The azido-tetrazole and diazo-1,2,3-triazole tautomerism in six-membered heteroaromatic rings and their relationships with aromaticity: Azines and perimidine

(Pyridin-2-ylmethyl)triel Derivatives as Masked Frustrated Lewis Pairs. Interactions and CO2 -Sequestration

The isolated (pyridin-2-ylmethyl)triel derivatives (triel=B, Al and Ga) show an intramolecular N⋅⋅⋅Tr triel bond as shown by compounds found in the Cambridge Structural Database and DFT calculations. The possibility to use them as masked frustrated Lewis pairs (mFLP) has been explored theoretically concerning their reaction with CO2 . The adduct formation proceeds in two steps. In the first one, the (pyridin-2-ylmethyl)triel derivatives break the intramolecular N⋅⋅⋅Tr bond assisted by CO2 and in the second step the adduct is formed with Tr-O and N-C covalent bonds. The corresponding energy minima and transition states (TS) of the reaction have been characterized and analyzed. The distortion/interaction model analysis of the stationary points indicates that the whole process can be divided in two parts: reorganization of the mFLP in the first steps of the reaction while the reaction with CO2 (associated to the distortion of this molecule) is more important in the formation of the final adduct. In all cases studied, the final products are more stable than the starting molecules that combine with reasonable TS energies indicating that these reactions can occur.

Annulation-Triggered Denitrogenative Transformations of 2-(5-Iodo-1,2,3-triazolyl)benzoic Acids

The ability of [1,2,3]triazolobenzoxazinones to act as a source of "hidden" diazo group was discovered. These diazo precursors can be easily prepared by the intramolecular cyclization of 2-(5-iodo-1,2,3-triazolyl)benzoic acids. The Cu-catalyzed capture of the hidden diazo group allows for further functionalization through the denitrogenative pathway. The transformations proceed via the formation of either diazoimine or diazoamide intermediates. Novel routes to various anthranilamides as well as thiolated benzoxazinones were developed using the one-pot cyclization/diazo capture procedure.

15N Chemical Shifts and JNN-Couplings as Diagnostic Tools for Determination of the Azide-Tetrazole Equilibrium in Tetrazoloazines

Selectively ¹⁵N-labeled tetrazolo[1,5-b][1,2,4]triazines and tetrazolo[1,5-a]pyrimidines bearing one, two, or three ¹⁵N labels were synthesized. The synthesized compounds were studied by ¹H, ¹³C, and ¹⁵N NMR spectroscopy in DMSO and TFA solutions, where the azide-tetrazole equilibrium can lead to the formation of two tetrazole (T, T') isomers and one azide (A) isomer for each compound. Incorporation of the ¹⁵N-label(s) leads to the appearance of ¹⁵N-¹⁵N coupling constants (J_NN), which can be easily measured via simple 1D ¹⁵N NMR spectra, even at natural abundance between labeled and unlabeled ¹⁵N atoms. The chemical shifts for the ¹⁵N nuclei in the azole moiety are very sensitive to the ring opening and azide formation, thus providing information about the azido-tetrazole equilibrium. At the same time, the ^1-2J_NN couplings between ¹⁵N-labeled atoms in the azole and azine fragments unambiguously determine the fusion type between tetrazole and azine rings in the cyclic isomers T and T'. Thus, combined analysis of ¹⁵N chemical shifts and J_NN values in selectively isotope-enriched compounds provides an effective diagnostic tool for direct structural determination of tetrazole isomers and azide form in solution. This method was found to be the most simple and efficient way to study the azido-tetrazole equilibrium.

Recent Advances in the Synthesis of Perimidines and their Applications

Perimidines are versatile scaffolds and a fascinating class of N-heterocycles that have evolved significantly in recent years due to their immense applications in life sciences, medical sciences, and industrial chemistry. Their ability of molecular interaction with different proteins, complex formation with metals, and distinct behavior in various ranges of light makes them more appealing and challenging for future scientists. Various novel technologies have been developed for the selective synthesis of perimidines and their conjugated derivatives. These methods extend to the preparation of different bioactive and industrially applicable molecules. This review aims to present the most recent advancements in perimidine synthesis under varied conditions like MW radiation, ultrasound, and grinding using different catalysts such as ionic liquids, acid, metal, and nanocatalyst and also under green environments like catalyst and solvent-free synthesis. The applications of perimidine derivatives in drug discovery, polymer chemistry, photo sensors, dye industries, and catalytic activity in organic synthesis are discussed in this survey. This article is expected to be a systematic, authoritative, and critical review on the chemistry of perimidines that compiles most of the state-of-art innovation in this area.

Crystal structure of 2-(4-methoxyphenyl)-2,3-dihydro-1H-perimidine, C18H16N2O

C18H16N2O, Monoclinic, P21/c, a = 12.1735(3) Å, b = 7.36483(18) Å, c = 16.1137(4) Å, β = 103.028(2)°, V = 1407.50(6) Å3, Z = 4, R gt (F) = 0.0387, wR ref (F 2 ) = 0.1087, T = 291.15 K.

Tandem deprotonation/azide-tetrazole tautomerization of 4,6-diazido-N-nitro-1,3,5-triazin-2-amine in dimethylsulfoxide solutions: a theoretical study

4,6-Diazido-N-nitro-1,3,5-triazin-2-amine (2) is a new promising high-energy organic compound that isomerizes in dimethylsulfoxide (DMSO) solutions to form unknown products with interesting 13C and 15N NMR spectroscopic characteristics. To identify these products, the relative energies and the 13C and 15N chemical shifts were calculated for various prototropic and valence isomers of 2. It was found that this diazide in DMSO solutions exists in equilibrium with the deprotonated form of 5-azido-N-nitrotetrazolo[1,5-a][1,3,5]triazin-7-amine (8). The anion 8 is also observed in DMSO solutions of energetic salts derived from 2 and guanidines or 4H-1,2,4-triazol-4-amines. The tandem transformations of 2 in DMSO solutions found may be of interest from both theoretical and practical points of view, for instance, in the synthesis of new energetic materials, using the reactions of anion 8 with various electrophilic agents.

1H/2H and azide/tetrazole isomerizations and their effects on the aromaticity and stability of azido triazoles

DFT studies on NAzTA, AAzTA, and AzTA show –NH₂ facilitates but –NO₂ impedes 1H/2H tautomerization. AZ/TZ isomerization of molecules with –N₃ only is the easiest. 1H/2H tautomerization decreases while AZ/TZ isomerization increases the stability.

Neutral alkaline-metal and alkaline-earth-metal derivatives of imidazole and benzimidazole

A theoretical study of the minima and connecting transition states of the neutral complexes formed by alkaline-metal and alkaline-earth-metal derivatives of imidazolate and benzimidazolate anions has been carried out using B3LYP/6-31+G(d,p), B3LYP/6-311+G(3df,2p), and G3B3 methods. Two and three nondegenerated minima and two and four TS structures have been identified for imidazole and benzimidazole derivatives, respectively. The most stable minima of the alkaline-metal derivatives of both systems correspond to the metal interacting with the imidazole ring, whereas in the alkaline-earth-metal derivatives, the preferred minima depend on the substituent. A remarkable feature of some minima is the fact that some of the metal-aromatic interactions follow the classical π-cation pattern, even though the global structure corresponds to a neutral salt, constituting a class of noncovalent interaction of great interest in the chemistry of aromatic and heterocyclic complexes. A CSD search has confirmed that the two bonding modes, N-σ and π, are present in the solid phase. The π mode has been analyzed by comparison with other azoles.

Calculations predict a novel desired compound containing eight catenated nitrogen atoms: 1-amino-tetrazolo-[4,5-b]tetrazole

A novel 8-N conjoined energetic compound 1-amino-tetrazolo-[4,5-b]tetrazole has been designed and investigated at the DFT-B3LYP/6-311++G** level of theory.

TAUTOMERISM IN NEUTRAL AND DEPROTONATED 6-AMINO-5-FORMYLURACILS: A PM3-COSMO APPROACH

In order to identify the structure of the most stable tautomers of 6-amino-5-formyluracil and its N-methylated derivatives in different pH conditions, relative stabilities of potential tautomers in aqueous phase have been calculated taking into account the entropy effects over the tautomeric equilibria. In each medium, the tautomer with lower energy must be the most representative form at the corresponding pH and the knowledge of the effect of the medium in the tautomerization energies allows evaluating the possible effect of the medium over the molecular stability. The results show that, in aqueous phase, the order of basicity of protonation sites in the 6-amino-5-formyluracil derivatives is N 9 > ( N 3 > N 1) > ( O 8 > O 4 > O 2). The 6-amino-5-formyluracil derivatives act as an amino-formyl-keto tautomer with a strong imino character, although, upon successive deprotonations, a growing contribution of enolyzed forms which explain the increasing labilization of carbonyl bonds must be pointed out.

A theoretical DFT study on the structural parameters and azide-tetrazole equilibrium in substituted azidothiazole systems

Azido-tetrazole equilibrium is sensitive to: substitution, solvent, temperature and phase. In this work, the effects of the type and position of substitution on the thiazole ring of azidothiazoles on its structural parameters and on the azido-tetrazole equilibrium have been theoretically investigated using the density functional procedures at the B3LYP/6-311G(∗∗) level of theory. This study includes the investigation of the equilibrium geometry, the transformation of the trans-conformer to the cis one then the ring closure to the tetrazole isomer. The transition states of the two steps were located, confirmed and the structural parameters were calculated. In all the steps of calculations, geometry optimization was considered. The results obtained indicate that substitution by: -NO(2) and -CN group shifts the equilibrium to the azide side and in some cases the tetrazole isomer is not obtained. On the other hand, substitution by: -NH(2) and -OH groups shifts the equilibrium to the tetrazole side and in some cases the azide isomer is not obtained and if formed changes spontaneously to the tetrazole isomer. The decisive parameters which determine the position of the equilibrium are: charge density on atoms N3 and N8, rearrangement of bond length and bond angles during the process of cyclization and variation of dipole moment as a result of cyclization. Results of this work indicate that substitution on C5 is more efficient than substitution on C4 of the thiazole ring.