One step synthesis of indirubins by reductive coupling of isatins with KBH 4

A tunable synthesis of indigoids: targeting indirubin through temperature

“…Spectroscopy: 1 H NMR was previously published for 11 and 12. 22 Indirubin 6,6 0 -dicarboxylic acid (13) and indigo 6,6 0 -dicarboxylic acid (14). Were synthesized by the general procedure above starting with indole 6-carboxylic acid to produce (a) 0.777 g, 2.22 mmol, 89%, 0 : 1; (b) 0.861 g, 2.46 mmol, 98%, 0 : 1; (c) 0.692 g, 1.97 mmol, 86%, 1 : 10.…”

“… 13 The most notable and direct comparison to the work in this publication is related to the reductive dimerization of isatin using potassium borohydride. 14 While only applicable to symmetrically substituted systems not prone to reduction, the scale of the reactions (10 mmol) and yields (63–91%) show potential for broader-scale use.…”

A theoretical and spectroscopic (NMR and IR) study of indirubin in solution and in the solid state

“…Chemical shifts from Cuong et al were unambiguously assigned. In a recent paper, a list of signals were reported but not assigned although they are almost identical to the previous ones . There are 26 E/Z isomers and tautomers of indirubin (Figure ).…”

Isatin and its derivatives: a survey of recent syntheses, reactions, and applications

“…in ethanol or methanol (Scheme 24). 59 Recently, a novel reaction has been studied that involves isatin and ethyl isocyanoacetate as reactants and CuIJI) as a catalyst. It is 1,3 dipolar cycloaddition that produces an intermediate, which undergoes inverse dipolar reaction to give 3-ylidene oxindoles, which are an important class of compounds (Scheme 25).…”