The reaction of di(methoxycarbonyl)tetrazine with substituted cycloprop-2-ene-1-carboxylates gives a series of 3,4-diazanorcaradienes and 1,2-diazepines. The influence of the nature of cyclopropenes and the reaction conditions on its selectivity was investigated. The addition of nucleophiles to norcaradienes was studied and a rare example of the “walk” rearrangement in this class of compounds was revealed.
7-Lithio-3-tert-butylpyrazolo[5,1-c][1,2,4]triazines have been generated for the first time using one-pot nucleophilic addition and metal-halogen exchange reactions in 7-bromopyrazolo[5,1-c][1,2,4]triazines. It was found that the stability of 7-lithio species depends highly on the substitution pattern at the C(4) ring position. The rate of the pyrazole ring opening reaction roughly followed the order of the electronegativity of substituents: rapid cycle cleavage took place already at −97 °C for C(4) = O, CH–Ar, CH–C≡CPh, while CH–Alk and CH2 substituted derivatives were stable in these conditions (Ar = Ph, 4-tolyl; Alk = t-Bu, n-Bu, n-Pr). Quantum chemical modeling showed that the ring opening is accompanied with simultaneous shift of the Li atom towards N(6). Calculated free activation energies are in range from 12.7 to 15.0 kcal*mol−1. Electrophile trapping of fairly stable 4-alkyl-1,7-metalated derivatives at −97 °C using H2O, DMF or PhCHO allowed the selective side-chain functionalization. Tautomeric exo- and endocyclic double bond equilibrium in the isolated 4-oxo and 4-aryl substituted ring opening products is also discussed on the basis of IR, 1H, 13C NMR, high resolution mass spectra and X-ray powder diffraction analysis.
Triallylborane-mediated thermal trans/cis-isomerization of α-allylated azaheterocycles is a unique stereoselective transformation providing straightforward access to important heterocycles. The main experimental features of this process, namely, thermodynamically controlled isomer ratio, 1,3-allylic strain as a driving force and regioselectivity are quantitatively described by quantum chemical calculations at B3LYP/6-31+G(d,p)/PCM(DMSO) level of theory.
In this paper, we formulate a field-theoretical model of dilute salt solutions of electrically neutral spherical colloid particles. Each colloid particle consists of a 'central' charge that is situated at the center and compensating peripheral charges (grafted to it) that are fixed or fluctuating relative to the central charge. In the framework of the random phase approximation, we obtain a general expression for electrostatic free energy of solution and analyze it for different limiting cases. In the limit of infinite number of peripheral charges, when they can be modelled as a continual charged cloud, we obtain an asymptotic behavior of the electrostatic potential of a point-like test charge in a salt colloid solution at long distances, demonstrating the crossover from its monotonic decrease to damped oscillations with a certain wavelength. We show that the obtained crossover is determined by certain Fisher-Widom line. For the same limiting case, we obtain an analytical expression for the electrostatic free energy of a salt-free solution. In the case of nonzero salt concentration, we obtain analytical relations for the electrostatic free energy in two limiting regimes. Namely, when the ionic concentration is much higher than the colloid concentration and the effective size of charge cloud is much bigger than the screening lengths that are attributed to the salt ions and the central charges of colloid particles. The proposed theory could be useful for theoretical description of the phase behavior of salt solutions of metal-organic complexes and polymeric stars.
The swelling of a poly (methyl methacrylate) in supercritical carbon dioxide was studied by means of full atomistic classical molecular dynamics simulation. In order to characterize the polymer swelling, we calculated various properties related to the density, structure, and dynamics of polymer chains as a function of the simulation time, temperature, and pressure. In addition, we compared the properties of the macromolecular chains in supercritical CO2 with the properties of the corresponding bulk system at the same temperature and atmospheric pressure. It was shown that diffusion of CO2 molecules into the polymer led to a significant increase in the chain mobility and distances between them. Analysis of diffusion coefficients of CO2 molecules inside and outside the poly(methyl methacrylate) sample has shown that carbon dioxide actively interacts with the functional groups of poly (methyl methacrylate). Joint analysis of the radial distribution functions obtained from classical molecular dynamics and of the averaging interatomic distances from Car-Parrinello molecular dynamics allows us to make a conclusion about the possibility of formation of weak hydrogen bonds between the carbon dioxide oxygen atom and the hydrogen atoms of the polymer methyl groups.
The selective addition of electrophilic C=C double bonds to the N?H bond of indoles is a challenging task due to the high nucleophilicity of indoles at their C3-position. Herein, we report the successful selective intermolecular N-functionalization of various indoles via aza-Michael addition of C=C double bond of a dehydroalanine Schiff base, which takes place in the ligand sphere of a chiral NiII complex in the presence of sodium hydride. The resulting hydroaminated NiII complexes were isolated in 55?82?% yields with excellent diastereoselectivity (dr > 99:1) (8 examples). And the actual products of interest, namely (S)-2-amino-3-(1H-indol-1-yl)propanoic acids, were subsequently released from the NiII complexes via aqueous HCl treatment of the NiII complexes and isolated with excellent enantioselectivity (> 99?% ee). The chiral auxiliary [(S)-BPB = (S)-2-(N-benzylprolyl)aminobenzophenone] and NiII ions can be easily recovered after the acidic complex cleavage step and reused for the synthesis of the starting NiII complex. Moreover, the indole?s preference for nucleophilic attack via its N1- over its C3-position was rationalized by DFT calculations.
Chiral copper(II) and cobalt(III) complexes (1–5 and 6, respectively) derived from Schiff bases of (S)-2-(aminomethyl)pyrrolidine and salicylaldehyde derivatives were employed in a mechanistic study of the Henry reaction-type condensation of nitromethane and o-nitrobenzaldehyde in CH2Cl2 (CD2Cl2), containing different amounts of water. The reaction kinetics was monitored by 1H and 13C NMR. The addition of water had a different influence on the activity of the two types of complexes, ranging from a crucial positive effect in the case of the copper(II) complex 2 to insignificant in the case of the stereochemically inert cobalt(III) complex 6. No experimental support was found by 1H NMR studies for the classical Lewis acid complexation of the carbonyl group of the aldehyde by the central copper(II) ion, and, moreover, density functional theory (DFT) calculations support the absence of such coordination. On the other hand, a very significant complexation was found for water, and it was supported by DFT calculations. In fact, we suggest that it is the Brønsted acidity of the water molecule coordinated to the metal ion that triggers the aldehyde activation. The rate-limiting step of the reaction was the removal of an α-proton from the nitromethane molecule, as supported by the observed kinetic isotope effect equaling 6.3 in the case of the copper complex 2. It was found by high-resolution mass spectrometry with electrospray ionization that the copper(II) complex 2 existed in CH2Cl2 in a dimeric form. The reaction had a second-order dependence on the catalyst concentration, which implicated two dimeric forms of the copper(II) complex 2 in the rate-limiting step. Furthermore, DFT calculations help to generate a plausible structure of the stereodetermining transition step of the condensation.
Two approaches for the synthesis of D-A chromophores containing arylhydrazonocyclopentadiene acceptor moieties were developed. The first approach includes the decarboxylative azo coupling reaction between penta(methoxycarbonyl)cyclopentadienyl potassium or sodium and aryldiazonium salts to give products containing four ester groups at the acceptor moiety. The second one includes the reaction of 1,3-dimethoxycarbonyl-4,5-diphenylcyclopentadienone with arylhydrazine hydrochlorides into arylhydrazonocyclopentadienes with two ester and two phenyl groups. Both series of compounds were investigated by means of absorption spectroscopy and the solvatochromic behavior of two representatives of each series was investigated in various dielectric environments. Both compounds demonstrated relative independence on the environment although the product with the stronger acceptor part was less stable and exhibited a slight hypsochromic shift in polar media. However, the optical properties of this product were strongly affected by the basicity of the medium due to the deprotonation of the NH-group. Quantum chemical modeling of the synthesized products adsorption spectra using different density functionals has shown that PBE0-D3/def2TZVP is an optimal method (out of three tested) for all compounds both in non-vibrationally-resolved and vibrationally-resolved TD-DFT calculations. Accounting for vibronic coupling in TD-DFT calculations is necessary to achieve good agreement with the experiment for compounds synthesized herein.
A straightforward protocol toward pharmacologically relevant (het)areno[x,y-b]pyrrolo[1,2-d][1,4]diazepines in good-to-high yields has been described. The designed approach consists of an acid-promoted furan ring opening in easily accessible N-(2- furylethyl)-2-nitroanilines or their heterocyclic analogues followed by the reductive cyclization of the corresponding nitro-1,4-diketones.