Unsymmetrical diaryl sulfones through palladium-catalyzed coupling of aryl boronic acids and arylsulfonyl chlorides

[reaction: see text] A simple and efficient method for the synthesis of unsymmetrical diaryl sulfones using the palladium-catalyzed coupling of aryl boronic acids and arylsulfonyl chlorides has been developed. High product yields, a short reaction time, and mild reaction conditions are important features of this method.     

2,4,6-Trichloro-1,3,5-triazine Catalyzed Chemoselective Transthioacetalization of Aldehyde Acetals and Oxathioacetals

Summary. A mild and efficient transthioacetalization of aldehyde acetals and oxathioacetals was carried out using 2,4,6-trichloro-1,3,5-triazine as a mild and inexpensive catalyst. Chemoselective transacetalization is impressive as aldehyde O,O- and O,S-acetals are converted into the corresponding S,S-acetals in the presence of ketones or their acetals and oxathiocetals in nearly quantitative yields.     

Palladium catalyzed ligand-free Suzuki cross-coupling reactions of benzylic halides with aryl boronic acids under mild conditions

A highly efficient Suzuki cross-coupling reaction between benzylic halides and aryl boronic acids using palladium chloride as catalyst in acetone:water (3:1) as the solvent system has been developed. High yields of products, mild reaction conditions and short reaction times in the absence of ligand are important features of this method.     

Selective Iodination of Benzylic Alcohols with KI/H<Subscript>2</Subscript>SO<Subscript>4</Subscript> Supported on Natural Kaolinitic Clay Under Microwave Irradiation

Summary.  Benzylic alcohols are selectively converted into their corresponding iodides using KI/H₂SO₄ supported on natural kaolinitic clay and microwaves. Received August 20, 2001. Accepted (revised) September 18, 2001     

Selective Iodination of Benzylic Alcohols with KI/H2SO4 Supported on Natural Kaolinitic Clay Under Microwave Irradiation

 Benzylic alcohols are selectively converted into their corresponding iodides using KI/H₂SO₄ supported on natural kaolinitic clay and microwaves.     

Highly enantioselective aerobic oxidation of alpha-hydroxyphosphonates catalyzed by chiral vanadyl(V) methoxides bearing N-salicylidene-alpha-aminocarboxylates

An unprecedented vanadyl(V) methoxide complex 4 derived from 3,5-dibromo-N-salicylidene-l-tert-leucinate enables highly enantioselective aerobic oxidations of alpha-hydroxyphosphonates at ambient temperature with selectivity factors ranging from 3 to >99.     

Hexamethylenetetraamine-Bromine Catalyzed Rapid and Efficient Synthesis of Bis(indolyl)methanes

Summary. Highly rapid and convenient syntheses of bis(indolyl)methanes in excellent yields were carried out using the inexpensive and easily available catalyst, hexamethylenetetraamine-bromine (HMTAB). Mild reaction conditions, short reaction times, and excellent yields are important features of this method.     

Synthesis of Chiral Aziridines Through Decarboxylative Generation of Sulfur Ylides and Their Reaction with Chiral Sulfinyl Imines

Reaction of sulfur ylides with a series of aryl substituted chiral nonracemic sulfinyl imines afforded the corresponding aziridines in good yields with good stereoselectivity. The sulfur ylides were generated by the thermally induced decarboxylation of carboxymethylsulfonium betaines. A drop in the diastereomeric ratio was observed when going from electron-deficient to electron-releasing aryl substituted imines. S-Methylene aziridinations involving the decarboxylation of carboxymethylsulfonium betaine functionality complements existing technologies with the advantages of the reaction protocol, levels of conversion, and scope.     

Influence of disorder on superconductivity in non-magnetic rare-earth nickel borocarbides

The effect of substitutional disorder on the superconducting properties of YNi₂B₂C was studied by partially replacing yttrium and nickel by Lu and Pt, respectively. For the two series of (Y, Lu)Ni₂B₂C and Y(Ni, Pt)₂B₂C compounds, the upper critical field H _c2(T) and the specific heat c _p(T, H) in the superconducting mixed state have been investigated. Disorder is found to reduce several relevant quantities such as T _c, the upper critical field H _c2(0) at T=0 and a characteristic positive curvature of H _c2(T) observed for these compounds near T _c. The H _c2(T) data point to the clean limit for (Y, Lu) substitutions and to a transition to the quasi-dirty limit for (Ni, Pt) substitutions. The electronic specific heat contribution γ(H) exhibits significant deviations from the usual linear γ(H) law. These deviations reduce with growing substitutional disorder but remain even in the quasidirty limit which is reached in the Y(Ni_1−x , Pt _x )₂B₂C samples for x=0.1.     

Asymmetric aerobic oxidation of alpha-hydroxy acid derivatives by C4-symmetric, vanadate-centered, tetrakisvanadyl(V) clusters derived from N-salicylidene-alpha-aminocarboxylates

A series of chiral vanadyl(V) methoxides bearing 3-t-butyl-5-substituted N-salicylene-L-valinate and L-t-leucinate as chiral auxiliaries has been prepared. In all cases except the 3,5-di-t-butyl analogue, they exist as monomers both in solution and in the single crystal state. In the case of the 3,5-di-t-butyl analogue, the architectural nature of the vanadyl(V) complex highly depends on the base used during the complex formation event. A pentanuclear C4-symmetric complex was formed when potassium salts were employed instead of the corresponding sodium salts. A central vanadate(V) unit serves to grip four identical chiral monomeric vanadyl(V) units together, by which a potassium ion sits on top of the four flanking units through carbonyl coordinations and serves to hold the whole cluster by cooperation with the central vanadate(V) unit. In comparison with the corresponding monomeric vanadyl(V) methoxide complex, the cluster complex was utilized to facilitate the asymmetric aerobic oxidations of various racemic alpha-hydroxyesters, -amides, and -thioesters with excellent selectivity factors (krel 40 to >500).