Fragmentation of nitrone triflates to 9-membered rings

A new fragmentative rearrangement of nitrone derivatives to form 9-membered rings is reported. The fragmentations are triggered when nitrones are treated with triflic anhydride; a C-C bond antiperiplanar to the cleaving N-O bond is activated either by an oxygen lone pair or by an electron-rich aromatic ring. In the former case, further cyclization of the 9-membered intermediate leads to a rearranged condensed ring system, but when triggered by arenes, 9-membered ring amides are isolated.     

Extended mesoionic systems: synthesis and characterization of monocyclic, polycyclic and macrocyclic pyrimidinium-olate derivatives and their photochemical behavior

Mesoionic pyrimidinium-olate derivatives have been known to undergo photoreactions upon irradiation with UV light to form bis(beta-lactame) structures for about two decades. Here, new mono-, poly- and macrocyclic mesoions were prepared and their photochemical rearrangement behavior was investigated. The synthesized compounds were characterized by NMR, IR, UV/Vis spectroscopy, elemental analysis and mass spectrometry. The extension of the aromatic core leads to a significant red-shift of the absorption maximum from ∼380 to ∼430 nm, indicating a strong electronic coupling of the mesoionic base chromophore with the annellated aromatic subunit. The rigidity of the extended aromatic system prevents polycyclic mesoions from shifting to their bis(beta-lactame) isomers, while the alkyl bridge of the 16-membered macrocycle in an ansa-mesoion does not inhibit photochemical rearrangement.     

Studies on 3-oxoalkanenitriles: novel rearrangement reactions observed in studies of the chemistry of 3-heteroaroyl-3-oxoalkanenitriles as novel routes to 2-dialkylaminopyridines

3-Aroyl and 3-heteroaroyl substituted 3-oxoalkanenitriles were synthesized by the reactions of activated aromatic and hetero-aromatic substances with cyanoacetic acid in the presence of acetic anhydride. As part of studies focusing on the preparation of cyanoacetyl-1-N-methylbenzimidazole, we observed that reaction of N-methyl-benzimidazole with the cyanoanhydride formed by condensation of cyanoacetic acid with acetic anhydride, leads to the formation of 2-(1,3-diacetyl-2,3-dihydro-1H-benzo[d]-imidazol-2-yl)acetonitrile (5), whose structure was confirmed by X-ray crystallographic analysis. 3-Oxoalkanenitriles 3a,b were observed to undergo condensation reactions with dimethylformamide dimethyl acetal (DMFDMA) to afford the corresponding enamino-nitriles, which react with malononitrile to give 2-dialkylaminopyridines through a pathway involving a new, unexpected rearrangement process. Reactions of 3-oxoalkanenitriles with ethyl acetoacetate were found to afford 2-oxopyran-3-carbonitriles, also occurring via this unexpected rearrangement process. Mechanisms to account for both rearrangement reactions are suggested. In addition, reactions of 3-oxoalkanenitriles with acetylacetone in acetic acid in the presence of ammonium acetate result in the formation of pyridine-3-carbonitriles. Finally, upon heating in the presence of zeolite 3-oxoalkanenitriles 3b,c self-trimerized to produce the corresponding aniline derivatives 23b,c.     

Une nouvelle synthese de l'ellipticine et ses analogues structuraux

Two new syntheses of the 6H-pyrido [4,3-b] carbazole system are described. The first method involves the cyclization of a (2-alkyl-skatyl)-piperidone whereas the second leads to ellipticine by the participation of the indole nucleus in the rearrangement of tertiary acetylenic alcohols in acidic medium.     

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.     

Reverse aromatic cope rearrangement of 2-allyl-3-alkylideneindolines driven by olefination of 2-allylindolin-3-ones: synthesis of alpha-allyl-3-indole acetate derivatives

The reverse aromatic Cope rearrangement of 2-allyl-3-alkylideneindolines obtained by Horner-Wadsworth-Emmons olefination of 2-allylindolin-3-ones was performed. When 2-allylindolin-3-ones were treated with phosphonium ylides in refluxing toluene, domino Wittig reaction and reverse aromatic Cope rearrangement took place to give alpha-allyl-3-indole acetate derivatives in good yields. The aromatization as a new driving force in the Cope rearrangement is preferable to the conjugation with the carbonyl and cyano groups and also to the alkyl substitution pattern, which are well-known driving forces.     

Synthese de composes aromatiques comportant les groupements OCF2Br et SCF2Br—II : Action de CF2Br2 et de cf2brcl sur des thiophenates et phenates de potassium diversement substitues

The reaction of dibromodifluoromethane and bromochlorodifluoromethane with substituted potassium thiophenoxides and phenoxides leads to the formation of new aromatic compounds bearing OCF₂Br and SCF₂Br groups.     

Synthèse photochimique de biaryles et hétérobiaryles à partir d'aryl-et hétéroarylamines,d'un nitrite d'alkyle et d'un substrat aromatique ou hétéroaromatique

Photochemical synthesis of biaryls and heterobiaryls from aryl and heteroarylamines, alkylnitrite and aromatic or heteromatic substrates The photochemical reaction of aromatic and heteroaromatic amines with excess t-butyl nitrite in aromatic solvents (benzene, p-xylene, mesitylene) and in hetero-aromatic solvents (furan, thiophene) leads to biaryls or heterobiaryls. t-Butyl nitrite is more convenient than isopentyl nitrite which gives by-products. This new method has been used to synthesize 28 compounds in 17 to 60% yield.     

The mass spectra of phenothiaphosphine derivatives

The molecular ion of the phenothiaphosphine derivatives is fairly stable. Under electronimpact, the phenothiaphosphines (I) and phenothiaphosphinic acids (IV, R = H) undergo a one-step elimination of the phosphorus atom together with the groups attached to it. Substitutents in the aromatic rings, as well as on the phosphorus, influence the fragmentation pattern; ring methyl, e.g. leads to tropylium structures. Phosphine oxides of type V lose RO˙, probably after a rearrangement, when R = aryl, but R˙ if it is methyl.     

Negative ions in organic mass spectrometry. II—Negative ion mass spectra of simple thio and dithio esters.

The 70 eV negative ion mass spectra of some simple aromatic and aliphatic thio and dithio esters are discussed. A characteristic fragmentation process, a rearrangement analogous to the nitro-nitrite conversion of aromatic nitro compounds, is observed for aromatic thio esters.     

Synthese et transposition thermique d'alcools α-ethyleniques β'-alleniques

Thirteen variously substituted α-ethylenic β'-allenic alcohols (1,5,6-triene-3-ols) have been synthesized by three different methods, for two of which the key step was the reaction of an organo copper reagent with a derivative of a β-hydroxy γ-ethylenic alcohol (1-ene-5-yne-3,7-diol). The[3,3]-sigmatropic rearrangement of these alcohols, following the heating of their solution in diglyme, leads to γ-dienic aldehydes and ketones. The yields are best (60–70%) for tertiary alcohols substituted on carbon 5. Comparisons of the reactivities of these 13 alcohols show that the mechanism of this rearrangement can probably vary, following the substitution from a cyclohexadiyl biradical process to a concerted pathway involving a cyclohexane transition state.     

Base-promoted aromatic [3,3] sigmatropic rearrangement of N-acyl-O-arylhydroxylamine derivatives

The base-promoted aromatic [3,3] sigmatropic rearrangement of N-acyl-O-arylhydroxylamines giving α-(2-hydroxyphenyl)amides was successfully demonstrated. The substrates were prepared from N-substituted hydroxylamines by N-acylation followed by copper(I)-mediated O-arylation with boronic acids. Treatment of the substrates with lithium hexamethyldisilazide (LiHMDS) in THF at 0?°C to room temperature generated the corresponding amide enolates. The aromatic [3,3] rearrangement of the enolates provided the desired products in moderate to good yields. A crossover experiment produced only intramolecular products and clarified that the reaction proceeds via the aromatic [3,3] sigmatropic rearrangement, not a bond-cleavage–recombination process. Our method is a formal α-arylation of amides.     

The characteristics of oxime ethers upon electron-impact

The O-methyl ethers of aromatic and aliphatic aldoximes and ketoximes are characterized by hydrogen and skeletal rearrangements involving four-membered cyclic transition states. In the aliphatic compounds, four-centered rearrangement sometimes yields the species with the higher ionization potential, in contradiction of Audier's rule. The n-propyl oxime ethers show a novel skeletal rearrangement involving CH₂O elimination. The [M—H]+ process in the aromatic aldoxime ethers and an [M—Cl]+ process in an o-chloro derivative involve atom elimination by intramolecular aromatic substitution. Aromatic aldoxime ethers and the isomeric nitrones behave completely differently upon electron-impact.     

Stereoselective Lewis acid-catalyzed alpha-acylvinyl additions

Silyloxyallenes derived from alpha-hydroxypropargylsilanes undergo efficient addition to aldehydes with catalytic amounts of Lewis acids. The allenes are accessed from the corresponding propargylsilanes in a base-catalyzed 1,2-Brook rearrangement/SE2' process. Enantioenriched propargylsilanes are synthesized by a new zinc-promoted addition of alkynes to acylsilanes in up to 74% ee. This work demonstrates that conversion to the silyloxyallenes occurs with minimal erosion in optical activity. The use of a chiral chromium(III) Lewis acid effects the catalytic asymmetric addition of racemic silyloxyallenes to aromatic aldehydes in up to 92% ee. The overall reaction is broad in scope and accommodates a wide variety of aromatic and aliphatic substituents on both the propargylsilane and aldehyde.     

Rearrangements in the electron-impact induced fragmentation of some β-aroyl-α-methylpropionic acids

A complex rearrangement on electron-impact for β-aroyl-α-methylpropionic acids, involving both hydrogen and hydroxy migration followed by loss of carbon monoxide and allyl radical, is described and discussed. The rearrangement process, resulting in an ion [ArCOOH₂]⁺, is favoured by electron-withdrawing substituents in the aromatic ring.     

Interaction of polyfluoroaromatic compounds with o-aminophenol. The Smiles rearrangement in the polyfluoroaromatic series

The reactions of polyfluoroaromatic compounds containing an electron-attracting substituent other than fluorine in the aromatic ring with o-aminophenol proceed at the amino or hydroxy group and lead to the corresponding hydroxydiarylamines (in neutral media) or aminodiaryl ethers (in alkaline media). The latter compounds, unlike 2,3,4,5,6-pentafluoro- 2'-aminodiphenyl ether, are transformed in dimethylformamide (DMFA) to isomeric polyfluoro-2-hydroxydiarylamines (the Smiles rearrangement). The increased electron-attracting capacity of substituent leads to the decreased activation energy and increased rearrangement rate constants.     

Cyanuric chloride catalyzed Beckmann rearrangement of ketoximes in biodegradable ionic liquids

Imidazolium-based ionic liquids (ILs) containing ester moieties in the side chain were successfully used as an alternative to traditional ILs in the Beckmann rearrangement of ketoximes catalyzed by 2,4,6-trichloro[1,3,5]triazine. The procedure is mild and suitable for both aromatic and cycloaliphatic substrates affording the rearrangement products in good to quantitative yields. The process is eco-sustainable since these ILs are biodegradable and in addition they can be recovered and reused.     

Effect of catalytic alkali metal bromide on Hofmann-type rearrangement of imides

The Hofmann-type rearrangement of aromatic and aliphatic imides using KBr as the catalyst proceeded to provide aromatic and aliphatic amino acid derivatives. We have also developed a new synthetic route to gabapentin with this method.     

Polythioamides aromatiques: Synthese et etude des comportements thermique et ensolution

Aromatic polythioamides are obtained by polycondensation of alkyl and/or carboxymethyl bis(dithioesters) with aromatic or aliphatic diamines in aqueous or organic solvents. We have identified the effect of aromatic rings on the behaviour of polymer in solution and thermal features on these condensation polymers. Their thermal stability is improved over that of aliphatic compounds, especially when the ring and the functional groups are conjugated.     

Synthesis of zwitterionic compounds: fully saturated pyrimidinylium and 1,3-diazepinylium derivatives via the novel rearrangement of 3-oxobutanoic acid thioanilide derivatives

An unusual rearrangement following cyclization of 2-anilino-2-ethoxy-3-oxothiobutanoic acid with aliphatic 1,3- as well as 1,4-diamine leads to zwitterionic derivatives of 2-hydroxypropanoic acid. Moreover, with aromatic 1,2-diamines, fused heterocyclic systems such as pteridine, quinoxaline, and pyrido[2,3-b]pyrazine are obtained.