SiO2-supported HClO4 catalyzed synthesis of (Z)-thiazolylhydrazonoindolin-2-ones and their electrochemical properties

In this paper, an environmentally benign silica-supported perchloric acid (HClO4–SiO2) catalyzed green FCDR strategy has been developed for the synthesis of (Z)-THIs (6) with high stereospecificity via an intramolecular hydrogen bond (IHB) directed approach, involving the reaction of methyl ketones (1), N-bromosuccinimide (NBS) (2), isatins (4) and thiosemicarbazide (5) in ethanol at reflux temperature for 45–60 min in one-pot. The reaction proceeds through the construction of C–Br (α-bromination), C–S & C–N (heterocyclization), and CN (condensation) bonds in one pot. The absolute structure of the compound (Z)-3-(2-(4-(4-bromophenyl)thiazol-2-yl)hydrazono)indolin-2-one (6e) has been confirmed by single-crystal XRD analysis. Further, the role of IHB on Z-configuration of the synthesized (Z)-THIs is proved by single-crystal XRD and 1H NMR studies. Wide substrate scope, good functional group tolerance, scalability, improved safety since the method circumvents the use of highly lachrymatric α-bromoketones as starting materials, high product yields (up to 98%), short reaction times, reusable solid Brønsted acid catalyst (HClO4–SiO2), and products that do not require column chromatography purification are all attractive features of this FCDR strategy. Electrochemical properties of THIs (6) are examined by cyclic voltammetry. The HOMO and LUMO energy level of THIs, 6a, 6c, 6d, 6j, 6o-6v, 6y, and 6aa are comparable with the reported ambipolar materials, and the HOMO levels of other THIs, 6b, 6e-6i, 6n, 6w, 6x, 6z and 6 ab-6ae are similar with the most commonly used hole transporting materials (HTMs). A practical, straightforward and green FCDR strategy has been demonstrated for the synthesis of (Z)-THIs (6) in the presence of HClO4–SiO2via an IHB directed approach. The reaction proceeds through the formation of C–Br, C–S, C–N & CN bonds in one-pot. The role of IHB on (Z)-configuration of the synthesized (Z)-THIs was confirmed by single crystal XRD and 1H NMR studies. The HOMO and LUMO energy level of (Z)-THIs are comparable with the most commonly used ambipolar and hole transporting materials. [Display omitted] •Environmentally benign HClO4–SiO2 catalyzed FCDR strategy for synthesis of (Z)-THIs.•Z-configuration of THIs confirmed by single crystal XRD and 1HNMR studies.•Construction of C–Br, C–N, C–S and CN bonds in a single-step operation.•(Z)-THIs could be promising ambipolar materials for efficient OLEDs.