Transposition bis-homoallénylique: solvolyse de γ-tosylates alléniques

Cyclisation (formation of derivatives of 2-methylidene-cyclopentanol or cyclohexanone) with inversion of configuration and retention of optical activity is observed during the solvolysis of secondary γ-allenic tosylates. Steric factors rather than electronic ones control the participation of one of the double bonds in the allenic system. Kinetic results and product distribution are discussed.     

Etude Stéréochimique par RMN 1H de Tetrahydropyrannes β-Chlorés α-Substitués

The ¹H NMR study of 2-alkyl-3-chlorotetrahydropyrans, obtained by reaction of Grignard reagents with a mixture of cis/trans-2,3-dichlorotetrahydropyrans, shows cis/trans configuration of two isomers in which the alkyl substituents are exclusively in the equatorial position. 3-Chloro-2-phenyltetrahydropyran exists in trans (eq-eq) configuration only. The ¹H NMR study of cis/trans 2-alkoxy (or aryloxy)-3-chlorotetrahydropyrans, obtained by reaction of alcohols or phenol with 2,3-dichlorotetrahydropyrans, shows the axial position of the alkoxy (or aryloxy) substituent.     

Transfert d'Hétéroatomes (Cl,Br, OH) lors de la Fragmentation d'Acétyléniques δ-Fonctionnalisés

The mass spectra of three δ-functionalized alkynes provide evidence for the migration of chlorine, bromine and hydroxyl towards the unsaturated portion of the molecules. The strong resemblance between these spectra and those of the isomeric allenes suggests that an acetylene→allene isomerization occurs after electron impact.     

Synthèse de polyéthers polycycliques. 1 Stéréosélectivité de l'hétérocyclisation d'alcools tétrahydrofurfuryliques γ,δ-éthyléniques par les sels mercuriques

The intramolecular oxymercuration of the l-(2-tetrahydrofuryl)4-penten-1-ols (5) by merruric salts followed by reductive demercuration affords the 2-methyl-5-tetrahydrofuryltetrahydrofuran (9) as a mixture of cis and trans isomers in good yields. By using mercuric acetate, each isomier threo 5a and erythro 5b gives the trans isomer, 9d and 9b, respectively, as the major products. On the other hand, cyclizations carried out with mercuric chloride are not stereoselective.     

Acylation des β-énaminoesters: Regio et stéréoformation des β-énaminoesters N- ou C-acylés

The reaction of acyl chlorides with cyclic five-membered β-enaminoesters gave exclusively N-acylated products while reaction of acyl chlorides with cyclic seven-membered β-enaminoesters gave only C-acylated products. In the case of cyclic six-membered β-enaminoesters, the reaction of acyl chlorides gave a mixture of N-acylated and C-acylated products.     

Effets des substituants sur la conformation du cycle γ-lactonique : I. Dérivés de la γ-butyrolactone

The structural study of some γ-butyrolactones substituted (i) in position 2 (position ): C₄H₄O₂Br₂ (II) and C₄H₅O₂R [R = Oφ (III); R = OCOφ (IV); R = OH (V); R = Br (VI); R = Cl (VII)] or (ii) in position 3 or 4 (β or β′): C₄H₅O₂Cl (VIII and IX) has been carried out by using different techniques of physical chemistry. Crystallographic data analysis demonstrates that in the solid state, 2,2-dibromo-γ-butyrolactone, unlike the 2,2-diphenyl-γ-butyrolactone, adopts an “envelope” structure which is comparable to those of compounds (III) and (IV). Spectroscopic data relative to the methylene bending mode δ(CH₂) are interpreted for the dissolved state in terms of rigid (III, IV, V, IX) or exchanging (VI, VII, VIII) “envelope” forms. For and β halogenated derivatives (VI, VII, VIII), quantitative analysis of infrared spectra shows a pseudo-axial predominance in apolar solvents, as found by application of the PCILO method. Interpretation of NMR spectra recorded at 250 MHz (III, IV, V, VI) confirms the data obtained by vibrational spectroscopy.     

Analogie Photochimique. II—Cyclisation des Aldéhydes δ,ε Insaturés sous Impact Electronique

The mass spectra of 4, 4-dimethyl δε-unsaturated aldehydes show an ion at m/e 126 which results from the elimination of a neutral olefin directly from the molecular ion. This fragmentation is shown to occur through a cyclohexanone intermediate involving a process whcih has its equivalent in the photochemistry of these aldehydes. The abundance ratios of the unimolecular metastable decompositions of these m/e 126 ions are in excellent agreement with the proposed mechanism.     

α,ω-Dihydroxyalkan-α,α-diphosphonsäuren durch Desaminierung von ω-Aminoalkandiphosphonsäuren

α,ω-Dihydroxyalkane-α,α-diphosphonic Acids by Desamination of ω-Aminoalkanediphosphonic Acids The title compounds represent a new group of complexing diphosphonic acids which are synthesized by desamination of ω-amino-α-hydroxyalkane-α,α-diphosphonic acids. In case of α,ω-dihydroxypropane-α,α-diphosphonic acid ( 1 ) a phosphonylated phostone is formed by dehydration. In contrast, the ω-phenyl drivative of ( 1 ) yields in a smooth reaction under the same conditions 2-hydroxy-5-phenyl-3-phosphono-1.2-oxaphosphol-3-en-2-oxide ( 6 ).     

Addition de dérivés maloniques sur des β-énaminones cycliques

The addition of activated acctonitriles 6 on cyclic and benzylic β-enaminoketones 5 under basic conditions (sodium ethoxide or trition B) have been investigated. This reaction leads exclusively to the formation of α-pyrones 8 and never to the pyridine ring. The strucutre of the newly synthesized α-pyrone derivatives 8 are supported by nmr and ir spectral data.     

Photochemische Reaktionen. 68. Mitteilung. Die Photoisomerisierung von α,β-ungesättigten γ,δ-Epoxyketonen: 9α, 10α- und 9β, 10β-Oxido-3-oxo-17β-acetoxy-Δ4-östren

Irradiation in the n→π* absorption band of the α,β-unsaturated γ,δ-epoxyketone 5 in ethanol at ?65° exclusively afforded the rearranged ene-dione 13 , whereas at + 24° under otherwise unchanged reaction conditions or upon triplet sensitization with Michler's ketone and with acetophenone at + 24° essentially identical mixtures of 13 (major product), 14 , and 15 were obtained. Selective π→π* excitation of 5 at ?78° and + 24° led to similar product patterns. The 9β,10β-epimeric epoxyketone 7 selectively isomerized to 14 and 15 at + 24° and n → π* or π → π* excitation. Neither the epoxyketones 5 and 7 nor the photoproducts 13–15 were photochemically interconverted. In separate photolyses each of the latter gave the double bond isomers 16 , 18 , and 19 , respectively. Cleavage of 13 to the dienone aldehyde 17 competed with the double bond shift ( → 16 ) when photolyzed in alcoholic solvents instead of benzene. The selective transformations 5 → 13 (at ?65° and n → π* excitation) and 7 → 14 + 15 are attributed to stereoelectronic factors facilitating the skeletal rearrangements of the diradicals 53 and 55 , the likely primary photoproducts resulting from epoxide cleavage in the triplet-excited compounds 5 and 7 , via the transition states 54 , 56 , and 57 . The loss of selectivity in product formation from 5 at higher temperature and n → π* excitation or triplet sensitization is explicable in terms of radical dissociation into 58 and 59 increasingly participating at the secondary thermal transformations of 53 . The similar effect of π → π* excitation even at ?78° indicates that some of the π,π* singlet energy may become available as thermal activation energy. It is further suggested that the considerably lesser ring strain in 14 and 15 , as compared with 13 , is responsible that selectivity in product formation from 7 is maintained also at +24° and at π → π* excitation.     

Etude par RMN 13C d'Hydrocarbures Benzéniques Tricycliques Condensés

Several new tricyclic benzocycienes have been investigated by ¹³C NMR. It has been shown that the small perturbations, which arise from the interaction between two semi-aromatic rings, were localized at quaternary carbons.