Practically Perfect Asymmetric Autocatalysis with (2‐Alkynyl‐5‐pyrimidyl)alkanols

Extremely high enantioselectivity (>99.5% ee) and chemical yield (>99%) are achieved in an asymmetric autocatalytic reaction. A (5‐pyrimidyl)alkanol with a tert‐butylethynyl group at its 2‐position ( 1 ) is a very efficient asymmetric autocatalyst in the enantioselective alkylation in Equation (1).     

A Versatile and Practical Synthesis of 1,1‐Diacetates from Aldehydes Catalyzed by Cyanuric Chloride

Structurally diverse aldehydes are successfully converted into 1,1‐diacetates with acetic anhydride using cyanuric chloride as a mild, convenient and inexpensive catalyst under solvent‐free conditions. The noteworthy features of the present system are shorter reaction times, and mild and solvent‐free conditions. Furthermore, it offers chemoselective protection of aldehydes.     

Zinc Chloride Anhydrous as New and Effective Catalyst for Conversion of Ketones and Aldehydes to Corresponding Gem‐dihydroperoxides

Zinc chloride anhydrous has been used as an efficient and new catalyst for conversion of ketones and aldehydes to corresponding gem‐dihydroperoxides by aqueous hydrogen peroxide (30%) in room temperature with excellent yields and notable reaction times.     

Reductive Coupling of Acrylates with Ketones and Ketimines by a Nickel‐Catalyzed Transfer‐Hydrogenative Strategy

Nickel‐catalyzed coupling of benzyl acrylates with activated ketones and imines provides γ‐butyrolactones and lactams, respectively. The benzyl alcohol byproduct released during the lactonization/lactamization event is relayed to the next cycle where it serves as the reductant for C−C bond formation. This strategy represents a conceptually unique approach to transfer‐hydrogenative C−C bond formation, thus providing examples of reductive heterocyclizations where hydrogen embedded within an alcohol leaving group facilitates turnover.     

Nickel‐Catalyzed Dimerization and Alkylarylation of 1,3‐Dienes with Alkyl Fluorides and Aryl Grignard Reagents

In the presence of a nickel catalyst, 1,3‐butadiene undergoes selective dimerization and alkylarylation with alkyl fluorides and aryl Grignard reagents to give 1,6‐octadienes with alkyl and aryl groups at the 3‐ and 8‐positions, respectively, by the consecutive formation of three carbon–carbon bonds. The formation of an anionic nickel complex plays an important role in forming C?C bonds with alkyl fluorides.     

N‐Heterocyclic Carbene‐Catalyzed α‐Alkylation of Ketones with Primary Alcohols

Several N‐heterocyclic carbene precursors are synthesized and used in the α‐alkylations of ketones with primary alcohols. With the assistance of a base, these N‐heterocyclic carbenes can catalyze the reaction smoothly to furnish dialkylated ketones in good‐to‐excellent yields.     

Nickel‐Catalyzed Carbofluoroalkylation of 1,3‐Enynes to Access Structurally Diverse Fluoroalkylated Allenes

A nickel‐catalyzed 1,4‐carbofluoroalkylation of 1,3‐enynes to access structurally diverse fluoroalkylated allenes has been established. This method has demonstrated high catalytic reactivity, mild reaction conditions, broad substrate scope, and excellent functional‐group tolerance. The key to success is the use of a nickel catalyst to generate different fluoroalkyl radicals from readily available and structurally diverse fluoroalkyl halides to access 1,4‐difunctionalization of 1,3‐enynes by a radical relay. This strategy provides facile synthesis of structurally diverse multisubstituted allenes, and offers a solution for batch production of various fluorinated bioactive molecules for drug discovery by further transformations.     

Nickel‐Catalyzed α‐Allylation of Aldehydes and Tandem Aldol Condensation/Allylation Reaction with Allylic Alcohols

An additive‐free nickel‐catalyzed α‐allylation of aldehydes with allyl alcohol is reported. The reaction is promoted by 1 mol % of in situ formed nickel complex in methanol, and water is the sole by‐product of the reaction. The experimental conditions allow the conversion of various α‐branched aldehydes and α,β‐unsaturated aldehydes as nucleophiles. The same catalyst and reaction conditions enabled a tandem aldol condensation of aldehyde/α‐allylation reaction.     

Nickel‐Catalyzed Reductive Coupling of Aldehydes with Alkynes Mediated by Alcohol†

A nickel‐catalyzed reductive coupling of aldehydes with alkynes using 1‐phenylethanol as reducing agent has been developed. The key achievement of this work is that we demonstrate environmentally benign 1‐phenylethanol can serve as a viable alternative reducing agent to Et₃B, ZnEt₂ and R₃SiH for the nickel‐catalyzed reductive coupling reaction of aldehyde and alkynes.     

Enantioselective Synthesis of Functionalized Arenes by Nickel‐Catalyzed Site‐Selective Hydroarylation of 1,3‐Dienes with Aryl Boronates

A catalytic method for the site‐selective and enantioselective synthesis of functionalized arenes by the intermolecular hydroarylation of terminal and internal 1,3‐dienes with aryl pinacolato boronates is reported. The reactions are promoted by 5.0 mol % of a readily available monodentate phosphoramidite‐Ni complex in ethanol, affording a variety of enantioenriched products in up to 96 % yield and 99:1 er. Mechanistic studies indicate that Ni–allyl formation is irreversible and related to the nature of the arylboronate.     

Cyanosilylation of Aldehydes and Ketones Catalyzed by Nanocrystalline Magnesium Oxide

Abstract

Cyanosilylation of various aldehydes and ketones with TMSCN proceeded smoothly under mild conditions to give the corresponding cyanohydrin trimethylsilyl ethers in the presence of nanocrystalline magnesium oxide. The cyanohydrin trimethylsilyl ethers of aldehydes produced cyanohydrins in good to high yields on treatment with 2 N HCl. ²⁹Si NMR spectral evidence proved that the reaction proceeds through the hypervalent silicate species by coordination to O^2?/O^? (Lewis basic site) of nanocrystalline magnesium oxide.     

Solvent-Free Crossed Aldol Condensation of Ketones with Aromatic Aldehydes Mediated by Magnesium Hydrogensulfate

Summary.  Crossed aldol condensations of ketones with aromatic aldehydes are carried out efficiently in the presence of magnesium hydrogensulfate under solvent-free conditions in good to excellent yield without the occurrence of any self-condensation. Similar reactions in solution do not proceed satisfactorily. Corresponding authors. E-mail: p-salehi@cc.sbu.ac.ir Received September 20, 2001. Accepted (revised) January 16, 2002