Synthesis of α, α′, β-trideuterovinyl acetate

Reaction conditions for the synthesis of α, α′, β-trideuterovinyl acetate by the continuous vapour phase catalytic reaction of deuteroacetylene and acetic acid-d (CH₃COOD) are described.     

Poly(α,α,α′,α′-tetrafluoro-p-xylylene)

Poly(α,α,α′,α′-tetrafluoro-p-xylylene) was prepared by the pyrolysis of cyclo-di-(α,α,α′,α′-tetrafluoro-p-xylylene) and by the pyrolysis of α,α′-bis(alkylsulfonyl)-α,α,α′,α′-tetrafluoro-p-xylene. The pyrolysis of α,α′-dibromo-α,α,α′,α′-tetrafluoro-p-xylylene also gave the polymer, but the method is less satisfactory. Poly(α,α,α′,α′-tetrafluoro-p-xylylene) shows remarkable thermal and oxidative stability at elevated temperatures. Useful mechanical and electrical properties are retained after aging for 3000 hr at 250° in air. After initial change due to crystallization, tensile strength remains near 10,000 psi, elongation above 5%, and dielectric constants and dissipation factors at approximately 2.4 and .001, respectively.     

Kinetics and thermal analysis of copolymerization of m-isopropenyl–α,α′-dimethylbenzyl isocyanate with styrene

The copolymerizations of m-isopropenyl–α,α′-dimethylbenzyl isocyanate (m-TMI) with styrene (STY) was investigated. The weight conversion of the copolymerization reaction increased as the duration of copolymerization increased. The reaction temperature was maintained between 60 and 75°C. Molecular weights of the copolymers decreased with increasing molar fraction of m-TMI in the feed. This study obtained reactivity ratios, Alfrey–Price parameters, Mark–Houwink constant, characteristic ratio, thermal degradation activation energy, difference of reactive propagation activation energy, and intrinsic viscosity for the copolymers. The copolymers were characterized by using elemental analysis (EA), gel permeation chromatography, thermogravimetric analysis, and differential scanning calorimetry. The copolymer chains in solution were observed to have a high degree of stiffness and a lack of rotational freedom. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2763–2770, 1999     

Reactions with the arylhydrazones of some α,β-diketoesters

Treatment of the α, β-diketo-ester-α-arylhydrazones 1a–e and 2a–d with GRIGNARD reagents results in the formation of the ketocarbinols 3a–h and 4a–g , respectively. The arylhydrazones of ethyl mesoxalate 5a–e react with phenylmagnesium bromide to yield compounds 3a–e . A novel synthesis of α-arylazo-β-arylchalcones 6a–e and their reaction with hydrazines are reported. Whereas the arylhydrazones 10a, b, 2a, b, d, 13a–c and 14a–c react with piperidine and formaldehyde to yield the MANNICH bases 11a, b, 12a–c and 15a–c , compound 5a was recovered unchanged.     

α-olefin oligomers and polymers with metallocene catalysts

Metallocenes offer new synthetic routes to olefin oligomers and polymers covering a wide range of molecular weights and melting points. This paper deals with some important features of the preparation of oligomers, wax-like polymers as well as highmolecular-weight polymers via metallocene catalysis. Taking the oligomerization of hexene as an example, a simple kinetic scheme is established, which is suitable to describe the course of the reaction and the resulting oligomer distribution with metallocenes as catalysts. For low and high-molecular-weight polymers, the metallocene route to polypropylene is compared to existent processes in terms of reaction conditions and product properties. An attempt is made to separate the effect of different chain defects like chain ends, regioirregularities and comonomers on the melting point.     

Photochemistry of α,α′-Disubstituted Azoalkanes. I. Photosolvolytic Inversion and Substitution of α,α′-Dichloro- and α,α′-Dialkoyloxyazoalkanes

A series of α,α′-dichloro (α DClA), α,α′-dialkoyloxy- (αDAlA) and α,α′-dibenzoxy-azoalkanes (αDBeA) without α-aryl substituents was found to undergo meso ? dl photointerconversion upon direct irradiation through Pyrex in the presence of oxygen in a number of solvents. Furthermore, irradiation of α,α′-dipropionoxy-azoalkanes in benzene in the presence of excess acetic acid leads to substitution of the propionoxy groups by acetoxy groups in addition to meso ? dl photointerconversion. Similar irradiation in the presence of CH₃CO₂D does not lead to deuterium substitution of the β-hydrogens. The presence of benzenethiol radical scavenger does not affect the course of these photoreactions. Photosolvolysis schemes involving heterolysis (in the case of αDAlA and αDBeA) or an unstable intermediate (in the case of αDClA) are proposed.     

Heck Arylation of α,β‐Unsaturated Aldehydes

The Heck arylation of α,β‐unsaturated aldehydes is strongly dependent on the catalyst, the solvent and the base. Optimized conditions yielded either selectively cinnamyl derivatives (83%) or double arylation products (88% based on aryl conversion). A new α‐arylation of β,β‐disubstituted acrolein is also realized.     

Influence of isomer ratio and ring substituents in decomposition activation energies of α,α,α′,α′‐tetrasubstituted dibenzyls

Diethyl‐2,3‐dicyano‐2,3‐di‐(X‐substituted phenyl) succinates (X = p‐OCH₃, p‐CH₃, p‐Cl, H, p‐NO₂) can initiate the free‐radical polymerization of styrene. The decomposition rate constant and activation energy were measured by means of a dilatometer, and the results showed that they were strongly dependent on the ratio of meso‐ and dl‐isomers in the polysubstituted dibenzyl compounds and the properties of the ring substituents. On the other hand, it was found that the polystyrenes, which were obtained by initiation with hydrogen, had a much larger average molecular weight than that with p‐OCH₃ and p‐CH₃. The experimental phenomena were correlated with the structure of the radical resulting from hydrogen. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2964–2971, 2001     

Chemoselective Hydrogenation of α,β‐Unsaturated Nitriles

The chemoselective hydrogenation of cinnamonitrile to 3‐phenylallylamine proceeds with up to 80% selectivity at conversions of >90% with Raney cobalt and up to 60% selectivity with Raney nickel catalysts. Best results were obtained with a doped Raney cobalt catalyst (RaCo/Cr/Ni/Fe 2724) in ammonia saturated methanol at 100 °C and 80 bar. Major problems are the formation of hydrocinnamonitrile and of secondary amines, and overreduction to 3‐phenylpropylamine. Important parameters are the catalyst type and composition, the solvent type and the presence and concentration of ammonia. The catalytic system tolerates functional groups like OH, OMe, Cl, CO, but not aromatic nitro groups. Preliminary experiments indicate that other unsaturated nitriles with di‐ or trisubstituted CC bonds are also suitable substrates.     

Ruthenium(II)‐Catalyzed Protocol for Preparation of Diverse α,β‐ and β,β‐Dihaloenones from Diazodicarbonyls

Efficient one‐step syntheses of α,β‐ and β,β‐dihaloenones were achieved by ruthenium(II)‐catalyzed reactions between cyclic or acyclic diazodicarbonyl compounds and oxalyl chloride or oxalyl bromide in moderate to good yields. This methodology offers several significant advantages, which include ease of handling, mild reaction conditions, one‐step reaction, and the use of an effective and non‐toxic catalyst. The synthesized compounds were further transformed into highly functionalized novel molecules bearing aromatic rings on the enone moiety using the Suzuki reaction.

     

Prostaglandins and prostaglandin intermediates. XIV. Synthesis of rac-9α, 11α, 13α-trihydroxy- and rac-9α, 11α, 13β-Trihydroxy-5(Z)-prosten-15-ynoic Acid

Attempts to rearrange a β-hydroxy-alkyne with a secondary hydroxy group into an α,β-unsaturated ketone failed in the case of a potential prostaglandin intermediate. However, it was possible to convert this intermediate into 13-hydroxy-5(Z)-prosten-15-ynoic acids, which are interesting prostaglandin analogues with a modified alkyl side chain.     

Partialsynthesen von Cardenoliden und Cardenolid-Analogen. I. α,β- und β,γ-ungesättigte Lactonring-methylierte Cardenolide

Partial Syntheses of Cardenolides and Cardenolide Analogues. I. α,β- and β,γ-Unsaturated Lactone Ring-Methylated Cardenolides Base-catalyzed methylation of digitoxigenin 1a with methyl iodide and sodium hydride in DMF leads to the α,β-unsaturated cardenolides 2–5 and, after rearrangement of the CC-double bond, to the β,γ-unsaturated cardenolides 6 and 7 . Opening of the lactone ring results in the formation of 8 . Allylic oxidation of 4b affords the 14,21-epoxide 10 . Only the 22-methyl derivative 4a and its 3-O-tridigitoxoside 4d show strong biological effectivity, whereas methylation at 21R- or 21S-position results in considerable loss in activity.     

Highly Stereoselective Halocyclopropanation of α,β‐Unsaturated Amides

A convenient highly stereoselective synthesis of chloro‐ and bromocyclopropanamides from di‐ tri‐ or tetrasubstituted (E)‐ or (Z)‐α,β‐unsaturated amides with total or high stereoselectivity promoted by chromium dichloride or dibromide is described. The transformation of chlorocyclopropanamides into the corresponding ketones or amines is also reported. A mechanism to explain these transformations is proposed.     

Regio‐ and Enantioselective Copper‐Catalyzed 1,4‐Conjugate Addition of Trimethylaluminium to Linear α,β,γ,δ‐Unsaturated Alkyl Ketones

A regio‐ and enantioselective copper‐catalyzed 1,4‐conjugate addition of trimethylaluminium to linear δ‐aryl‐substituted α,β,γ,δ‐unsaturated alkyl ketones was developed. A series of γ,δ‐unsaturated alkyl ketones were obtained in good yields with high regio‐ and enantioselectivity (up to 88% ee and 96:4 dr). Expansion of the reaction scope to substrates containing aromatic heterocycles also afforded good yields and enantioselectivities (up to 91% ee) with very high regioselectivities, exclusively providing the single 1,4‐products.

     

The Reaction of α,β-Unsaturated Ethyl Esters with Vinylmagnesium Chloride

While the reaction of linear α,β-unsaturated ethyl esters with vinylmagnesium chloride yields vinyl ketones as the main product, the reaction of substituted α,β-unsaturated ethyl esters yields triethylenic carbinols.