Direct Decarboxylative Alkynylation of α,α‐Difluoroarylacetic Acids under Transition Metal‐Free Conditions

An efficient and generally applicable protocol for decarboxylative coupling of α,α‐difluoroarylacetic acids with ethynylbenziodoxolone (EBX) reagents has been developed, affording α,α‐difluoromethylated alkynes bearing various functional groups in moderate to excellent yields. Remarkably, this potassium persulfate (K₂S₂O₈)‐promoted reaction employs water as solvent under transition metal‐free conditions, thus providing a green synthetic approach to α,α‐difluoromethylated alkynes.

     

Organocatalytic Enantioselective Aziridination of α‐Substituted α,β‐Unsaturated Aldehydes: Asymmetric Synthesis of Terminal Aziridines

The first example of a highly enantioselective organocatalytic aziridination of α‐substituted α,β‐unsaturated aldehydes is presented. The reaction is catalyzed by simple chiral amines and gives access to highly functional terminal azirdines containing an α‐tertiary amine stereocenter in high yields and enantiomeric ratios (95.5:4.5–98:2).     

Catalytic Hydrogenation of α‐Iminophosphonates as a Method for the Synthesis of Racemic and Optically Active α‐Aminophosphonates

It was shown that the catalytic hydrogenation of α‐iminophosphonates by molecular hydrogen can serve as a convenient method for the synthesis of racemic and optically active α‐aminophosphonates. Up to 94% ee was achieved in the rhodium‐catalyzed enantioselective hydrogenation using chiral ligand (R)‐BINAP.     

Palladium(II)‐Catalyzed Aerobic Intermolecular Cyclization of Acrylic Acid with Alkenes to α‐Methylene‐γ‐butyrolactones

The methodology in this article is a palladium(II)/copper(II)‐ or palladium(II)‐catalyzed intermolecular cyclization of acrylic acid with alkenes to produce α‐methylene‐γ‐butyrolactone derivatives using molecular oxygen as an environmentally benign oxidant. In this system, the carboxylato, especially trifluoroacetato, or trimethylacetato ligand, plays a quite important role to afford a high catalytic activity by suppressing the deposition of palladium(0) black.     

Structural characterization of α‐ and β‐nucleated isotactic polypropylene

Modification of isotactic polypropylene (iPP) with two nucleation agents, namely 1,3:24‐bis(3,4‐dimethylobenzylideno) sorbitol (DMDBS) (α‐nucleator) and N, N′‐dicyclohexylo‐2,6‐naphthaleno dicarboxy amide (NJ) (β‐nucleator), leads to significant changes of the structure, morphology and properties. Both nucleating agents cause an increase in the crystallization temperature. The efficiency determined in a self‐nucleation test is 73.4 % for DMDBS and 55.9 % for NJ. The modification with NJ induces the creation of the hexagonal β‐form of iPP. The addition of DMDBS lowers the haze of iPP while the presence of NJ increases the haze. Copyright © 2004 Society of Chemical Industry     

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.

     

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.

     

Highly Enantioselective Phase‐Transfer Catalytic α‐Alkylation of α‐tert‐Butoxycarbonyllactams: Construction of β‐Quaternary Chiral Pyrrolidine and Piperidine Systems

A new enantioselective α‐alkylation of α‐tert‐butoxycarbonyllactams for the construction of β‐quaternary chiral pyrrolidine and piperidine core systems is reported. α‐Alkylations of N‐methyl‐α‐tert‐butoxycarbonylbutyrolactam and N‐diphenylmethyl‐α‐tert‐butoxycarbonylvalerolactam under phase‐transfer catalytic conditions (solid potassium hydroxide, toluene, −40 °C) in the presence of (S,S)‐3,4,5‐trifluorophenyl‐3,3′,5,5′‐tetrahydro‐2,6‐bis(3,4,5‐trifluorophenyl)‐4,4′‐spirobi[4H‐dinaphth[2,1‐c:1′,2′‐e]azepinium] bromide [(S,S)‐NAS Br] (5 mol%) afforded the corresponding α‐alkyl‐α‐tert‐butoxycarbonyllactams in very high chemical (up to 99%) and optical yields (up to 98% ee). Our new catalytic systems provide attractive synthetic methods for pyrrolidine‐ and piperidine‐based alkaloids and chiral intermediates with β‐quaternary carbon centers.     

Cationic copolymers of α,β‐poly‐(N‐2‐hydroxyethyl)‐DL‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy): synthesis and characterization

In the present study the derivatization of two water‐soluble synthetic polymers, α,β‐poly(N‐2‐hydroxyethyl)‐DL ‐aspartamide (PHEA) and α,β‐polyasparthylhydrazide (PAHy), with glycidyltrimethylammonium chloride (GTA) is described. This reaction permits the introduction of positive charges in the macromolecular chains of PHEA and PAHy in order to make easier the electrostatic interaction with DNA. Different parameters affect the reaction of derivatization, such as GTA concentration and reaction time. PHEA reacts partially and slowly with GTA; on the contrary the reaction of PAHy with GTA is more rapid and extensive. The derivatization of PHEA and PAHy with GTA is a convenient method to introduce positive groups in their chains and it permits the preparation of interpolyelectrolyte complexes with DNA. © 2000 Society of Chemical Industry     

Highly Enantioselective Michael Addition of Cyclic 1,3‐Dicarbonyl Compounds to β,γ‐Unsaturated α‐Keto Esters

A highly enantioselective Michael addition of cyclic 1,3‐dicarbonyl compounds to β,γ‐unsaturated α‐keto esters catalyzed by amino acid‐derived thiourea‐tertiary‐amine catalysts is presented. Using 5 mol% of a novel tyrosine‐derived thiourea catalyst, a series of chiral coumarin derivatives were obtained in excellent yields (up to 99%) and with up to 96% ee under very mild conditions within a short reaction time.     

Interface formation of Ca with poly(p-phenylene α,α′-diphenyl vinylene) and poly(p-phenylene α-phenyl vinylene)

We have investigated the interface formation of Ca with poly(p-phenylene α,α′-diphenyl vinylene) (PPV-DP) and poly(p-phenylene α-phenyl vinylene) (PPV-P) using X-ray photoemission spectroscopy (XPS). Similarly to our earlier findings in metal/PPV interface formation, the O 1s peak shifted toward a lower binding energy as soon as Ca was deposited on to the polymers. This was accompanied by the formation of Ca? O, suggesting a chemical origin for the O 1s shift. By contrast, the C 1s peak shift toward a lower binding energy was observed relatively later, after about 4 Å of Ca deposition. At the same time, a new C 1s component became noticable at about ?1.5 eV relative to the initial C 1s peak. This component signifies the possibility of polymer disruption by the Ca atoms to form Ca? C species. The C 1s peak shift is attributed to Ca induced surface band bending and barrier formation as in the case of metal/PPV interface formation. The disruption of the polymer may also induce changes in the interface electronic states and contribute to the C 1s peak shift. From the intensity attenuation analysis, we conclude that the initial 15 Å of Ca overlayer is contaminated by the Ca? O and Ca? C species and the overlayer is pure beyond 15 Å of Ca coverage.     

Commercial synthesis of α-D-cellobiosyl bromide heptaacetate

A detailed commercial process for the synthesis and purification of the activated disaccharide, α-D -cellobiosyl bromide heptaacetate ( 1 ) was developed. Reaction of α-D -cellobiose octaacetate (CBO) with HBr in glacial acetic acid or in glacial acetic acid/methylene chloride combination affords α-D -cellobiosyl bromide heptaacetate in high yield and excellent quality. Process variables such as reaction solvent, reaction time, reaction temperature, HBr stoichiometry, isolation methods and product purification options were optimized for large-scale synthesis. α-D -Cellobiosyl bromide heptaacetate was successfully prepared in a commercial manufacturing plant.     

Efficient Synthesis of β,γ‐Alkynyl α‐Amino Acid Derivatives by Ag(I)‐Catalyzed Alkynylation of α‐Imino Esters

The first catalytic synthesis of β,γ‐alkynyl α‐amino acid derivatives was achieved by direct addition of terminal alkynes to α‐imino esters in the presence of an Ag(I) salt under mild reaction conditions.     

Oxidation at elevated temperatures: competition between α‐tocopherol and unsaturated triacylglycerols

The competitive oxidation between α‐tocopherol and unsaturated fatty acyls at thermoxidation conditions (180 and 240 °C) was evaluated using purified triacylglycerols from nine fats and oils (refined coconut, palm, tallow, olive, high oleic sunflower, sunflower, corn, soybean, and flaxseed oil). α‐Tocopherol degraded faster in less unsaturated lipids and a linear correlation between the iodine value (x) and the residual tocopherol content (y) was obtained after 2 h of heating at 240 °C (y = 3.72x + 137.5, R² = 0.9463). The formation of polar oxidation products was established and the results were explained by a non‐selective oxidation of unsaturated fatty acyls and α‐tocopherol by highly reactive alkoxyl and hydroxyl radicals generated by decomposition of hydroperoxides.     

Asymmetric Synthesis of 3,4‐Dihydrocoumarins Bearing an α,α‐Disubstituted Amino Acid Moiety

An organocatalytic approach for the stereoselective synthesis of 3,4‐dihydrocoumarins with an α,α‐disubstituted amino acid moiety incorporated is presented. The developed methodology is based on the cascade reaction between α‐substituted azlactones and 2‐hydroxychalcones. It is initiated by a chiral Brønsted base‐catalyzed enantio‐ and diastereoselective Michael reaction followed by the azlactone ring opening to construct a 3,4‐dihydrocoumarin framework. Products bearing two adjacent stereogenic centers, one being quaternary, were formed with high enantioselectivities and excellent diastereoselectivities. Furthermore, the complete regioselectivity of the new cascade reactivity is worthy of notice.

     

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.     

RuO4 staining and lamellar structure of α‐ and β‐PP

Monoclinic (α) and hexagonal (β) polypropylene (α‐ and β‐PP) were stained in the vapor of a ruthenium tetroxide solution prepared in situ. The effect of staining on the fusion behavior was investigated using a DSC. A staining duration between 10 and 24 h was found suitable for obtaining a good electron contrast between the crystalline and amorphous regions for TEM examination without causing severe damage to the crystals. The spherulites of the water‐quenched α‐PP were found to be composed of very fine cross‐hatched lamellae whose long period was about 10 nm. In comparison, the β‐PP spherulites crystallized isothermally at 130°C had a category 2 morphology and the lamellae have a long period of 20 nm. The morphology of the spherulite boundary varied depending on the contact angle between the lamellae of the neighboring spherulites. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1529–1538, 1999     

The Synthesis of trans‐Perhydroindolic Acids and their Application in Asymmetric Domino Reactions of Aldehyde Esters with β,γ‐Unsaturated α‐Keto Esters

(2S,3aR,7aS)‐Perhydroindolic acid, the key intermediate in the synthesis of trandolapril, and its trans‐isomers, were readily prepared. These proline‐like molecules are unique in that they contain a rigid bicyclic structure, with two hydrogen atoms trans to each other at the bridgehead carbon atoms. These molecules were used successfully as chiral organocatalysts in asymmetric domino Michael addition/cyclization reactions of aldehyde esters with β,γ‐unsaturated α‐keto esters. They proved to have excellent catalytic behavior, allowing for the synthesis of multi‐substituted, enantiomerically enriched hemiacetal esters. Under optimal conditions (using 10 mol% catalyst loading), a series of β,γ‐unsaturated α‐keto esters was examined with up to 99% de, ee and yield, respectively. Additionally, the enantiomerically enriched hemiacetal esters could be readily transformed into their corresponding bioactive pyrano[2,3‐b]pyrans (possessing a multi‐substituted bicyclic backbone).     

Synthesis of α‐Arylphosphonates using Copper‐Catalyzed α‐Arylation and Deacylative α‐Arylation of β‐Ketophosphonates

Efficient methods for the direct arylation and deacylative arylation of β‐ketophosphonates with iodoarenes in presence of a copper(I) or a copper(II) salt as the catalysts have been developed. The corresponding α‐arylphosphonates were obtained in high yields. A tentative mechanism for the deacylative arylation reaction was proposed on the basis of the experimental data.