The reaction of 3-propylindole with aldehydes preparation of 2-(α-aminoalkyl) indoles

Abstract

Abstract 2,2′-Benzylidenebisindoles ( 5 ) are produced by the condensation of 3-propylindole with aromatic aldehydes. It is shown that aromatic aldehydes react initially, but reversibly, at nitrogen. N-substituted products can be trapped as acetate derivatives ( 7 ) and are converted to 2,2′-benzylidenebisindoles ( 5 ) under the original reaction conditions. 3-Propylindole reacts with formaldehyde and piperidine under mild conditions to give 1-piperidinomethyl-3-propylindole. 2-Piperidinomethyl-3-propylindole is obtained when the reaction with formaldehyde in acetic acid is carried out at 100° in the presence of excess piperidine. The condensation of 3-propylindole with formaldehyde and primary amines involves initial attack at nitrogen followed by intramolecular substitution at the 2-position to yield 1H-imidazo[1,5 a ]indole and 2,3,4,5-tetrahydrotriazepino[1,7 a ]indole derivatives. Hydrolysis of cyclohexylimidazoindole ( 11 ) affords 2-cyclohcxylaminomethyl-3-propylindole.