An ultrasound-promoted green approach for the N-formylation of amines under solvent- and catalyst-free conditions at room temperature

A new environmentally benign, convenient, and facile methodology for the N-formylation of amines is reported using ultrasound irradiation under solvent- and catalyst-free conditions at room temperature. Compared with conventional methods, the main advantages of the present procedure are milder, cleaner and greener conditions, shorter reaction time, higher purity and yields, simpler work-up, and lower generation of waste or pollutions.     

A remarkably simple N-formylation of anilines using polyethylene glycol

N-Formylation of anilines has efficiently been carried out at room temperature in excellent yields by treatment with formic acid in polyethylene glycol (PEG-400). No additional solvent and catalyst are required.     

Formylation without catalyst and solvent at 80 °C

A simple and efficient protocol for N-formylation of aliphatic and heterocyclic amines has been described with formic acid in the absence of catalyst and solvent.     

Lewis acid-catalyzed Friedel-Crafts acylation reaction using carboxylic acids as acylating agents

Rare-earth metal Lewis acids, in particular Eu(NTf₂)₃, were found to be efficient catalysts for Friedel-Crafts acylation reaction using aliphatic as well as aromatic carboxylic acids as acylating agents at high temperature.     

Direct N-alkylation of amines with alcohols using AlCl_3 as a Lewis acid

A substitution reaction of amines with alcohols for N-alkylated amines has been developed using inexpensive AlCl_3 without any ligand or additive.Either aromatic or aliphatic amines and primary or secondary alcohols perform the AlCl_3-mediated reaction smoothly to afford various N-alkylated amines in satisfactory yields.     

Synthesis of 1-tetralones by intramolecular Friedel-Crafts reaction of 4-arylbutyric acids using Lewis acid catalysts

Intramolecular Friedel-Crafts reaction of 4-arylbutyric acids efficiently proceeded in the presence of catalytic amounts of Lewis acids such as Bi(NTf₂)₃ and M(OTf)₃ (M=Bi, Ga, In and rare-earth metals) to form 1-tetralones. Chroman-4-one and thiochroman-4-one were also obtained in good yields from 3-phenoxypropionic acid and 3-phenylthiopropionic acid, respectively.     

Assessment of fluoroalkyltin compounds as fluorous Lewis acid catalysts

The synthesis of a variety of organotin compounds with 1H, 1H, 2H, 2H‐perfluorooctyl groups is reported, together with an improved method for the corresponding distannoxane. Unique properties of this compound are disclosed in terms of fluorophilicity and activity as a Lewis acid catalyst in comparison with other mono‐nuclear derivatives. A new criterion for obtaining high solubility in fluorocarbon solvents is presented. Copyright © 2003 John Wiley & Sons, Ltd.     

Fluorous reverse-phase silica gel-supported Lewis acids as recyclable catalysts in water

Fluorous reverse-phase silica gel (FRPSG)-supported Lewis acids which have fluorous ligands acted as effective catalysts of Baeyer-Villiger and Diels-Alder reactions in water. Direct esterification of carboxylic acid with alcohol in organic media was also catalyzed. The FRPSG-supported Lewis acids could be recycled by simple filtration after the reaction.     

Polyphosphoric acid supported on silica-coated NiFe2O4 nanoparticles: An efficient and magnetically-recoverable catalyst for N-formylation of amines

A rapid, green and simple method for the N-formylation of various aromatic amines with formic acid using polyphosphoric acid supported on silica-coated NiFe₂O₄ magnetic nanoparticles (NiFe₂O₄@SiO₂–PPA) under solvent-free conditions at room temperature has been developed. The magnetic catalyst can be easily removed by a simple magnet and reused at least three times without any loss of its high catalytic activity. In addition to its facility, this protocol enhances product purity and promises economic and also environmental profits.     

Rapid and facile Lewis acid catalysed Boc protection of amines

Efficient Boc protection of amines was carried out using (Boc)₂O in the presence of a catalytic amount of ZrCl₄ (10 mol %) in acetonitrile at room temperature. The reaction times are very short and the yields are generally high.     

A novel reaction of titanacyclopentenes and aldehydes with or without Lewis acids

Oxatitanacyclopentenes were prepared in high yields from the reaction of aldehydes with titanacyclopenetens via substitution of ethylene. No insertion product was obtained in this reaction. The combination of alkynes and aldehydes played an important role in the successive formation of oxatitanacyclopentenes. Some oxatitanacyclopentenes are very stable and can be purified using column chromatography. The cooperation between Ti and LA led to very different results from that between Zr and LA.     

Lewis acid-assisted oxidative cross-coupling of 2-naphthol derivatives with copper catalysts

The oxidative coupling reactions between 2-naphthol and 3-hydroxy-2-naphthoic acid derivatives using a copper catalyst under an O₂ atmosphere in the presence of a catalytic amount of the Lewis acid, such as Yb(OTf)₃, were carried out. A highly cross-coupling selective or specific reaction effectively proceeded to give a C₁ symmetrical BINOL derivative.     

A green protocol for the N-formylation of amines using molybdate sulfuric acid as a reusable solid catalyst

A novel and efficient method for the N-formylation of amines via the reaction of orthoformates and amines is developed. The reactions are mediated by a catalytic amount of molybdate sulfuric acid as a heterogeneous solid acid.     

The search for tolerant Lewis acid catalysts. Part 2: Enantiopure cycloalkyldialkylsilyl triflimide catalysts

A series of 2-aryl- and arylmethyl-3-dialkylphenylsilyl cycloalkanones have been prepared and resolved. The pure enantiomers were reduced to the corresponding cycloalkane derivatives. These were used for the in situ generation of enantiopure cycloalkylsilyl triflimides by protodesilylation with bis(trifluoromethanesulfonyl)imide. The association of a bulky leaving group with a silicon atom carrying large substituents was again shown to favour the complexation of silicon with carbonyl groups: all these trialkylsilyl triflimides showed a high catalytic activity for Diels-Alder reactions. Enantiomeric excesses up to 59% were observed. This is the highest enantioselectivity ever observed for a Diels-Alder reaction catalysed by a silicon Lewis acid.     

Utilization of organogallium and organoindium compounds as alkylation reagents in organic synthesis: the addition of trialkylgallium and trialkylindium to aldehydes catalyzed by Lewis acids

The utilization of organogallium and organoindium compounds as alkylation reagents to aldehydes was realized with titanium tetrachloride as the strong Lewis acid catalyst. Furthermore, the catalytic asymmetric addition of organogallium to aldehydes was investigated with chiral titanium complexes, which were formed from titanium tetrachloride and salan ligands, with mediocre to good chemical yields and enantioselectivities. Copyright © 2005 John Wiley & Sons, Ltd.     

One-step novel synthesis of methylene bisphenols and methylene bisnaphthols using Lewis acid mediated rearrangement

Mono- and di-substituted isomeric methylene bisphenols and methylene bisnaphthols have been synthesized by rearrangement of the corresponding O-methoxyacetyl derivatives of phenols and naphthols, respectively, in presence of aluminium chloride under dry conditions. The chemistry observed is different from the usual Fries rearrangement reaction and involves an intermolecular rearrangement. The reactions reported here also reflect the influence of substituents present in the substrate as is supported by the substitution of the bridging methylene at a position meta to the phenolic hydroxyl in some of the minor products formed along-side the majorly formed ortho substituted products.     

Efficient catalysts for telomerization of butadiene with amines

In situ-generated N-heterocyclic carbene (NHC) palladium catalysts and isolated NHC-palladium complexes have been tested for the telomerization reaction of 1,3-butadiene with primary and secondary amines. Superior catalyst activity (TON up to 400.000) and selectivity are obtained. Applying optimized conditions a variety of octa-2,7-dienylamines were prepared in high yield and excellent selectivity.     

Development of efficient Lewis acid catalysts for intramolecular cycloaddition reactions of ester-tethered substrates

We have developed novel bidentate Lewis acids that efficiently promote the intramolecular cycloaddition reactions of ester-tethered substrates. Bis-aluminated triflic amide derivatives [TfN(AlR(1)R(2))2], which are generated by simply mixing triflic amide and 2 equiv of methyl aluminum or aluminum hydride, catalyzed intramolecular Diels-Alder (DA) reactions of ester-tethered 1,7,9-trienes and intermolecular DA reactions of alpha,beta-unsaturated lactones. We also found that bimetallic Lewis acid derived from 1,1'-biphenyl-2,2'-di(triflyl)amide and dimethylaluminum chloride promoted the intramolecular [3 + 2] cycloaddition reaction of acrylate derivatives having an allylsilane part.     

An in-depth look at the effect of Lewis acid catalysts on Diels-Alder cycloadditions in ionic liquids

The present work explores in detail the Diels-Alder reaction between cyclopentadiene and a series of dienophiles, performed in an innovative medium such as an ionic liquid. The potential activation of different Lewis acid catalysts and their load effect when used in combination with this solvent have been explored, in order to settle the improvement on rates and selectivities.