Massenspektrometrische Untersuchung von Amiden. VIII—Vinyloge α-Spaltung und Nachbargruppenbeteiligung bei der Fragmentierung von Piperididen α,β-ungesättigter Carbonsäuren

The electron-impact-induced fragmentation of piperidides from β-substituted α, β-unsaturated carboxylic acids proceeds preferentially via 4-membered cyclic transition states. The development of a 6-membered ring, which is typical for α,β-unsaturated esters, occurs only to a minor extent. The mechanism of the reaction is best rationalised by the assumption of a vinylogous α-cleavage and a simultaneous neighbouring group participation of the amide function     

α,β-Epoxyketon → Alkinon-Fragmentierung II: Pyrolytischer Zerfall der Hydrazone aus α,β-Epoxyketonen und N-Amino-aziridinen. Über synthetische Methoden, 4. Mitteilung

Numerous examples illustrate the course of the thermolysis of hydrazones derived from α,β-epoxyketones and 2-phenyl- or trans-2,3-diphenyl-1-amino-aziridines. This process constitutes a preparatively useful method for the fragmentation of α,β-epoxyketones to acetylenic carbonyl compounds including acetylenic aldehydes. Monohydrazones from phenylglyoxal and substituted N-amino-aziridines decompose smoothly and stereospecifically to the corresponding olefins and diazoacetophenone; such a process might also be useful for the preparation of other α-diazocarbonyl compounds.     

Photochemische Reaktionen. 82. Mitteilung. Zur Photochemie der α,β-Epoxylketone: γ-Wasserstoffabstraktion versus Epoxyketon-Umlagerung

Photochemistry of α,β-epoxyketones: γ-H-abstraction versus epoxyketone-rearrangement. The photochemical behaviour of conformationally mobile α,β-epoxyketones that could undergo competing reactions has been studied. The UV.-irradiation of 5 yields the stereoisomeric cyclobutanols 9 and 10 as well as the fragmentation product 11 . Irradiation of 6 gives only the cyclobutanols 12 and 13 , whereas 4 and 8 in inert solvents yielded only intractable gums. The non-occurrence of the typical isomerization of α,β-epoxylketones to the corresponding β-diketones is attributed to steric factors.     

Fragmentierung von α,β-Epoxy-ketoximen zu Acetylenketonen. Vorläufige Mitteilung

A new version of the oxidoketone-alkynone fragmentation is described. Two steroidal α,β-oxido-oximes are shown to fragment to the corresponding alkynones when treated with hydroxylamine-O-sulfonic acid in alcaline solution at room temperature.     

Eine neue Version der Epoxyketon → Alkinon-Fragmentierung: Thermischer Zerfall der Hydrazone aus α,β-Epoxycarbonyl-verbindungen und N-Amino-aziridinen. Vorläufige Mitteilung

A new version of the epoxyketone → alkynone fragmentation is described. Hydrazones derived from cyclic α,β-epoxy-ketones and N-amino-aziridines decompose thermally into molecular nitrogen, an olefinic fragment and an acetylenic carbonyl compound (compare scheme 1). The reaction of phenylglyoxal with N-amino-phenyl-aziridine at room temperature produces styrene and diazo-acetophenone in high yield (compare scheme 3).     

High-resolution mass spectra of two α,β-unssaturated γ-dilactones

The fragmentations of two α,β-unsaturated γ-dilactones in a mass spectrometer are studied. The main feature is conecutive carbon monoxide expulsions. Strong indication of ejection of a fragment C₂O₂ is presented, however. Masses were determined by the high resolution rechnique and metastable transitions were detected by defocusing. Corresponding deuterated dilactones were also studied to verify the fragmentation mechanism.     

Studies in organic mass spectrometry-XIII: Investigation of electron-induced isomerisation of αβ- and βγ-unsaturated esters

The mass spectral fragmentation of methyl esters of α,β- and β,γ-unsaturated carboxylic acids has been studied. Deuterium labelling, metastable ion analysis and high resolution mass spectrometry have been utilised to elucidate the mechanism of a number of fragmentations and to check possible double bond migration prior to fragmentation. Some breakdown modes were found to occur through double bond migration. Additional support was provided by application of the ‘Metastable Ion Characteristics’ method. Partial isomerisation of molecular ions must therefore be accepted.     

Chelate von β-Dicarbonylverbindungen und ihren Derivaten. XV. Komplexchemische Reaktivität von β-Mercaptovinylaldehyden

The reactivity of α-phenyl-β-mercaptocinnamaldehyde and α-(2-pyridyl)-β-mercaptocinnamaldehyde towards thiophilic metals was studied and some complexes of nickel, cobalt, copper, palladium, zinc, lead and mercury with these ligands were prepared. The chemical bonding in the complexes was examined by IR spectroscopy. The reaction of the Bis(α-phenyl-β-mercaptocinnamaldehydato)-nickel with amines gave the corresponding aldimine chelates, by the action of hydrogen sulfide the nickel chelate of α-phenyl-β-mercaptocinnamthioaldehyde was formed.     

α-Silyl ketones: A high resolution mass spectrometric study

The mass spectrometric fragmentation modes of a series of α-silyl phenyl ketones are reported. For comparison, the fragmentation modes of the analogous silanol and α,β-epoxysilane are also reported. Migration of phenyl moieties to silicon is common throughout the ketone series.     

The high resolution mass spectra of α,β-unsaturated and α-chloromercuri-α,β-unsaturated steroidal ketones

The high resolution mass spectra (500 eV) of some α,β-unsaturated steroidal ketones have been studied and compared with the spectra of the corresponding α-chloromercuri ketones. In the latter, the carbon-mercury bond frequently remains intact at the expense of the fission of two carbon-carbon bonds. The abundance of mercury-containing ions allows the use of the mercury atom fingerprint in confirming ring B fragmentation of the steroid nucleus at C(6)–C(7) and C(9)–C(10) for 5α-androst-1-ene-3,17-dione, 1,4-androstadiene-3,17-dione and their 2-chloromercuri derivatives; and at C(7)–C(8) and C(9)–C(10) for 1,4,6-androstatriene-3,17-dione, 1,4,6-androstarien-17 β-ol-3-one and their 2-chloromercuri derivatives. 2-Chloromercuri-1,4,6-androstatriene-3,17-dione and 2-chloromercuri-1,4,6-androstatrien-17 β-ol-3-one also give an abundant ion as the result of ring C fragmentation at C(8)–C(14) and C(11)–C(12), the chloromercuri group being replaced by a hydrogen atom. This ring C cleavage gives the only recognizable distinctive fragmentation ion for 1,4,6-pregnatriene-3,20-dione and 2-chloromercuri-1,4,6-pregnatriene-3,20-dione. For most of the mercurated steroids, the low resolution mass spectra (70 eV) are reported. In these spectra, the fragmentation patterns are similar to those obtained using the higher ionization energy employed for the high resolution spectra.     

Säurekatalysierte Isomerisierung von α,β-Cyclopropyl-oxiranen

Using the epoxycarane derivatives 3 and 6 , the behaviour of α,β-epoxycyclopropy. compounds in the presence of acids has been examined and the main reaction products elucidated Proposals for the reaction mechanism are made.     

A novel synthesis of α,β-unsaturated phosphonates

A stereoselective synthesis of α,β-unsaturated phosphonates based on the reaction of S-(β-oxoalkyl)-dithiophosphates and Se-(β-oxoalkyl)selenophosphates with sodium dialkyl phosphites is described.     

Conjugate addition of grignard reagents to N-(α,β-unsaturated)acylpyrazoles. Diastereoselective β-alkylation using 3-phenyl-l-menthopyrazole

The conjugate additions of N-(α,β-unsaturated)acylpyrazoles were carried out by the treatment with Grignard reagents in the presence of cuprous halides. The reaction of 2-(α,β-unsaturated)acyl-3-phenyl-l-menthopyrazoles 3a-h occurred in higher chemical yields and with asymmetric inductions on β-position, where the addition of magnesium bromide as a Lewis acid influenced to the yields and the diastereoselectivities. In the case of α-methylated 2-(α,β-unsaturated)acyl-3-phenyl-l-menthopyrazoles 3i-n , the excellent asymmetric induction on the α-position was also observed through the diastereofacial protonation.     

Beckmann-Umlagerung und Fragmentierung,IV. Teil. 5- und 7-Zentren-Fragmentierung von γ-Keto-ketoximen: Fragmentierungsreaktionen, 21. Mitteilung

A heterolytic 7-centre fragmentation reaction of the type a-b-c-d-e-f-X → a b + c = d + e = f + X has been demonstrated for the first time utilizing γ-keto-ketoximes. This system may also undergo a novel 5-centre fragmentation. With sodium hydroxide in aqueous ethanol and with sodium ethoxide in ethanol the p-toluene-sulfonate of 1-oxo-9-methyl-5-oximino-trans-decalin (7b) is converted quantitatively into 9-cyano-6-methyl-non-5-enoic acid (10b) and the corresponding ethyl ester, respectively. With lower concentrations of nucleophile normal Beckmann rearrangement to the lactam 13a and the lactimether 19b predominates. In the case of the p-toluenesulfonate of the 9-nor-derivative 7a a base-induced 5-centre fragmentation reaction to the α,β-unsaturated ketone 12 competes with 7-centre fragmentation to 9-cyano-non-5-enoic acid (10a), strong bases favouring the former reaction. In the absence of strong bases of nucleophiles Beckmann rearrangement again dominates.     

Reactions of β-heteroatom substituted α,β-unsaturated ketones with dimethylsulfonium methylide

β-Alkoxy- and β-alkylthio α,β-unsaturated ketones react with dimethylsulfonium methylide (DMSM) to give a furan, while β-anilino α,β-unsaturated ketones give the pyrrole. β,β-Bis(alkylthio) α,β-unsaturated ketones react with DMSM to afford the methylene inserted products, λ,λ-bis(alkylthio) β,λ-unsaturated ketones.     

Destabilized carbenium ions. Secondary and tertiary α-acetylbenzyl cations and α-benzoylbenzyl cations

The secondary α-acetylbenzyl and α-benzoylbenzyl cations, as well as their tertiary analogues, have been generated in a mass spectrometer by electron impact induced fragmentation of the corresponding α-bromoketones. These ions belong to the interesting family of destabilized α-acylcarbenium ions. While primary α-acylcarbenium ions appear to be unstable, the secondary and tertiaiy ions exhibit the usual behaviour of stable entities in a potential energy well. This can be attributed to a ‘push-pull’ substitution at the carbenium ion centre by an electron-releasing phenyl group and an electron-withdrawing acyl substituent. The characteristic unimolecular reaction of the metastaible secondary and tertiary α-acylbenzyl cations is the elimination of CO by a rearrangement reaction involving a 1,2-shift of a methyl group and a phenyl group, respectively. The loss of CO is accompanied by a very large kinetic energy release, which gives rise to broad and dish-topped peaks for this process in the mass-analysed ion kinetic energy spectra of the corresponding ions. This behaviour is attributed to the rigid critical configuration of a corner-protonatei cyclopropanone derivative and a bridged phenonium ion derivative, respectively, for this reaction. For the tertiary α-acetyl-α-methylbenzyl cations, it has been shown by deuterium labelling and by comparison of collisional activation spectra that these ions equilibrate prior to decomposition with their ‘protomer’ derivatives formed by proton migration from the α-methyl substituent to the carbonyl group and to the benzene ring.     

Synthesis of α-hydroxy-β-lactams

A convenient synthesis of α-hydroxy-β-lactams has been devised that involves the annelation of an inline with benzyloxyacetyl chloride and triethylamine and subsequent hydrogenolysis in the presence of palladium on carbon. In most cases a cis-β-lactam was obtained. A thioimidate can also be used as the imino component in the annelation reaction but the hydrogenolysis step fails. The annelation of the appropriate thiazoline to a 6-epi-penicillin derivative occurred much more readily with benzyloxyacetyl chloride than with azidoacetyl chloride.     

Isoxazolium enolates derived from α,β-unsaturated and 1,3-dicarbonyl compounds. The through-space effect of the enolate moiety on the chemical shift of α-protons

The reaction of 4-phenyl-3,5-dihydroxyisoxazole with α,β-unsaturated cyclic ketones and 1,3-cyclic diketones was studied. β-Substituted α,β-unsaturated ketones give pairs of isomeric isoxazolium enolates. The remarkable influence of the heterocyclic betaine on the proton chemical shifts is discussed. 1,3-Cyclic diketones reacted spontaneously with 4-phenyl-3,5-dihydroxyisoxazole yielding isoxazolium enolate enols and enol ethers.     

Regioselective synthesis of 3-hydroxyisoxazoles and 5-isoxazolones from β-amino α,β-unsaturated esters

The regioselective synthesis of 3-hydroxyisoxazoles and 5-isoxazolones is accomplished by the reaction of β-amino α,β-unsaturated esters with hydroxylamine hydrochloride in the presence of appropriate bases. The total yield of isoxazole derivatives is sensitively influenced on the β-substituent group of the esters.     

Substituted γ-lactones. XXX. Reactions of α-Keto-β-Subtituted-γ-butyrolactones with diamines

The condensation reaction between α-keto-β-aroyl (or acyl) -γ-butyrolactones, 4a-4e and o-phenylenediamine or 2, 3-diaminonaphthalene leads under retrograde aldol condensation involving loss of formaldehyde to formation of 3-substituted-3, 4-dihydro-2 (1H) quinoxalinones or benzo [g] quinoxalinones, 7a-7g , respectively as a new convenient synthesis of this type of heterocyclic systems. The reaction of type 4 compound with 4, 5-diaminopyromidine, 8 , was found to proceed differently. 2-[(4-Amino-5-pyrimidinyl)amine]-4-oxo-3-(hydroxymethyl)-4-phenyl-2-butenoic acid 9 was the only product formed when the reaction between 4a and 8 was run in ethanol. The same reaction in glacial acetic acid proceeds with loss of formaldehyde, to afford 7-phenacylidene-7,8-dihydro-6 (1H)-pteridione 10 . The reaction between type 4 compounds and ethylenediamine or 1, 4-phenylenediamine leads to the formation of the bis-condensation products 13–15 , respectively.