A catalyst-free approach to regioselective synthesis of multi-functional 1 H -pyrrolo[1,2- a ]fused[1,3]diazaheterocycle using ketene dithioacetals in water–ethanol media

Substrate-Controlled Three-Component Synthesis of Diverse Fused Heterocycles

A chemoselective strategy toward a variety of fused heterocyclic scaffolds relying on a three-component condensation of heterocyclic ketene aminals (HKAs) or corresponding thioaminals with aryl glyoxals and cyclic 1,3-dicarbonyl compounds has been developed and explored. Depending on the applied combination of substrates, the strategy can be tuned to provide straightforward access to imidazo[1,2-a]quinoline, pyrrolo[1,2-a]imidazole, and pyrrolo[2,1-b]thiazole frameworks.

Synthesis of diverse spiro-imidazo pyridine-indene derivatives via acid-promoted annulation reaction of bindone and heterocyclic ketene aminals

A new multi-component reaction for the synthesis of novel and diverse spiro-imidazo pyridine-indene derivatives named spiro[imidazo[1,2-a]indeno[2,1-e]pyridine-5,1′-indene and indenylidene-1H-spiro[imidazo[1,2-a]pyridine-7,1′-indene was successfully developed by the reaction between heterocyclic ketene aminals (generated from 1,1-bis(methylthio)-2-nitro ethylene and diamine) and [1,2′-biindenylidene]-1′,3,3′-trione (bindone) (in situ generated from self-condensation of 1,3-indandion) by using malononitrile as a promoter or as one of the precursors respectively in the presence of p-TSA as the acid catalyst in EtOH as reaction medium under reflux conditions. Depending on whether the reaction is single-step or two-step, malononitrile can act as a promoter or reactant. The convenient one-pot operation, straightforward isolation without using additional purification methods, and the use of a variety of diamines and cysteamine hydrochloride causing a variety of structural products are attractive aspects of the present approach. The synthesized bindone and final product contains active methylene and this active site can be involved in further reactions to synthesize more complex heterocycles.

A one-pot synthesis of piperidinium spirooxindoline-pyridineolates and indole-substituted pyridones in aqueous or ethanol medium

Piperidinium spirooxindoline-pyridineolate has been prepared via one-pot multicomponent reaction of isatin, malononitrile, cyanoacetohydrazide, and piperidine in water or ethanol medium at room temperature. In addition, the synthesis of two indole-substituted 2-pyridones from indole-3-carbaldehyde, malononitrile, and cyanoacetohydrazide in the presence of piperidine is described.

Chemoselective cyclization of 3-arylamino-2-hydroxy-tetrahydroindol-4-one in water at room temperature

A convenient and green protocol is developed for the chemoselective synthesis of indole derivatives by the one-pot, multi-component reaction of 5,5-dimethyl-3-(arylamino)cyclohex-2-enone derivatives (derived from the addition of various anilines to dimedone) with phenylglyoxal monohydrate, and diverse anilines, in water at room temperature. Advantages of this reaction include the availability of starting materials, use of water as a green solvent, catalyst-free approach, simple work-up, high yields, and preparation of potentially bioactive compounds.

Catalyst-free four-component domino synthetic approach toward versatile multicyclic spirooxindole pyran scaffolds

A new versatile strategy involving a sequential four-component reaction of the nitroketene dithioacetals, alkylamine/benzylamine, isatin and various enolizable active methylene structures (pyrazolone, barbituric acid, 1,3-indandione and 2-hydroxy-1,4-naphthoquinone) as precursors under mild and catalyst-free conditions results in the synthesis of new functionalized spirooxindole pyrans named spiro[indoline-3,4′-pyrano[2,3-c]pyrazol], spiro[indoline-3,5′-pyrano[2,3-d]pyrimidine], spiro[indeno[1,2-b]pyran-4,3′-indoline] and spiro[benzo[g]chromene-4,3′-indoline] in moderate to good yields. The use of various active methylene compounds affords a range of skeletally distinct spirooxindole-based heterocycles with potential biological properties. The present strategy has many advantages, such as convenient one-pot operation, simple workup procedures and straightforward isolation without using tedious purification steps such as column chromatography, progress under catalyst-free condition and high molecular diversity.

Synthesis of spirooxindole pyrans by a sequential four-component reaction of nitroketene dithioacetals, alkylamine/benzylamine, isatin, and active methylene compounds.