Indium-mediated diastereoselective addition of allyl bromides to enantiomerically pure N-tert-butylsulfinyl aldimines

The reaction of different N-tert-butylsulfinyl aldimines 1 with allyl bromides 2 and indium powder in THF at 60 °C affords, after hydrolysis with water, the corresponding N-tert-butylsulfinylamines 3 with high chemical yields and diastereoselectivities.     

A novel four-component tandem protocol for the stereoselective synthesis of highly functionalised thiazoles

The reaction of bis(aroylmethyl) sulfides with aromatic aldehydes and ammonium acetate in 1:2:1 molar ratio under solvent-free microwave irradiation afforded predominantly a series of thiazoles, viz., 1-aryl-2-[5(Z)-5-arylmethylidene-2,4-diaryl-2,5-dihydrothiazol-2-yl]ethanones stereoselectively. This reaction presumably occurs via a Knoevenagel condensation-Michael addition-cyclocondensation-ring opening-ring closing Michael addition sequence. The intermediacy of (Z,Z)-2,2′-thiobis(1,3-diarylprop-2-en-1-ones) in the above transformation is demonstrated by their conversion to the thiazoles upon reaction with ammonium acetate under solvent-free microwave irradiation.     

Solvent-Free Mechanochemical Synthesis of Aryl Glycosides[ 1 ]

Aryl glycosides have been prepared from a range of readily available glycosyl halides by a solvent-free mechanochemical procedure employing a planetary ball mill in excellent yields. Besides being a solvent-free reaction, the procedure has been successful in eliminating the need for employing any phase-transfer catalyst in the reaction.     

Reduction of Solid Benzophenones with Sodium Borohydride

The solvent-free reduction of benzophenone and five substituted benzophenones with sodium borohydride to the corresponding alcohols was studied by thermal analysis, X-ray powder diffractometry, NMR spectroscopy, and scanning electron microscopy. In most cases, the reaction occurs via liquid eutectic phases that are formed between the benzophenone and the resulting benzohydrol. Nevertheless, this reaction can be carried out without the need for a solvent, leading to pure alcohol without side products. In some cases, heating may be necessary to achieve a reasonably short reaction time. In conclusion, this reaction type appears to be feasible as a preparative organic reaction that avoids a solvent.This revised version was published online in November 2005 with corrections to the Cover Date.     

Synthesis and structure of bis(methylaluminium · HCCH3) p-tert-butylcalix[4]arene

Treatment of p-tert-butylcalix[4]areneH₄ iwth AlMe₃ in toluene at elevated temperature affords after work-up the complex {[MeAl(NCMe)]₂(p-tert-butylcalix[4]arene)}, which adopts a flattened partial cone conformation as characterized by X-ray crystallographu.     

Solvent-Free Organic Syntheses

Ecological points of view must nowadays be taken into consideration in the development of new syntheses and apportioned due importance in assessing the viability of a new synthesis. A crucial factor here is the need to restrict the use of ecologically harmful organic solvents. Examples are presented which show that solvent-free reactions are not only of interest from an environmental viewpoint, but also offer considerable advantages in terms of yield, selectivity, and simplicity of the reaction procedures.     

Potassium phthalimide catalyzed efficient synthesis of 2-Amino-3-phenylsulfonyl-4H-chromenes under Solvent-Free Conditions

An efficient and eco-friendly protocol for the preparation of 2-amino-3-phenylsulfonyl-4H-chromenes employing a three component, one-pot condensation reaction between aromatic aldehydes, phenylsulphonylacetonitrile and 1-naphthol has been developed. The reaction of 1-naphthol with phenylsulphonylacetonitrile and various aromatic aldehydes was carried under solvent-free conditions using 10 mol% of potassium phthalimide as a catalyst to give the corresponding products in good to excellent yields. It was also found that potassium phthalimide can be recycled at least four times without loss of activity. General applicability, operational simplicity, mild reaction conditions, short reaction time, non-toxic, inexpensive and recyclable catalyst, and solvent-free conditions are the advantages of the present procedure.     

Photodecomposition of several compounds commonly used as sunscreen agents

The photolysis reactions of three compounds commonly used as a sunscreen agents, Parsol 1789 (1-[4-(1,1-dimethylethyl)phenyl]-3-(4-methoxyphenyl)-1,3- propanedione), Oxybenzone ((2-hydroxy-4-methoxyphenyl)phenyl-methanone) and Padimate O (2-ethylhexyl-4-(dimethylamino)benzoate), were investigated to provide a chemical background to aid in the understanding of the photosensitization of the sunscreen agents. Photolysis was carried out in cyclohexane for 70–140 h using a mercury vapor lamp (450W) without excluding oxygen.

Irradation of Parsol 1789 in cyclohexane yielded tert-butylbenzene, p-tert-butylbenzoic acid and p-methoxybenzoic acid; products obtained from the combination of the sunscreen with the solvent included the cyclohexyl esters of p-methoxybenzoic acid, p-tert-butylbenzoic acid and methanoic acid; products obtained from the solvent included cyclohexanol, cyclohexanone and dicyclohexyl ether.

Irradiation of Oxybenzone in the cyclohexane for 100 h produced no detectable products by either gas or liquid chromatographic analysis. Oxybenzone was recovered unchanged and no products were observed from the photoinitiated reaction of oxygen with the solvent.

Irradiation of Padimate O in cyclohexane yielded the ethylhexyl esters of p-aminobenzoic acid, p-monomethylaminobenzoic acid and p-dimethylamino (o/m)-methylbenzoic acid, as well as products from the photoinitiated reaction of oxygen with the solvent.     

A novel isocyanide-based three-component reaction: a facile synthesis of substituted 2H-pyran-3,4-dicarboxylates

An efficient method for synthesis of 2H-pyran-3,4-dicarboxylates using the three-component reaction of dithiocarbamates, dialkyl acetylenedicarboxylates, and isocyanides in solvent-free conditions is described. In these reactions, synthesis of dithiocarbamates is possibly based on the one-pot reaction of secondary amines, CS₂, and alkyl halides in solvent-free conditions without using a catalyst. The mild reaction conditions and high yields of the reaction exhibit the good synthetic advantage of these methods.     

ortho-Selective ethylation of phenol with ethanol catalyzed by bimetallic mesoporous catalyst, CoAl-MCM-41

CoAl-MCM-41 (X) catalysts with X = n_Si/(n_Co + n_Al) various ratios were synthesized and ethylation of phenol with ethanol was studied in vapor-phase at temperatures between 250 and 450 °C. The products obtained were O-alkylated product (ethyl phenyl ether), C-alkylated products (2-ethylphenol and 4-ethylphenol), and C-/O-alkylated products (ethyl ethylphenyl ether). The phenol conversion increased significantly with reaction temperature over all the catalysts. The activity of the catalysts followed the order CoAl-MCM-41 (20) > CoAl-MCM-41 (50) > CoAl-MCM-41 (80). Selectivity between the C-alkylation and the O-alkylation depended on the factors such as acidity of the catalyst and the reaction temperature. CoAl-MCM-41 (20) catalyst displayed a phenol conversion of 40% and a selectivity of more than 80% for 2-ethylphenol under the optimized reaction condition. The ethanol to phenol ratios and the reactant flow rate are also influential for both activity and selectivity of CoAl-MCM-41 catalysts.     

4-Toluenesulfonic acid: an environmentally benign catalyst for Nazarov cyclizations

An efficient metal-free catalytic protocol for the electrocyclization of α-alkoxydienones to cyclopentenones (Nazarov reaction) in near to quantitative yields is described. The key parameters are the use of inexpensive 4-toluenesulfonic acid in 5 mol % at room temperature in acetonitrile or under solvent-free conditions. The versatility of the transformation is demonstrated with unpolarized dienones with good regioselectivities and excellent yields.     

二氧化铅电极上氧发生反应的交流阻抗研究

测定了二氧化铅电极上氧发生反应的交流阻抗。用曲线拟合法解析组抗谱,求得了反应电阻R_t、吸附电阻R_a、双层电容C_d、吸附电容C_a的值。认为(OH)吸+H₂O→(O)吸+H₃O⁺+e^-是氧发生反应的控制步骤。讨论了C_d、C_a与OH^-离子浓度变化的关系。     

Synthesis, characterization and catalytic activity in Heck-type reactions of orthometallated Pd and Pt complexes derived from (1R,2R)-1,2-diaminocyclohexane

The chiral bis-imine (1R,2R)-C₆H₁₀-[E---N=CH---C₆H₃---3,4-(OMe)₂]₂ 1 (LH) reacts with [Pd(OAc)₂] (1:1 molar ratio; OAc=acetate) giving the orthometallated [Pd(OAc)(C₆H₂---4,5-(OMe)₂---2-CH=N-(1R,2R)-C₆H₁₀---N=CH---C₆H₃-3′,4′-(OMe)₂-κ-C,N,N)] 2 (abbreviated as [Pd(OAc)(L-κ-C,N,N)]), through C---H bond activation on only one of the aryl rings and N,N-coordination of the two iminic N atoms. 2 reacts with an excess of LiCl to give [Pd(Cl)(L-κ-C,N,N)] 3. The reaction of 3 with AgClO₄ and neutral or anionic ligands L′ (1:1:1 molar ratio) affords [Pd(L-κ-C,N,N)(L′)](ClO₄) (L′=PPh₃ 4a, NCMe 5, pyridine 6, p-nitroaniline 7) or [Pd(I)(L-κ-C,N,N)] 8. Complex 4a reacts with wet CDCl₃ giving [Pd(C₆H₂---4,5-(OMe)₂---2-CH=N-(1R,2R)---C₆H₁₀---NH₂-κ-C,N,N)(PPh₃)](ClO₄) 4b as a result of the hydrolysis of the C=N bond not involved in the orthometallated ring. The molecular structure of 4b·CH₂Cl₂ has been determined by X-ray diffraction methods. Cleavage of the Pd---N bond trans to the C_aryl atom can be accomplished by coordination of strongly chelating ligands, such as acetylacetonate (acac) or bis(diphenylphosphino)ethane (dppe), forming [Pd(acac-O,O′)(L-κ-C,N)] 9 and [Pd(L-κ-C,N)(dppe-P,P′)](ClO₄) 12, while classical N,N′-chelating ligands such as 1,10-phenantroline (phen) or 2,2′-bipyridyl (bipy) behave as monodentate N-donor ligands yielding [Pd(L-κ-C,N,N)(κ¹-N-phen)](ClO₄) 10 and [Pd(L-κ-C,N,N)(κ¹-N-bipy)](ClO₄) 11. Treatment of 1 with PtCl₂(DMSO)₂ (1:1 molar ratio) in refluxing 2-methoxyethanol gives Cl₂Pt[(NH₂)₂C₆H₁₀---N,N′] 13a and [Pt(Cl)(C₆H₂---4,5-(OMe)₂---2-CH=N-(1R,2R)---C₆H₁₀---NH₂-κ-C,N,N)] 13b, while [Pt(Cl)(L-κ-C,N,N)] 14 can be obtained by reaction of [Pt(μ-Cl)(η³-2-Me---C₃H₄)]₂ with 1 in refluxing CHCl₃. Complexes 2 and 3 catalyzed the arylation of methyl acrylate giving good yields of the corresponding methyl cinnamates and TON up to 847 000. Complex 3 also catalyzes the hydroarylation of 2-norbornene, but with lower yields and without enantioselectivity.     

Efficient and Facile Three-Component Reaction for the Synthesis of 2-Amine-4,6-diarylpyrimidine Under Solvent-Free Conditions

An efficient and convenient multicomponent reaction for the preparation of 2-amine-4,6-diarylpyrimidine by aromatic aldehydes, aromatic ketones, and guanidine carbonate in the presence of sodium hydroxide under solvent-free conditions is reported. The short reaction time coupled with the simplicity of the reaction procedure make this method one of the most efficient methods for the synthesis of this class of compounds.     

An efficient and solvent-free one-pot multi-component synthesis of novel highly substituted pyrido[2′,3′:3,4]pyrazolo[1,5-a]pyrimidine-3-carbonitrile derivatives catalyzed by tetramethylguanidine

Abstract

An efficient solvent-free access towards highly substituted pyrido[2′,3′:3,4]pyrazolo[1,5-a]pyrimidine-3-carbonitrile derivatives has been established through multi-component reaction of 1H‐pyrazolo[3,4‐b]pyridin‐3‐amine, aldehyde, 3-(1H-indol-3-yl)-3-oxopropanenitrile catalyzed by 1,1,3,3-tetramethylguanidine (TMG). The reaction allows the formation of one C?C and two C?N bonds with high yield. The significant features of this solvent-free reaction include mild reaction condition, readily accessible substrates, short reaction time, excellent yield, and broad substrate scopes as well as simple one-pot operation, no column chromatographic purification, which makes this strategy highly attractive.     

A New Bismuth Nitrate–Catalyzed Electrophilic Substitution of Indoles with Carbonyl Compounds Under Solvent-Free Conditions

An expeditious synthetic method for the preparation of bis(indollyl)methane derivatives has been developed through a bismuth nitrate-catalyzed reaction of indole with various carbonyl compounds in mortar and pastle under solvent-free conditions.     

LiBr catalyzed solvent-free ring expansion of epoxides to 1,4-oxathian-2-ones with α-mercaptocarboxylic acids

An efficient and rapid (10-20 min) one-pot synthesis of chemically and pharmaceutically interesting 1,4-oxathian-2-ones is reported. The protocol involves LiBr catalyzed regioselective ring-opening-ring-closing reaction cascade of terminal epoxides with α-mercaptocarboxylic acids at rt under solvent-free conditions. Recycling of the catalyst, atom economy, and formation of water as the only by-product in the present synthesis are additional advantages relevant to green chemistry.     

Ab initio molecular orbital study of potential energy surface for the H2NO(B1)→NO(Π)+H2 reaction

The mechanism of the H₂NO(²B₁)→NO(²Π)+H₂ reaction has been examined using ab initio molecular orbital methods. Ground-state and first-excited-state potential surfaces were plotted at the FOCI/cc-pVTZ level of theory as functions of two appropriate internal degrees of freedom. A conical intersection was found on the C_s pathway that is symmetric with respect to the plane perpendicular to the molecular plane of C_2v H₂NO(²B₁). It is therefore considered that trajectories that start from H₂NO(²B₁) towards the product region detour around the conical intersection, pass through the neighborhood of the transition state that is located at the saddle point on the C_s pathway, and finally reach the products, NO(²Π)+H₂. Thus we can explain the mechanism of the H₂NO(²B₁)→NO(²Π)+H₂ reaction, which has remained unclear to date.     

Factorial analysis of a chemiluminescence system for bromate detection in water

A chemiluminescent flow system for bromate detection, based on the reaction of bromate with sulphite in acid medium and using the steroid hydrocortisone as sensitiser, was studied. A factorial analysis strategy for the study of the effect on the system response of the experimental factors, flow rates of two pumps (Q₁ — acid sulphite plus hydrocortisone aqueous solution; Q₂ — carrier, water), sample injection volume (V_L), reactor volume (V_R), sulphite concentration (C_S), hydrocortisone concentration (C_H) and acid concentration (C_A), was used. Screening analysis of the system performance was made using Plackett Burman designs. The system optimisation procedure was achieved by three levels three factors full factorial designs. V_L and C_H are the most significant factors — a quadratic C_H term was also observed to be significant. The optimised system responded linearly (logarithm of the detector signal as function of the logarithm of the bromate concentration) in the concentration range between 3.6×10⁻⁷ and 5.0×10⁻⁴ M with a limit of detection of about 8.0×10⁻⁸ M (about 10 microg/l). An analysis of some interfering ions was made and it was suggested that bromide and chloride begin to quench chemiluminescence when they are in a 10-fold excess relatively to bromate concentration.     

Solvent-free cascade reaction: direct multicomponent assembling of 2-amino-4H-chromene scaffold from salicylaldehyde, malononitrile or cyanoacetate and nitroalkanes

The new type of solvent-free cascade reaction was found: the direct heating of the mixture of salicylaldehyde, malononitrile or cyanoacetate and nitroalkanes at 60 °C in the presence of catalytic amounts of KF or NaOAc results in the formation of 2-amino-4-(1-nitroalkyl)-4H-chromene-3-carbonitriles or methyl 2-amino-4-(1-nitroalkyl)-4H-chromene-3-carboxylates in 80-90% yields. Thus, the new simple and efficient solvent-free ‘one-pot’ way to substituted medicinally privileged 2-amino-4H-chromene scaffold was found directly from such simple and reasonable starting compounds as salicylaldehyde, malononitrile or cyanoacetate and nitroalkanes.