Preparation of α,β-unsaturated diazoketones employing a Horner-Wadsworth-Emmons reagent

A new method for the preparation of α,β-unsaturated diazoketones from aldehydes and a Horner-Wadsworth-Emmons reagent is reported. The method was applied to the short synthesis of two substituted pyrrolidines.     

Selective Hydrogenation of α,β-Unsaturated Aldehydes Catalyzed by Amine-Capped Platinum-Cobalt Nanocrystals

More Greasy, More Selective: Amine-capped Pt(3) Co nanocatalysts were synthesized and used for the hydrogenation of cinnamaldehyde (CAL). Capping the catalysts with amines that contain long carbon chains results in an ordered surface "array", in which high selectivity towards C?O hydrogenation can be achieved because the C?C bond in CAL does not interact with the surface. The longer the carbon chains in the amine, the higher the selectivity.     

Selective Phosphorylation of α,β-Unsaturated Carbonyl Compounds

Abstract

Elaboration of effective methods of selective phosphorylation of α,β-unsaturated carbonyl compounds containing simultaneously C[dbnd]C and C[dbnd]O bonds, which may compete with each other or react consistently one after another, is one of the most complex problems in the modern organophosphorus synthesis. On the basis of our previous systematic investigations of kinetics and mechanism of the Pudovik and Abramov reactions in the series of α,β-unsaturated carbonyl compounds we have suggested three possible ways to solve this problem: a) soft reaction conditions, regulated by solvent, catalyst and temperature; b) interface catalysis; c) metallocomlex catalysis (reaction in the coordination sphere of transition metal).     

Homogeneous Pyrolysis of α-Naphthol

Homogeneous pyrolysis of -naphthol in argon (1 : 25 volume ratio) at 750-900°C and contact time of 1.5-4.5 s was studied. The conversion and group composition of the liquid products, and component composition of the gaseous pyrolysis products and hydrocarbons were determined; the asphaltenes formed were characterized. The kinetic parameters of -naphthol degradation and formation of methane, hydrogen, and carbon monoxide were calculated; the possible mechanisms of these processes are proposed.     

Selective synthesis of α-fluoro-β-keto- and α-fluoro-β-aminophosphonates via electrophilic fluorination by selectfluor

A series of α-mono- and α,α-difluoro-β-ketophosphonates were synthesized in moderate to good yields with excellent selectivities via electrophilic fluorination by Selectfluor. Subsequently, synthetic potential of the obtained α-monofluoro-β-ketophosphonates was demonstrated by their application in synthesis of α-monofluoro-β-aminophosphonates, useful building blocks in the preparation of phosphapeptides.     

Preparation of α-Halovinyl Sulfides by Eliminative Deoxygenation of α-Halosulfoxides

Abstract

Vinyl sulfides are useful synthetic intermediates¹ which have received increasing attention recently both as masked carbonyl moieties² and in carbon-carbon bond forming reactions.³ With regard to the latter, vinyl sulfide derivatives which are substituted in the α-position with halogen, tin, selenium, etc., are particularly useful due to the ready formation of anions upon treatment with a variety of organometallic reagents.^{3 d ? 1} We report here that synthetically useful halovinyl sulfides can be produced in high yield by the eliminative deoxygenation of the corresponding α-halosulfoxides induced by electrophilic silicon reagents.     

Selective reduction of α,β-unsaturated esters in the presence of olefins

Several α,β-unsaturated esters containing also isolated olefins or other functionalities subject to saturation were selectively reduced to the corresponding saturated esters by magnesium in methanol.     

Photocontrolled Cobalt Catalysis for Selective Hydroboration of α,β-Unsaturated Ketones

Selectivity between 1,2 and 1,4 addition of a nucleophile to an α,β-unsaturated carbonyl compound has classically been modified by the addition of stoichiometric additives to the substrate or reagent to increase their “hard” or “soft” character. Here, we demonstrate a conceptually distinct approach that instead relies on controlling the coordination sphere of a catalyst with visible light. In this way, we bias the reaction down two divergent pathways, giving contrasting products in the catalytic hydroboration of α,β-unsaturated ketones. This includes direct access to previously elusive cyclic enolborates, via 1,4-selective hydroboration, providing a straightforward and stereoselective route to rare syn-aldol products in one-pot. DFT calculations and mechanistic experiments confirm two different mechanisms are operative, underpinning this unusual photocontrolled selectivity switch.     

Pyrolysis of α-Halophosphoranes → Haloacetylenes

α-Halophosphoranes upon pyrolysis give haloacetylenes moderate yields.     

Preparation of sugar derived β,β′-dihydroxy α,α-disubstituted α-amino acids

A novel strategy for the preparation of β,β′-dihydroxy α,α-disubstituted α-amino acids bearing a sugar moiety has been developed. The procedure is based on two Henry reactions: the first Henry reaction involves a sugar aldehyde and nitroethanol to furnish a sugar derived α-hydroxymethyl α-nitroalkanol while the second Henry reaction is between this nitro sugar and formaldehyde. This sequence provided the expected epimers of sugar derived α,α-dihydroxymethyl α -nitroalkanols, from which the corresponding β,β′-dibenzyloxy α-N-benzyloxycarbonylamino esters were easily obtained. All rights reserved.     

Preparation of high-resolution 238U α-sources by electrodeposition: a comprehensive study

In this paper the source preparation procedures for high-resolution ²³⁸U sources are described and compared. This work was done within collaboration between CIEMAT and IRMM in the frame of MetroFission, a project of the European Metrology Research Programme, in order to determine the alpha-emission probabilities of ²³⁸U. ²³⁸U was deposited from organic (iso-propanol) and inorganic-H₂SO₄/(NH₄)₂SO₄, saturated NH₄NO₃-electrolyte solutions on metal backings. The parameters affecting electrodeposition were studied and optimized. The activity distribution of uranium was checked by autoradiography. Results show that the ²³⁸U source quality is significantly better using the saturated NH₄NO₃ than the two other electrolytes. By this method, sources of 18.6–22 mm diameter, 26 μg cm^?2 surface density, ~15–18 keV resolution and a peak to valley ratio higher than 50 could be made. This reconciles the inherently opposing requirements of high resolution and sufficient count rate needed to determine the alpha–emission probabilities accurately.     

Preparation of α-galactooligoglycosides by cell walls from Cryptococcus laurentii using a novel α-galactosyl donor

The cell walls of an acapsular strain of the yeast Cryptococcus laurentii catalyze the regioselective formation of α-galactooligosaccharides through self-condensation of 4-nitrophenyl α-d-galactopyranoside and of a novel activated α-galactosyl donor 2,2,2-trifluoroethyl α-d-galactopyranoside. The latter substance can be easily prepared by several methods and is highly soluble in water and therefore can be used in higher initial concentrations suppressing secondary product hydrolysis. The preparative reaction catalyzed by cell walls provided 17.4% and 2% of corresponding 2,2,2-trifluoroethyl galactobioside and galactotrioside, respectively, while the reaction with 4-nitrophenyl α-d-galactopyranoside provided the corresponding 4-nitrophenyl galactobioside and galactotrioside in 6.6 and 2.5% yields, respectively. The reactions proceeded with strict α-(1 → 6)-regioselectivity.     

Preparation of α,α-difluoroalkanesulfonic acids

Chlorodifluoromethanesulfonic acid (1) was prepared using a new procedure starting from perchloromercaptan, which is readily obtained from chlorination of CS₂. Modified Swarts reaction transformed N,N-diethyl trichloromethanesulfenamide into N,N-diethyl chlorodifluoromethanesulfenamide, and the latter species was further oxidized and hydrolyzed into chlorodifluoromethanesulfonic acid. The preparations of other two new α,α-difluoroalkanesulfonic acids, phenyl difluoromethanesulfonic acid (2) and 2-phenyl-1,1,2,2,-tetrafluoroethanesulfonic acid (3), are also disclosed. The acids 2 and 3 are stable in the forms of sodium (lithium) salts or in aqueous solutions; however, the pure forms of 2 and 3 can readily undergo defluorinations. 1-3 and their salts have potential applications as superacid catalysts and lithium battery electrolytes.     

Selective hydrogenation of α,β-unsaturated carbonyl compounds by rhodium trichloride and aliquat®-336 in a two-phase liquid system

The solvated ion pair [(C₈H₁₇)₃NCH₃]⁺[RhCl₄]⁻, formed from aqueous rhodium trichloride and Aliquat^®-336 in a two-phase liquid system, was shown to hydrogenate α,β-unsaturated ketones and esters selectively at the C-C double bonds. The reduction of benzylideneacetophenone was found to follow first-order kinetics in the substrate only below 0.2 M, and to approach second-order in H₂; at partial pressures of < 0.12 atm. The catalysis also proved to depend on the nature of the solvent, the phase transfer catalyst and the stirring rate. The observed activation energy E_a = 12.4 kcal mol⁻¹ suggests that the process is both chemically and diffusion controlled.     

Z-Selective Preparation of β-Monosubstituted α,β-Unsaturated Amides Using Diphenylphosphonoacetamides

The Horner-Wadsworth-Emmons reaction of diphenylphosphonoacetamides [(PhO) 2 P(O)CH 2 CONRR'] ( 2a : R, R' = CH 2 Ph; 2b : R = CH 2 Ph, R' = H; 2c : R = Me, R' = OMe) was examined. The reaction of 2a was found to be Z -selective for benzaldehyde with selectivities up to 94:6. Reagent 2b led to reasonable selectivity for both benzaldehyde (85:15) and 3-phenylpropionaldehyde (87:13), while 2c was somewhat effective only for the latter aldehyde (83:17).     

An Efficient Preparation of Alkyl α-Bromomethylacrylates by Dehydrobromination of Alkyl β,β′-Dibromoisobutyrates with Potassium Fluoride

1° and 2° alkyl esters of β,β′-dibromoisobutyric acid are efficiently dehydrobrominated to alkyl α-bromomethylacrylates by anhydrous potassium fluoride (2.5 equiv) in refluxing acetonitrile/DMF (85:15). 3° isobutyrates give reduced yields of acrylates due to accompanying cleavage of the ester by the HF produced.     

Preparation of α-methylene ketones by the palladium-catalyzed decarboxylation-deacetoxylation of allyl α-acetoxymethyl-β-keto carboxylates under mild conditions

α-Methylene ketones are prepared in high yields by the palladium-catalyzed decarboxylation-deacetoxylation of allyl α-acetoxymethyl-β-keto carboxylates. The reaction proceeds rapidly at room temperature under neutral conditions in acetonitrile.     

Enantioselective Hydrogenation of α,β-Unsaturated Cyclic Ketones by Double Asymmetric Induction Preparation of (R)-Muscone

(R)-Muscone[(R)-6]isanodoriferouscomPoundisolatedfromthemalemuskdeer.BecauseofthenatUralsupplyisseverelylbotofanumberofSyntheticmethodshaveaPPearedintheliteratUre['].However,eachofthepublishedenahoselechveopthehcprocessessuffersfromoneormoreofthefollowingflollgandcomplicatedprocess,lowcheforcalandophcalvields,andscarcityofstartingmaterials[2].Inl98o,TrostetaldeveloPedashortprocesstoopthesize(dl)-musconeingoodcheforca1yteld,andthestartinmaterialiseasil3'a.ailablef3];Ouradriistoobtain(R)-mu…     

2-Phenylbenzimidazoline as a Reducing Agent in the Preparation of Malononitriles from α,β-Unsaturated Dinitriles

The development of methods applicable to the selective reduction of carbon-carbon double bonds conjugated with strong electronwithdrawing group such as cyano, nitro, ester or sulfonate group has been a synthetic subject. Although several procedures¹⁾ have been employed for such selective reduction, virtually no sufficient method is known. Recently we have found²⁾ that benzylmalononitriles and 2-nitroethylbenzenes were obtained in good yields by the reactions of benzylidene-malononitriles and β-nitrostyrenes with a half molar amount of o-phenylenediamine (1), and showed that the products resulted from the reduction of the olefins by 2-phenylbenzimidazolines formed from equimolar amounts of the olefins and diamine (1). However, this reaction mode is not effective as a synthetic procedure for the reduction of the olefins because a half molar amount of the olefins is consumed to form 2-phenylbenzimidazolines.