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.     

Utilisation d'ylides du phosphore non stabilisés en chimie des sucres. II. Action du méthylthiométhylène-triphénylphosphorane sur les aldéhydo-surces

The action of methylthiomethylene-triphenylphosphorane on 2,3: 4,5-di-O-isopropylidene-Aldehydo--L-arabinose led with good yield to the corresponding unsaturated sugar which underwent electrophilic addition with a high regiospecificity. This provides a useful new route for a one-carbon chain extension in the carbohydrate series.     

Dérivés C-glycosyliques. VII. Synthèse et réactions de nitrones dérivées de sucres. Communication préliminaire

The syntheses of three types of sugar nitrones (aldonitrone, ketonitrone and α-β unsaturated aldonitrone) are described. On 1,3-dipolar cycloaddition with phenylacetylene, the aldonitrone gave two Δ₄-isoxazolines epimeric at the new asymetric carbon, while the same reaction on the ketonitrone led to a spiro-Δ₄-isoxazoline. The reaction of these nitrones with carbon nucleophiles like phenylethynylmagnesium bromide constitutes a novel chain-extension reaction in carbohydrate chemistry.     

Allongement de la chaîne carbonée d'un aldéhydosucre à groupements hydroxyles bloqués par l'utilisation d'ylides du phosphore non stabilisés

The action of the unstabilized WITTIG reagents methylene triphenylphosphorane and methoxymethylene triphenylphosphorane on 2,3:4,5-di-O-isopropylidene aldehydo-L -arabinose led with acceptable yields to the corresponding unsaturated sugars, providing a direct route for a one-carbon chain extension in the carbohydrate series.     

Réactions d'addition-élimination à partir d'hétérocycles germaniés du type I. Cas des dioxolannes germaniés

Addition-elimination reactions from germanium heterocycles I. Germadioxolanes (X?Y?O) The reactivity of 2-germa-1,3-dioxolanes is studied with unsaturated compounds such as carbonyl compounds (aldehydes and ketones) or heterocumulenes (PhNCO, PhNCS). The formation of mono- and di-insertion derivatives is observed. The structure of these adducts is established and their decomposition process, at atmospheric pressure or at high pressure, is precised. The mechanism of these addition-elimination reactions is established from 4,5-disubstitued germadioxolanes. The reaction takes place under steric control. The consecutive elimination reaction proceeds by a mechanism of intramolecular nucleophilic substitution.     

Synthèse de nouveaux polyesters insaturés styrèniques à partir de diols isomoléculaires à ponts thio-éthers. Étude par RMN et tenue thermique

The synthesis of unsaturated polyesters cross-linked by means of styrene have been carried out from high isomolecular weight diols containing thio-ether bonds. The ¹H-NMR peaks have been attributed. Those polyesters exhibit softness to a certain extent in conjunction with relatively high degradation temperatures (T_d 400°C).     

Synthèse de spiro-pyrazolines par cycloaddition du diazométhane sur des sucres insaturés ramifiés. Influence de l'isomérie géométrique sur l'orientation de la réaction Communication préliminaire

The orientation of the cycloaddition of diazomethane on unsaturated branchedchain sugars has been studied. For 3-C-cyanomethylidene-3-deoxy-1,2-O-isopropylidene-α-D-glycero-tetrofuranose the orientation was ‘normal’ and did not depend on the configuration at the double bond. The same situation prevailed with derivatives of 3-deoxy-1,2:5,6-di-O-isopropylidene-3-C-methylidene-α-D-xylo-hexofuranose. For the 3-C-acylmethylidene- and the 3-C-cyanomethylidene-3-deoxy-1,2:5,6-di-O-isopropylidene-α-D-ribo-hexofuranoses, the trans-(H–C(3′)–C(2))-isomer gave the ‘normal’ cycloadduct whereas the cis-isomer gave predominantly the αabnormal spiro-pyrazoline. This observation represents the first instance where the regioselectivity of a cycloaddition reaction is affected by the geometrical isomerism of the dipolarophile. The most probable explanation of the phenomenon is the conformational perturbation about the C(4)--C(5) bond of the unsaturated sugars induced by a change in the configuration at C(3). The consequence of that ‘conformational transmission’ of a difference in configuration at C(3) is that the steric crowding on the cis- than in the trans-isomer. Several novel examples of a new series of C-glycosylidenic derivatives, the spiro-pyrazolines, are described.     

Préparation de phosphonates de sucres ramifiés par addition nucléophile conjuguée. Communication préliminaire

Preparation of unsaturated sugars phosphonates using nucleophilic conjugate addition Different types of phosphorus nucleophiles underwent conjugate addition reaction with one of the branched-chain sugars 4, 5 or 11 the addition taking place either on the endo or the exo face of the furanose ring (or on both faces in the case of 11 ). The configuration at C(3) of these new phosphorus-bearing types of sugars as well as the configuration at the phosphorus atom of the cyclic phosphinates 9 and 10 was established by NMR. (³J_P,H–C(2), ³J_P,C(1)). Small amounts (7%) of the spiro enol phosphonate 16 were formed when 11 reacted with trimethyl phosphite.     

Utilisation d'ylides du phosphore en chimie des sucres,X. Synthèse stéréospécifique de l'épimère en C3 du streptose et d'autres sucres ramifiés,dérivés de désoxy-5-pentoses, à groupements gem-hydroxy-formyle ou gem-hydroxy-hydroxyméthyle

The synthesis of branched-chain sugars of the gem-hydroxy-formyl and the gem-hydroxy-hydroxymethyl types is described. A 5-deoxy-1,2-O-isopropylidene-furanos-3-ulose is treated with cyanomethylene-triphenyl-phosphorane, yielding the two geometrical isomers of the corresponding branched-chain unsaturated sugar. Cis-dihydroxylation(KMnO₄) of these cyanomethylenic compounds affords stereoselectively and in high yield the gem-hydroxy-formyl branched chain sugars whose formyl group is on the more hindered face of the furanose ring. The hydroxymethyl analogues of the latter compounds are readily prepared by their borohydride reduction. This method constitutes a new general route to type A branched-chain sugars epimeric at the branching-point with the sugars which would have been obtained by the classical procedure involving Grignard reagents.     

Influence de l'Insaturation Δ20(22) sur la Fragmentation du Cycle D des Stéroides

The mass spectra of two series of Δ20(22) unsaturated steroids have been studied. The analysis of the D-ring fragmentation shows that C-15? C-16 bond rupture is characteristic of the presence of this unsaturated sidechain.     

Réactions d'addition-élimination à partir d'hétérocycles germaniés du type R2Ge. II. Les germa-2-diazolidines-1,3

Addition-elimination reactions from germanium heterocycles . II. 2-Germa-1,3-diazolidines (X ? Y ? NMe). The reactivity of 2-Germa-1,3-diazolidines with unsaturated compounds such as heterocumulenes (CS₂, PhNCO, PhNCS) and with carbonyl compounds (aldehydes and ketones) has been investigated. Generally the formation of mono- and diinsertion derivatives is observed. The elimination reactions of (Et₂GeO)_n and (Et₂GeS)₃ from these addition derivatives lead to corresponding carbon diazolidines. The mechanism of these addition-elimination reactions is precised. The interest of these reactions in organic synthesis is underlined.     

σ Aromaticity Dominates in the Unsaturated Three‐Membered Ring of Cyclopropametallapentalenes from Groups 7–9: A DFT Study

Aromaticity, an old but still fantastic topic, has long attracted considerable interest of chemists. Generally, π aromaticity is described by π‐electron delocalization in closed circuits of unsaturated compounds whereas σ‐electron delocalization in saturated rings leads to σ aromaticity. Interestingly, our recent study shows that σ aromaticity can be dominating in an unsaturated three‐membered ring (3MR) of cyclopropaosmapentalene. An interesting question is raised: Can the σ aromaticity, which is dominant in the unsaturated 3MR, be extended to other cyclopropametallapentalenes? If so, how could the metal centers, ligands, and substituents affect the σ aromaticity? Here, we report a thorough theoretical study on these issues. The nucleus‐independent chemical shift calculations and the anisotropy of the current‐induced density plots reveal the dominant σ aromaticity in these unsaturated 3MRs. In addition, our calculations show that substituents on the 3MRs have significant effects on the σ aromaticity, whereas the ligand effect is particularly small.     

Etude par RMN du carbone des systèmes CN: imines,phénylhydrazones,semicarbazones, amidines,iminoéthers

A carbon-13 NMR study of compounds containing C?N or conjugated C? N bonds (iminoethers, saturated and unsaturated aliphatic imines, amidines, oximes, phenylhydrazones, semicarbazones) is presented. The influence of the Z/E isomerism, the substituents and the steric effects on the chemical shifts are discussed.     

Utlisation d'ylides du phosphore en chimie des sucres. XIII. Synthèse de dérivés des hydroxyméthyl-3-D-glucose et-D-galactose et de composés voisins

The treatment of the 1, 2:5, 6-di-O-isopropylidene-α-D -ribo- and xylo-hexofuranos-3-uloses with cyanomethylenetriphenylphosphorane led in each case, and in almost quantitative yields, to a pair of geometrical isomers of C-cyanomethylenic sugars having respectively the ribo and the xylo configurations. Permanganate oxidation of these branched-chain unsaturated sugars afforded the corresponding gem-hydroxyformyl compounds bearing the formyl group on the more hindered face of the molecule. The formyl group of these sugars is easily derivatized to an oximino or reduced to a hydroxymethyl. The configuration at the new asymmetric carbon has been established by comparison with known compounds or by synthesis of a C(3) epimer by the classical route involving a Grignard reagent.     

Peroxydation du dihydro-2,3 4H pyranne et du dihydro-2,3 furanne. Etude de réactivités

Free radical reactions of unsaturated O-heterocycles with t-butyl hydroperoxide in the presence of cuprous salt gives peroxides. Their analysis leads to the determination of reactivities in H-abstraction. Allylic hydrogen is ten times more reactive than hydrogen in the α position of the heteroatom.     

Utilisation d'ylides du phosphore en chimie des sucres. XVIII Synthèse de furannoses à insaturation conjuguée. Communication préliminaire

Several sugars with conjugated unsaturation (dienes or α, β-unsaturated carbonyl compounds) have been synthesised by use of Wittig reactions. Keto-sugars bearing a carbonyl group α to a furanose ring are prone to undergo an elimination leading to conjugated unsaturated systems. This constitutes a novel kind of side-reaction in the application of Wittig reactions to carbonyl sugars. The synthesis of a new kind of acetylenic sugar is also described.     

Utilisation d'ylides du phosphore en chimie des sucres. XI. Synthèse des quatre didésoxy-3, 5-méthyl-3-pentoses parl'intermédiaire de sucres insaturés ramifiés

Treated with methylthiomethylenetriphenylphosphorane, 5-deoxy-1,2-O-iso-propylidene-β-D -threo- and -α-D -erythro-furanos-3-uloses led with good yields to a mixture of the cis-trans isomers of the corresponding methylthiovinylidenic sugars. There was no inversion of configuration at C(4) with the thero-furanosulose and a small one (7%) with its erythro isomer. These unsaturated branched-chain thio-sugars are useful synthetic intermediates. For examples, the desulfurization-hydrogenation (Raney Nickel) of each of these alkenes afforded in good yield two 3-deoxy-3-C-methyl-pentoses epimeric at C(3) and having the same configuration at C(4) as the starting alkenes. In all cases the isomer formed by attack from the less hindered face of the double bond was the preponderant one.     

C-nucleosides aminoisoxazoliques. Communication préliminaire

Aminoisoxazoles C-nucleosides Upon treatment with bromocyanomethylenetriphenylphosphorane, a series of aldehydosugar derivatives gave in good to excellent yields the corresponding terminal gem-bromocyanoenoses 3 , 7–10 and 16 . Reacted with hydroxylamine, these unsaturated sugars led to the expected [3] 5-amino-3-glycosylisoxazoles 4 , 11 , 12 and 17 , whereas using hydroxyurea as a binucleophile they gave the corresponding 3-amino-5-glycosylisoxazoles 13 and 14 as previously described in other series [3]. The major interest of these compounds rests in their being close analogs (or enantiomers of analogs) of important biological compounds as f.e. AICAR.     

Réactions d'addition-élmination à partir d'hétérocycles germaniés du type . III. Cas des diéthyl-2,2-germa-2-oxazolidines-1,3 (R = et; X = O; Y = NH,NMe)

Addition-elimination reactions from germanium heterocycles . III. 2,2-Diethyl-2-germa-1,-3-oxazolidines (R = Et; X = O; Y = NH, NMe) . The reactions of 2,2-diethyl-2-germa-1,3-oxazolidines with heterocumulenes (PhNCO, PhNCS, CS₂, CO₂, CH₂?C?O) and carbonyl compounds (aldehydes and ketones) are studied. Generally, monoinsertion derivatives are formed by addition of one molecule of the unsaturated compound accross the Ge? N bond. This bond is always the most reactive center of the molecule. In the case of the carbonyl compounds used, diinsertion may occur in a second step by a further addition across a Ge? O bond. Generally, this latter reaction is reversible. By thermal eliminat on of (Et₂GeO)_n or (Et₂GeS)₃ the monoaddition derivatives yield the corresponding oxazolidines and thiooxazolidines. The mechanisms of these reactions are discussed.     

Utilisation d'ylides du phosphore en chimie des sucres VII. Synthèse de sucres ramifiés des types «streptose» et «apiose». Communication préliminaire

A new high-yielding route to branched-chain sugars of the streptose or the apiose type having at the branching point a configuration epimeric with that which would be obtained by the classical synthesis using Grignard reagents is described. The main steps are the preparation of branched-chain unsaturated cyano sugars by reaction of cyanomethylene triphenylphosphorane with keto sugars and the cis-dihydroxylation (KMnO₄) of the so obtained cyano sugars. The cis and the trans isomers of a series of cyanovinylidenic sugars have been separated and the stereodependence of the long-range coupling constants in this class of compounds has been examined.