Synthesis of 4H‐1,3,4‐oxadiazino[5,6‐b]quinoxalines from 2‐substituted quinoxaline 4‐oxides

Abstract

The reaction of 6‐chloro‐2‐(1‐methylhydrazino)quinoxaline 4‐oxide 8 with acetic anhydride resulted in the intramolecular cyclization to give 8‐chloro‐2,4‐dimethyl‐4H‐1,3,4‐oxadiazino[5,6‐b]quinoxaline 7a, while the reaction of compound 8 with acetic anhydride/pyridine or acetic anhydride/acetic acid afforded 3‐(2,2‐diacetyl‐1‐memymydrazmo)‐7‐chloro‐2‐oxo‐1,2‐dihydroquinoxaline 9, effecting no intramolecular cyclization. The reaction of 2‐(2‐acetyl‐1‐methylhydrazino)‐6‐chloroquinoxaline 4‐oxide 10a or 6‐chloro‐2‐(1‐methyl‐2‐trifluoroacetylhydrazino)quinoxaline 4‐oxide 10b with phosphoryl chloride provided compound 7a or 8‐chloro‐4‐memyl‐2‐trifluoromethyl‐4H‐1,3,4‐oxadiazino[5,6‐b]quinoxaline 7b, respectively. The reaction of compound 7b with phosphorus pentasulfide gave 7‐chloro‐3‐(1‐methyl‐2‐trifluoroacetylhydrazino)‐2‐thioxo‐1,2‐dihydroquinoxaline 11, whose dehydration with sulfuric acid in acetic acid afforded 8‐chloro‐4‐methyl‐2‐trifluoromemyl‐4H‐1,3,4‐thiadiazino[5,6‐b]quinoxaline 12.