Lithium perchlorate is found to catalyze efficiently the electrophilic substitution reactions of indoles with aldehydes and ketones in diethyl ether to afford the corresponding bis(indolyl)methanes in high yields. LiOTf is also found to be an efficient catalyst for the synthesis of these compounds.Indoles and their derivatives are used as antibiotics in the field of pharmaceuticals. 2 The acid-catalyzed reaction of electron-rich heterocyclic compounds with p-dimethylaminobenzaldehyde is known as Ehrlich test 3 for p-electron excessive heterocycles such as pyrroles and indoles. The analogous reaction of indoles with other aromatic or aliphatic aldehydes and ketones produces azafulvenium salts. The azafulvenium salts can undergo further addition with the second indole molecule to afford bis(indolyl)methanes. 4 Protic acids 5 as well as Lewis acids 6,7 are known to promote these reactions. Lanthanide triflates 8 are also found to catalyze these reactions. However, many Lewis acids are deactivated or sometimes decomposed by nitrogen containing reactants. Even when the desired reactions proceed, more than stoichiometric amounts of the Lewis acids are required because the acids are trapped by nitrogen. 9 Lithium perchlorate in diethyl ether (LPDE, 5 M) is found to retain its activity even in the presence of nitrogen-containing compounds. 10In recent years, lithium perchlorate in diethyl ether has received considerable attention as a powerful reaction medium for effecting various organic transformations 11,12 such as cycloaddition reactions, sigmatropic rearrangements, ring-opening reactions of epoxides, glycosidation reactions, selective carbonyl protection as dithioacetals, Michael reactions and aldol condensation reactions. LPDE medium offers a convenient procedure to carry out the reactions under essentially neutral reaction and workup conditions. These special properties inherent to LPDE medium prompted us to disclose a mild and efficient procedure for the synthesis of bis(indolyl)methanes.In this report, we wish to introduce a 5 M ether solution of lithium perchlorate as a mild and highly efficient medium for the preparation of bis(indolyl)methanes under neutral reaction conditions. Bis(indolyl)methanes were formed in high yields when indole was treated with aldehydes or ketones in the presence of 5 M lithium perchlorate in diethyl ether. The electrophilic substitution reactions of indole with aldehydes or ketones proceeded smoothly at room temperature to afford the corresponding bis(indole) derivatives in high yields in a short reaction time. The reactions were carried out in diethyl ether as well as in acetonitrile. The reactions proceeded with 10% lithium perchlorate in acetonitrile at room temperature. The catalyst is effective in both solvent systems. The results, summarized in the Table, clearly indicate the scope of the reaction with respect to various substituted aldehydes and ketones. The effect of electron deficiency and the nature of the substituents on the aromatic ring showed some effect on this conve...
a-Aminophosphonates are synthesized by three component condensation of aldehydes, amines and diethyl phosphite using montmorillonite KSF under microwave irradiation in solvent-free conditions to afford enhanced yields and reduced reaction times compared to conventional methods.
The alkoxy groups present ortho to carbonyl group in alkoxybenzaldehydes are selectively deprotected in high yields leaving other alkoxy groups unaffected by cerium(III) chloride–NaI in refluxing acetonitrile under neutral reaction conditions.
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