Series Of Regioisomers Research Articles

Widely Electronically Tunable 2,6-Disubstituted Dithieno[1,4]thiazines-Electron-Rich Fluorophores Up to Intense NIR Emission.

2,6‐Difunctionalized dithieno[1,4]thiazines were efficiently synthesized by (pseudo)five‐ or (pseudo)three‐component one‐pot processes based on lithiation‐electrophilic trapping sequences. As supported by structure–property relationships, the thiophene anellation mode predominantly controls the photophysical and electrochemical properties and the electronic structures (as obtained by DFT calculations). From molecular geometries and redox potentials to fluorescence quantum yields in solution, the interaction of the dithieno[1,4]thiazine‐core with the substituents causes striking differences within the series of regioisomers. Most interestingly, strong acceptors introduced in anti–anti dithieno[1,4]thiazines nearly induce a planarization of the ground‐state geometry and a highly intense NIR fluorescence (ΦF=0.52), whereas an equally substituted syn–syn dithieno[1,4]thiazine exhibits a much stronger folded molecular structure and fluoresces poorly (ΦF=0.01). In essence, electrochemical and photophysical properties of dithieno[1,4]thiazines can be tuned widely and outscore the compared phenothiazine with cathodically shifted oxidation potentials and redshifted and more intense absorption bands.

InCl3-Promoted Synthesis of Pyrazolyl-Substituted Quinolines in Green Media

A series of regioisomers of pyrazolyl-substituted quinolines has been synthesized through the simple condensation reaction between hydrazinylquinolines with aliphatic 1,3-diketones with InCl3 as a catalyst under microwave irradiation. This method produces pure products in good yield in a rapid manner compared to conventional procedures and withneat reaction condition. The approach has the advantages of operational simplicity and increased safety for a shortened synthesis of pyrazolyl-substituted quinolines.

Differentiation of trifluoromethylbenzylpiperazines (TFMBZPs) and trifluoromethylbenzoylpiperazines (TFMBOPs) by GC–MS

Two series of regioisomers – the trifluoromethylbenzylpiperazines (TFMBZPs) and the trifluoromethylbenzoylpiperazines (TMFBOPs) were synthesized and analyzed as potential “hybrid” derivatives of the benzylpiperazine (BZP) and 1-(3-trifluoromethylphenyl)piperazine (TMFPP) drugs of abuse. The TFMBZPs are readily differentiated from TMFBOPs by their mass spectra including differences in their mass, the base peaks in their mass spectra as well as several other unique fragment ions. However the mass spectra of each regioisomer in each of these two series have fragment ions of identical mass and thus cannot be differentiated by this analytical method alone. Furthermore, chemical derivatization by perfluoroacylation did not offer any additional unique marker fragment ions in the mass spectrum to allow identification of one regioisomer in a series to the exclusion of the other two regioisomers. The perfluoroacylamides of the regioisomers in the TFMBZP series and the regioisomers in the TMFBOP series were readily separated by GC on the stationary phase Rtx-200 and eluted in an order similar to other perfluoroacyl-derivatives of other benzyl- and benzoylpiperazine compounds reported earlier.

Origin of a Large Temperature Dependence of Regioselectivity Observed for [2 + 2] Photocycloaddition (Paternò-Büchi Reaction) of 1,3-Dimethylthymine with Benzophenone and Its Derivatives: Conformational Property of the Intermediary Triplet 1,4-Diradicals

[reaction: see text] The [2 + 2] photochemical additions of 1,3-dimethylthymine (DMT) with benzophenone and its 4,4'-substituted derivatives (BPs), difluoro, di-tert-butyl, and dimethoxy benzophenones, have been investigated at a temperature range from -40 to 70 degrees C. The photochemical reactions, which are cycloaddition of the 5-6 double bond of DMT with the carbonyl group of BPs, the so-called the Paternò-Büchi (PB) reaction, reveal largely temperature-dependent regioselectivity. The chemical yields of one series of regioisomers, 2, decrease with the increase of the reaction temperature, but those of another regioisomer series, 3, increase, and thus the ratio of 2/3 is strongly dependent on the temperature (2/3 = ca. 70:30 to 30:70). The temperature dependence of the regioselectivity yields two linear functions in the corresponding Eyring diagrams. The Eyring plot with changed slopes is clearly indicative of the change for the selectivity-determining step in the PB reaction, in which the triplet 1,4-diradicals play a crucial role. Computational studies reveal the conformational equilibrium structures of the triplet 1,4-diradicals, energy barriers between the conformers, and the conjectural equilibrium constants from relative potential energies of the stable conformers. A proposed mechanism can reasonably explain the temperature-dependent regioselectivity and chemical yields of two regioisomers varying with the reaction temperature.