Abstract
A green and efficient procedure for the preparation of bis(indolyl)methanes via the condensation of indoles with various carbonyl compounds in the presence of catalytic amount of nanosilica gel under ultrasonic irradiation in good to excellent yields (83% to 94% ) in solvent-free condition is described. Short reaction time, easy and quick isolation of the products, environmentally friendly procedure, excellent chemoselectivity, and excellent yields are the main advantages of this procedure. Native nanosilica gel was used as an inexpensive and readily available catalyst without any support of reagent or modification on it. The reaction is carried out in solvent-free condition in the absence of ultrasonic irradiation at 80°C, too. This methodology offers significant improvements for the synthesis of bis(indolyl)methanes with regard to the yield of products, simplicity in operation, and green aspects by avoiding toxic catalysts and solvents. Recovery and recycling of the silica nanoparticle catalyst were also described.
Highlights
The applications of nanoparticles (NPs) in catalysis have attracted considerable attention because of their improved efficiency and facile reaction conditions [1,2]
Silica NPs are prepared in room temperature, and their sizes can be tuned
Silica NPs are stable in organic solvent and are environmentally friendly materials [3,4,5,6,7,8,9,10,11,12]
Summary
The applications of nanoparticles (NPs) in catalysis have attracted considerable attention because of their improved efficiency and facile reaction conditions [1,2]. To develop the application of ultrasound in organic reaction, we wish to describe the reaction of indoles with aldehydes in the presence of a catalytic amount of native silica gel nanoparticles under ultrasonic irradiation (Scheme 1). Syntheses of this class of molecules under mild conditions have been reported, with promoters such as montmorillonite clay K-10 [23,24], trichloro-1,3,5-triazine [25], AlPW12O40 [26], sodium dodecyl sulfate [27], ZrCl4 [28], I2 [29], In. Scheme 1 Reaction of indoles with aldehydes in the presence of a catalytic amount of native silica gel nanoparticles.
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