Perspectives of ionic liquids applications for the synthesis of five- and six-memberedO,N-heterocycles

Synthesis of Benzalacetophenone Based Isoxazoline and Isoxazole Derivatives

Abstract:

The demand for natural product based drugs with less cost and efficient procedures has become a challenge to researchers. Benzalacetophenone is a natural product based species that is modified into numerous heterocyclic compounds including isoxazoline and isoxazole derivatives. The utility of isoxazoline and oxazole derivatives has been increased for the synthesis of the new and effective chemical entities to serve medicinal chemistry in the past few years. Isoxazoline and isoxazole are fascinating classes of heterocyclic compounds, which belong to N- and O-heterocycles, and are widely used as precursors for the development of drugs. This review highlights the recent work for the synthesis of mono and bis isoxazoline and isoxazole derivatives using stable benzalacetophenone and functionalization of isoxazoline and isoxazole, along with the prevailing biological properties.

Investigating Variation of the Pnicogen Nucleophilic Heteroatom on Ionic Liquid Solvent Effects in Bimolecular Nucleophilic Substitution Processes

A series of nucleophiles containing Group 15 nucleophilic heteroatoms has been used to expand and develop the current understanding of ionic liquid solvent effects on bimolecular nucleophilic substitution processes. It was found that when using arsenic-, antimony- and bismuth-based nucleophiles, rate constant enhancement was observed for all solvent compositions containing ionic liquids. This rate constant enhancement was driven by ionic liquid/transition state interactions, which contrasts with previous studies on earlier Group 15 nucleophiles. This study provides a holistic understanding and augments the predictive framework for the effects of ionic liquids on bimolecular nucleophilic substitution processes, with the potential for these periodic trends to be broadly applied.

Recent Developments on 1,3-Dipolar Cycloaddition Reactions by Catalysis in Green Solvents

The use of eco-compatible synthetic procedures in organic reactions and, in particular, in 1,3-dipolar cycloaddition reactions, has recently received a great deal of attention and considerable progress has been achieved in this area in the last years. This review summarizes the approaches currently employed to synthesize heterocyclic compounds by catalyzed 1,3-dipolar cycloadditions in green solvents in the last six years. Our choice to do a selection of the literature from 2014 to 2019 was made considering the absence of a recent review about this period, to our knowledge. Several examples to construct heterocycles by 1,3-dipolar cycloadditions will be discussed in this work subdivided in function of the most important class of non-conventional and green solvents, i.e., ionic liquids (ILs), deep eutectic solvents (DES), and water.

Understanding the effects of solvate ionic liquids as solvents on substitution processes

The effects of solvate ionic liquids as solvents have been considered for two substitution processes where the solvent effects of typical ionic liquids have been extensively investigated previously; the bimolecular nucleophilic substitution (SN2) reaction between pyridine and benzyl bromide and the nucleophilic aromatic substitution (SNAr) reaction between ethanol and 1-fluoro-2,4-dinitrobenzene. It was found that use of solvate ionic liquids gave rise to similar trends in the activation parameters for both substitution processes as typical ionic liquids, implying the microscopic interactions responsible for the effects were the same. However, different effects on the rate constants compared to typical ionic liquids were observed due to the changes in the balance of enthalpic and entropic contributions to the observed rate constants. From these data it is clear that the reaction outcome for both of these substitution reactions fall within the 'predictive framework' established in previous studies with a cautionary tale or two of their own to add to the general knowledge of ionic liquid solvent effects for these processes, particularly with respect to potential reactivity of the solvate ionic liquids themselves.

The Dependence of Ionic Liquid Solvent Effects on the Nucleophilic Heteroatom in SN Ar Reactions. Highlighting the Potential for Control of Selectivity

Nucleophilic aromatic substitution (S_N Ar) reactions of 1-fluoro-4-nitrobenzene using similar nitrogen and sulfur nucleophiles were studied through extensive kinetic analysis in mixtures containing ionic liquids. The interactions of the ionic liquid components with the starting materials and transition state for each process were investigated in an attempt to construct a broad predictive framework for how ionic liquids affect reaction outcome. It was found that, based on the activation parameters, the microscopic interactions and thus the ionic liquid solvent effect were different for each of the nucleophiles considered. The results from this study suggest that it may be possible to rationally select a given ionic liquid mixture to selectively control reaction outcome of an S_N Ar reaction where multiple nucleophiles are present.