Organomagnesien reactif reducteur : VII. Mise en evidence de l'influence des interactions donneur—accepteur au cours de la reduction de benzylidenemalononitriles

The reduction of benzylidenemalononitriles by chiral aromatic organomagnesium halides and the same kind of reduction where there is no or one phenyl group gives opposite stereochemistry. These results suggest the existence of a donor—acceptor interaction between the phenyl groups in one of the transition states.     

Nouvelle Synthese du β-D-Glucopyranoside de 2,2,6,6-Tetramethylpiperidin-l-Oxyl-4-Yle et de Son Derive Peracetyle

Abstract

The title compound has been synthesized with a significant yield improvement by the triflate glycosylation method and the specific protection of the nitroxide group by reduction and acetylation prior to glycosylation.     

Structure de l'iturine C de Bacillus subtilis

The hydrolysate of iturin C contains α-aminoacids and liposoluble β-aminoacids in the same molar ratios as in iturin A. Electrophoretic migration and alkaline titration indicate the presence of one carboxyl group in iturin C. The reduction of iturin C with diborane shows that this carboxyl group in in an aspartyl residue. The sequence was determined by mass spectrometry of permethylated iturin C in comparison with mass spectrometry of permethylated iturin A. The aspartyl residue is linked to the carboxyl group of the β-aminoacid. In addition, a liposoluble compound seryl→β-aminoacid was isolated from partial hydrolysis which confirmed the cyclic structure of iturin C. In contrast to iturin A, iturin C has no antibiotic activity.     

Catalyse asymetrique avec des complexes chiraux de rhodium-diop—V: Effets des substituants lors de la reduction d'acides N-acylamino cinnamiques

Asymmetric synthesis of phenylalanine and its derivatives can be accomplished by asymmetric reduction of N-acylamino-cinnamic acid derivatives with CIRh(+)DIOP² as catalyst. The optical yield is influenced by the stereochemistry of the double bond, the para-substituent on the N-benzoyl group and the esterification of the carboxy group. The mechanism of the reduction is discussed.     

Selectivite de la reduction de l'androsten-4 dione-3,17 et de la progesterone par divers borohydrures: role de l'assistance electrophile par le cation ou un solvant hydroxyle

The reduction of Δ⁴-androsten-3, 17 dione 1 and of progesterone 2 by nBu₄NBH₄ is highly chemioselective: in THF only the a-enone moiety is reduced, the saturated C₁₇ or C₂₀ keto group being kept unchanged. When TMEDA is added, saturated alcohols are obtained, without any allylic alcohol when the reaction goes to completion. However this reduction is poorly stereoselective as 70:30 mixtures of A/B cis and trans ring junction compounds are obtained. In MeOH, the saturated keto group is more than 90% selectively reduced. However, the reduction of 1 and 2 by LiBH₄ and Zn(BH₄)₂ is poorly chemioselective. These results are interpreted in terms of competition between electrophilic assistance and steric effects.     

Regioselectivite de la reduction de tropones de la quinoxaline

The reduction of quinoxalinotropones by some borohydrides is studied. We calculate the electronic structures, ab initio STO 3G method, of the various possible complexes and compare to the α-enones. It is demonstrated that the borohydride reduction of these tropones is under orbital frontier control and that the important element is carbonyl complexation by the cation.     

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.     

Hydrodimerisation electrochimique de cetones aromatiques encombrees en milieu aprotique et en presence de chlorure de chrome

The electrochemical reduction of hindered aromatic ketones which are difficult to reduce alone, can be achieved in an aprotic medium (DMF) on a mercury pool cathode, in presence of Cr(III) chloride, at the reduction potential or the Cr(II)/Cr(0) system, but at a less negative potential than that of the ketone itself. There is selective hydrodimerisation into an α-glycol, with total lack of polymerisation. With dissymetric ketones, the dl-diastereoisomers of the diols are produced. The effect of chromium is due either to the reduction of a Cr-ketone complex or to the reduction of the ketone by a film of colloidal chromium on the electrode surface.     

Reduction stereospecifique de complexes aziridinyl-cetones-bromure de zinc

Specific reduction of ketoaziridine is obtained by NaBH₄ in protic solvent. The ketoaziridine must be previously complexed by ZnBr₂. Crystal structure determination shows that the complex is formed by two molecules of ketoaziridine and that no complexation between the nitrogen and the ketogroup is possible.     

Etude comparative de l'alkylation des tetraphenylporphyrines de l'etain et de leurs formes reduites par les reactifs de grignard

A comparative study of alkylation by Grignard reagents of PSn(OH)₂ (P = tetraphenylporphyrin (TPP), tetraphenylchlorine (TPC), tetraphenylisobacteriochlorine (TPiBC)) shows that dialkylstannylisobacteriochlorines are the most easily obtained. The presence of transition metals in the magnesium crystals directs the reaction towards reduction of the macrocycle instead of alkylation on tin. This is supplementary proof for the intervention of a single electron transfer mechanism (SET) in alkylation of a macrocycle by Grignard reagents.These results fit very well with earlier electrochemical experiments and the measurements of the reduction potentials of the Group IVB metalloporphyrins and their reduced forms.     

Stereochimie—li controle orbitalaire de la stereochimie des reactions—ii : Reductions par le tritertiobutoxyaluminohydrure de lithium de cyclohexanones substituees en β par des groupes nitriles et methyles en position ax

LiAlH(O-tBu)₃ reduction of 2-decalones and 5α-cholestane-3-ones, unsubstituted or β-substituted by axial or equatorial CN or CH₃ groups show relative rates of attack on both sides of cyanodecalones and decalone which can be interpreted in terms of orbital control by axial C-H bonds α and α' to the carbonyl group. With axial methyl groups, the stereoselectivity depends on unequal 1,3 diaxial interactions which induce ring flattening favouring this orbital control.     

Reduction selective de composes carbonyles par catalyse heterogene a la surface des sels

The reduction of carbonyl compounds carried out with ethoxyhydrogenosilanes and alkali metal fluorides as catalyst and without solvent is highly selective. The reactivity order is aldehyde > ketone > ester. The reduction of aldehydes is possible in the presence of ketones, and of ketones in the presence of esters. The keto-group in a keto-ester can be selectively reduced. The high selectivity of this system is due to three factors: hydrogenosilane reactivity (EtO)₂SiMeH<(EtO)₃SiH), nature of the salt (KF<CsF) and temperature. Chlorides, amides, anhydrides and ethylenic, bromo, nitro groups are not reduced. This enables the selective reduction of the carbonyl group in bifunction compounds.     

Spectres de masse de composes alleniques—I : Transposition de type McLafferty de groupes heteroatomiques et de phenyle sur le carbone allenique central

Mass spectra of allenic compounds substituted with a hydrocarbon chain bearing a heteroatomic group (hydroxy, alcoxy, halogen, dialkylamino) or a phenyl in the γ position exhibits a strong peak corresponding to the loss of C₂H₄ (28a.m.u.) from the molecular ion. This is commonly the base peak of the spectra and due to a McLafferty type transfer of the heteroatom or phenyl group to the central allenic carbon atom. The methyl group shows a lower migratory aptitude in such a process. This type of fragmentation involving the migration of heteroatomic groups is not observed in the spectra of γ-halogen and γ-hydroxyketones, alkenes, alkynes or arenes and seems to be characteristic of the allenic linkage. A nucleophilic attack by heteroatom group (or phenyl) on the central allenic carbon atom is proposed.     

Nouveau mode de synthese des decalones—I

The action of sodium t-amyloxide on 3-(ω-bromobutyl) cyclohexanones (cycloalkylation) yields -decalones. When the 2-position of the initial cyclohexanone is unsubstituted, the reaction yields an equilibrium mixture of isomers (largely trans); but when the cyclohexanone bears a 2-alkyl group, the only product is the cis -decalone with an angular alkyl group. This cycloalkylation thus appears to be stereospecific.

The synthesis of the four -decalones (Va, Vb, V′a, V′b) is described.

The 3-(ω-bromobutyl) cyclohexanones were prepared by the action of the Grignard reagent from the tetrahydropyranyl ether of 4-chloro-1-butanol on the 1,3-cyclohexanedione enol ethers (I, I′), reduction of the resulting 3-(ω-hydroxybutyl) cyclohexenones (II, II′) to the cyclohexanones (III, III′), and finally treatment of the latter with phosphorus tribromide.

A variant is described in which the cycloalkylation is carried out on the 3-(ω-bromobutyl) cyclohex-2-enones (VI).     

Synthese de la trifluoromethyl-vinyl-cetone

The synthesis of trifluoromethylvinylketone $\text{6}$ is described. The metal hydride reduction of ethyl trifluoroacetoacetate $\text{1}$ gives the glycol $\text{2}$. Selective tosylation of $\text{2}$ occurs on the primary hydroxyl group and leads to $\text{3}$. Tosyl-chloride exchange produces the chlorohydrin $\text{4}$ which is oxydized to the β chloroketone $\text{5}$. The dehydrohalogenation of $\text{5}$ leads to the fluorinated ethylenic ketone $\text{6}$.     

Reductions par le zinc en presence d'acides—II : Formation de cyclopropanes lors de la reduction des aldehydes aromatiques par le zinc en presence de trifluorure de bore et d'olefines

The reduction of several p-substituted aromatic aldehydes by zinc in the presence of boron trifluoride and cyclic or open chain olefins, vinyl or allyl ethers or acetates, leads to the corresponding substituted arylcyclopropanes by way of carbene intermediates.     

Etude de steroides fluores par spectrometrie de masse—III: Spectres de masse de quelques cetones fluorees

A series of 24 fluorinated steroidal ketones was studied by mass spectrometry. The different locations of the keto group or fluorine atom, permitted of fragmentation patterns to be derived.     

Cyclisations homolytiques sur un carbonyle: reexamen des reductions des γ-chlorobutyrophenone et chloro-6 hexanal par l'hydrure de tributyletain

Determination of the reactivity of Bu₃Sn· with the carbonyl group of an alkyl aryl ketone and the chlorine atom of a primary alkyl chloride have shown similar types of reaction. These results led us to reconsider the mechanism of 2-phenyltetrahydrofuran formation in reduction reactions of γ-chlorobutyrophenone by tributyltin hydride. This cyclic ether was obtained by elimination of tributyltin chloride from the product of carbonyl hydrostannation. A similar study on an aldehyde and 1-chloroalkane revealed the mechanism of cyclohexanol formation in reduction reactions of 6-chlorohexanal by tributyltin hydride. Tributyltin hydride treatment of 7-chloroheptan-2-one and 6-chlorohexan-2-one led to heptan-2-one and hexan-2-one in good yields; no cyclization product is observed.     

Selectivite de la reduction d'α-enones polycycliques par les borohydrures: effet de l'addition de tetramethyl-ethylenediamine au borohydrure de tetrabutylammonium

3^1,9octalone, 3^1,9-10-methyl octalone and testosterone were reduced by NBu₄BH₄. alone or in the presence of tetramethylethylenediamine (TMEDA), in THF and in toluene. With TMEDA, the first step of the reduction is the regioselective 1,4 attack by BH^?₄ which leads either to the saturated ketones or to the corresponding saturated alcohols. The results observed under different conditions were interpreted by the intervention of various reductive species: diborane, enoxyborohydrides in the absence of TMEDA, amine-borane in its presence.     

Etude de l'acylation de l'acétyl-3 acétoxy-8 indolizine par action de chlorures d'acide en présence de chlorure d'aluminium

Study of acylation of 3-acetyl-8-acetoxyindolizine by miscellaneous acid chlorides in the presence of aluminium chloride shows that this reaction is either limited to a transesterification (in the case of benzoyl chloride) or leads to introduction of an acyl group in position 1 with simultaneous liberation of the phenol function in position 8. When acylation takes place, acetyl chloride resulting from the cleavage of the acetoxy group competes with the acid chloride used in the reaction. Predominant acylation by the latter is observed when the reaction is performed with ethoxalyl chloride or with non branched aliphatic acid chlorides; by contrast solely acetylation takes place when pivaloyl or phenylacetyl chloride is used. These results are tentatively explained by a process related to the Fries rearrangement. The hypothesis of intramolecular transfer of an acyl group from the ester function in position 8 can be discarded by the observed results.