KI‐assisted Sulfur Activation/Insertion/Denitration Strategy towards Dual C−S Bond Formation for One‐pot Synthesis of β‐Carboline‐tethered 2‐Acylbenzothiophenes

Abstract

A simple and efficient KI promoted sulfur activation‐insertion/de‐nitration strategy has been developed for the synthesis of β‐carboline C1 tethered 2‐acylbenzothiophenes via one‐pot assembly of 1‐acetyl β‐carbolines (an alkaloid based scaffold), 2‐nirobenzaldehydes and elemental sulfur. This expeditious reaction proceeds through the formation of β‐carboline linked nitro‐chalcones followed by embodiment of elemental sulfur to generate the multifunctional β‐carboline linked benzothiophene derivatives. The highlighted features of this efficient methodology are transition metal‐free conditions, use of inexpensive and non‐toxic catalyst, easy procedure, short reaction time, and broad substrate scope with good yields. The scope of this protocol has been extended for the synthesis of a range of novel compounds with significant diversity.

DABCO Mediated Sulfur Activation‐Intramolecular De‐Nitration Strategy for the Synthesis of Novel Dihydrothiochromeno[4,3‐c]pyrazoles

“…[21] Recently, our group also disclosed that elemental sulfur activated by KI may trigger de-nitration of nitroarenes containing an enone system resulting in 5-membered sulfa-heterocycles. [22] In continuation of our previous findings, it was envisaged to explore de-nitrative CÀ S coupling strategy that could lead to formation of novel 6 or 7-membered sulfa-heterocycles from nitroarenes. Accordingly, a pyrazole-based system containing a nitroarene moiety coupled with enone skeleton was investigated for the synthesis of intended 7-membered benzo [2,3]thiepino [4,5-c]pyrazoles, however, we ended with dihydrothiochromeno[4, 3-c]pyrazoles with a 6-membered ring.…”

“…More recently, Sekar group accessed the thiochromane derivative for the first time via de‐nitration C−S coupling of 2‐nitrochalcones using potassium ethylxanthate as a sulfurating source which was activated by iodine and sodium acetate (Scheme 1). [21] Recently, our group also disclosed that elemental sulfur activated by KI may trigger de‐nitration of nitroarenes containing an enone system resulting in 5‐membered sulfa‐heterocycles [22] …”

Synthesis of 2-carboxyaniline-substituted maleimides from 2′-nitrochalcones

“…The 2- and 2′-nitrochalcones, which are readily available via the Claisen–Schmidt condensation between the corresponding ortho -nitro acetophenones and benzaldehydes, 1 have long been a convenient starting point for the preparation of a wide range of heterocyclic compounds like pyrrolo[2,3- b ]quinolones, 1 quinoline N -oxides, 2 3-aminoindoles, 3 carbazoles, 4 benzothiophenes, 5 indolin-3-ones, 6 quinolines, 7 thioaurones, 8 sulphonamides 9 and tetralones 10 (Scheme 1). Herein, we would like to report an alternative, quite non-trivial domino-type transformation of 2′-nitrochalcones affording 4-(het)aryl-3-(2-carboxyanilino)maleimides (Scheme 1).…”