Functionalization of imidazole N-oxide: a recent discovery in organic transformations

Nowadays heterocyclic compounds are widely used in medicinal chemistry and industry to develop life-saving drugs and medicines. Imidazole is one of the pharmacologically important heterocyclic motifs found in widely used and well-known medicines and bioactive molecules. The applications of imidazole derivatives displaying various biological activities, motivated researchers for the development of more potent and significant drugs containing imidazole moieties. The formation of imidazole derivatives can be achieved using imidazole N-oxide as starting material. In this review, the scope of substrates and reaction mechanisms of various synthetic approaches using imidazole N-oxides as substrates are summarized so that the chemists, researchers, and pharmaceutical industries find its effectiveness in near future for the synthesis of potent, novel, and non-toxic drug molecules.

Novel Room Temperature Ionic Liquid for Liquid-Phase Microextraction of Cannabidiol from Natural Cosmetics

This study presents the synthesis of a novel asymmetric 1,3-di(alkoxy)imidazolium based room temperature ionic liquid, more precisely 1-butoxy-3-ethoxy-2-ethyl-imidazolium bis(trifluoromethane)sulfonimide, and its application as an extraction solvent in liquid-phase microextraction of cannabidiol from natural cosmetics. Quantification was implemented, using a high performance liquid chromatography system coupled to ultraviolet detection. Molecular structure elucidation was performed by nuclear magnetic resonance spectroscopy. The extraction procedure was optimized by means of two different design of experiments. Additionally, a full validation was executed. The established calibration model, ranging from 0.6 to 6.0 mg g−1, was linear with a coefficient of determination of 0.9993. Accuracy and precision were demonstrated on four consecutive days with a bias within −2.6 to 2.3% and a maximum relative standard deviation value of 2.5%. Recoveries, tested for low and high concentration within the calibration range, were 80%. Stability of extracted cannabidiol was proven for three days at room temperature and fourteen days at 4 °C and −20 °C. An autosampler stability for 24 h was validated. Liquid-phase microextraction of cannabidiol from different formulated cream based cosmetics was performed, including four ointments and four creams. The results show that a significantly higher selectivity could be achieved compared to a conventional extraction methods with methanol.

2-Unsubstituted Imidazole N-Oxides as Novel Precursors of Chiral 3-Alkoxyimidazol-2-ylidenes Derived from trans-1,2-Diaminocyclohexane and Other Chiral Amino Compounds

‘Desymmetrization’ of trans-1,2-diaminocyclohexane by treatment with α,ω-dihalogenated alkylation reagents leads to mono-NH₂ derivatives (‘primary-tertiary diamines’). Upon reaction with formaldehyde, these products formed monomeric formaldimines. Subsequently, reactions of the formaldimines with α-hydroxyiminoketones led to the corresponding 2-unsubstituted imidazole N-oxide derivatives, which were used here as new substrates for the in situ generation of chiral imidazol-2-ylidenes. Upon O-selective benzylation, new chiral imidazolium salts were obtained, which were deprotonated by treatment with triethylamine in the presence of elemental sulfur. Under these conditions, the intermediate imidazol-2-ylidenes were trapped by elemental sulfur, yielding the corresponding chiral non-enolizable imidazole-2-thiones in good yields. Analogous reaction sequences, starting with imidazole N-oxides derived from enantiopure primary amines, amino alcohols, and amino acids, leading to the corresponding 3-alkoxyimidazole-2-thiones were also studied.

Crystal structure of the phosphorescent complex diethyldithiophosphonato-κ2 S,S′-bis(2-phenylpyridinato-κ2 C,N)iridium(III), C26H26N2O2PS2Ir

C26H26N2O2PS2Ir, orthorhombic, P212121 (no. 19), a = 9.4097(6) Å, b = 13.2837(9) Å, c = 20.6400(14) Å, V = 2579.9(3) Å3, Z = 4, R gt(F) = 0.0202, wR ref(F 2) = 0.0471, T = 293(2) K.

Crystal structure of the fluorescent fipronil derivative 5,5′-(methylenebis(azanediyl))bis(1-(2,6-dichloro-4-(trifluoromethyl)phenyl)-4-((trifluoromethyl)sulfinyl)-1H-pyrazole-3-carbonitrile), C25H6N8O2Cl4F12S2

C25H6N8O2Cl4F12S2, monoclinic, C2/c (no. 15), a = 20.0584(9) Å, b = 16.1373(7) Å, c = 10.6232(5) Å, β = 93.238(4)°, V = 3433.1(3) Å3, Z = 8, R gt(F) = 0.0543, wR ref(F 2) = 0.1427, T = 293(2) K.

Synthesis and selected transformations of 2-unsubstituted 1-(adamantyloxy)imidazole 3-oxides: straightforward access to non-symmetric 1,3-dialkoxyimidazolium salts

Adamantyloxyamine reacts with formaldehyde to give N-(adamantyloxy)formaldimine as a room-temperature-stable compound that exists in solution in monomeric form. This product was used for reactions with α-hydroxyiminoketones leading to a new class of 2-unsubstituted imidazole 3-oxides bearing the adamantyloxy substituent at N(1). Their reactions with 2,2,4,4-tetramethylcyclobutane-1,3-dithione or with acetic acid anhydride occurred analogously to those of 1-alkylimidazole 3-oxides to give imidazol-2-thiones and imidazol-2-ones, respectively. Treatment of 1-(adamantyloxy)imidazole 3-oxides with Raney-Ni afforded the corresponding imidazole derivatives without cleavage of the N(1)–O bond. Finally, the O-alkylation reactions of the new imidazole N-oxides with 1-bromopentane or 1-bromododecane open access to diversely substituted, non-symmetric 1,3-dialkoxyimidazolium salts. Adamantyloxyamine reacts with glyoxal and formaldehyde in the presence of hydrobromic acid yielding symmetric 1,3-di(adamantyloxy)-1H-imidazolium bromide in good yield. Deprotonation of the latter with triethylamine in the presence of elemental sulfur allows the in situ generation of the corresponding imidazol-2-ylidene, which traps elemental sulfur yielding a 1,3-dihydro-2H-imidazole-2-thione as the final product.