Synthesis of 2-aminoazulene derivatives. Nucleophilic and palladium-catalyzed amination of 2-substituted azulene

Synthesis of C3-functionalized indole derivatives via Brønsted acid-catalyzed regioselective arylation of 2-indolylmethanols with guaiazulene

The first Brønsted acid catalyzed method for the construction of guaiazulenyl C3-functionalized indole derivatives was established. The reactions proceeded smoothly at ambient temperature by used (±)-10-camphorsulfonic acid (CSA) as catalyst,...

Copper-Catalyzed 3-Positional Amination of 2-Azulenols with O-Benzoylhydroxylamines

A copper-catalyzed ortho-selective amination of 2-azulenols with O-benzoylhydroxylamines (RR'N-OBz) to synthesize ortho-aminoazulenols is reported. A wide range of functional groups on amines are compatible, furnishing the corresponding amino-azulene derivatives in moderate to good yields. The further synthetic elaboration using 3-amino-2-azulenols as starting materials is demonstrated.

Quantum-Chemical Search for Keto Tautomers of Azulenols in Vacuo and Aqueous Solution

Keto-enol prototropic conversions for carbonyl compounds and phenols have been extensively studied, and many interesting review articles and even books appeared in the last 50 years. Quite a different situation takes place for derivatives of biologically active azulene, for which only scanty information on this phenomenon can be found in the literature. In this work, quantum-chemical studies have been undertaken for symmetrically and unsymmetrically substituted azulenols (constitutional isomers of naphthols). Stabilities of two enol (OH) rotamers and all possible keto (CH) tautomers have been analyzed in the gas phase {DFT(B3LYP)/6-311+G(d,p)} and also in aqueous solution {PCM(water)//DFT(B3LYP)/6-311+G(d,p)}. Contrary to naphthols, for which the keto forms can be neglected, at least one keto isomer (C1H, C2H, and/or C3H) contributes significantly to the tautomeric mixture of each azulenol to a higher degree in vacuo (non-polar environment) than in water (polar amphoteric solvent). The highest amounts of the CH forms have been found for 2- and 5-hydroxyazulenes, and the smallest ones for 1- and 6-hydroxy derivatives. The keto tautomer(s), together with the enol rotamers, can also participate in deprotonation reaction leading to a common anion and influence its acid-base properties. The strongest acidity in vacuo exhibits 6-hydroxyazulene, and the weakest one displays 1-hydroxyazulene, but all azulenols are stronger acids than phenol and naphthols. Bond length alternation in all DFT-optimized structures has been measured using the harmonic oscillator model of electron delocalization (HOMED) index. Generally, the HOMED values decrease for the keto tautomers, particularly for the ring containing the labile proton. Even for the keto tautomers possessing energetic parameters close to those of the enol isomers, the HOMED indices are low. However, some kind of parallelism exists for the keto forms between their relative energies and HOMEDs estimated for the entire molecules.

The anionic Fries rearrangement: a convenient route to ortho-functionalized aromatics

The scope and mechanism of anionic (hetero-) Fries rearrangements are summarized for various migrating groups and arenes, including applications and computational studies.

Synthesis of 2-amino- and 2-arylazoazulenes via nucleophilic aromatic substitution of 2-chloroazulenes with amines and arylhydrazines

The S_NAr reaction of 2-chloroazulene derivative 1 with ethoxycarbonyl groups at the 1,3-positions of the azulene ring with several amines afforded the corresponding 2-aminoazulenes 3-9 in excellent yields. 2-Chloroazulene (2) without the electron-withdrawing groups reacted with highly nucleophilic cyclic amines (i.e., morpholine, piperidine and pyrrolidine) under the high-temperature conditions in a sealed tube to produce the corresponding 2-aminoazulenes 10-12 in good yields. 2-Aminoazulenes 10-14 without the electron-withdrawing groups were also obtained in good yields by the treatment of compounds 3-7 with 100% H₃PO₄, but in the cases of the reaction of 8 and 9 with a secondary amine function, the decomposition of the products resulted. The synthesis of 2-arylazoazulenes 15-18 was also established via the S_NAr reaction of 1 with arylhydrazines. The optical and electrochemical properties of the 2-arylazoazulene derivatives were examined by UV/Vis spectroscopy, theoretical calculations and voltammetric experiments.

Azulene-substituted aromatic amines. synthesis and amphoteric redox behavior of N,N-Di(6-azulenyl)-p-toluidine and N,N,N',N'-tetra(6-azulenyl)-p-phenylenediamine and their derivatives

[reaction: see text] N,N-Di(6-azulenyl)-p-toluidine (1a) and N,N,N',N'-tetra(6-azulenyl)-p-phenylenediamine (2a) and their derivatives with 1,3-bis(ethoxycarbonyl) substituents on each 6-azulenyl group (1b and 2b) were prepared by Pd-catalyzed amine azulenylation and characterized as a study into new aromatic amines for multistage amphoteric redox materials. The redox behavior of each compound was characterized by cyclic voltammetry. These compounds undergo facile reduction to stable anion radicals and dianion diradicals owing to the resonance stabilization between the 6-azulenyl groups and exhibit electrochemical oxidation depending on the amine subunits. The ESR measurement of anion radicals and a dianion diradical generated by the electrochemical reduction of amine 1b and diamine 2b revealed that the unpaired electron of these radicals delocalizes over the entire azulene ring including the central nitrogen atoms. UV-vis spectral analysis of amines 1a,b and diamines 2a,b, taken during the electrochemical reduction, exhibited a gradual decrease of the absorption bands of the neutral species along with an increase of the new absorption maxima at 625, 605, 640, and 610 nm, respectively, with the development of well-defined isosbestic points at 502, 562, 478, and 545 nm, respectively. As indicated by a combined ESR and UV-vis spectral study, the species giving rise to the new absorption maxima are concluded to be the generation of anion radicals and dianion diradicals of aromatic amines and diamines with high thermodynamic stability.