A Simple and Efficient Protocol for Proline-Catalysed Asymmetric Aldol Reaction

The proline-catalysed asymmetric aldol reaction is usually carried out in highly dipolar aprotic solvents (dimethylsulfoxide, dimethylformamide, acetonitrile) where proline presents an acceptable solubility. Protic solvents are generally characterized by poor stereocontrol (e.g., methanol) or poor reactivity (e.g., water). Here, we report that water/methanol mixtures are exceptionally simple and effective reaction media for the intermolecular organocatalytic aldol reaction using the simple proline as the catalyst.

Allan White and Solvento/Aqua Complexes: ScIII Solvation

Addition of various oxygen-donor ligands (L, all dipolar, aprotic solvents), to a solution of hydrated scandium picrate in weakly coordinating solvents (S), has yielded several crystalline adducts of the form Sc(pic)3(L)m(·nS) in which all ligands L are coordinated, subsequently characterised by a series of single crystal X-ray studies. For L=dmso, m=3 and the picrate anions are all bound as phenoxide-O donor units, while for nmp, dma, tmp, and hmpa, m=2 and one of the bound picrates becomes bidentate through phenoxide- and nitro-O donation. For L=ompa, m=2 and two picrate ligands are bound through phenoxide-O while one is displaced from the primary coordination sphere. All complexes contain six-coordinate ScIII, confirming that this coordination number is a consequence of ligand bulk.

Replacement strategies for non-green dipolar aprotic solvents

Despite their wide use in many fields, common dipolar aprotic solvents are urged to be replaced because of their detrimental effects on health and environment. Therefore, green replacement strategies in synthesis have been summarized.

Direct comparison of safer or sustainable alternative dipolar aprotic solvents for use in carbon–carbon bond formation

Direct comparison of safer dipolar aprotic solvents for use in carbon–carbon bond formation is of vital importance for industrial applications. Cyrene exhibited high initial reaction rates, yields and solvent recovery in the Baylis–Hillman reaction.

SYNTHESIS AND INVESTIGATION OF PROPERTIES OF POLYETHERNAFLUYLENEBENZIMIDAZOLES USING REACTION OF NUCLEOPHILIC POLYNITRO-SUBSTITUTION

Soluble polyethernaftoylenbenzimidazoles (PENBI) not previously described are obtained by reacting bis (nitronaphthoylenbenzimidazole) arylene with bisphenols using nucleophilic polynitrosubstitution reaction. The synthesis conditions and the influence of the introduced "bridge" flexible ether, dichloroethylene and carbonyl groups between the phenyl cores of the central fragments of macromolecules on the solubility, thermal and strength properties of the synthesized polymers were studied. Improving melting and solubility (PENBI) without a significant effect on the thermal and strength characteristics is achieved by introducing naphthylamide cycles into them, in combination with flexible bridging fragments into macromolecules of target polymers. The initial bis (nitronaphthoylenbenzimidazole) arylenes were obtained on the basis of (3 or 4-nitronaphthalic anhydride) and bis (o-phenylene diamines), which are derivatives of chloral. In this aspect, the bis (o-phenylenediamine) and bis (nitronaphthoylenenbenzimidazole) arylenes synthesized by us are unique, both in terms of availability of raw materials and price. Bis (nitronaphthoylenbenzimidazole) arylenes were obtained by the interaction of two moles (3 or 4-nitronaphthalic anhydride) with one mole of bis (o-phenylenediamine) under conditions of high-temperature catalytic cyclocondensation in organic solvents. All reactions of the synthesis of bis (nitronaphthoylenbenzimidazole) arylene proceeded homogeneously and resulted in well-cyclized dinitro compounds. As a comonomer of bis (nitronaphtho-ylenbenzimidazole) arylenes, bis-phenols containing also flexible “bridge” groups between phenyl nuclei were used in the synthesis of polyethernaphthoylenbenzimidazoles. The synthesis of polyethernaphthoylenebenzimidazoles was carried out by the interaction of bis (3 or 4-nitronaphthylenebenzimidazole) arylenes with bis-phenols under mild conditions in dimethyl sulfoxide or its mixture with toluene at a temperature of 70 ° C for 2 h in an absolutely dry environment. The obtained composite polymers were well soluble in dipolar aprotic solvents and had a rather wide interval between the temperatures of active destruction and softening temperatures (~ 250-260 ° С). Analysis of the primary thermal characteristics of the obtained polymers showed that they are characterized by relatively high temperatures of destruction (510-550 ºС). Polyethernaphthoylenebenzimidazoles are amorphous: this fact, combined with the presence in the macromolecules of a large number of flexible and “hinged” groups, determine their increased solubility in chlorinated and phenolic solvents. The significant difference between the softening temperature and the temperature of active destruction determines the possibility of their processing into products by injection molding. An analysis of the fire resistance of polymers showed that the highest oxygen index is for polymers, where macromolecules contain more dichloroethylene groups (KI = 62), and the lowest - for polymers with a high oxygen content (OI = 38.3).

PREPARATION OF NEW POLYETHERPHTHALIMIDES BASED ON CHLORAL DERIVATIVES USING NUCLEOPHILIC POLYNITRO SUBSTITUTION REACTIONS

Non-previously described new bis (3-nitropthalimide) arylenes activated with two carbonyls and containing flexible “bridging” groups, in particular dichloroethylene and ketones between the phthalimide fragments of the dinitrocompounds were obtained. The reactivity of the dinitrophthalimides used is determined, first of all, by the position of (3 or 4) nitro groups, and not by the nature of the Ar residue; monomers containing nitro groups in position 3 are more reactive than systems containing nitro groups in position 4. The interaction of synthesized bis (nitropthalimide) arylenes containing central dichloroethylene and ketone groups between phthalimide fragments and bis-phenolate derivatives of chloral was carried out. Synthesis of polyetherphthalimides using the process of polynitro substitution was carried out under modified conditions with complete absence of moisture. In general, the reactions of polynitro substitution proceed rapidly under relatively mild conditions; when dipolar aprotic solvents or a mixture of them with toluene are used, relatively high molecular weight polymers are formed. It has been established that the rate of dissolution of monomers is an important factor affecting the reaction rate; this determines the possibility of the formation of relatively high-molecular polymers, even with some deviation from the equimolarity of the monomers. As the general conditions for the synthesis of polyetherphthalimides based on synthesized bis (3-nitropthalimide) arylenes and bis-phenols, the optimal conditions were: reaction temperature -60 °C, reaction time -1 h with equimolar monomer ratio and concentration of each of them 0.25 mol/l. The influence of moisture on the synthesis of polyetherimides using the reaction of nucleophilic polynitro substitution was studied. It is shown that the process in the maximally dry system in the DMSO medium or (DMSO / toluene) leads to the formation of polymers with hr at least 0.63 dl/g. All the polymers obtained are readily soluble in dipolar and aprotic solvents. The structure of all the obtained intermediates and monomers was confirmed by elemental analysis and IR spectroscopy. An analysis of the primary thermal characteristics of the polymers obtained showed that they are characterized by relatively high and near destruction temperatures was found that the largest oxygen index (CI) in polymers, where more macromolecules contain more dichloroethylene fragments, and the lowest CI in polymers with a high oxygen content. It is shown that the polymers obtained have satisfactory deformation-strength characteristics. A feature of synthesized polyetherphthalimides is a significant difference between the temperatures of intensive destruction and softening temperatures, which determines the possibility of their processing into products by injection molding.