A method of synthesis comprising the steps of, in order: nitrosyl reduction, in which an N, N -disubstituted-3-optionally substituted-4-nitrosyl aniline, 2, is reduced to form said N, N -disubstituted-1,4-diamino-5-optionally substituted benzene, 3: thiosulfonic acid formation (TSAF), in which an N, N -disubstituted-1,4-diamino-5-optionally substituted benzene, 3, is oxidized in the presence of a thiosulfate, preferably a thiosulfate which is or comprises Na 2 S 2 O 3, to give said thiosulfuric acid S-{2-(amino)-3-(optionally substituted)-5-(disubstituted-amino)-phenyl} ester, 4: oxidative coupling, in which a thiosulfuric acid S-{2-(amino)-3-(optionally substituted)-5-(disubstituted amino)-phenyl} ester, 4, is oxidatively coupled to an N, N -disubstituted-3-optionally substituted-aniline, 5, using an oxidizing agent that is or comprises Cr, to give a [4-{2-(thiosulfate)-4-(disubstituted amino)-6-(optionally substituted)-phenyl-imino}-3-(optionally substituted)-cyclohexa-2,5-dienylidene]-N,N-disubstituted ammonium, 6: wherein; each of R 1 and R 9 is independently selected from: -H; C 1-4 alkyl; C 2-4 alkenyl; and halogenated C 1-4 alkyl; each of R 3NA and R 3NB is independently selected from: C 1-4 alkyl; C2-4alkenyl; and halogenated C 1-4 alkyl; each of R 7NA and R 7NB is independently selected from: C 1-4 alkyl; C 2-4 alkenyl; and halogenated C 1-4 alkyl; and and wherein; the nitrosyl reduction, thiosulfonic acid formation (TSAF), and oxidative coupling steps are completed in a single reaction vessel; and wherein said reduction in said nitrosyl reduction step is by reaction with a reducing agent that is or comprises Fe. nitrosyl reduction, in which an N, N -disubstituted-3-optionally substituted-4-nitrosyl aniline, 2, is reduced to form said N, N -disubstituted-1,4-diamino-5-optionally substituted benzene, 3: thiosulfonic acid formation (TSAF), in which an N, N -disubstituted-1,4-diamino-5-optionally substituted benzene, 3, is oxidized in the presence of a thiosulfate, preferably a thiosulfate which is or comprises Na 2 S 2 O 3, to give said thiosulfuric acid S-{2-(amino)-3-(optionally substituted)-5-(disubstituted-amino)-phenyl} ester, 4: oxidative coupling, in which a thiosulfuric acid S-{2-(amino)-3-(optionally substituted)-5-(disubstituted amino)-phenyl} ester, 4, is oxidatively coupled to an N, N -disubstituted-3-optionally substituted-aniline, 5, using an oxidizing agent that is or comprises Cr, to give a [4-{2-(thiosulfate)-4-(disubstituted amino)-6-(optionally substituted)-phenyl-imino}-3-(optionally substituted)-cyclohexa-2,5-dienylidene]-N,N-disubstituted ammonium, 6: wherein; each of R 1 and R 9 is independently selected from: -H; C 1-4 alkyl; C 2-4 alkenyl; and halogenated C 1-4 alkyl; each of R 3NA and R 3NB is independently selected from: C 1-4 alkyl; C2-4alkenyl; and halogenated C 1-4 alkyl; each of R 7NA and R 7NB is independently selected from: C 1-4 alkyl; C 2-4 alkenyl; and halogenated C 1-4 alkyl; and and wherein; the nitrosyl reduction, thiosulfonic acid formation (TSAF), and oxidative coupling steps are completed in a single reaction vessel; and wherein said reduction in said nitrosyl reduction step is by reaction with a reducing agent that is or comprises Fe. each of R 1 and R 9 is independently selected from: -H; C 1-4 alkyl; C 2-4 alkenyl; and halogenated C 1-4 alkyl; each of R 3NA and R 3NB is independently selected from: C 1-4 alkyl; C2-4alkenyl; and halogenated C 1-4 alkyl; each of R 7NA and R 7NB is independently selected from: C 1-4 alkyl; C 2-4 alkenyl; and halogenated C 1-4 alkyl; and and wherein; the nitrosyl reduction, thiosulfonic acid formation (TSAF), and oxidative coupling steps are completed in a single reaction vessel; and wherein said reduction in said nitrosyl reduction step is by reaction with a reducing agent that is or comprises Fe.