A new protocol for the chemoselective aromatization of tetrahydro‐β‐carboline‐3‐carboxylic acids to direct biomimetic one step synthesis of β‐carboline‐3‐carboxylic acids 2 A‐L using catalytic amount of I2 in DMSO/H+ produces very good yield. This method was also successfully extended for the aromatization of tetrahydro‐β‐carboline‐3‐methyl esters 5 A‐G as well as one‐step synthesis of Marinacarbolines‐D analog, respectively. Further, the mechanism and role of iodine–DMSO in aromatization has been studied by Density Functional Theory Calculation. [ABSTRACT FROM AUTHOR]