Cobalt(II) Sulfamate as An Efficient Catalyst for Synthesis of Bis(1H-Indol-3-yl)methanes

Abstract

The catalytic activity of eleven metal sulfamates for synthesis of bis(1H-indol-3-yl)methanes was compared under the same condition, cobalt(II) sulfamate proved to be the best. Cobalt sulfamate catalyzing the electrophilic substitution reactions of indole with aromatic, heterocyclic and unsaturated aldehydes as well as alicyclic and aromatic ketones were carried out in 90.6-99.2 % yield at room temperature in ethanol through conventional stirring or under ultrasound irradiation. More significant improvements were observed by carrying out the reactions under lower frequencies of ultrasound irradiation.