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An efficient protocol has been developed for the synthesis of a novel fluorescent probe, 1,2-disubstituted-indeno[1,2,3-gh]phenanthridine, derived from a series of α-oxo-ketene dithioacetals (OKDTAs) and indenoquinoline under essential conditions via a [4+2] annulation in excellent yield.

The stereo/regio/chemoselective syntheses of a library of novel spiro[acenaphthylene-1,3′-pyrrolizin]-2-one and spiro[acenaphthylene-1,5′-pyrrolo[1,2-c]thiazol]-2-one have been achieved through 1,3-dipolar cycloaddition. Intermediate azomethine ylides generated in situ from α-amino acids and acenaphthylene-1,2-dione react with α-aroylidine ketenedithioacetal (AKDTA) derivatives to give the target product in excellent yield under ultrasound irradiation. Further, spiro-S,S-acetals are converted to spiro-2H-pyranones by a one-pot cyclization strategy.

A highly efficient domino protocol has been developed for the synthesis of 6-aryl-4-(methylthio/amine-1-yl)-2-oxo-2H-pyran-3-carbonitriles and 4-aryl-2-(amine-1-yl)-5,6,7,8-tetrahydronaphthalene-1-carbonitriles from simple and readily available α-aroylketene dithioacetals, malononitrile, secondary amines, and cyclohexanone. This elegant domino process involved consecutive addition–elimination, intramolecular cyclization, and ring opening and closing sequences. Notably, in situ generated 2-imino-4-(methylthio/amine-1-yl)-6-aryl-2H-pyran-3-carbonitrile plays multiple roles in the construction of various novel polyaromatic hydrocarbons.

Design and synthesis of a novel tetraphenylethene-2-pyrone (TPEP) conjugate exhibiting donor-acceptor characteristics is reported. The localized frontier molecular orbitals (DFT studies) and the solvent polarity dependent photoluminescence characteristics directly corroborate the presence of intramolecular charge transfer character in TPEP. TPEP is poorly emissive in the solution state. In contrast, upon aggregation (THF/water mixtures), TPEP exhibits aggregation-induced emission enhancement. Upon aggregation, dyad TPEP forms a fluorescent nanoaggregate which was confirmed by transmission electron microscopy imaging studies. The luminescence nanoaggregates were elegantly exploited for selective detection of nitro aromatic compounds (NACs). It was found that nanoaggregates of TPEP were selectively sensing the picric acid over the other NACs. Efficiency of the quenching process was further evaluated by the Stern-Volmer equation. TPEP-based low-cost fluorescent test strips were developed for the selective detection of picric acid.

An efficient chemo/regio/stereoselective synthesis of novel and functionalized spiro-oxindole/pyrrolizine/pyrrolidine scaffolds has been achieved. The in situ generated azomethine ylide from isatin & L-proline/phenyl alanine underwent 1,3-dipolar cycloaddition with α-aroylidineketene dithioacetals under simple reaction conditions affording spiro-oxindole derivatives. This protocol exhibits an interesting double bond selectivity of α-aroylidineketene dithioacetals. Furthermore, utilizing this spiro-oxindoles scaffold, biologically important benzimidazole and pyrimidine based poly heterocycles were also synthesized.

An efficient green synthetic approach has been developed towards the synthesis of 2-aryl substituted benzimidazoles from α-aroylketene dithioacetals (AKDTAs) 1 and o-phenylenediamine (OPD) 2. The reaction has been achieved in water with a catalytic amount of acetic acid. 2-Arylbenzimidazoles have been synthesized in remarkable yields under both thermal and microwave conditions. The metal catalyst free condition makes this transformation very green, practical and attractive.

Various spiro-oxindole derivatives are obtained by 1,3-dipolar cycloaddition of in situ generated azomethine ylide from isatin and L-proline/L-phenylalanine with α-aroylidineketene dithioacetals.

2-Arylbenzimidazoles [(III) and (V)] are efficiently synthesized by green procedures under microwave as well as thermal conditions which give slightly more yields in 2h.