Action des dialkylcuprates de lithium sur les aldéhydes α,β -éthylénioues

Nearly exclusive 1-4 addition produts obtained by action of lithium dialkylcuprates with α,β ethylenic aldehydes. Non polar solvents and low temperatures favour this reaction .Only α,β-ehylenic aldehydes having a trisubstituted double bond give a relatively important proportation of 1–2 addition product.     

Selective Reductions with Sodium Borohydride in Dimethyl Sulphoxide with Added Metal Salts

Sodium borohydride in Dimethyl Sulphoxide in the presence of added metal salts selectively reduces aldehydes in the presence of ketones and converts α,β -unsaturated ketones to the corresponding unsaturated alcohols.     

Oxidation of Alcohols with Polymeric Reagent of Poly [Vinyl (Pyridinium Fluorochromate)]

Poly [Vinyl (Pyridinium Fluorochromate)] is a new reagent for the selective oxidation of primary and secondary alcohols under mild conditions. It also oxidises aromatic and α,β - unsaturated alcohols to the corresponding aldehydes and ketones in good yield.     

Acid catalysis in aldol condensation of α-amino silyl ketene acetals. Diastereoselective synthesis of α-amino-β-hydroxyacids.

The aldol-type condensation between α-dibenzylamino trimethylsilyl ketene acetals and various achiral and chiral aldehydes in the presence of a Lewis acid furnishes α-amino-β -hydroxyacids in moderate yields with preferential C₂C₃$\text{threo}$ configuration.     

A novel approach to Morita-Baylis-Hillman (MBH) lactones via the Lewis acid-promoted couplings of α,β-unsaturated lactone with aldehydes

The Morita-Baylis-Hillman (MBH)-type reaction of α,β unsaturated δ-lactone with various aldehydes has been achieved without the direct use of a Lewis base. The new MBH process can be conveniently carried out by the slow addition of the diethylaluminum iodide into the solution of lactone and aldehyde in dichloromethane at 0°C. Modest to good yields were obtained (50-65%) for eight examples.     

Probing α-Amino Aldehydes as Weakly Acidic Pronucleophiles: Direct Access to Quaternary α-Amino Aldehydes by an Enantioselective Michael Addition Catalyzed by Brønsted Bases

The high tendency of α-amino aldehydes to undergo 1,2-additions and their relatively low stability under basic conditions have largely prevented their use as pronucleophiles in the realm of asymmetric catalysis, particularly for the production of quaternary α-amino aldehydes. Herein, it is demonstrated that the chemistry of α-amino aldehydes may be expanded beyond these limits by documenting the first direct α-alkylation of α-branched α-amino aldehydes with nitroolefins. The reaction produces densely functionalized products bearing up to two, quaternary and tertiary, vicinal stereocenters with high diastereo- and enantioselectivity. DFT modeling leads to the proposal that intramolecular hydrogen bonding between the NH group and the carbonyl oxygen atom in the starting α-amino aldehyde is key for reaction stereocontrol.     

Aldehyde enolates III direct sulfenylation and iodination of aldehyde anions.

Directly generated potassium enolates of aldehydes react with diphenyldisulfide to give the α-sulfenylated aldehydes. Reaction with iodine likewise provides the α-iodo aldehydes.     

Diastereoselective synthesis of β-substituted α-hydroxyphosphinates through hydrophosphinylation of α-heteroatom-substituted aldehydes

The diastereoselective synthesis of β-substituted α-hydroxyphosphinates was achieved by hydrophosphinylation of α-oxy aldehydes and α-amino aldehydes with ethyl allylphosphinate catalyzed by lithium phenoxide.     

Organocatalyzed asymmetric α-hydroxyamination of α-branched aldehydes: asymmetric synthesis of optically active N-protected α,α-disubstituted amino aldehydes and amino alcohols

Enantioselective direct α-hydroxyamination and α-aminoxylation of α-branched aldehydes using a proline-derived tetrazole catalyst is described herein. α-Hydroxyamination adducts with up to 90% ee were obtained by the reaction of nitrosobenzene with unactivated α-branched aldehydes under mild reaction conditions.     

Regio and stereoselective synthesis of 1-methylseleno-1-vinyl and 1-phenylseleno-1-vinyl cyclopropanes

The Z and E teomers of the title compounds are regioselectivity and stereoselectively prepared respectively by reaction of phosphorus ylides with α-selenocyclopropyl aldehydes and by addition of α-lithio seleno-cyclopropanes on α-seleno aldehydes.     

Influence of α-methyl substitution of proline-based organocatalysts on the asymmetric α-oxidation of aldehydes

The direct asymmetric organocatalytic α-oxidation of aldehydes using trans-2-(p-methylphenylsulfonyl)-3-phenyloxaziridine is reported. This method affords the S isomer of α-hydroxy aldehydes, thereby complementing the selectivity for the R isomer observed using the two-step nitrosobenzene method. Use of α-methylproline and α-methylproline tetrazole significantly increases the enantioselectivity observed for the α-oxidation of aldehydes compared to analogous unsubstituted organocatalysts.     

Primary amine catalyzed electrophilic amination of α,α-disubstituted aldehydes

Organocatalytic α-amination of α,α-disubstituted aldehydes promoted by 9-amino-(9-deoxy)-epi-quinine is described. α-Hydrazino aldehydes bearing a quaternary stereogenic center are obtained in good to excellent yields and enantioselectivities.     

Nucleophilic acylation of α-haloketones with aldehydes: an umpolung strategy for the synthesis of 1,3-diketones

The first example of N-heterocyclic carbene (NHC)-promoted intermolecular acylation of α-haloketones with aldehydes and α,β-unsaturated aldehydes (enals) is reported. The protocol involves carbonyl umpolung reactivity of aldehydes and enals in which the carbonyl carbon attacks nucleophilically on electrophilic terminal of α-haloketones to afford 1,3-diketones and α,β-unsaturated 1,3-diketones, respectively. Short reaction time, ambient temperature, operational simplicity, and high yields are the salient features of the present procedure.     

Synthetic applications of the amine-base treatment in the ozonolysis of substituted-allyl silyl ethers or -allyl esters via a novel ene-diol type rearrangement

The ozonolysis of substituted-allyl silyl ethers or -allyl esters followed by treatment with bases gave the corresponding α-silyloxy ketones or α-acyloxy ketones in good yields. The reaction is proposed to proceed via a novel ene-diol rearrangement of the corresponding α-silyloxy aldehydes or α-acyloxy aldehydes intermediates.     

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.     

Synthesis of 1-hydrocarbon substituted cyclopropyl silyl ketones

The synthesis of cyclopropyl silyl ketones possessing a hydrocarbon group at 1-position of three-membered ring was investigated. The reaction of sulfoxonium ylide with α,β-unsaturated acylsilanes derived from α,β-unsaturated aldehydes did not afford the desired acylsilane derivatives. Instead, the corresponding silyl enol ethers were yielded exclusively. On the other hand, the Corey-Chaykovsky cyclopropanation of α-substituted α,β-unsaturated aldehydes proceeded well to give 1-substituted cyclopropyl aldehydes. The silyl substitution of formyl proton in the obtained aldehydes via umpolung of carbonyl group afforded the target acylsilanes.     

Direct proline catalyzed asymmetric α-aminooxylation of aldehydes

The direct catalytic enantioselective α-aminooxylation of aldehydes has been developed using nitrosobenzene as the oxygen source and l-proline as catalyst, affording versatile α-aminooxylated aldehydes in high yield with excellent enantioselectivities.     

Domino‐Hydroformylation/Aldol Condensation Catalysis: Highly Selective Synthesis of α,β‐Unsaturated Aldehydes from Olefins

A general and highly chemo‐, regio‐, and stereoselective synthesis of α,β‐unsaturated aldehydes by a domino hydroformylation/aldol condensation reaction has been developed. A variety of olefins and aromatic aldehydes were efficiently converted into various substituted α,β‐unsaturated aldehydes in good to excellent yields in the presence of a rhodium phosphine/acid–base catalyst system. In view of the easy availability of the substrates, the high atom‐efficiency, the excellent selectivity, and the mild conditions, this method is expected to complement current methodologies for the preparation of α,β‐unsaturated aldehydes.     

Direct organocatalytic asymmetric α-hydroxymethylation of ketones and aldehydes

Direct organocatalytic asymmetric α-hydroxymethylation of ketones and aldehydes with formaldehyde has been developed, which furnished the corresponding α-hydroxymethylated adducts with high chemo- and enantioselectivity. The reaction is catalyzed by proline derivatives and is a simple method for the enantioselective synthesis of α-hydroxymethylated ketones and aldehydes, and C-2 symmetric diols.     

Proline and Lewis base co-catalyzed addition of α,β-unsaturated aldehydes to nitrostyrenes

A novel proline and DABCO co-catalyzed reaction between unmodified α,β-unsaturated aldehydes and nitrostyrenes, which gives access to α-(1-aryl-2-nitro)ethyl-α,β-unsaturated aldehydes, is presented.