The effect of an N-substituent on the recyclization of (2-aminoaryl)bis(5-tert-butyl-2-furyl)methanes: synthesis of 3-furylindoles and triketoindoles

The recyclization of (2-aminophenyl)bis(5-tert-butyl-2-furyl)methane derivatives has been studied. It was shown that the acid-catalyzed recyclization of N-tosylamides leads to the formation of 2-(3-oxoalkyl)-3-(2-furyl)indoles. In contrast, under the same reaction conditions, acetamides are transformed into indoles containing three keto groups. The acid-catalyzed removal of the acetyl group from these substrates facilitated protolytic furan ring opening. The same triketones can be directly obtained from (2-aminoaryl)bis(5-tert-butyl-2-furyl)methanes.