Download PDF Abstract The reaction of isatin and N-substituted isatins with o-phenylenediamine readily gives rise to quinoxaline and spiro-indole derivatives respectively under controlled microwave irradiation in xylene.
The re- minated dehydroamino acids and arylboronic acids by using sponse of the new synthesised compounds towards fluoride a strategy developed in our research group that involves a ion F— was evaluated. It was found that methyl 3-methyl- sequential Suzuki—Miyaura cross-coupling reaction and a 1H-dibenzo[e,g]indolecarboxylate, methyl 3- phen- metal-assisted C—N intramolecular cyclisation.
The cyclised anthrenyl -1H-dibenzo[e,g]indolecarboxylate and products were obtained either by direct cyclisation or by iso- methyl 1- naphthalenyl -3H-benzo[e]indolecarboxyl- merisation followed by cyclisation. The photophysical prop- ate showed significant spectral changes in fluorescence erties of these compounds were studied in four solvents of emission upon F— addition with a decrease in intensity and different polarity cyclohexane, diethyl ether, acetonitrile the appearance of a new band at longer wavelengths.
These results indicate that the indole derivatives pre- Introduction moieties to be studied as fluorescent probes and also to evaluate their behaviour in the presence of In our laboratories, we have been interested in the syn- fluoride F—.
These compounds were then yaura cross coupling followed by a metal-mediated C—N in- treated with palladium and copper acetate to give the corre- tramolecular cyclisation developed in our research group. The photophysical Recently, we have used this strategy to synthesise a phen- properties of the latter were studied in several solvents.
The fluorescence proper- cognition sites, we decided to study the behaviour of the ties of these compounds in solution and in lipid membranes compounds prepared towards this anion. Due to the impor- showed their potential as fluorescent probes for biological tance of F— in biology, medicine, food and environmental systems.
These molecules contain a binding site that interacts Campus de Gualtar, Braga, Portugal with the anion and a signaling subunit with the ability of Fax: In the case of the Z isomers, when we irradiated the 3 Z -4 5.
As reported by 11 Z -8 5. We also found this relation in the case of the OCH3 protons of dehydrophenylalanines Table 1. This is probably due to the shielding anisotropic effect of the aryl moiety.
This reaction involved the electrophilic attack of PdII on the aromatic ring and a nucleophilic at- tack of N, forming a palladacycle. Compounds E -4 and E -8 gave 14 and 20 in similar yields to those obtained by using Z -4 and Z -8 as Scheme 1.
In the case of Z -6, although the major drophenylalanine derivatives. The synthesis in- Scheme 2.
The latter gave the 13—21 in four solvents of different polarity cyclohexane, methyl 1H-dibenzo[e,g]indolecarboxylate by thermolysis. The maximum ab- www. A similar behaviour has Table 3. The influence of the solvent on the absorption spectral shape was negligible.
The effect on the emission spectra was more pronounced for 17, where the spectral shift between cyclohexane and ethanol was 44 nm. We ob- served a similar behaviour due to a high CT character of the excited state for a pyrenylindolecarboxylate.
All the other compounds 13, 15, 16, 18, 19 and 21displayed fluorescence spectra with well-defined vibrational structure, especially in solvents of low polarity Figures 1, 2 and 3. Compounds 13 and 15 had similar absorption and Figure 2.
The addition of F— to solutions of 13 in polar solvents for 18 and 21 Figures 2 and 3indicating and 15 led to an intensely coloured fluorescence blue and the CT character of the excited state in polar solvents.
The green, respectively upon irradiation with near-UV light effect was more significant in ethanol, probably due to con- see the Supporting Information. The extension of the conjugation by the substitu- tion of a methyl group 16 and 19 by an aromatic moiety 18 and 21, respectively provides a significant increase in excited-state CT character.
The generally high fluorescence quantum yields of these new indole derivatives and the different solvent sensitivity of their fluorescence emission make them good candidates for fluorescent probes.
It has been established that compounds containing pyr- role, urea, amide, amine or phenol units can act as F— sen- Figure 5. We performed fluorescence titration experiments on and equiv. We observed significant spectral changes in emission upon F— addition for 13, 15 and 21 Figures 4, 5 and 6especially for 13 and The emission spectrum of each compound decreased in intensity, and a new unstructured band appeared at longer wavelengths maximum at ca.
In all cases, we observed a clear isoemissive point [at nm for 13 Figure 4nm for 15 Figure 5 and nm for 21 Figure 6 ]. Compounds 13 Figure 6. The excitation spectrum, and equiv. Queiroz similar to the absorption spectrum in the absence of F—.indole ring of tryptophan, as well as benzofuran and benzoth- iophene heterocycles.
61 However, tryptophan, phenyethylamine, and pyrrole derivatives are not accepted. Diaryliodonium salts featuring indole substituents constitute a relatively uncommon and poorly characterized class of compounds to date.
The chapter will discuss the synthesis of diaryliodonium salts that feature 2- and 5-indole substituents, and will report nucleophilic substitution of these compounds with a variety of nucleophiles. Indole is an important substance used in organic syn- thesis (Bajtos et al., ), and its physiological activities attracted a lot of scientiﬁc attention as well (Bittner et al.
Isatin (1H-indole-2,3-dione, Figure 1) was ﬁrst obtained by Erdman and Laurent in as a product from the oxidation of indigo by nitric and chromic acids.
1 Since then, isatin and its derivatives have become important heterocycles. widely known as the Larock indole synthesis, is a powerful method for the preparation of structurally complex 2,3-disubstituted indoles that has found tremendous utility in accessing indole building blocks, unnatural tryptophan derivatives, and indole-containing.
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