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A series of novel fused polyhalogeno-7a-hydroxy-[1,2-a]indol-5-one derivatives has been synthesized with good yields based on the Nenitzescu reaction of heterocyclic ketene aminals (HKAs) with halogenated quinones without catalyst in acetone under room temperature. The highly efficient, catalyst-free and one pot synthesis serves as a nice addition to group-assisted-purification (GAP) chemistry, and the pure products were obtained simply by washing the crude products with 95% ethanol.

A novel C–N cleavage strategy for the regioselective synthesis of 2-nitroso heterocyclic ketene aminals (HKAs) has been established. In this procedure, the C–N bond of nitrobenzenyl nitroethene is cleaved by the oxidation reaction and selective nitroso reaction of the α-carbon in HKAs. The presented synthetic route features excellent selectivity, straightforward purification and simple starting materials.

The title compounds (IV), (VI), (VIII), (X) are efficiently and regioselectively obtained by cascade reaction of ketene aminals with triethoxymethane (II), and 4-hydroxy coumarin derivatives (III) without any catalyst and solvent.

A series of novel fused polyhalogeno-7a-hydroxy-[1,2-a]indol-5-one derivatives has been synthesized with good yields based on the Nenitzescu reaction of heterocyclic ketene aminals (HKAs) with halogenated quinones without catalyst in acetone under room temperature. The highly efficient, catalyst-free and one pot synthesis serves as a nice addition to group-assisted-purification (GAP) chemistry, and the pure products were obtained simply by washing the crude products with 95% ethanol.

The reaction proceeds with 2-aryloylmethylidene-1,3-diazacycloalkanes with high regioselectivity forming the corresponding α-nitroso compounds.

The title compounds (IV), (VI), (VIII), (X) are efficiently and regioselectively obtained by cascade reaction of ketene aminals with triethoxymethane (II), and 4-hydroxy coumarin derivatives (III) without any catalyst and solvent.

A one-step synthesis of the title compounds is developed via a base catalyzed cyclocondensation of heterocyclic ketene aminals (I) and (IV) with 4-chloro-3-carbaldehyde derivatives (II).

A method for regioselective synthesis of 9,10-dihydro-6H-chromeno[4,3-d]imidazo[1,2-a]pyridin-6-one derivatives has been developed. The reaction was readily performed by reacting inexpensive materials, 4-chloro-3-formylcoumarin and HKAs, in EtOH catalyzed by Et3N. This protocol has many advantages including convenient operation, short reaction times, green solvent, and simple purification by washing the crude products with 95% EtOH, defined as GAP (Group-Assistant-Purification) chemistry. The library of 9,10-dihydro-6H-chromeno[4,3-d]imidazo[1,2-a]pyridin-6-one derivatives has been constructed with excellent yields.

An efficient one-pot three-component synthesis of novel 1H-pyrazol-5(4H)-one-based heterocyclic ketene aminal libraries was performed by simply refluxing a mixture of heterocyclic ketene aminals (HKAs), 1-phenyl-1H-pyrazol-5(4H)-ones and triethoxymethane under solvent-free and catalyst-free conditions. The protocol has the advantages of being highly efficient and environmentally benign, with excellent yields and easy work-up, making it suitable for large-scale and parallel combination synthesis. These compounds are promising candidates for drug discovery. Consequently, a library of diverse 1H-pyrazol-5(4H)-one-based HKAs was rapidly constructed using this method.