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N-Polyheterocycles
Published in Navjeet Kaur, Metals and Non-Metals, 2020
Bi(OTf)3·xH2O and BiOClO4·xH2O catalyze electrophilic substitution reactions of indoles with many ketones and aldehydes at room temperature, under ultrasound irradiation, in acetonitrile to afford good to excellent yields of bis(indolyl)methanes. Even Bi(NO3)3.5H2O or PANI-BC can be used to catalyze this reaction. Bis(indolyl)methanes are also synthesized efficiently from primary alcohols by a one-pot method under solvent-free conditions promoted in the presence of Bi(NO3)3·5H2O [27]. The 3,3-di(3-indolyl)oxindoles can be prepared with high regioselectivity and excellent yields when indoles undergo a rapid condensation with isatin (1H-indole-2,3-dione) in the presence of Bi(OTf)3·xH2O catalyst (Scheme 5) [28].
Cipargamin: Biocatalysis in the Discovery and Development of an Antimalarial Drug
Published in Peter Grunwald, Pharmaceutical Biocatalysis, 2019
Thomas Ruch, Elina Siirola, Radka Snajdrova
Initially, ketone 13 was formed as a minor side product (circa 4%) in the racemic route (via a Nef reaction of partly reduced 3) and hence experiments were carried out to see whether variation of the reaction conditions could be identified which would favor the formation of this key intermediate. Indeed, it was possible to increase the yield of ketone 13% up to 68%, however, the synthesis gained extra step. An alternative proposal was suggested starting from fluoro, chloro-isatin rather than fluoro, chloro-indole, and using its properties of an “umpoled” indole, for introduction of ketone moiety (Scheme 15.10; in analogy to Garden et al., 2002). An Aldol reaction with acetone would introduce the required sidechain. Reduction with borane converted the oxindole ring to the required indole system; however, concurrent reduction of the ketone to the corresponding racemic alcohol occurred. It became necessary to introduce an oxidative step to provide the desired ketone 13 (Scheme 15.8). Initially envisaged synthesis to ketone 13.
Name Reactions
Published in Benny K.G. Theng, Clay Mineral Catalysis of Organic Reactions, 2018
Using an unspecified clay mineral as catalyst, Shaikh et al. (2001) were able to carry out a Michael type addition of aliphatic amines to α,β-ethylenic compounds but curiously enough, they failed to do the same with aromatic amines. Not long after, Chakrabarty and Sarkar (2002) reported that K10 montmorillonite could catalyze the dry tandem addition-elimination (Michael) reaction of indoles with 3-formylindole to yield tri-indolylmethanes. This catalyst was similarly efficient in promoting the solvent-free Michael addition of indoles (and pyrrole) to nitroolefins (Chen and Li 2009; An et al. 2010). Nikpassand et al. (2010) obtained 3,3-di(indolyl)indolin-2-one by refluxing isatin and indole in ethanol in the presence of KSF montmorillonite. Singh et al. (2006) also found that the Fe3+-exchanged form of K10 was remarkably active in catalyzing the conjugate addition of indoles to α,β-unsaturated carbonyls. De Paolis et al. (2009) used K10 montmorillonite and microwave irradiation to promote the Michael type addition of aniline derivatives to cinnamaldehyde, followed by cyclization and oxidation to yield quinolines.
Efficient, selective and mild oxidation of sulfides and oxidative coupling of thiols catalyzed by Pd(II)-isatin Schiff base complex immobilized into three-dimensional mesoporous silica KIT-6
Published in Journal of Sulfur Chemistry, 2020
Saeedeh Pakvojoud, Mehdi Hatefi Ardakani, Samira Saeednia, Esmaeil Heydari-Bafrooei
Isatin (1H-indole-2,3-dione) is a natural heterocyclic compound comprised of an indole ring and two keto groups at 2nd and 3rd positions of the ring. It is a unique class of heterocycles acting as a biological agent [26]. Isatin is the most reported agent for the preparation of Schiff base ligands owing to its reaction with the primary amines [27]. Isatin Schiff base ligands coordinate with a wide variety of transition metal ions. The resulting stable metal complexes display notable clinical, pharmacological and biological properties [28].