative yields of the products were independent of the changes in the reaction temperature and in the concentration of the hydrogen azide examined. Methoxyamine or ethoxyamine, a possible insertion product of the singlet NH into the O–H bond of alcohol, was detected as a form of oxime ether by the reactions with the aldehyde eventually formed. It was concluded that the singlet NH radicals can effectively insert into the O–H bond of the alcohol.

ChemInform Abstract: EXCLUSIVE SYN‐AXIAL ALKYLATION OF O‐METHYL OXIMES RESULTING FROM AN ORBITAL SYMMETRY EFFECT

AbstractDurch Lithiierung des O‐Methyl‐oxims (I) mit Lithiumdiisopropyamid bei ‐78°C in Tetrahydrofuran in Gegenwart von Hexamethylphosphorsäuretriamid und anschließende Methylierung erhält man in stereoselektiver Weise das Methylderivat (II), das beim Erhitzen in Hexachlorbutadien zu den Isomeren (III) und (IV) führt.

Exclusive syn-axial alkylation of O-methyl oximes resulting from an orbital symmetry effect

Lithiation and subsequent methylation of several conformationally fixed oxime O-methyl ethers has been shown to give only one product resulting from axial attack at the α-carbon atom syn to the oxygen atom.

Structural studies by nuclear magnetic resonance—XVII : Conformations and configurations of N-methylhydrazones

Conformations and configurations were assigned to several aliphatic N-methylhydrazones from analysis of their 60-Mc NMR spectra. Interpretation of the vicinal spin-spin coupling constants, J H 1Hα , of the syn isomers (N-methylamino cis to hydrogen) of the aldehyde N-methylhydrazones in terms of rotamers I and II gave ΔH° values that are similar to those found in hydrazones, oximes, and oxime O-methyl ethers. The anisotropic effects of the CN double bond, the association between solute and solvent, several aspects of the chemical shifts, and other problems related to configurational isomerism about the CN double bond are discussed.

Structural studies by nuclear magnetic resonance—XI: Conformations and configurations of oxime o-methyl ethers

Conformations and configurations were assigned to several aldehyde and ketone oxime O methyl ethers from analysis of their 60-Mc. NMR spectra. Interpretation of the data from the cis-isomers (methoxy cis to hydrogen) of the aldehyde derivatives in terms of rotamers I and II, whereby a single bond eclipses the double bond, led to the following conclusions: For α-mono-substituted derivatives, when R was varied from methyl to t-butyl, ΔH° for I → II varied from +390 to +4,5000 cal/mole. A similar range was obtained for α,α,-disubstituted derivatives. Interpretation of the data from the trans-isomers led to the conclusion that, whereas I is the only significant rotamer for α,α-disubstituted derivatives, for α-mono-substituted I and III are equally important.