Fragmentation sous impact electronique de l'acetate de tertiobutyle

The mass spectral fragmentation of tert-butylacetate has been studied by means of high resolution studies, deuterium labelling and metastable transition determinations. Besides the McLafferty rearrangement, two less classical rearrangement mechanisms of oxygen-containing ions are observed and some isotope effects are reported.     

Facteurs stériques influençant la transposition de Wagner-Meerwein des carbocations de type pinanyle

Steric factors influencing Wagner-Meerwein rearrangement of pinanyl carboniumions. The course of the Wagner-Meerwein rearrangement of ions obtained by protonation of substituted α- or β-pinenes is strongly dependent on the configuration of the substituents. The situation is complicated by the possibility of double bond isomerisation (α-→β-pinenes) before rearrangement. Simple rules for predicting the products are given.     

Transposition de Cycles Satures en Spectrometrie de Masse III—Etude des Spectres en Basse Tension des Cyclanones

The fragmentation mechanism of cyclanones (cycloheptanone, cyclooctanone and some methylated or deuterated derivatives) was reinvestigated. All the peaks observed can be interpreted on the basis of a rearrangement of the molecular ion. This rearrangement is particularly important at low voltage.     

Obtention de nouveaux squelettes diterpéniques au cours de l'isomérisation des époxydes-7,8 isopimarates de méthyle par l'éthérate de trifluorure de bore

The action of borontrifluoride etherate on methyl isopimarate 7,8 epoxides has been studied. A backbone rearrangement and the obtention of compounds with new skeletons are reported.     

Etude d'un Couple de Diastereoisomeres en Spectrometrie de Masse: Les 2,3-Diphenyl-butanes Thréo et Erythro

The mass spectra of erythro and threo 2,3-diphenylbutanes are assigned to one rearrangement and one simple cleavage. After calculation of these spectra, it is suggested that their differences are issued essentially from the enthalpy difference of the molecular ions and not from the enthalpy difference between the rearrangement transition states. It is shown that in the gaseous state the threo 2,3-diphenylbutane is more stable than the erythro isomer.     

Orientation de la Fragmentation en Spectrométrie de Masse Par Introduction de Groupements Fonctionnels. XII—Ethylene Acetals Derives de Cyclopentanones et Cyclopentanones α Substituees

The mass spectrometric fragmentations of ethylene ketals corresponding to α substituted ketones were re-examined. A new type of rearrangement has been established.     

Le rearrangement de claisen en series siliciee et germaniee: silaethylene et germaethylene

Thermolysis of silicon and germanium isologues of allyl aryl ethers via transient metal π-bonded intermediates leads to aromatic Claisen-type rearrangement. Para-Claisen type reaction is not observed when the aromatic ring is ortho-disubstituted. In that case the Cope rearrangement is replaced by a radical process. The Claisen rearrangement leads to new oxametallacylohexanes by intramolecular trapping of the metal-carbon double-bond, when the homolytic process gives rise to new oxametallacycloheptanes.     

Isomerisations acides de cyclobutanones tetrasubstituees

The acid-catalysed rearrangement of substituted cyclobutanones has been studied. The treatment of the the α,α′ - or α,β-tetrasubstituted compounds with trifluoroacetic acid gives α,β- or β,γ-unsaturated ketones, by a succession of Wagner-Meerwein migrations.     

Mecanismes de la protonolyse des organo-chromiques issus de bromures propargyliques.

The reaction of CrCl₂ with propargylic bromides leads to an allenic organo—chromic derivative protonated without rearrangement by carboxylic acids. Alcohols like methol transform this metallic to its propargylic isomer and then protonate it with rearrngement (S_Ei′ type mechanism).     

Conversion des furfurylalkyl et arylcetones en derives de l'isocoumarine et de l'isoquinoleine

Cycoladducts of furfurylakyl and arylketones with methyl acetylendicarboxylate undergo acid-catalysed rearrangement in high yield to 6-hydroxyphthalates bearing an acetonly or a phenacyl group in the 3-positionl. These phthalic compounds are useful intermediates for the synthesis of polyfunctional derivatives in the isocoumarin and the isoquinoline series.     

Contraction de cycle a partir de la tosyloxy-8 bicyclo[4.2.0]octanone-7 cis

Cis 8-endo tosyloxybicyclo[4.2.0]oct-3-en-7-one treated with H₄AlLi undergoes a stereospecific ring contraction to give endo 7-formyl bicyclo[4.1.0]hept-3-ene and endo 7-hydroxymethyl bicyclo[4.1.0]hept-3-ène. On the contrary, the same compound treated with MeONa in ether or methanol (conditions of the Favorski rearrangement) gives, beside solvolysis products when CH₃OH is solvent, the two epimeric esters 7-endo and 7-exo carbomethoxybicyclo[4.1.0]hept-3-ène. Several pathways are postulated for the rearrangement.     

Mecanisme d'epimerisation des cetones cycliques α-halogenees en milieu acide—VI: Cinétiques d'énolisation et de migration de l'atome de chlore de la position - 2ála position - 9 des chloro-2a et 2e décalones-1 trans. Stéréochimie et mécanisme de la migration

The rates of α- and α′ -deuteration in acidic medium of 2a-chloro and 2e-chloro 1-décanoles have shown, as in the other cases when no rearrangement concurrently occurs, that epimerisation at C_α involves enol formation. A mechanism for the rearrangement according to kinetic results, is postulated and its stereochemistry determined.     

Reactivite des carbenes et carbenoides issus de diazomalonates mixtes de methyle et de benzyles substitues. Synthese de composes cycloheptatrieniques

The title diazomalonates, when treated with copper powder in octane, yield lactones of 1-hydroxymethyl 7-carboxy cycloheptatrienes. The yields of cyclisation product from such diazoesters may be increased either by a gem-dimethyl grouping or by an electron rich mesomeric group attached to the benzene ring. The methoxy-cycloheptatriene compound 3d is hydrolysed to the spirodienone 8. The carbenes formed from the diazomalonates 2a and b by photolysis or thermolysis undergo Wolff rearrangement and yield insertion products into CH bonds of solvent.     

Intermediaires dans le rearrangement de dimroth d'imidazo[1,2-a]pyridines

Imidazo[1,2-a]pyridines activated by a nitro group at position 6 or 8 undergo the Dimorth rearrangement in aqueous basic media. Intermediates of the rearrangement have been detected and their structures spectroscopically investigated.     

An Efficient Synthesis of de novo Imidates via Aza-Claisen Rearrangements of N-Allyl Ynamides

A novel thermal 3-aza-Claisen rearrangement of N-allyl ynamides for the synthesis of α-allyl imidates is described. Also, a sequential aza-Claisen, Pd-catalyzed Overman rearrangement is described for the synthesis of azapine-2-ones.     

Transposition des Cycles Satures en Spectrometrie de Masse IV—Dioxolanes Derives de Cetones a Cycle Moyen et Grand

The fragmetation mechanism of cyclanone ethylene acetals in the medium ring and macrocyclic series has been re-investigated. The fragmentation pattern can be explained entirely on the basis of a new rearrangement, involving a ring contraction and hydrogen migrations, which have been checked by using deuterated compounds.     

Transposition de neber en série tétrahydropyrannone

The Neber rearrangement applied to the oxime tosylates of the 4- and 3-tetrahydropyranones gives the α-aminoacetals 5 and 20 , as well as 3-amino-4,4-diethoxy and 2-amino-3,3-diethoxy-tetrahydropyranes. The hydrolysis of the former gives the pyrazine 6 and the latter gives the aminoketone 21. On the other hand the aminoacetal 5 allows one to obtain the 4-acetoxy-3-trimethylammonium tetrahydropyran iodide ( 12 ) with a preferential cis axial acetoxy equatorial trimethylammonium conformation. The oxime tosylate of the 3-tetrahydropyranone readily undergoes the Beckman rearrangement into lactam 18 whose open chain product is the (3-aminopropoxy)acetic acid ( 19 ).     

Rearrangement de la catharine en milieu acide: action de l'acide trifluoroacetique

Cleavage of catharine 1 by trifluoroacetic acid led to a pentacyclic product formed by rearrangement of the ibogane moiety with participation of the enamide function. The N-formyl group of compound 5, obtained after NaBH₃CN reduction, was hydrolyzed leading to a hexacyclic derivative, the structure of which was established by X-ray analysis.     

Spectrometrie de Masse des Epoxydes Phenyles—II

The fragmentation of aromatic epoxides proceeds either directly through loss of one molecule of aldehyde or ketone which leads to a symmetrical ion, or through rearrangement of the molecular ion into the isomeric carbonyl radical ion. Substituents on the aromatic ring have a marked influence on the fragmentation.     

Utilisation du 13C en Spectrométrie de Masse: Etude de la Fragmentation de Disaccharides

Twenty-nine α,β-(1 → 3) and (1 → 4) or β-(1 → 6) disaccharides, in the glucose series were analysed by electron impact mass spectrometry. In addition to the known mechanism, a few ¹³C labelled compounds led us to suggest that the ion c was formed from the reducing unit B and the C-1′ of the non-reducing residue A, while A was the starting point for rearrangement and fragmentation processes.