Halogen bonding in cadmium(II) MOFs: influence on the structure and on the nitroaldol reaction in aqueous medium

A solvothermal reaction of Cd(II) with the dicarboxyl-functionalized arylhydrazone pro-ligands - 5-(2-(2,4,6-trioxotetrahydro-pyrimidin-5(2H)-ylidene)hydrazineyl)isophthalic acid (H5L1) and 5-(2-(2,4-dioxopentan-3-ylidene)hydrazineyl)isophthalic acid (H3L2), or their halogen bond donor centre(s) decorated versions 2,4,6-triiodo-5-(2-(2,4,6-trioxotetrahydropyrimidin-5(2H)-ylidene)hydrazineyl)isophthalic acid (H5L3) and...

Interdependent Dynamic Nitroaldol and Boronic Ester Reactions for Complex Dynamers of Different Topologies

Complex dynamic systems displaying interdependency between nitroaldol and boronic ester reactions have been demonstrated. Nitroalkane-1,3-diols, generated by the nitroaldol reaction, were susceptible to ester formation with different boronic acids in aprotic solvents, whereas hydrolysis of the esters occurred in the presence of water. The boronic ester formation led to significant stabilization of the nitroaldol adducts under basic conditions. The use of bifunctional building blocks was furthermore established, allowing for main chain nitroaldol-boronate dynamers as well as complex network dynamers with distinct topologies. The shape and rigidity of the resulting dynamers showed an apparent dependency on the configuration of the boronic acids.

Preparation of Optically Active Biphenyl Compounds via an Albumin-Mediated Asymmetric Nitroaldol Reaction

: Human serum albumin (HSA) was found to catalyze the asymmetric nitroaldol reaction of biphenyl aldehydes with nitromethane to afford the corresponding optically active 2-nitro alcohols. Careful optimization of the conditions for the reaction of 4-phenylbenzaldehyde with nitromethane in water at a neutral pH improved both the reactivity and the enantioselectivity. Finally, the reaction of 4-phenylbenzaldehyde (56 mg, 0.30 mmol) in nitromethane (2.8 mL) and water (1.1 mL) using HSA (68 mg) at 5 °C for 240 h gave (R)-1-([1,1ʹ-biphenyl]-4-yl)-2-nitroethanol in 71% yield (52 mg), with an ee up to 85% ee. Subsequent recrystallization improved the eeup to 95%. The reaction was useful in a preparative-scale operation, and the biocatalyst could be reused several times. The procedure was also applicable to other substrates with different substitution patterns. Although the nitroaldol reaction of 2-phenylbenzaldehyde with nitromethane proceeded with low enantioselectivity to afford the corresponding (R)-2-nitro alcohols (35% ee), the reactions of the substrates bearing Br, Me, OMe, or CN group at the 4ʹ-position of the benzene ring gave the corresponding optically active compounds with high enantioselectivities (80-88% ee).

Group 11 Pincer Oxazoline Complexes

The synthesis and characterization of new copper pincer complexes via cyclometallation of potentially anionic pincer ligands with C1 point group symmetry is reported. All of these complexes have been characterized by single crystal X-ray diffraction method, which confirms the proposed tridentate binding mode of pincer ligand and the formation of an amido N-Cu bond. The reactivity of two of the complexes was investigated towards C-C bond formation reaction, notably the Henry reaction. One of the complexes, which was derived from the achiral pincer ligand, is shown to be a suitable catalyst for the Henry reaction under the standard conditions. The Henry or nitroaldol reaction is one of the organic reactions which affords a C-C bond. The product of this reaction is a β-nitro alcohol which is formed by addition of a nitroalkane to a carbonyl compound.

Group 11 Pincer Oxazoline Complexes

The synthesis and characterization of new copper pincer complexes via cyclometallation of potentially anionic pincer ligands with C1 point group symmetry is reported. All of these complexes have been characterized by single crystal X-ray diffraction method, which confirms the proposed tridentate binding mode of pincer ligand and the formation of an amido N-Cu bond. The reactivity of two of the complexes was investigated towards C-C bond formation reaction, notably the Henry reaction. One of the complexes, which was derived from the achiral pincer ligand, is shown to be a suitable catalyst for the Henry reaction under the standard conditions. The Henry or nitroaldol reaction is one of the organic reactions which affords a C-C bond. The product of this reaction is a β-nitro alcohol which is formed by addition of a nitroalkane to a carbonyl compound.

Heteroaromatic N-Oxides Modified with a Chiral Oxazoline Moiety, Synthesis and Catalytic Applications

Interesting properties of N-oxides and pyridine oxazoline compounds have become the starting point to synthesize compounds connecting both groups. A multi-step synthesis of a series of chiral oxazoline substituted pyridine N-oxides, alkyl derived of pyridine N-oxides, bipyridine N-oxides, and isoquinoline N-oxides, based on amino alcohols derived from natural amino acids or other previously prepared, is presented herein. Various synthetic pathways have been designed and tested according to the properties and limitations imposed by the target products. The encountered problems related to the stability of the products were discussed. The resulting compounds (eighteen structures) were tested as catalysts in th e allylation of benzaldehyde (obtaining up to 79% ee) as well as in nitroaldol reaction (obtaining up to 48% ee).

Ketones as Electrophile in Nitroaldol Reaction: Synthesis of β,β-Disubstituted- 1,3‑dinitroalkanes and Allylic Nitro Compounds

β,β-Disubstituted-1,3-dinitro compounds were obtained exclusively with an overall yield of 83% through a domino nitroaldol/elimination/1,4-addition process, when excess nitromethane was added to cyclohexanone or butanone using DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), as a basic catalyst. On the other hand, β-nitroalcohols could be obtained in 30-84% yield, when nitromethane reacts with different aliphatic ketones in stoichiometric amounts, in the presence of catalytic amounts of K2CO3(s), Amberlyst®-A21 or TBAF.3H2O (tetra-n-butylammonium fluoride trihydrate)/THF (tetrahydrofuran). In addition, a new and versatile route to obtainment of allylic nitro compounds, by treatment of acetylated nitroalcohols and aldehydes in catalytic amounts of DBU or TBAF.3H2O, via a one-pot elimination/nitroaldol reaction sequence, was developed.

A nanostructured bifunctional acid–base catalyst resin formed by lyotropic liquid crystal monomers

An ordered, nanoporous polymer resin was prepared from the self-assembly of lyotropic liquid crystal monomers and employed as a heterogeneous, bifunctional catalyst. This material contains antagonistic acid and base sites in the periodic nanopores and efficiently catalyzes a model tandem reaction (i.e., the deacetalization–nitroaldol reaction between benzaldehyde dimethyl acetal and nitromethane to yield β-nitrostyrene) with excellent product selectivity. This lyotropic liquid crystal-based solid catalyst represents one of the few examples of polymeric tandem catalysts synthesized by a “bottom-up” strategy that imparts control over the stoichiometry of acidic and basic monomers and is the only reported example of a lyotropic liquid crystal-based polymer that contains mutually incompatible catalytic groups. Furthermore, this heterogeneous catalyst is highly active, exhibiting a turnover frequency for this tandem test reaction that exceeds other reported catalytic polymeric materials.

Heteroaromatic N-Oxides in Asymmetric Catalysis: A Review

An increasing interest in the synthesis and use of optically active pyridine N-oxides as chiral controllers for asymmetric reactions has been observed in the last few years. Chiral heteroaromatic N-oxides can work as powerful electron-pair donors, providing suitable electronic environments in the transition state formed within the reaction. The nucleophilicity of the oxygen atom in N-oxides, coupled with a high affinity of silicon to oxygen, represent ideal properties for the development of synthetic methodology based on nucleophilic activation of organosilicon reagents. The application of chiral N-oxides as efficient organocatalysts in allylation, propargylation, allenylation, and ring-opening of meso-epoxides, as well as chiral ligands for metal complexes catalyzing Michael addition or nitroaldol reaction, can also be found in the literature. This review deals with stereoselective applications of N-oxides, and how the differentiating properties are correlated with their structure. It contains more recent results, covering approximately the last ten years. All the reported examples have been divided into five classes, according to the chirality elements present in their basic molecular frameworks.