Beilstein Journal of Organic Chemistry最新文献

In this paper, the behavior of a bicolor fluorescent indicator for the detection of barium cations formed by double-beta decay of ¹³⁶Xe is analyzed by means of computational tools. Both DFT and TDDFT permit to understand the origin of the bicolor fluorescent signal emitted by 1-arylbenzo[a]imidazo[5,1,2-cd]indolizines in the free and Ba²⁺-bound states. The aromatic character of the fluorophore is analyzed by means of energetic (hyperhomodesmotic equations), structural (harmonic oscillator model of aromaticity, HOMA) and magnetic (nucleus independent chemical shifts, NICS) criteria. It is concluded that the aromatic character of the fluorophore is better described as the combination of two aromatic subunits integrated in the polycyclic system. Different DFT functional are used to analyze the photochemical behavior of this family of sensors. It is concluded that PBE0 and M06 functionals describe better the excitation process in the free state, whereas interaction of the sensor with Ba²⁺ requires the M06L functional. TDDFT analysis of the emission spectra shows larger errors, which have been corrected by means of a structural model. The bicolor behavior is rationalized based on the decoupling between the para-phenylene and benzo[a]imidazo[5,1,2-cd]indolizine components that results in a blue shift upon Ba²⁺ coordination.

The influence of transition-state aromaticity on the barrier heights of concerted pericyclic reactions is summarized herein. To this end, selected representative examples ranging from fundamental processes such as Diels-Alder or Alder-ene reactions to double-group transfer reactions or 1,3-dipolar cycloadditions involving metal complexes are presented. It is found that while more synchronous processes tend to exhibit greater aromatic character in their transition states, this increased aromaticity does not necessarily correlate with lower activation barriers. State-of-the-art computational methods on reactivity, such as the combined activation strain model (ASM)-energy decomposition analysis (EDA) method, reveal that factors other than aromaticity govern the barrier heights of these pericyclic reactions.

A high-yielding method for the synthesis of 3-arylbenzo[4,5]thieno[3,2-b]pyrroles has been developed via pyrrole ring annulation to the aromatic benzo[b]thiophene system, using 3-arylazirines as a N‒C=C synthon. The reaction is catalyzed by Ni(hfacac)₂ and proceeds through the azirine ring opening across the N=C3 bond. Azirines with both electron-donating and electron-withdrawing C3-aryl substituents tolerate the reaction conditions. The reaction of the N-methylindole analog also provides the annulation product but in moderate yield. The described synthesis is the first example of a dealkoxycarbonylative annulation reaction, in which 2H-azirines act as the annulation reagent.

Optically active higher-ordered structures, such as one-handed helical and propeller-shaped structures, can be constructed by folding the π-conjugated system using [2.2]paracyclophane as the chiral crossing unit, leading to circularly polarized luminescence (CPL) properties. Chiral cyclic dimers and trimers were synthesized using planar chiral [2.2]paracyclophane-containing enantiopure ribbon-shaped compounds as the chiral monomers. Unicursal π-conjugated systems were folded at the [2.2]paracyclophane units, and exhibited good photoluminescence quantum efficiencies and CPL anisotropy factors. Opposite chiroptical properties were observed between the dimer and trimer, despite the same absolute configuration of the planar chiral [2.2]paracyclophane units, which was reproduced by theoretical studies.

Chemical synthesis of monophosphorylated glycan motifs from the antitumor agent PI-88 has been achieved through an orthogonal one-pot glycosylation strategy on the basis of glycosyl ortho-(1-phenylvinyl)benzoates, which not only accelerated synthesis, but also precluded the potential issues inherent to one-pot glycan assembly associated with thioglycosides. The following aspects were featured in synthetic approaches: 1) synthesis of trisaccharide and tetrasaccharide PI-88 glycans via [1 + 1 + 1] and [1 + 1 + 1 + 1] one-pot orthogonal glycosylation, respectively; 2) synthesis of PI-88 glycan motif pentasaccharide via [1 + 1 + 1] and [1 + 1 + 3] one-pot orthogonal glycosylation; 3) synthesis of hexasaccharide via [1 + 1 + 1] and [1 + 1 + 1 + 3] one-pot assembly.

We report the excited-state dynamics of π-orthogonal donor-acceptor dyads based on perylene (Pe) and phenothiazine (PTZ), in which triphenylamine (TPA) units and a phenyl spacer were introduced to modulate donor strength and spatial separation. Among the series, Pe-PTZ(TPA)₂ exhibits a distinct thermal equilibrium between the locally excited (LE) state of the PTZ moiety and the photoinduced charge-transfer (CT) state. Femtosecond to microsecond transient absorption spectroscopy reveals that this equilibrium is facilitated not simply by enhanced donor ability, but presumably by excited-state planarization of the PTZ moiety, which lowers the energy of the LE state of the PTZ moiety. In contrast, Pe-Ph-PTZ(TPA)₂, in which the donor-acceptor distance is increased by a phenyl spacer, does not show clear equilibrium behavior. These results underscore the crucial role of excited-state structural relaxation in tuning photoinduced charge separation, and demonstrate that precise electronic and geometric design can enable controllable excited-state behavior in orthogonal molecular systems.

pH-Responsive molecular switches and motors are a class of organic molecules whose three-dimensional structure can be changed by acid-base stimuli. To date, pH-responsive molecular switches have been developed using various functional groups, but further advances require expanding the range of pH-responsive systems and discovering new molecular architectures. Here, we investigate the pH-responsive behavior of ortho-disubstituted benzamidine, which generates atropisomers and E/Z isomers. The amidine moiety allows modulation of the C-N and C-N/C-C rotational barriers by protonation, providing a novel approach to control the kinetics of isomerization via pH adjustment. The results showed that protonation of the amidine moiety significantly suppresses both C-N bond rotation and C-N/C-C concerted rotation, demonstrating the potential of ortho-disubstituted benzamidine derivatives as a novel pH-responsive molecular switch.

The cycloaddition of 1,3-dipoles at C=N bonds is a relatively rare process, in contrast to the widespread cycloaddition reactions at C=C, C≡C, and C=S bonds. In this study, we present the syntheses of novel hydantoin/1,2,4-oxadiazoline spiro-compounds using a 1,3-dipolar cycloaddition of nitrile oxides to C=N bonds of 5-iminohydantoins. The efficiency of the approach was demonstrated by varying the substituents at four positions of the resulting spirocyclic molecules. Cytotoxicity of the target hydantoin/1,2,4-oxadiazolines was shown to exceed previously known spiro-compounds bearing only hydantoins or 1,2,4-oxadiazolines (IC₅₀ values were 30-50 μM, HCT116 cell lines).

The intramolecular oxidative fusion reaction of macrocyclic heteroaromatic arrays has provided strained polycyclic heteroaromatic macrocycles as promising functional molecules. In this study, we prepared an ortho-phenylene-pyrrole-thiophene hybrid icosamer, as the largest cyclic array in the series. The oxidative fusion reaction with [bis(trifluoroacetoxy)iodo]benzene (PIFA) afforded a cyclophane-type aza[5]helicene-incorporated macrocycle, the structure of which was unambiguously revealed by X-ray diffraction analysis. Its optical properties have been investigated in detail.

It was demonstrated that Cyrene^TM, as a biomass-originated polar aprotic solvent, could be utilized as an alternative reaction medium for one-pot copper(I)-catalyzed azide-alkyne cycloaddition (click or CuAAC) reactions, for the synthesis of various 1,2,3-triazoles under mild conditions. Nineteen products involving N-substituted-4-phenyl-1H-1,2,3- and 1-allyl-4-substituted-1H-1,2,3-triazoles were synthesized under one-pot conditions and isolated with good to excellent yields (50-96%) and purity (>98%). The observed results represent an example that proves that biomass-derived safer solvents can be introduced into a synthetically important transformation exhibiting higher chemical and environmental safety.