Asymmetric allylation of aldehydes with allyltrichlorosilane using aza-paracyclophane-oxazoline-N-oxide catalysts

Novel aza-paracyclophane-oxazoline catalysts 4, 5 were produced from Vögtle’s R_p-2-cyano-aza-paraclycophane and amino alcohols reacted with zinc chloride followed by m-chloroperbenzoic acid. 4′-Benzyl and tert-butyl-S and R-oxazoline variants were produced and explored as catalysts for asymmetric allylation of aldehydes using trichloroallylsilane. With R_p,S-4a (R = tert-butyl) (1.5 mol %) aromatic aldehydes reacted with high yields and selectivities, as with benzaldehyde (95%, 93% ee). R_p,S-4b (R = benzyl) was superior with dihydrocinnamaldehyde (77%, 85% ee).     

Palladacyclic catalysts in C-C and C-heteroatom bond-forming reactions

Palladacycles are amongst the most active catalysts in Heck-type carbon-carbon bond formation and related carbon-heteroatom bond forming reactions. For instance they have recently emerged as showing the highest activity in the Suzuki coupling of electronically challenging aryl chloride substrates. In addition to the high activity they display, their ease of synthesis, facile modification and comparative stability all act to enhance their appeal.     

Development of chiral dinitrones as modular Lewis base catalysts: asymmetric allylation of aldehydes with allyltrichlorosilanes

Chiral dinitrones were synthesized by the condensation of a C₂-symmetrical chiral dihydroxylamine with various aldehydes. The electronic and steric properties of the dinitrones can be modified by changing the aldehyde component. The activity of dinitrones as Lewis base catalysts was examined for the asymmetric allylation of aldehydes with allyltrichlorosilanes. Using DMPU as an additive in chloroform, the reaction proceeded at room temperature to afford allylated products in good yields and good enantioselectivities.     

Rhenium complex-catalyzed allylation of aldehydes with allyltributylstannane

It was confirmed that the rhenium complex, ReBr(CO)₅, catalyzed the allylation of aldehydes with allyltributylstannane to give the corresponding homoallylic alcohols in moderate to good yields. Similarly, the reaction of aldehydes with enol silyl ether was efficiently promoted by the rhenium catalyst to afford the corresponding β-hydroxy carbonyl compounds.     

Pentamethylcyclopentadienyl-ruthenium catalysts for regio- and enantioselective allylation of nucleophiles

Ruthenium(II) complexes containing the pentamethylcyclopentadienyl ligand efficiently perform the activation of allylic carbonates and halides to generate cationic and dicationic ruthenium(IV) complexes. This activation has been transferred as a key step to the catalytic allylation of nucleophiles. The structural and electronic properties of the allylic moieties lead to the regioselective formation of chiral products resulting from nucleophilic addition to their most substituted terminus. The catalytic activity of various Ru(Cp*) precatalysts in several allylic substitutions by C and O nucleophiles will be presented. The enantioselective version that has been demonstrated by using optically pure bisoxazoline ligands will also be discussed.     

Bis(NHC)-Pd(II) complexes as highly efficient catalysts for allylation of aldehydes with allyltributyltin

Novel cis-chelated bidentate bis(NHC)-Pd(II) complexes derived from 1,1′-binaphthyl-2,2′-diamine (BINAM) bearing weakly coordinating acetate or trifluoroacetate counterions have been synthesized and their structures have been characterized by X-ray diffraction of single crystals. We found that these bis(NHC)-Pd(II) complexes were highly effective in the allylation of aldehydes with allyltributyltin to give the corresponding products in good to excellent yields in most cases at room temperature.     

Barbier-Grignard-type allylation of aldehydes with metallic antimony

Metallic-antimony-induced allylation of aldehydes by allylic halides and phosphates gave high yields of the corresponding homoallylic alcohols, regioselectively. α,β-Unsaturated aldehydes afforded only 1,2-addition products.     

Mesoporous aluminosilicate-catalyzed allylation of aldehydes with allylsilanes

Mesoporous aluminosilicate (Al-MCM-41) was found to catalyze the allylation of both aromatic and aliphatic aldehydes with allylsilanes although amorphous silica-alumina or mesoporous silicates (MCM-41, SBA-15) could not catalyze the reaction under the same reaction conditions. The solid acid catalyst Al-MCM-41 could be reused three times without significant loss of activity.     

Palladacyclic complexes bearing CNN-type ligands as catalysts in the Heck reaction

Preparations of novel unsymmetrical, tridentate nitrogen ligand precursors, PhN=C(CMe2)(NPh)C=N(CH2)2NMe2(1) and PhN=C(CMe2)(NPh)C=N(CH2)Py (2), are described. Treatment of 1 with 1 molar equiv. (COD)PdCl2 in the presence of NEt3 or with 1 molar equiv. Pd(OAc)2 affords orthometallated palladium(II) complexes, [PhN=C(CMe2)(N-eta1-Ph)C=N(CH2)2NMe2]PdX (X=Cl (3); X=OAc (4)), respectively. Compound can be yielded via the reaction of with an excess of LiCl in methanol. Treatment of with 1 molar equiv. of (COD)PdCl2, Pd(OAc)2 or Pd(TFA)2 affords orthometallated palladium(II) complexes, [PhN=C(CMe2)(N-eta1-Ph)C=NCH2Py]PdX (X=Cl (5); X=OAc (6); X=TFA (7)), respectively. The crystal and molecular structures are reported for compounds 2, 3, 5 and 6. The application of these novel palladacyclic complexes to the Heck reaction with aryl halide substrates was examined.     

Aqueous Barbier allylation of aldehydes mediated by tin

The aqueous tin-mediated Barbier reaction affords good to excellent yields and moderate syn diastereoselectivity under basic and acidic conditions. The high yields and stereoselectivity observed in the case of o-substituted aldehydes suggest a cyclic organotin intermediate or transition state in K2HPO4 solution. A practical and efficient aqueous tin allylation of methoxy- and hydroxybenzaldehydes can be carried out in HCl solution in 15 minutes to afford the corresponding homoallylic alcohols in high yields. Aliphatic aldehydes give moderate to excellent yields with reaction times ranging from 30 to 60 minutes. Under these conditions, crotylation gives exclusively the gamma-product and the syn isomer is formed preferentially. For 2-methoxybenzaldehyde, an equilibration of the isomers to a syn/anti ratio of 1:1 can be observed after several hours. Control experiments with radical sources or scavengers give no support for radical intermediates. NMR studies suggest a mechanism involving an organotin intermediate. The major organotin species formed depends on the reaction medium and the reaction time. The use of acidic solution reduces the reaction times, due to the acceleration of the formation of the allyltin(IV) species.     

烯丙基溴和锡与醛的选择性加成反应

应用烯丙基溴和锡粉在少量水存在下和四氢呋喃中可使醛选择性烯丙基化,这一反应可用于那些同时含有对格氏试剂有反应活性的羟基、酚羟基、芳香族硝基和酮羰基等官能团的醛类以引入烯丙基生成相应的高烯丙基醇.     

Polymer-supported formamides as reusable organocatalysts for allylation of aldehydes with allyltrichlorosilane

New types of polymer-supported formamides have been synthesized from chloromethylated resins and formamides; it was found that the polymers worked well as organocatalysts in the allylation of aldehydes with allyltrichlorosilane to afford homoallylic alcohols in high yields; the polymers were easily recovered and reused several times without loss of activity.     

Efficient allylation of aldehydes promoted by carboxylic acids

A variety of carboxylic acids have been screened for mediating the allylation of aldehydes with allytributyltin in different solvents. A novel, general, and practical method of allylation of aldehydes promoted by carboxylic acids under mild reaction conditions has been developed. Among them, p-nitrobenzoic acid afforded high to quantitative yields of the homoallylic alcohol products, and can be easily recovered after workup by aqueous HCl. Glyoxylic acid self-catalyzed the allylation without adding any other promoter or catalyst to give the corresponding allylation product in good yield. The regioselectivity of the crotylation of aldehydes is tunable by controlling the acidity of the carboxylic acids. The crotylation of aldehydes produced the alpha-adduct as major products in moderate to good yields with CF(3)CO(2)H as a promoter. A possible mechanism for the allylation is also discussed.     

Iron-mediated allylation of aryl aldehydes in aqueous media

Iron metal was found to be able to mediate the allylation reaction of aryl aldehydes in aqueous media with sodium fluoride as the promoter. The possible implication of an allyliron intermediate was examined.     

Chiral sulfoxides in the enantioselective allylation of aldehydes with allyltrichlorosilane

The use of chiral sulfoxides as Lewis base catalysts in the allylation of aldehydes with allyltrichlorosilane is reported.     

Enantioselective allylation of aldehydes with chiral allyl organolanthanide reagents

The first example of enantioselective allylation of aldehydes with chiral allyl organolan-thanide reagents has been achieved in high chemical yield and moderate optical purity (up to 54% e.e.).     

Carbohydrates in asymmetric synthesis: enantioselective allylation of aldehydes

An enantioselective metal-mediated addition of allylic bromides to carbonyl compounds was achieved in the presence of the inexpensive and easily accessible carbohydrates saccharose and β-cyclodextrin. The desired products were obtained in moderate to excellent yields and with up to 93% enantiomeric excess.     

Asymmetric allylation of aldehydes with chiral platinum phosphinite complexes

Platinum phosphinite complexes made from chiral diols catalyze the enantioselective allylation of cinnamaldehyde. This reaction proceeds with better yields at shorter reaction times in the presence of acetic acid. Enantiomeric excesses were greater when reactions were carried out with phosphinite ligands having hydrogen bond donors or acceptors.