Abstract A number of 1-aryl-2-oxo-1, 2, 3, 6-tetrahydro [1, 4] diazepino [6, 5-b] indole 4- oxides were synthesized based on 3-[N-aryl-N-(chloroacetyl) amino]-2-formylindoles. The nature of the substituent in the 1-aryl fragment has a pronounced influence on the course of reactions throughout the whole sequence of transformations during the synthesis of diazepinoindoles. The reduction of 4-oxides by formamidinosulfinic acid, hydrogen in the ...