Stereoselective organic reactions in water

Phosphine-Triggered Complete Chemo-Switch: From Efficient Aldehyde−Alkyne−Amine Coupling to Efficient Aldehyde−Alkyne Coupling in Water

[reaction: see text] A phosphine ligand served as a remarkable chemo-switch for the silver-catalyzed reaction of alkynes with aldehydes in the presence of amines in water. Exclusive aldehyde-alkyne-amine coupling product was observed in the absence of phosphine, whereas in the presence of a phosphine ligand, exclusive aldehyde-alkyne coupling product was obtained.

Rhodium-Catalyzed Asymmetric Aqueous Pauson-Khand-Type Reaction

An interesting rhodium-catalyzed asymmetric aqueous Pauson-Khand-type reaction was developed. A chiral atropisomeric dipyridyldiphosphane ligand was found to be highly effective in this system. This operationally simple protocol allows both catalyst and reactants to be handled under air without precautions. Various enynes were transformed to the corresponding bicyclic cyclopentenones in good yield and enantiomeric excess (up to 95 % ee). A study of the electronic effects of the enyne substrates revealed a correlation between the electronic properties of the substrates and the ee value obtained in the product of the Pauson-Khand-type reaction. A linear free-energy relationship was observed from a Hammett study.

Pd-Catalyzed Copper-Free Carbonylative Sonogashira Reaction of Aryl Iodides with Alkynes for the Synthesis of Alkynyl Ketones and Flavones by Using Water as a Solvent

The Pd-catalyzed copper-free carbonylative Sonogashira coupling reaction to synthesize alkynyl ketones from terminal alkynes and aryl iodides was achieved by using water as a solvent. The reaction was carried out at room temperature under balloon pressure of CO with Et(3)N as a base. The developed method was successfully applied to the synthesis of flavones.

Metal-mediated entry to functionalized 3-substituted 3-hydroxyindolin-2-ones via regiocontrolled carbonylallylation, bromoallylation, 1,3-butadien-2-ylation, propargylation, or allenylation reactions of isatins in aqueous media

Reactions of 2,3-indolinediones (isatins) with stabilized organometallic reagents were investigated in aqueous media. Isatins and a variety of stabilized organic halides undergo coupling under Barbier-type conditions in the presence of different metals (indium, tin, zinc) and additives (ammonium chloride, hydrobromic acid, bismuth(III) chloride, hafnium(IV) chloride). The regiochemistry of the processes (carbonylallylation, bromoallylation, 1,3-butadien-2-ylation, propargylation, or allenylation reactions) were generally excellent. On this basis, simple and fast protocols for the synthesis of the potentially bioactive 3-substituted 3-hydroxyoxindole moiety were developed.

A Recyclable Electrochemical Allylation in Water

To develop environmentally benign processes for C-C bond formation, electrochemistry is applied in a tin-mediated allylation reaction in water. In this electrochemical process, the corresponding homoallylic alcohols are prepared in excellent yields, while both tin salt and water can be recycled and electrode materials are not consumed.

Novel Carbonyl Bromoallylation/Heck Reaction Sequence. Stereocontrolled Access to Bicyclic β-Lactams

[reaction: see text] The reaction of 2,3-dibromopropene with racemic as well as enantiopure 4-oxoazetidine-2-carbaldehydes 1 in aqueous media was promoted by tin in the presence of several additives to afford the corresponding bromohomoallyl alcohols 2 in high diastereoselectivities. However, indium or zinc were unable to promote the bromoallylation reaction of aldehydes 1 under similar Barbier-type conditions. Vinyl bromides 2 bearing an extra alkene tether were used for the preparation of differently sized, fused bicyclic beta-lactams of nonconventional structure via Heck cyclization.

Review on green chemistry — Suzuki cross coupling in aqueous media

The Suzuki cross-coupling reaction is a very efficient, reliable, and environmentally friendly method for the introduction of novel carbon–carbon bonds into molecules. This review summarizes recent advances in the use of the reaction in aqueous media with a focus on different types of ligands and the ligandless protocols currently in use. Several synthetic targets for the reaction have been mentioned. The work summarizes recent results from studies on asymmetric Suzuki reactions performed in organic – aqueous mixed solvents.Key words: Suzuki reaction, green chemistry, metal-catalyzed cross-coupling reactions, aqueous synthesis media.

Substrate dependence in aqueous Diels-Alder reactions of cyclohexadiene derivatives with 1,4-benzoquinone

A reactivity difference based on the position of substituents on cyclohexa-1,3-diene was observed for the title reaction. The effect of water as solvent was more distinct for 1-methyl-4-isopropylcyclohexa-1,3-diene than for 2-methyl-5-isopropylcyclohexa-1,3-diene or non-substituted cyclohexa-1,3-diene. The effect of NaCl (salting-out) and guanidium chloride (salting-in) was also large for 1-methyl-4-isopropylcyclohexa-1,3-diene.

Surfactant/I2/Water: An Efficient System for Deprotection of Oximes and Imines to Carbonyls under Neutral Conditions in Water

I2/surfactant/water system deprotecting oximes and imines to the corresponding carbonyl compounds under neutral conditions in water at 25-40 degrees C with very high to excellent yields.

Rh(ii) catalysed intramolecular C–H insertion of diazo substrates in water: a simple and efficient approach to catalyst reuse

Water is an efficient solvent for the Rh2(OAc)4 catalysed intramolecular C-H insertion of a range of diazo substrates without competitive water insertion. Due to the high solubility and stability of the catalyst in water, the catalyst can be efficiently reused.

Efficient asymmetric synthesis of an azasugar in water

An extremely efficient asymmetric synthesis of a pyrrolidine azasugar was completed in only four steps in water, without the use of protecting groups and in 60% overall yield from a simple, achiral bis-electrophile.

Intramolecular iodoarylation reaction of alkynes: easy access to derivatives of benzofused heterocycles

The iodoarylation reaction of heteroatom-tethered omega-arylalkynes offers an efficient and straightforward entry to heterocycles. As a result, both C-C ring-closing from readily available precursors, and concomitant selective iodination take place. The first related study conducted in water is presented.

Organocatalytic asymmetric epoxidation reactions in water–alcohol solutions

The diastereo- and enantioselective organocatalytic epoxidation of alpha,beta-unsaturated aldehydes in aqueous solutions is presented. By the screening of the reaction conditions for the epoxidation of cinnamic aldehyde applying hydrogen peroxide as the oxidant and 2-[bis-(3,5-bis-trifluoromethyl-phenyl)-trimethylsilanyloxy-methyl]-pyrrolidine as the catalyst, a highly stereoselective reaction has been developed. The scope of the diastereo- and enantioselective organocatalytic epoxidation in aqueous solutions is documented by the asymmetric epoxidation of alpha,beta-unsaturated aldehydes with enantioselectivities up to 96% ee.

α-Aminoallylation of aldehydes in aqueous ammonia

alpha-Aminoallylation of aldehydes in aqueous ammonia has been developed; commercial aqueous ammonia was successfully used, and this method does not require anhydrous conditions thus leading to easy and practical operations.

Ligand-accelerated vanadium-catalysed epoxidation in water

Vanadium-catalysed epoxidation of allylic alcohols, a classical example of ligand-decelerated catalysis, in water it turns into a ligand-accelerated process.

Ru(iv)-catalyzed isomerization of allylamines in water: A highly efficient procedure for the deprotection of N-allylic amines

A general and efficient method for the deprotection of N-allylic substrates in aqueous media, using catalytic amounts of the bis(allyl)-ruthenium(IV) complexes [Ru(eta3:eta2:eta3-C12H18)Cl2] and [{Ru(eta3:eta3-C10H16)(micro-Cl)Cl}2], has been developed.

Transition-metal- and organic-solvent-free: a highly efficient anaerobic process for selective oxidation of alcohols to aldehydes and ketones in water

A new system, I2-KI-K2CO3-H2O, selectively oxidized alcohols to aldehydes and ketones under anaerobic condition in water at 90 degrees C with excellent yields. The process is green, mild and inexpensive.

Sugar-amide surfactant micelles as effective reaction fields for enantioselective hydrolysis of alpha-amino acid esters

The enantioselective hydrolysis of p-nitrophenyl esters of alpha-amino acids (Phe, Leu, Ala) was accomplished in micelles formed with the surfactants bearing one or two sugar-amide headgroups. The effect of structural variations in such sugar-amide surfactants on the rates and enantioselectivity (kD/kL) for hydrolysis of p-nitrophenyl esters of D- and L-phenylalanine hydrogen bromides (D- and L-PheONp) was studied. Both the hydrolysis rate of D-PheONp and the enantioselectivity increased with an increase in the alkyl chain length as well as an increase in the number of the alkyl chains in the maltobionamide-type surfactants. Enantioselectivity also increased with an increase in the sugar chain length from bisgluconamide to bismaltobionamide (by one glucose unit per each sugar chain) in the double-sugar-chain surfactants, but enantioselectivity was no longer influenced by a further increase to bismaltotrionamide. The stereochemistry of the linkage between the sugar units in the sugar chain remarkably affected the enantioselectivity: the maltobionamide-type surfactant, in which the two sugar units are connected by an alpha-1,4-glucosidic linkage, showed high enantioselectivity (kD/kL = 5.5), whereas the surfactant bearing cellobionamide headgroups (beta-1,4-glucosidic linkage) showed no enantioselectivity. Similar trends were observed when p-nitrophenyl esters of D- and L-leucine hydrogen bromides were used as substrates. On the other hand, the rates and enantioselectivity for hydrolysis of p-nitrophenyl esters of D- and L-alanine hydrogen bromides were not so largely affected by the structural variations in the sugar-amide surfactants. Additionally, the effects of the surfactant concentration and the reaction temperature on the rates and enantioselectivity for the hydrolysis of D- and L-PheONp were examined.

Preparation of an Amphiphilic Resin-Supported BINAP Ligand and Its Use for Rhodium-Catalyzed Asymmetric 1,4-Addition of Phenylboronic Acid in Water

[reaction: see text] The axially chiral bisphosphine ligand, 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl (binap), was supported on a polystyrene-poly(ethylene glycol) copolymer (PS-PEG) resin and was used successfully for the rhodium-catalyzed asymmetric 1,4-addition of phenylboronic acid to alpha,beta-unsaturated ketones in water.