Enantioselective Friedel-Crafts alkylation of 4,7-dihydroindoles with enones catalyzed by primary-secondary diamines

A study was conducted to demonstrate the development of a new chiral primary-secondary diamine catalyst derived from amino acid and its application in the asymmetric Friedel-Crafts alkylation of 4,7-dihydroindoles with α-βunsaturated enones. A array of primary amines derived from amino acids were investigated in the asymmetric Friedel-Crafts alkylation of 4,7-dihydroindole with benzylideneacetone in toluene. It was found that the length of the alkyl chain influenced the catalytic activity of the primary amine catalyst and the n-propylated catalyst gave the best result. It was also observed that the acid co-catalyst had a great impact on the reaction. The scope and limitations of the method was examined with regard to the enone and 4,7-dihydroindole substrates after establishing optimal reaction conditions.