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The reactivity of α-azidochalcones has been explored for the preparation of highly substituted oxazoles via a 2H-azirine intermediate. The azidochalcones, when treated with potassium thiocyanate in the presence of potassium persulfate, lead to 2,4,5-trisubstituted oxazoles in good yields. Incidentally, 2-aminothiazoles are the products when ferric nitrate is employed instead of persulfate in the above reaction.

We study the effect of molecular conformation on the electronic coupling between the donor amines and acceptor 1,8-naphthalimide (NPI) in a series of D-A systems 1-4 (A = NPI; D = phenothiazine, phenoxazine, carbazole, diphenylamine, respectively, for 1, 2, 3, and 4). Weakly coupled systems show dual emission in the solution state, while strongly coupled systems show single emission bands. The energy of transitions and photoluminescence (PL) quantum yield are sensitive to the molecular conformation and donor strength. These compounds show delayed emission in the solutions and aggregated state and phosphorescence in the solid state. Compounds 3 and 4 with weak donors exhibit intermolecular slipped π···π interactions in the solid state and consequently exhibit dual (intra- and inter-) phosphorescence at low temperature. Steady state and time-resolved PL studies at variable temperature together with computational and crystal structure analysis were used to rationalize the optical properties of these compounds. The delayed emission of these compounds is sensitive to molecular oxygen; accordingly, these molecules are utilized for differential imaging of normoxia and hypoxia cancer cells.

We studied the dual emission characteristics of a series of boryl-BODIPYs (1-6) comprised of triarylborane (TAB) as an energy donor and BODIPY as an energy acceptor. The molecular conformations of dyads 1-6 were systematically tuned by judiciously changing the spacer that bridged the boryl and BODIPY moieties. Frontier molecular orbitals (FMOs) are localized in 3, 4, and 6 with a twisted molecular conformation. In contrast, FMOs are significantly delocalized in 1, 2, and 5 with the least-twisted molecular conformation. Dyads 1-6 showed dual emission features when they were excited at the TAB-dominated absorption band. However, the ratio between the two emission bands in 1-6 significantly varied depending on the molecular conformations. Systematic photoluminescence (PL) studies (both steady-state and time-resolved PL) together with computational, crystal structure, and anion binding studies established that the frustrated excited-state energy transfer from borane to BODIPY is the cause of the dual emission features in these molecular dyads. These studies also revealed that the energy transfer from borane to BODIPY can be elegantly tuned by modulating the dihedral angle between these two moieties.

Reactivity of α-aroylidineketene dithioacetals 2 was investigated to synthesize novel 2-styrylbenzimidazole derivatives 4 and their hydrothiolated product 2-(2-(methylthio)-2-arylethyl)-1H-benzo[d]imidazoles 5 has been reported. Compounds 4 and 5 were synthesized by cyclocondensation of α-aroylidineketene dithioacetals 2 and o-phenylene diamine (OPD) 3 in the presence and absence of copper catalyst respectively. Regioselective one-pot tandem hydrothiolation of olefin functionality in 4 was achieved under AcOH conditions.

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.

We have developed an easy method to construct diheteroaryls from α-aroylidineketene dithioacetals in a multicomponent manner. The reaction proceeded with high chemo/regioselectivity to yield 4-alkoxy-6-(4-aryl-1H-pyrrol-3-yl)pyrimidin-2-amines under milder conditions. It is found that α-aroylidineketene dithioacetals (2) undergo cycloaddition with (p-tolylsulfonyl)methyl isocyanide (3) [TosMIC], guanidine nitrate (5) and alcohol in the presence of NaH/THF to furnish the target 6-pyrrolylpyrimidines (8) in excellent yields.

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.

Reactivity of α-aroylidineketene dithioacetals 2 was investigated to synthesize novel 2-styrylbenzimidazole derivatives 4 and their hydrothiolated product 2-(2-(methylthio)-2-arylethyl)-1H-benzo[d]imidazoles 5 has been reported. Compounds 4 and 5 were synthesized by cyclocondensation of α-aroylidineketene dithioacetals 2 and o-phenylene diamine (OPD) 3 in the presence and absence of copper catalyst respectively. Regioselective one-pot tandem hydrothiolation of olefin functionality in 4 was achieved under AcOH conditions.

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.

A facile preparation method for 6-pyrrolylpyrimidines from aryl dithioacetals under mild conditions is described.

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.

A one-pot synthesis of some new 2,8-disubstituted 3H-phenoxazin-3-ones from 4-substituted-2-aminophenols through a selective oxidative condensation by lead tetraacetate in acetic acid is described.