An efficient method for the synthesis of 1-chlorophenazines based on the selective cathodic reduction of 3,3,6,6-tetrachloro-1,2-cyclohexanedione

An efficient method for the synthesis of 1-chlorophenazines has been established. It is based on the use of 3,6,6-trichloro-2-hydroxy-2-cyclohexen-1-one as a synthetic equivalent of 3-chloro-1,2-benzoquinone . The intermediate was prepared in near quantitative yield by electroreductive monodechlorination of 3,3,6,6-tetrachloro-1,2-cyclohexanedione , which is an inexpensive and easily available starting material. Efficient reactions of with primary 1,2-phenylenediamines provided the corresponding 1,1,4-trichloro-1,2,3,4-tetrahydrophenazines , which were directly aromatized by treatment with 2,6-lutidine to give the title compounds in high yields. X-ray crystallographic structures for 1,1,4-trichloro-1,2,3,4-tetrahydro-6-methylphenazine , 8-benzoyl-1,1,4-trichloro-1,2,3,4-tetrahydro-phenazine , and 1,7-dichlorophenazine have been determined.