An efficient, expeditious, and diastereoselective one-pot pseudo-five-component reaction for the synthesis of new bis-Betti bases under catalyst-free conditions

Catalyst-free and additive-free reactions enabling C-C bond formation: a journey towards a sustainable future

This review focuses on the catalyst- and additive-free C-C bond forming reactions reported mostly from the year 2005 to date. C-C bond forming reactions are highly important as large and complex organic molecules can be derived from simpler ones via these reactions. On the other hand, catalyst- and additive-free reactions are economical, environmentally friendly and less sensitive to air/moisture, allow easy separation of products and are operationally simple. Hence, a large number of research articles have been published in this area. Though a few reviews are available on the catalyst-free organic reactions, most of them were published a few years ago. The current review excludes catalysts as well as additives and is specific to only C-C bond formation. Besides many organic name reactions, catalyst/additive-free C-H functionalizations, coupling reactions and UV-visible-light-promoted reactions are also discussed. Undoubtedly, the contents of this review will motivate readers to do more novel work in this area which will accelerate the journey towards a sustainable future.

Access to molecular complexity. Multicomponent reactions involving five or more components

The evaluation of the significance of a chemical transformation addresses many factors, including such important characteristics as the number of chemical bonds formed in one step, the reaction time, labour intensity, the cost of reactants and catalysts and so on. The amount of waste produced in the reaction has also gained increasing importance in recent years. Multicomponent reactions (MCRs) occupy a special place as a synthetic tool in modern organic chemistry. These reactions allow the synthesis of target products with complex structures, minimizing labour costs. This review summarizes the literature on multicomponent reactions involving five or more components. The data in the review are classified according to the number of reactants participating in the reaction and the types of reactions. It is worth noting that in some cases, these transformations can be a part of a domino process, making this classification difficult, if not impossible. The structural diversity of the reaction products greatly increases with increasing number of components involved in the MCR, which becomes virtually unlimited when using combinations of MCRs. This review highlights the main trends of past decades in the field of MCRs. The last two decades have witnessed an explosive growth in the number of publications in this area of chemistry.

The bibliography includes 309 references.

Estrone derived 2-naphthol analogue in the diastereoselective one-pot Betti-condensation

The utility of deoxy-isoequilenine synthesized from estrone as valuable 2-naphthol analogue is demonstrated in the three components Betti-condensation. A simple, efficient and green procedure for the synthesis of aminobenzylnaphthol analogues (so-called Betti bases) has been realized highly diastereoselectively by using (S)-phenylethylamine and 1- or 2-naphthaldehyde. The absolute configuration of the new chiral compounds obtained has been determined by means of NMR experiments and confirmed by X-ray crystallography. The chiral steroidal aminobenzylnaphthols have been evaluated as pre-catalysts for the addition of diethylzinc to aldehydes with enantioselectivities of up to 98% ee.

Recent advances in the synthesis and synthetic applications of Betti base (aminoalkylnaphthol) and bis-Betti base derivatives

The multicomponent reaction between 2-naphthol, arylaldehydes and ammonia yields aminobenzylnaphthols in a process known as the Betti reaction, which was first uncovered at the beginning of the 20th century. Various methods have been reported for the synthesis of aminobenzylnaphthol (Betti base) and bis-Betti base derivatives using various types of naphthols, aromatic amines, heteroaromatic amines, and aliphatic and cyclic amines instead of ammonia or diamines and aliphatic and aromatic aldehydes or dialdehyde compounds under various conditions in recent years. The Betti reaction produces racemic and non-racemic aminobenzylnaphthol ligands. It is also clear that the most important area of application of the non-racemic aminonaphthols prepared in this manner is their use in asymmetric synthesis, either as chiral ligands or as chiral auxiliaries. The functional groups in these Mannich products offer many ring closure possibilities. Some of these products or the starting bifunctional compounds possess biological activity. Herein, we present a selection of the relevant studies on this topic.

Aminoazole-Based Diversity-Oriented Synthesis of Heterocycles

The comprehensive review contains the analysis of literature data concerning reactions of heterocyclization of aminoazoles and demonstrates the application of these types of transformations in diversity-oriented synthesis. The review is oriented to wide range of chemists working in the field of organic synthesis and both experimental and theoretical studies of nitrogen-containing heterocycles.

New tricks of well-known aminoazoles in isocyanide-based multicomponent reactions and antibacterial activity of the compounds synthesized

The well-known aminoazoles, 3-amino-5-methylisoxazole and 5-amino-N-aryl-1H-pyrazole-4-carboxamides, were studied as an amine component in Ugi and Groebke-Blackburn-Bienaymé multicomponent reactions. The first example of an application of aminoazoles in an Ugi four-component reaction was discovered and novel features of a Groebke-Blackburn-Bienaymé cyclocondensation are established and discussed. The heterocycles obtained were evaluated for their antibacterial activity and several of them demonstrated a weak antimicrobial effect, but for most of the compounds a 30-50% increase in biomass of Gram-positive strains (mainly B. subtilis) compared to control was observed.

Stereochemistry and spectroscopic analysis of bis-Betti base derivatives of 2,3-dihydroxynaphthalene

Density functional theory (DFT) was used to study the stereochemistry, thermodynamic stability, and spectra of recently synthesized bis-Betti base derivatives of 2,3-dihydroxynaphthalene obtained through multicomponent reactions of 2,3-dihydroxynaphthalene with aminoisoxazole and benzaldehyde derivatives. The stereochemistry of the products was investigated by theoretically calculating the infrared (IR) and proton nuclear magnetic resonance ((1)H NMR) spectra of the diastereomers and comparing them to the corresponding experimental data. The thermochemical properties of the reactions, including the enthalpy, internal energy, entropy, and Gibbs free energy, were also calculated. The diastereoselectivity of the reactions was estimated from the equilibrium distribution of diastereomers. According to the results, the synthesis of bis-Betti bases is exothermic and accompanied by a decrease in entropy. The energy difference between the diastereomers is quite small, but the Gibbs free energy change for the equilibrium syn <−> anti favors the anti over syn configuration. These results are in good agreement with experimental observations.

Solvent-free preparation of novel 2-[phenyl (pyridine-2-ylamino) methyl] phenols as pseudo-betti processor for natural products

BACKGROUND

2-Aminopyridine and benzaldehydes mixture readily reacted with phenols at 80°C without any solvents to produce novel 2-[phenyl (pyridine-2-yl amino (methyl] phenol derivatives as pseudo-Betti products in good to high yields. These compounds are efficient processor for synthesis of the natural products.

OBJECTIVES

We decided to report the synthesis of a series of novel N-heteroaryl-arylmethyl phenols via a simple three-component, one-pot method, using aromatic aldehydes, heteroaryl amines, and phenols in the absence of any acid catalysts and under solvent-free conditions.

MATERIALS AND METHODS

All starting materials were purchased from Merck and Aldrich companies. The IR spectra were recorded on a Perkin-Elmer RXI infrared spectrometer.

RESULTS

The reaction is convenient, operationally simple, proceeds quickly, and does not need solvents or expensive starting materials. The structures of the products were characterized by their spectral (1H NMR and IR) data.

CONCLUSIONS

We have developed a new, simple, and efficient method for one-pot aminoalkylation of active phenol compounds with various imines prepared from 2-aminopyrimidine and benzaldehydes in good to high yields (40%-97%).

Construction of an all-substituted pyrrolidine derivative with multiple stereogenic centers and Betti-base-derived γ-amino alcohols by [1,2]-Wittig rearrangement

The construction of Betti base-derived γ-amino alcohols and all-substituted pyrrolidine derivative with multiple stereogenic centers has been developed successfully through neighboring lithium-assisted [1,2]-Wittig rearrangement (NLAWR).

Solvent-free and catalysts-free chemistry: a benign pathway to sustainability

In the past decade, alternative benign organic methodologies have become an imperative part of organic syntheses and chemical reactions. The various new and innovative sustainable organic reactions and methodologies using no solvents or catalysts and employing alternative energy inputs such as microwaves, sonication, conventional and room temperature heating conditions, mechanochemical mixing, and high-speed ball milling are discussed in detail. Environmentally benign and pharmaceutically important reactions such as multicomponent, condensation, and Michael addition reactions; ring opening of epoxides; and oxidation and other significant organic reactions are discussed. An overview of benign reactions through solvent- and catalyst-free (SF-CF) chemistry and a critical perspective on emerging synergies between SF-CF organic reactions are discussed.

Synthesis of trans-1,3-diaryl-2-(5-methylisoxazol-3-yl)-2,3-dihydro-1H-naphtho[1,2-e][1,3]oxazines via bismuth(III)-catalyzed one-pot pseudo-four component reaction

An expeditious, straightforward and efficient synthesis of diversely naphtho[1,2-e][1,3]oxazines via one-pot condensation reaction of β- naphthol, 3-amino-5-methylisoxazole and arylaldehydes catalyzed by bismuth(III) trifluoromethanesulfonate is described. The reaction preferentially afforded 1,3-trans oxazines.