Study of the Addition Mechanism of 1H-Indazole and Its 4-, 5-, 6-, and 7-Nitro Derivatives to Formaldehyde in Aqueous Hydrochloric Acid Solutions

The reaction of NH-indazoles with formaldehyde in aqueous hydrochloric acid has been experimentally studied by solution and solid-state nuclear magnetic resonance (NMR) and crystallography. The mechanism of the formation of N₁-CH₂OH derivatives was determined. For the first time, 2-substituted derivatives have been characterized by multinuclear NMR. Theoretically, calculations with gauge-invariant atomic orbitals (GIAOs) at the Becke three-parameter (exchange) Lee–Yang–Parr B3LYP/6-311++G(d,p) level have provided a sound basis for the experimental observations. The first X-ray structures of four (1H-indazol-1-yl)methanol derivatives are reported.

Synthesis of a Novel Series of Cu(I) Complexes Bearing Alkylated 1,3,5-Triaza-7-phosphaadamantane as Homogeneous and Carbon-Supported Catalysts for the Synthesis of 1- and 2-Substituted-1,2,3-triazoles

The N-alkylation of 1,3,5-triaza-7-phosphaadamantane (PTA) with ortho-, meta- and para-substituted nitrobenzyl bromide under mild conditions afforded three hydrophilic PTA ammonium salts, which were used to obtain a new set of seven water-soluble copper(I) complexes. The new compounds were fully characterized and their catalytic activity was investigated for the low power microwave assisted one-pot azide-alkyne cycloaddition reaction in homogeneous aqueous medium to obtain disubstituted 1,2,3-triazoles. The most active catalysts were immobilized on activated carbon (AC), multi-walled carbon nanotubes (CNT), as well as surface functionalized AC and CNT, with the most efficient support being the CNT treated with nitric acid and NaOH. In the presence of the immobilized catalyst, several 1,4-disubstituted-1,2,3-triazoles were obtained from the reaction of terminal alkynes, organic halides and sodium azide in moderate yields up to 80%. Furthermore, the catalyzed reaction of terminal alkynes, formaldehyde and sodium azide afforded 2-hydroxymethyl-2H-1,2,3-triazoles in high yields up to 99%. The immobilized catalyst can be recovered and recycled through simple workup steps and reused up to five consecutive cycles without a marked loss in activity. The described catalytic systems proceed with a broad substrate scope, under microwave irradiation in aqueous medium and according to "click rules".

Discovery of a new HIV-1 inhibitor scaffold and synthesis of potential prodrugs of indazoles

A new oxazole scaffold showing great promise in HIV-1 inhibition has been discovered by cell-based screening of an in-house library and scaffold modification. Follow-up SAR study focusing on the 5-aryl substituent of the oxazole core has identified 4k (EC50=0.42μM, TI=50) as a potent inhibitor. However, the analogues suffered from poor aqueous solubility. To address this issue, we have developed broadly applicable potential prodrugs of indazoles. Among them, N-acyloxymethyl analogue 11b displayed promising results (i.e., increased aqueous solubility and susceptibility to enzymatic hydrolysis). Further studies are warranted to fully evaluate the analogues as the potential prodrugs with improved physiochemical and PK properties.

1-Chloromethyl-1H-1,2,3-benzotriazole

In the title compound, C₇H₆ClN₃, the benzotriazole ring is essentially planar with a maximum deviation of 0.0110 (15)Å, and makes a dihedral angle of 0.46 (8)° with the benzene ring. In the crystal, mol­ecules are linked through inter­molecular C—H⋯N hydrogen bonds, forming chains along the c axis.

Electronic structure and stability of benzotriazoles

The electronic structures and relative stabilities of N-substituted benzotriazoles (BtR) have been studied by UV photoelectron spectroscopy (UPS) and high-level ab initio methods. We show that the UPS spectrum of 1H-benzotriazole corresponds to a mixture of tautomers. The N-substituent effects in benzotriazoles were shown to depend on the mode of attachment of the substituent to the Bt residue. We have estimated the conjugation effects between benzene and triazole rings in N-substituted benzotriazoles by using isodesmic reactions and high-level composite ab initio methods. The 2H-benzotriazoles (Bt2R) appear to be stabilized upon ring conjugation while on the other hand the 1H-benzotriazoles (Bt1R) are destabilized. The electronic structure of benzotriazoles can be related to photocycloaddition reactions and to regioselectivity exhibited during nitration.

Efficient synthesis of 2-substituted-1,2,3-triazoles

In this three-component reaction, alkynes undergo a copper(I)-catalyzed cycloaddition with sodium azide and formaldehyde to yield 2-hydroxymethyl-2 H-1,2,3-triazoles, which are useful intermediates that can be readily converted to polyfunctional molecules. The hydroxymethyl group can also be removed, providing convenient access to N H-1,2,3-triazoles. The reaction is experimentally simple and readily scalable.

1,2,3-Triazoles

Rapid progress in the synthetic application of benzotriazole derivatives in the last 20 years has resulted in over 1000 scientific papers on the subject. This fact is reflected in Section 5.01.7, which involves almost a half of the volume of this chapter. The section is arranged according to hybridization of the C-α atom and atomic numbers of the atoms in positions β and γ to allow an easy access to the material of interest. Recent discovery of copper catalysis in [3+2] cycloadditions of azides to acetylenes, the so-called ‘click chemistry’, which boosted application of the 1,2,3-triazole derivatives, especially in medicinal chemistry, is presented in Section 5.01.9. From the point of view of practical applications, Section 5.01.11 is organized according to the number, position, and combination of the substituents at the aromatic rings. Another novel feature that has no precedence in the previous editions of Comprehensive Heterocyclic Chemistry is an addition of triazole and benzotriazole complexes with various transitions metals to Section 5.01.4.