A general and efficient reduction of acyl chlorides to aldehydes by Sm(0)/Bu3P

A facile and efficient reduction of aromatic and aliphatic acyl chlorides to their corresponding aldehydes in the presence of Sm(0)/Bu₃P has been developed with broad scope. This method prevents over reduction of products, that is, the over-reduction of aldehydes to alcohols.     

Propylphosphonic anhydride(T3P~) catalyzed one-pot synthesis of α-aminonitriles

The Strecker reaction was performed via a one-pot three component condensation of hetero aromatic/aromatic aldehydes, secondary amines and trimetylsilyl cyanide in the presence of propylphosphonic anhydride(T3P~) to accomplish the corresponding a-aminonitriles. The main advantages of this method are very short reaction time and excellent yields.     

A Molecularly Defined Iron‐Catalyst for the Selective Hydrogenation of α,β‐Unsaturated Aldehydes

A selective iron‐based catalyst system for the hydrogenation of α,β‐unsaturated aldehydes to allylic alcohols is presented. Applying the defined iron–tetraphos complex [FeF(L)][BF₄] (L=P(PhPPh₂)₃) in the presence of trifluoroacetic acid a broad range of aldehydes are reduced in high yields using low catalyst loadings (0.05–1 mol %). Excellent chemoselectivity for the reduction of aldehydes in the presence of other reducible moieties, for example, ketones, olefins, esters, etc. is achieved. Based on the in situ detected hydride species [FeH(H₂)(L)]⁺ a catalytic cycle is proposed that is supported by computational calculations.     

Stereoselective Aldol Reaction of α-Phenylseleno Esters

Abstract

The TiCl₄-catalyzed reaction of a-phenylseleno esters with aldehydes in the presence of Ph₃P or Ph₃P=O gives aldol products with high syn selectivity.     

Analytical applications of crown ethers : III. Extraction and determination of nitrophenol isomers

The oxidation of aldehydes by dicyclohexyl-18-crown-6-potassium permangante complex is presented. Results obtained by this procedure showed that the presence of crown ether (DCC) and the catalyst play an important role in the oxidation of the aldehydes. The stoichiometry found corresponds to 2 μeq of permanganate per 1 μmol of aldehydes in all cases. Alcohols and ketones are not oxidized. Finally, a method for quantitative evaluation of aldehydes is proposed.     

Transition metal-free synthesis of primary amides from aldehydes and hydroxylamine hydrochloride

Primary aromatic amides can be synthesized from aldehydes and hydroxylamine hydrochloride in the presence of Cs₂CO₃. Various aromatic aldehydes (include some heteroaromatic aldehydes) are able to generate the corresponding aromatic amides in moderate to excellent yields.     

Study on the propylphosphonic anhydride (T3P®) mediated Ugi-type three-component reaction. Efficient synthesis of an α-amino amide library

In the present work, a mild and simple synthesis of α-amino amides has been developed via the one-pot three-component ABC type Ugi reaction of a wide variety of aromatic aldehydes and primary aromatic amines, and two different aliphatic isocyanides. The reactions took place rapidly at room temperature in the presence of 1-propanephosphonic acid cyclic anhydride (T3P^®), rendering possible the highly efficient preparation of an α-amino amide library in medium to excellent yields. This study represents the first case in which T3P^® has been used in the Ugi reaction.     

T3P®-promoted Kabachnik–Fields reaction: an efficient synthesis of α-aminophosphonates

A simple and efficient synthesis of α-aminophosphonates has been developed via the one-pot three-component reactions of aldehydes, amines, and trialkyl phosphites. The reactions occurred rapidly at room temperature in the presence of 1 equiv of propylphosphonic anhydride (T3P®) as the condensing agent, and the α-aminophosphonate products were obtained in high yields.     

Green and diasteroselective oxidative cyclization of bisnaphthols to spirans

Hydrogen peroxide/MoO₃, as an efficient and clean oxidizing system was used to afford diasteroselective oxidative cyclization of bisnaphthols to spirans in ethanol at 60 °C with high yields. Bisnaphthols were prepared by the reaction of a series of aldehydes and 2-naphthol in the presence of a catalytic amount of H₃[P(Mo₃O₁₀)₄].nH₂O (HPa) in refluxing dichloromethane.     

One-pot tandem approach for the synthesis of benzimidazoles and benzothiazoles from alcohols

Propylphosphonic anhydride (®T3P) has been demonstrated to be an efficient and mild reagent for the one-pot synthesis of benzimidazoles and benzothiazoles from variety of alcohols. Mild conditions, short reaction time, broad functional group tolerance, low epimerization, easy and quick isolation of the products, excellent chemo selectivity, and excellent yields are main advantages of this procedure. Thus, the present method is utilizing alcohols instead of aldehydes.     

Lanthanoids in organic syntheses 7. selective reductions of carbonyl groups in aqueous ethanol solution.

Trivalent lanthanoid ions were shown to permit the selective reductions of conjugated aldehydes in the presence of non-conjugated ones. CrCl₃ is also effective in selective ketone reduction in the presence of aldehydes.     

(R)- and (S)-4-TIPS-3-butyn-2-ol. Useful precursors of chiral allenylzinc and indium reagents

A convenient route to the enantiomers of 4-TIPS-3-butyn-2-ol of >95% enantiomeric purity by reduction of the ynone precursor 4 with the Noyori N-tosyl-1,2-diphenylethylenediamineruthenium cymene catalyst is described. The mesylate derivative of the (S) enantiomer (1c) is converted in situ to an allenylzinc or indium reagent in the presence of a catalyst derived from Pd(OAc)2 and Ph3P and either Et2Zn or InI. A second in situ addition of these reagents to aldehydes leads to anti homopropargylic alcohol adducts. The additions proceed in generally high (60-90%) yield with modest to excellent diastereoselectivity and high enantioselectivity. Only slight mismatching (<5%) is observed with chiral alpha-methyl and alpha-silyloxy aldehydes. Additions to alpha-substituted enals are highly diastereoselective, while beta,beta-disubstituted enals afford ca. 2:1 mixtures of anti and syn adducts.     

Generation of phosphoranes derived from phosphites. A new class of phosphorus ylides leading to high E selectivity with semi-stabilizing groups in Wittig olefinations

Tosylhydrazones derived from aryl aldehydes react with t-BuOK, ClFeTPP, (MeO)3P, and aldehydes to furnish olefins with high E selectivity. These reactions occur through a Wittig-type pathway via the corresponding diazo compounds, metal carbenes and phosphorous ylides, with the water-soluble trimethyl phosphate as the byproduct. Similar reactions can also be performed using ethyl diazoacetate; however, high E selectivity was only observed in the presence of LiBr. In this case, the reaction is believed to occur via the phosphonate anion, formed through an Arbuzov reaction. Thus this olefination reaction occurs through a Horner-Wadsworth-Emmons (HWE) reaction but the phosphonate anion is generated under completely base-free conditions.     

Kinetics of catalytic Meerwein-Ponndorf-Verley reduction of aldehydes and ketones using boron triethoxide

Catalytic Meerwein-Ponndorf-Verley (MPV) reduction of various aliphatic, aromatic, and unsaturated aldehydes and ketones to corresponding alcohols (analyzed by GC-MS) in the presence of boron triethoxide (B(OEt)₃) were studied. Kinetics of this reduction reaction was also studied and the respective rate constants were determined. It was found that B(OEt)₃ catalyzes the reduction of aliphatic aldehydes and ketones to alcohols at room temperature while aromatic aldehydes and ketones were not reduced under the same conditions. In addition, MPV reduction using B(OEt)₃ was found to be chemoselective as unsaturated aldehydes and ketones afforded the corresponding alcohols without affecting unsaturated groups. The mechanism proposed involves a six-membered transition state in which both the alcohol and the carbonyl are coordinated to the same boron centre of a boron alkoxide catalyst.     

Synthesis of novel 5-hydroxyalkenylphosphonates by addition of aromatic aldehydes to zirconacyclopentenylphosphonates

Novel 5-hydroxyvinylphosphonates were obtained in a regio- and stereoselective manner, by addition of aromatic aldehydes to zirconacyclopentenylphosphonates in the presence of AlMe₃, in 68-82% isolated yields. The reaction is specific for aromatic aldehydes.     

Rare earth triflates/chlorotrimethylsilane induced activation of triethylamine as a latent acetaldehyde anion: a new synthesis of α,β-unsaturated aldehydes

A synthetic methodology for α,β-unsaturated aldehydes employing rare earth triflate is reported. Activated triethylamine reacts with aldehydes to form two carbon extended aldehydes, which is promoted by a catalytic amount of Yb, Sc, Y, and In(OTf)₃, in the presence of chlorotrimethylsilane. We investigated the conditions applicable to aromatic aldehydes as well as heterocyclic compounds as substrates. A deuterium labeling experiment supported our proposed reaction mechanism.     

A new Yb-catalyzed pinacol and imine-coupling reaction

Ytterbium triflate, Yb(OTf)₃, catalyzes the intermolecular reductive homocouplings of imines, aldehydes, and ketones at loadings of 5 mol % in the presence of Mg and Me₃SiCl to give isolated yields of up to 95%. Diastereoselectivity of up to 4/96 (dl/meso) is achieved for aromatic aldehydes, up to 100% dl for aliphatic aldehydes, and 100% dl for an intramolecular imine coupling.     

Barbier allylation-Prins reaction of PEG-bound aldehydes—soluble polymer-supported synthesis of 2,4,6-trisubstituted tetrahydropyrans

PEG-bound aldehydes undergo zinc-mediated Barbier allylation to form homoallylic alcohols, which on further reaction with various aldehydes in the presence of BF₃·Et₂O through a Prins cyclization afford 4-hydroxytetrahydropyrans and 4-fluorotetrahydropyrans.     

One-pot synthesis of diaryl ketones from aldehydes via palladium-catalyzed reaction with aryl boronic acids

A Pd-catalyzed coupling-type reaction of aldehydes and organoboronic acids was achieved in the presence of P(1-nap)₃, using Cs₂CO₃ in toluene, providing diaryl ketones with yields ranged from moderate to excellent. The efficiency of this reaction was demonstrated by the compatibility with nitro, cyano, trifluoromethyl, fluoro and chloro groups. Moreover, the rigorous exclusion of air/moisture is not required in these transformations.     

Allylcyanation of alkynes: regio- and stereoselective access to functionalized di- or trisubstituted acrylonitriles

Allyl cyanides are found to add across alkynes in the presence of a nickel catalyst prepared from Ni(cod)2 and P(4-CF3-C6H4)3 in situ to give variously functionalized di- or trisubstituted acrylonitriles in highly stereoselective manners possibly via a pi-allylnickel species as an intermediate. alpha-Siloxyallyl cyanides also react at the gamma-position of a cyano group with both internal and terminal alkynes having various functional groups to give silyl enol ethers, which give the corresponding aldehydes or ketones upon hydrolysis.