RESUMO
Indium-catalyzed, solvent-enabled regioselective C6- or N1-alkylations of 2,3-disubstituted indoles with para-quinone methides are developed under mild conditions. Notably, highly selective and switchable alkylations were selectively achieved by adjusting the reaction conditions. Moreover, scalability and further transformations of the alkylation products are demonstrated, and this operationally simple methodology is amenable to the late-stage C6-functionalization of the indomethacin drug. The reaction pathways were explained with the support of experimental and density functional theory studies.
RESUMO
Pd(II)-catalyzed C-H arylations of free (NH) indoles including different carbonyl directing groups on C3-position with aryl iodides are demonstrated. Importantly, the reactions are carried out using the same catalyst system without any additional transient directing group (TDG). In this study, the formyl group as a directing group gave the C4-arylated indoles versus C2-arylation. Using this catalyst system, C-H functionalization of 3-acetylindoles provided domino C4-arylation/3,2-carbonyl migration products. This transformation involves the unusual migration of the acetyl group to the C2-position following C4-arylation in one pot. Meanwhile, migration of the acetyl group could be simply controlled and N-protected 3-acetylindoles afforded C4-arylation products without migration of the acetyl group. Functionalization of indole-3-carboxylic acid (or methyl ester) with aryl iodides using the present Pd(II)-catalyst system resulted in decarboxylation followed by the formation of C2-arylated indoles. Based on the control experiments and the literature, plausible mechanisms are proposed. The synthetic utilities of these acetylindole derivatives have also been demonstrated. Remarkably, C4-arylated acetylindoles have allowed the construction of functionalized pityiacitrin (a natural product).
RESUMO
Aggregation-induced emission (AIE) is an extraordinary photochemical phenomenon described by Tang's group in 2001, where the aggregation of some organic molecules enhances their light emission by limiting intramolecular activity in the aggregate state. This phenomenon offers new opportunities for researchers due to its potential applications in optoelectronics, energy, and biophysics. Tetraphenylethylenes (TPEs) are reliable AIE luminogens with a wide range of successful applications in material chemistry. To expand the library of AIE-active TPEs, both a series of TPE analogues, in which the phenyl rotor has been replaced by the indole ring, and indole-substituted TPE derivatives were designed and synthesized through vinyl-aryl and aryl-aryl bond formations using the Suzuki coupling reaction. Efficient synthetic routes that delivered indole-modified and indole-substituted TPEs have been developed, and almost all heterocyclic TPE analogues have demonstrated AIE behavior. Furthermore, to test whether the indole ring can be diversified, two title compounds were converted to a series of bis(indolyl)methane (BIM), and these BIM-TPE materials showed typical AIE properties. Interestingly, two compounds indicated a solvent vapor fuming reversible switch between bright blue emission and greenish-yellow emission. Upon fuming with dichloromethane, their fluorescence spectra showed 8 and 32 nm red-shift and could return to the original state after fuming with hexane. Furthermore, we have explored the effects of replacing the phenyl ring in TPE with indole together with the substitution of TPE with indole ring(s) on the performance of organic light-emitting diode (OLED) device applications. In addition, density functional theory calculations; the optical, electrochemical, light emission, electroluminescence characteristics; and admittance spectroscopic analysis of OLED devices of four representative TPEs have been investigated in detail. As a result, the indole-TPEs are potential blue emitters with AIE features for conventional OLEDs, which is a significant color in displays and lighting.
RESUMO
Functionalization from nonperipheral positions of triazatruxene is representing a challenge. Triarylation of the nonperipheral positions (1, 6, and 11) in triazatruxene scaffold has been achieved for the first time via two approaches. The transformations involve arylation/cyclotrimerization and cyclotrimerization/arylation sequences. POCl3-mediated direct cyclotrimerization of oxindoles containing electron-deficient substituents on the aryl group at the C7-position resulted in the formation of 2-chloroindoles, whereas oxindoles containing electron-donating substituents gave the triazatruxenes. Furthermore, desired triazatruxenes were achieved through cyclotrimerization of 7-bromooxindole followed by coupling with arylboronic acids. NMR structural analysis exhibited that two of the suitably substituted oxindole and triazatuxene may have atropisomerism at room temperature. As a representative triazatruxene scaffold, the optoelectronic properties of 9a have also been studied via ultraviolet-visible (UV-vis) absorption spectra and fluorescence spectra of 9a thin films. Also, density functional theory calculation was realized to get knowledge about frontier molecular orbitals. In the light of the information obtained, an organic light-emitting diode (OLED) device utilizing 9a as an emissive layer was applied to obtain white emission. In brief, this study provides the first examples of the synthesis of triazatruxenes bearing aryl substituents at the nonperipheral positions as candidate compounds for organic electronics, optoelectronics, and material chemistry.
