A facile access to indigodianiles

Abstract

Bis‐imidoylchlorides derived from oxalic acid can easily be transformed into the corresponding bis‐imino benzotriazoles. The fact that benzotriazole is a well‐established leaving group has been exploited for an improved synthesis of indigodianiles. Employing metallic lithium, the benzotriazoles can be converted in a cascade reaction into indigo bis‐arylimines in yields up to 45%. Formation of the reduced form of dimeric isocyanides is suggested as a key step.

Protoisomerization of indigo di- and monoimines

“…(3) Indigo bis(aryl imines) (i.e. Nindigos) were originally reported over a century ago 16 (although the specific synthetic route has not been reproducible 10,17 ). Included in this original report were reactions of indigo bis(phenylimine) with strong acids (HCl, H2SO4, picric acid) which gave green solutions or crystalline materials.…”

Redox-Active Bridging Ligands Based on Indigo Diimine (“Nindigo”) Derivatives

“…Aryl isonitriles decompose to give diaryl derivatives of 1 in small quantities, 27 and multistep, low-yield syntheses have been reported. 28,29 The first reported Nindigo synthesis involved condensation of the famous dye molecule indigo with aniline. 30 Unfortunately, neither we nor others 29 could replicate this reaction.…”

“…1 H NMR (300 MHz, CD 2 Cl 2 ): δ 7.51À7.44 (m, 2H), 7.38À7.31 (m, 2H), 7.05À6.96 (m, 4H), 6.30 (s, 2H), 1.43 (s, 18H). 13 C NMR (125.8 MHz, CD 2 Cl 2 ): δ 176.1 (q, J = 35.6 Hz), 174.6 (q, J = 35.5 Hz), 142.3,138.4,126.2,120.8,119.4,117.3,117.1 (q,J = 283.8 Hz),116.9 (q,J = 284.8 Hz),115.6,109.6,92.8,67.1,29.3. 19 [cis-Indigo bis(2,4,6-trimethylphenylimine)]hexafluoroacetylacetonatopalladium (5h).…”

“…Aryl isonitriles decompose to give diaryl derivatives of 1 in small quantities, and multistep, low-yield syntheses have been reported. , The first reported Nindigo synthesis involved condensation of the famous dye molecule indigo with aniline . Unfortunately, neither we nor others could replicate this reaction. However, we found that the protocols developed by Hall et al for imine condensation of relatively unactivated carbonyl groups could be adapted for the synthesis of indigo bis(imines).…”