Transpositions a etapes multiples d'epoxydes sesquiterpeniques—II : Action d'acides de lewis sur l'epoxyde de cyperene

Cyperene epoxide 1, on treatment with stannic chloride, gives the cyclopentanone 2 (70% yield) and the methyl ketone 3 (10% yield) by multi-step rearrangements comprising six elementary rearrangements. At least two of these elementary rearrangements cannot be concerted and it seems that in such compact globular polycyclic systems, the bond which migrates is not necessarily the one which is the better geometrically disposed for migration, but the one which would give a thermodynamically more stable product.Treatment of cyperene epoxide 1 with activity grade 1 alumina leads to two conjugated dienes which are the dehydration products of a rearranged allylic alcohol.     

Phénylation d'alcools allyliques acycliques : II. Regioselectivite du transfert d'hydrogene

PdCl₂, HNaCO₃-catalysed phenylation of deuterium-labelled allylic butenols, a Heck type reaction, proceeds by a highly regioselective 1,2-hydrogen shift $\text{via}$ a Wacker type intermediate. No decomplexed enol was formed during this reaction.     

Photoreduction d'arylcetones par les amides et les lactames: applications synthetiques

Benzophenone is photoreduced by lactams and amides. In this reaction the hydrogen atom α to the lactam nitrogen is abstracted regioselectively, and radical coupling leads to adducts. The reaction is general and comparable to an hydroxyalkylation α to the nitrogen atom. Its quantum yield is 0.13 in the case of N-methyl 2-pyrrolidone in CH₃CN or in C₆H₆. Adducts obtained with acetophenone and p,p'-dimethoxy benzophenone are described. The reduction of adduct 12yields the diphenylethanolamine 22 and 12 is dehydrated to give the enamide 21.     

Reactions de dechlorhydratation d'organochlorohydrogermanes et -polygermanes

1,8-Diazabicyclo[5.4.0]undec-7-ene appears to be an efficient dehydrochlorination agent for the organochlorohydrogermanes PhCl₂GeH, R₂ClGeH (R = Et, Ph). In diluted solutions the intramolecular α-elimination process leads to germylene through germanate

formation while in concentrated solutions intermolecular reactions are predominant and give organochlorohydropolygermanes in good yields. The latter reaction is an interesting and selective way to obtain digermanes with bulky substituents (R = mesityl).Both intra- and inter-molecular dehydrochlorination mechanisms are discussed.     

Etude des petits cycles—XXXVI. Photo-oxygenation d'alkylidenecyclopropanes. Syntheses specifiques d'alkenylcyclopropanols,de β′-hydroxy α-enones et d'α,α′-dienones

The dye-sensitized photo-oxygenation of alkylidenecyclopropanes 1a–4a at –50°C gives the hydroperoxydes 1b–4b, which were reduced in situ by PPh₃ into 1-alkenylcyclopropanols 1c–4c in high yield. At higher temperatures, 1b–4b rearranged exclusively into β′-hydroxy α-enones 1d–4d if pyridine was added (α,α′-dienones 1e–4e are also formed competitively in absence of pyridine). At 3°C the photosensitised oxygenation of alkylidenecyclopropanes 1a–4a gives ketones 1k–4k, cyclobutanones 1i–4i and β′-hydroxy α-enones 1d–4d. The origin of products is discussed.     

Sels d'alkyloxyphosphonium—XVI: Activation de l'hydroxyle anomere des 2,3,4,6 tetra-o-acyl-d-mannopyranoses

The joint action of tris(dimethylamino)phosphine-carbon tetrachloride on a tetra-O-acyl-2,3,4,6-d-mannopyranose leads to one α anomeric oxyphosphonium chloride (ATDP salt). This salt is not isolable, but decomposes to yield an anomeric mixture of 1-chloro derivatives. The reaction with alcohols give rise to the formation of orthoesters while thiophenol reacts to yield only the β-thiomannoside. These results are discussed and interpreted.     

Stereochimie d'heterocycles du groupe IVB—II : Syntheses stereoselectives d'hydrogeno-1 et d'alkyl-1 sila-1 cyclobutanes

The reaction between n-butyllithium and 1,2 (or 1,3)-dimethyl-1-t-butoxy-1-silacyclobutanes proceeds with retention of configuration at silicon, and yields 10/90 (or 80/20) Z/E mixture of 1,2 (or 1,3)-dimethyl-1-n-butyl-1-silacyclobutanes. Methylation of 2 (or 3)-methyl-1-t-butoxy-1-silacyclobutanes (Z/E = 15/85 or 65/35) by methylmagnesium iodide gives 15/85 (or 65/35) Z/E mixture of 1,2 (or 1,3)-dimethyl-1-silacyclobutanes. The proposed configurations for substituted silacyclobutanes are supported by spectroscopic data (RMN) and chemical results (correlation of configuration and stereomutation of hydrogenosilacyclobutanes).     

Hydroboration d'amines insaturees—II: Régio et stéréosélectivité de l'hydroboration-alkylation d'amines acétyléniques

The hydroboration reaction of acetylenic amines R¹R²NCH(R³)CCR⁴ was studied. We report the first results of a study of the reactivity of dialkylborane R₂BH towards these amines which allow us to propose a new method for the synthesis of differently substituted β-ethylenic amines. The regioselectivity and the stereoselectivity of this reaction are examined and allow us to set out the possibility of a trans hydroboration.     

Quelques aspects du mecanisme de l'oxydation anodique de quelques halogenures d'adamantyl-2

For the anodic oxidation in acetonitrile of some 2-adamantyl halides, the distribution of reaction products is dependent upon the halogen and substitution at the bridgehead positions. Iodides gave exclusively 2-adamantyl acetamides. 2-Chloroadamantane yields to chloroadamantyl acetamides. From bromides both 2-adamantyl acetamides and bromoadamantyl acetamides are formed. Part of the reaction products obtained with 2-fluoroadamantane are formed from the cleavage of C₂F bond; this result is explained by analogy with the mass spectrometric fragmentation behavior of this compound. A general reaction mechanism covering all our experimental results is proposed.     

Etude des interferences spectrophotometriques par utilisation d'une matrice d'experiences factorielle

(Use of a factorial design to study interferences in spectrophotometry.) Ozonation of aqueous solutions leads to the formation of hydrogen peroxide and oxalic acid. Hydrogen peroxide is determined spectrophotometrically by the classical method in which TiO·H₂O₂²⁺ is formed, but oxalic acid interferes by forming a complex with titanium. The interference is studied by using a simple factorial design. The results, calculated by linear regression, show the existence of both translational and rotational effects on the absorbance signals.     

Alcaloïdes stéroïdiques—CLXXVIII: synthèse d'azides tertiaires—VIII: Synthèse d'azido et d'amino-14β cardénolides

The use of hydrazoic acid in the presence of BF₃-etherate allows the synthesis of the potentially interesting 14β-amino cardenolides. The 17βH configuration allows a quantitative yield of the 14β-azido cordenolide, but by this method, the 17αH configuration does not. However, the synthesis of the 14β-azido cardenolide of 17αH configuration can be achieved by the elaboration of a 14β-azido 17αH-pregnane.     

Synthese d'azides tertiaires—V: Formation d'azido- et d'amino-8α et 8β dans la serie du labdan

HN₃/BF₃-Et₂O was used in the synthesis of tertiary azides from sclareol and dihydrosclareol. An ion-pair mechanism was observed. Under appropriate conditions, stereoselective introduction an azido-group at C-8 was observed. Manoyl-oxide and 13-epimanoyl oxide provided azido-ketones by CC vinylic fragmentation with loss of C₁₄ and C₁₅.     

Alkylations en absence de solvant organique—3 : Preparation d'ethers aliphatiques par alkylation des alcoolates dans des conditions douces et economiques

n-Octyl ethers are obtained by reacting n-octyl halides with preformed alkoxides, or better, prepared in situ from ROH and solid KOH. Reactions are performed without any solvent but in the presence of a catalytic amount of tetra-alkyl ammonium salt (Aliquat 336). Good yields (?92% for primary R) are obtained at moderate temperatures and with easy work-up; for t-C₄H₉O-, elimination is a side reaction, and the effects of temperature and of the nature of the leaving group were examined, so that t-C₄H₉OC₈H₁₇ could then be obtained (yield 77%) within 20 h at 36° from n-octyl tosylate.     

Complexes dinucleaires pontes des metaux d8: VII. Reactions d'addition oxydante d'halogenures d'alkyle et d'acycle aux complexes μ-halogenes du rhodium(i) [RhX(CO)(PR3)]2. Structure cristalline de [RhCl(CO)(PMe2Ph)(Me)(Br)]2

The halogen bridged binuclear complexes of rhodium(I) [RhCl(CO)(PR₃)]₂ undergo oxidative addition with methyl halides to yield the complexes [RhCl(CO)(PR₃)(Me)(X)]₂ (X = Cl, Br). The crystal and molecular structures of [RhCl(CO)(PMe₂Ph)(Me)(Br)]₂ have been determined from a single crystal by use of X-ray crystallographic methods. The space group is Pca2₁ or Pacm with a 19.501(5), b 10.381(4), c 13.641(5) e? Z = 4. Parameters of 30 nonhydrogen atoms in the space group Pca2₁ were refined by the full-matrix least squares technique to a conventional R factor of 0.073. In a binuclear unit, each rhodium atom is in an octahedral environment being bonded to a carbonyl group, a methyl group and a tertiary phosphine ligand and three halogen atoms for which, due to a disorder phenomenon, the diffusion factors have been determined as the average between those of chlorine and bromine atoms. In solution the cis-migration of the methyl groups occurs, leading to the acetyl complexes. In the case of CH₃I, it is shown that an equilibrium is present in solution: [RhCl(CO)(PR₃(Me)(I)]₂ ? [RhCl(COMe)(PR₃)(I)(solvant)]₂] Carbonylation reactions shift this equilibrium to give the complexes [RhCl(CO)(COMe)(PR₃(I)]₂. Such complexes are readily prepared by direct oxidative addition of acyl halides to the compounds [RhCl(CO)(PR₃)]₂.     

2,2,4,4-Tetramethyl-2,4-disila-cyclo-butylzinkchlorid · TMEDA und verwandte Verbindungen

2,2,4,4-Tetramethyl-2,4-disila-cyclo-butylzinc Chloride · TMEDA and Related Compounds The reaction of (tmeda)lithium 2,2,4,4-tetramethyl-2,4-disila-cyclo-butanide with anhydrous zinc(II) chloride in pentane in the molar ratio of 2:1 does not yield the expected dialkylzinc derivative but the monosubstitution product 2,2,4,4-Tetramethyl-2,4-disila-cyclo-butylzinc chloride · tmeda 1 . This derivative crystallizes in the orthorhombic space group Pnma with a = 1 235.0(1); b = 1 696.8(2); c = 1 148.0(1) pm and Z = 4. The Zn? C bond lengths lie with 198,4 pm in the characteristic region for compounds containing a tetrahedrally coordinated zinc atom. The thermolysis of 1 leads under elimination of ZnCl₂ to the formation of Bis(2,2,4,4-tetramethyl-2,4-disila-cyclo-butyl)zinc · tmeda 2 . (tmeda)LiCH(SiMe₃)₂ reacts analogously with one equivalent of ZnCl₂ to Bis(trimethylsilyl)methylzinc chloride · tmeda 3 . Lithium methanide or Lithium butanide add to a Si-C bond of 1,1,3,3-tetramethyl-1,3-disila-cyclo-butane, and these acyclic lithium alkanides 4 ( a : R = Me, b : R = n-Bu) yield with zinc(II) chloride the destillable dialkyl zinc compounds Bis(2,2,4,4-tetramethyl-2,4-disilapentyl)- 5 a and Bis(2,2,4,4-tetramethyl-2,4-disila-octyl)zinc 5 b .     

Reactivite d'hydrocarbures methylenecyclo-hexaniques—I : Stereochimie de la reaction d'oxymercuration-demercuration

Methylenecyclohexanes, prepared in excellent yield by Corey and Chaykovsky then Cornforth reactions, give on oxymercuration followed by reductive demercuration tertiary alcohols resulting from axial attack by solvent. The attack takes place trans to the substiuent when the latter is at the 2 position. α-Hydroxy or methoxy compounds behave similarly to each other. For acetoxy compounds, the cis alcohols are obtained preferentially, by intramolecular attack of acetoxy group on the mercurinium ion intermediate. The results can be explained satisfactorily on the assumption that the factors inducing stereochemistry are short distance interactions.     

Stereochimie d'heterocycles du groupe IVB—I : Syntheses stereoselectives d'alcoxy-1 et d'amino-1 sila-1 cyclobutanes

Stereoselective synthéses (60 to 90%) of some silacyclobutanes were performed by alcoholysis or aminolysis of 2 (or 3)-methyl-1-chloro-1-silacyclobutanes. Relative configurations of 2 (or 3)- methyl-1-alkoxy (or 1-amino)-1-silacyclobutanes thus prepared have been assigned from their NMR spectra. The mechanism of these stereoselective reactions, based on the rapid stereomutation of 1-chloro-1-silacyclobutanes, is discussed.     

Methode simple pour la synthese rapide et stereoselective d'enoxysilanes d'aldehydes et de cetones

A new highly regio- and stereo-selective method for the preparation of enoxysilanes, viz. treatment of Me₃SiCl, NaI, Et₃N with enolizable aldehydes and ketones is described.     

Oxydation photochimique d'amines tertiaires et d'alcaloïdes—X : Introduction d'un groupement fonctionnel en α de l'azote nb de la yohimbine par oxydation photosensibilisee

Dye-sensitized photooxidation of the imino-ether 5, prepared from yohimbine 1a, led to the α-amino nitrile 9a when the reaction was performed in the presence of oxygen and KCN. Derivative 9a was hydrolyzed to the amide 9b, the transformation of which to carboxamido-5β-yohimbine 15 was studied.     

Systemes de strecker et apparentes—II : Mécanisme de formation en solution aqueuse des α-alcoylaminoisobutyronitrile à partir d'acétone,d'acide cyanhydrique et d'ammoniaque,methyl ou diméthylamine

The formation of N-substituted tertiary α-aminosobutyronitriles from acetone, alkali, cyanide amine, has been studied in aqueous solutions of pH 8–12. Competition between the cyanide and amine for acetone first favours cyanohydrin formation. The α-aminonitrile is then slowly formed. The kinetic study of the reaction, as a function of cyanide concentration, shows two successive slow steps. In the presence of excess cyanide, the first step, limiting the reaction rate, is formation of intermediate imine. This is catalysed neither by OH^? or H₃O⁺ and depends only on the concentration of amine in basic form. The mechanism of the second step, the imine forming the α-aminonitrile, is discussed in terms of acid catalysed addition of the cyanide ion to the imine.