The chemistry of thujone. IX. Thujone as a chiral synthon for the synthesis of optically active steroid analogues. The vinylpicoline route

The thujone-derived enone 1 , upon base-catalyzed reaction with 2-methyl-6-vinylpyridine is converted to the pyridine analogue 5 (Scheme 1). Catalytic reduction of the latter to 6 generates two new centers of chirality which eventually become C(8) and C(14) in the ultimate synthetic steroid analogue 12 . An X-ray analysis of 6 establishes the structure and absolute configuration so as to determine its suitability in subsequent synthetic studies. The acetal derivative 7 , via Birch reduction, hydrolysis, and internal aldol cyclization, is converted into the cyclohexenone analogue 10 (Scheme 2). This ‘one-pot’ process affords an efficient conversion of the pyridine ring into a cyclohexenone system required for A-ring construction of the steroid skeleton. Finally, conversion of 10 , via the unsaturated diketone 11 , provides the chiral steroid analogue 12 .     

The formation of mixed ligand complexes by metal chelates and some buffer components

A method for the determination of the stability constants of mixed ligand Complexes of metals is described. The influence of the buffer components ammonia (NH₃), imidazole (Im)and hexamethylenetetramine (U) on the murcury (II)-TTHA system was investigated. The binuclear mercury (II)-TTHA chelate has a strong tendancy to coordinate two additional ligands. The following stability constants of mixed ligand chelates were determined:

. Potentiometric titrations were performed to check the effects of the buffers on compleximetric titrations.     

Coupling of narrow-bore liquid chromatography to thin-layer chromatography : Part I. Interfacing

The coupling of liquid chromatography (l.c.) on narrow-bore columns to thin-layer chromatography (t.l.c.) is described. The effluent from a l.c. column can be deposited on a t.l.c. plate after a normal-phase or reversed-phase separation without serious loss of chromatographic information. Both silica and alkyl-modified silica plates can be used for storage. The interface is a fused silica capillary which connects the column outlet to the spray jet assembly of a Linomat applicator for t.l.c. The stored chromatogram can serve as starting point for a new separation, but also allows the use of detection principles which are normally not compatible with l.c. The chromatography of some polynuclear aromatic hydrocarbons is used to illustrate the possibilities of the combinations.     

A novel synthesis of vinyl esters from vinylversatate-10

Vinylversatate-10 (VV10)¹ has successfully been used to synthesise a large number of lower vinyl esters by transvinylation in presence of mercuric acetate and sulfuric acid. The synthesis of vinylhalo esters proceeds with more difficulty. It has been observed that neither Hg(OAc)₂ nor H₂SO₄ alone is capable of initiating the transvinylation. Furthermore, it has been found that a molar ratio 2:1 of VV10 to carboxylic acid is sufficient to drive the reaction to the right by continuous distillation of the vinyl ester formed, and as a result a high yield of vinyl ester is obtained. A mechanism for this reaction and for the formation of side products has been proposed.     

A study of the gold/aqueous electrolyte interphase by modulated reflection spectroscopy

The admittance and differential reflectivity of an electrode of polycrystalline gold in contact with aqueous 0.02 M NaF, KClO₄, 0.01 M Na₂SO₄ and KCl have been measured in the range of potential where the electrode is ideally polarized (?0.7 V to 0.8 V NHE). In NaF and KClO₄ evidence was obtained for the compression of the adsorbed layer of water. The increase of the number of water molecules, with respect to the number in the least original state (at?4μC cm^?2), is 3% at +8 μC cm^?2 and at?17 μC cm^?2. At the potential of zero charge the water dipoles are oriented preferentially with the oxygen towards the metal. In KCl the optical measurements confirm the existence of two types of Au?Cl^? interaction and the covalent character of the bond at the most positive charges.     

Chemical ionization mass spectrometry of bifunctional cyclopentanes and cyclohexanes. A correlation between stereochemistry and chemical ionization spectra

A correlation has been fround between the stereochemistry of 3-methoxyeyclopentyl and 3-methoxyccyelohexyl acetic acid esters and their methane or isobutane themical ionizaion spectra: only the cis compounds yield quasimolecular ions and the [MH? CH₃OH]⁺ ions are more abundant for the trans isomers. A similar situation occurs in the iow temperature methane chemical ionization spectra of the coresponding trimethylsilylethers.     

Synergistic mechanisms of β-diketone derivatives and zinc-calcium soaps in PVC stabilisation

It has been possible to explain the mechanisms of stabilisation and of the synergistic effects of the β-diketone derivatives claimed in a patent as new stabilisers for improving the efficiency of those recipes based upon zinc and calcium soaps in the prevention of the initial discoloration of poly(vinyl chloride).Using chlorohexene as a model compound for allylic chloride structures and benzoylacetone as a model compound for enolised β-diketone derivatives, it has been shown that the benzoylacetone can substitute allylic chlorine atoms through a C-alkylation reaction which takes place only in the presence of ZnCl₂ as catalyst. This reaction drastically changes the percentage of the enol and causes the appearance of two bands at 1720 cm^?1 and 1680 cm^?1 in the infra-red spectrum due to the ketonic structures During the processing of the PVC on a rolling mill at 180°C in the presence of zinc and calcium stearates and benzoylacetone there is grafting of the ketone derivative through a C-alkylation reaction. There is a closed parallelism between the influence of the benzoylacetone on the dehydrochlorination of the chlorohexene and on the accumulation of chloride ions in the polymer matrix in the presence of zinc and calcium stearate. The synergistic effect of the benzoylacetone in the prevention of the initial discoloration is related to the substitution reaction through a C-alkylation which takes place only in the presence of zinc stearate which generates ZnCl₂ which, in turn, acts as a catalyst for both the C-alkylation and dehydrochlorination.     

Synthesis of Pyranthiones

A general method for the preparations of pyranthiones is particularly useful for preparing substituted xanthiones which are unavailable by established procedures. Reaction of a xanthone with p-tosyl isocyanate or with trichloroacetyl isocyanate produces the corresponding imino derivatives, which upon treatment with n-butylamine followed by hydrogen sulfide gives the desired xanthione in good yield.     

Topological degree of a family of convex functions and localization of nash equilibrium points

We define the degree of a family of convex functionsf _x, wherex , and prove that, if this degree is different from zero, one has at least one Nash equilibrium point in . This is a criterion of localization of such equilibrium points.     

Nmr study of the VixSiX4−x compounds with X = Cl,Br; x = 0, 1, 2, 3

¹H, ¹³C and ²⁹Si NMR data for the compounds Vi_xSiX_4?x are reported. While the ¹H and ¹³C resonances from the π system are indicative of the electron-withdrawing inductive effect (-I) of the halogens, the ²⁹Si chemical shift data reveal not only a shift contribution originating from this inductive effect but also the important influence of a {d, σ^*-π} hyperconjugation [1]. This back-donation originates from the vinyl π system and not from the halogens. The chemical shift data and the coupling constants also show an important influence from steric interaction and even from an electric field effect caused by polarization of the silicon—halogen bond.