Conjugated schiff's bases—141: Cycloaddition of heterocumulenes to some 1-oxa-4-azabutadienes

1-Oxa-4-azabutadienes proved to be prone to react with some heterocumulenes after 1,3-cycloaddition patterns yielding various 5,5-disubstituted derivatives of 1,3-diaryl-hydanotoins as it was shown by the chemical and spectroscopic analysis. Relatively high yields, mild reaction conditions and a very weak effect of solvent polarity on the reaction rate suggested a synchroneous mechanism involving 1,2-migration of a substituent.     

ConjugatedSchiff bases. 15. substituent effect on the cycloaddition of heterocumulenes to some 1-oxa-4-azabutadienes

The substituent effect on the cycloaddition of aryl isocyanates to some 1-oxa-4-azabutadienes has been investigated. It has been found that electron-withdrawing groups located in the aryl isocyanate ring distinctly increase the rate of the cycloaddition. The importance of isocyanate nitrogen unshared electrons has been considered. Rate constants and activation parameters have been discussed with respect to the mechanism.

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KonjugierteSchiff-Basen, 15. Mitt.: Substituenteneffekte bei der Cycloaddition einiger Heterocumulene mit 1-Oxa-4-azabutadienen

Zusammenfassung Der Substituenteneffekt bei der Cycloaddition von Arylisocyanaten an einige 1-Oxa-4-azabutadiene wurde untersucht. Es wurde festgestellt, daß e-anziehende Gruppen am Aryl-isocyanat-Ring deutlich die Geschwindigkeit der Cycloaddition erhöhen. Geschwindigkeitskonstanten und Aktivierungsparameter werden im Hinblick auf den Reaktionsmechanismus diskutiert.

     

Conjugated Schiff bases. VII—Decarbonylation of some 1,3-hetrodienes under electron impact

The mass spectra of some 1,3- heterodienes containing the 1-oxa-4-aza-butadiene system have been determined and the characteristic fragmentation pathways are discussed. The pathways suggested are supported by the appropriate metastables, the spectra of model compounds and by deuterium labelling. The 1, 3-heterodienes substituted by the thioarylamide group from ions involving participation of the sulphur atom.     

The electron impact induced fragmentation of aromatic aldoximes—II. Substituent effects on the loss of MCN

Loss of HCN from the molecular ion of benzaldoximes occurs via two distinct involving a 4-membered and a 5-membered intermediate, respectively. Both low energy high energy molecular ion decomposition were investigated by means of metastable peak shapes and the energetics of further decomposition of ions, respectively. Substituent effects previously held responsible for differences in the behaviour of m- and p-methoxybenzaldoximes are shown to be negligible; the differences are due to the differense in internal energy contents.     

The fragmentation behaviour of some spirobenzthiazoles under electron impact

The electron impact induced fragmentations of ten spiro-benzthiazoles have been studied. The principal decomposition reactions have been elucidated by metastable studies, exact mass measurements, and by deuterium exchange of the imino hydrogen. The primary fragmentation step is an α-cleavage reaction, which leads to ring opening of the ring fused to the benzthiazole moiety of the molecule. The subsequent decompositions resemble those of cyclohexylamines. They follow a general pattern, the details of which are discussed with respect to the nature and position of the heteroatom in the saturated ring.     

Mass spectrometry of transition metal π-complexes. XV—The effect of substituents on the fragmentation of benchrotrenyls under electron impact

Mass spectra of substituted benchrotrenyls RC₆H₅Cr(CO)₃ where R?H, F, CI, I, CH₃, OCH₃, COOCH₃, C₂H₅, N(CH₃)₂, NH₂, C₆H₅, C(CH₃)₃, p-C₆H₄NH₂, CH₂C₆H₅, CH₂CH₂C₆H₅), 1,3,5-(CH₃)₃C₆H₃Cr(CO)₃ and 1,2,3,5-(CH₃)₄C₆H₂Cr(CO)₃ have been studied. It has been found that for monosubstituted benchrotrenyls there is a linear dependence of the parameter log [Cr]⁺/[RC₆H₅Cr]⁺) on the number of degrees of freedom of the [RC₆H₅Cr]⁺ ion. Decarbonylation of the molecular ions is not affected by the nature of the substituent R. The results are interpreted in terms of the quasi-equilibrium theory of mass spectra.     

Effects of stereoisomerism on the electron impact fragmentation of some compounds with an eburnane skeleton1

The mass spectra of five sets of stereoisomers possessing an eburnane basic skeleton (vincamine, vincaminic acid ethyl ester, deoxyvincamine, deoxyvincaminic acid ethyl ester, apovincaminic acid ethyl ester and all their possible epimers) have been compared. All of the epimers, among them the 3H-β isomers, not studied formerly, have characteristically different electron impact spectra. For vincamine and its epimers similar differences were also found in the argon charge exchange ionization, mass-analysed ion kinetic energy and collisionally activated mass-analysed ion kinetic energy spectra. The main effects of stereoisomers on the abundance ratios clearly indicated the occurrence of some highly stereospecific or stereoselective decomposition processes. Conclusions concerning the mechanism of these reactions, based on the normal and metastable ion spectra as well as on some energetic data for the epimers, have also been drawn. For several fragment ions the observed unexpected abundance differences seem to be rationalized in terms of the competing effects of other decomposition processes of higher stereoselectivity.     

Mass spectrometry in structural and stereochemical problems—CLXVI. The electron impact promoted fragmentation of some aliphatic 1,2-glycols

The mass spectra of nineteen aliphatic 1,2-glycols containing a variety of substituents have been recorded and mechanistic rationalizations are presented for the more important degradation processes observed. Fragmentation of the hydroxylated carbon-carbon bond in these compounds occurred to an appreciable degree often accompanied by the transfer of a hydroxylic hydrogen atom.     

Aziridinone intermediates in electron impact induced fragmentation of some new hydantoins

Mass spectra of some 5-substituted 1,3,5-triarylimidazolidin-2,4-diones have been determined and the chief fragmentation pathways considered. The fragmentation sequences and ion structures are discussed with the help of the appropriate metastables, precursor ion measurements and high resolution measurements.     

Charge location and fragmentation under electron impact. IV—the behaviour under electron impact of some N-methyl,N′-R-1,2,4-phosphadiazetidine-3-ones and related compounds

The ionization potentials of a series of N-methyl,N′-R-1,2,4-phosphadiazetidine-3-ones and related compounds have been determined. The nature of the highest occupied orbital of the molecules and the use of empirical rules to rationalize the variations in the ionization potentials are discussed. The changes in the fragmentation patterns are related to the different low ionization potential site(s) in each molecule. The occurrence of various rearrangement ions are discussed on a similar basis.     

The electron impact fragmentation of 3- and 4-styrylpyridazine

The electron impact mass spectrometric fragmentation of trans-3- and trans-4-styrylpyridazine is reported in detail, including a comparison with other aza-stilbenes. With regard to a distinction between the two isomeric styrylpyridazines, the intensity ratio of the M⁺ and [M-1]⁺ ions, the general degree of fragmentation and the elimination pathways of nitrogen proved to be most characteristic.     

Unimolecular reaction sequence in the electron impact induced fragmentation of some methylenoxazolidinones

The unimolecular processes of some methylenoxazolidinones bombarded in the gas phase by electrons have been investigated by MIKE analysis, precise mass measurements and isotopic labelling studies. The overall delocalisation effect of the substitution on the nitrogen contained has been ascertained through the study of the reaction mechanism and of the possible reacting ionic structures.     

Mass spectrometry of condensed N-heterocycles: II—A novel ortho effect in the electron impact induced fragmentation of some C-(2-nitrophenyl)-azoles and -azoloazines

Heterocycles containing an integrated 2-nitrobenzaldehyde imine moiety produce ions of m/z 134 with high abundance under electron impact. As shown by kinetic energy release measurements these ions have the same structure in all the cases studied, identical to m/z 134 formed from the reference compound 2-nitrobenzoylpiperidide. The mechanism of formation of m/z 134 most probably involves isomerization of its precursor ion to give a spiro intermediate, from which m/z 134 arises either synchronously or after a second isomerization. Both alternatives formally represent an oxygen transfer from the nitro group to the imino carbon via a 5-membered transition state.     

Mass spectrometry in structural and stereochemical problems—CLVIII electron impact promoted fragmentation of triphenylmethyl ethers

The triphenylmethyl (trityl) moiety is frequently used for the protection of alcohols but the mass spectra of such trityl ethers have hitherto escaped scrutiny. It has now been found that triphenylmethyl derivatives of primary alcohols yield abundant molecular ions which permit the determination of the isotopic purity of the parent alcohol. Upon electron impact the triphenyl-methyl entity directs the fragmentation of trityl ethers as demonstrated by a detailed study of n-pentyl trityl ether and its deuterated analogs. Ions formed by migration of phenyl groups were observed in the mass spectra of the trityl ethers investigated as well as in the spectrum of triphenyl-methane itself.     

Ortho effect in the fragmentation of 2-acetoxychalcones under electron impact

2-Acetoxychalcones decompose under electron impact conditions by loss of an acetoxy fragment to form flavylium ions. The effect is restricted to the ortho position and is reduced after hydrogenation of the chalcone double bond. The intense flavylium ion originates—as shown by specific labelling with ¹⁸O—from two different fragmentation lines: (a) direct loss of an acetoxy radical by cleavage of the phenolic Ar? O bond and (b) sequential elimination of ketene and a hydroxy radical.     

The fragmentation of 1-phenyl-2-propen-1-ol under electron impact

The electron impact mass spectra of 1-phenyl-2-propen-1-ol and its specifically deuterated analogues have been investigated. Most of the decomposition pathways involve skeletal rearrangements or hydrogen atom transfers, such that a rearrangement of the excited molecular ions of 1-phenyl-2-propen-1-ol to molecular ions of cinnamic alcohol and/or cinnamaldehyde can be anticipated.     

Substituent effects on retro-Diels-Alder reactions in some 3,6-diphenyl-5-aryl-4-amino-Δ′cyclohexenes

The variation in the ratio of the relative abundances of the diene and ene ions formed by competing retro-Diels-Alder reactions with electron energy and subtituents has been studied. This ratio represents the ratio of the rate constants of the processes and depends on the internal energy distribution within the decomposing molecular ions.     

Dual mechanisms for the fragmentation of 1-benzoylbenzotriazole upon electron impact

The electron impact induced fragmentation of 1-benzoylbenzotriazole has been studied by ¹³C labelling experiments. It has been found that the loss of CO from the [M ? N₂]⁺˙ ions proceeds by two routes; about 78% of the ions decompose via the molecular ions of the corresponding thermal fragmentation product, 2-phenylbenzoxazole, and 22% via those of the corresponding photochemical fragmentation product, 6-phenanthridone.