Pratik Yadav

Microwave assisted base dependent regioselective synthesis of partially reduced chromenes, isochromenes and phenanthrenes.

We have reported a microwave assisted base directed regioselective synthesis of partially reduced chromenes, isochromenes and phenanthrenes. Functionalized 4-(piperidin-1-yl)-5,6-dihydro-2H-benzo[h]-chromen-2-one-3-carbonitriles have been used as precursors, which on reaction with functionalized acetophenones in the presence of KOH in DMF under microwave irradiation yield (Z)-2-(2-aryl-5,6-dihydro-4H-benzo[f]isochromen-4-ylidene)acetonitriles. The use of NaH in DMF provides 3-aryl-1-(piperidin-1-yl)-9,10-dihydro phenanthrene-2-carbonitriles in excellent yield regioselectively. The use of cyclohexanone as a nucleophile source yields (Z)-2-(3,4,7,8-tetrahydro-1H-naphtho[2,1-c]chromen-6(2H)-ylidene)acetonitriles. The structure and geometry of isochromene have been proved without any ambiguity by single crystal X-ray diffraction.

One pot synthesis of tetrasubstituted thiophenes: [3 + 2] annulation strategy

A simple, efficient and economical synthesis of dimethyl 3-amino-5-(2-oxo-2-arylethyl)thiophene-2,4-dicarboxylates has been reported by ring opening of methyl 3-amino-6-aryl-4-oxo-4H-thieno[3,2-c]pyran-2-carboxylates by alkoxide ions. Pyranothiophenes have been obtained by the reaction of methyl thioglycolate and 6-aryl-4-methylthio-2H-pyran-2-one-3-carbonitriles in the presence of triethylamine. A one-pot multicomponent protocol for the synthesis of tetrasubstituted thiophenes has been developed by reaction of 6-aryl-4-methylthio-2H-pyran-2-one-3-carbonitriles and methyl thioglycolate in the presence of sodium methoxide in excellent yields. The structure of the isolated compound was confirmed by single crystal X-ray diffraction and spectroscopic studies.

Substituent dependent tunable fluorescence in thieno[3,2-c]pyrans

A series of thieno[3,2-c]pyrans were designed and synthesized by L-proline catalyzed reaction of 6-aryl/5,6-diaryl-4-methylthio-2H-pyrane-2-one-3-carbonitriles or 4-(methylthio)-2-oxo-5,6-dihydro-2H-benzo[h]chromene-3-carbonitrile and methylthioglycolate in good yields. These thieno[3,2-c]pyrans exhibit substituent dependent fluorescence. The 6-aryl-thieno[3,2-c]pyrans 3a–3e exhibit high fluorescence quantum yields (95%) with large Stokes shifts, whereas the 6,7-di-substituted-thieno[3,2-c]pyrans 3f–3h show poor fluorescence in solution and exhibit an aggregation-induced emission (AIE). Interestingly, fused 6,7-di-substituted-thieno[3,2-c]pyran is highly fluorescent in the solution state, which reveals that restricted intramolecular rotation is the cause for AIE in 3f–3h.

Precursor directed regioselective synthesis of partially reduced benzo[e]indene through oxidative cyclization and benzo[h]quinolines

We have reported a simple, unprecedented base promoted synthesis of 7-substituted-1-(2-cyano-phenyl/phenyl)-3-sec amino-4,5-dihydro-1H-benz[e]indene-1,2-dicarbonitriles by reaction of 2-oxo-4-sec amino-5,6-dihydro-2H-benzo[h]chromene-3-carbonitriles and 2-cyanomethyl-benzonitrile/phenyl-acetonitrile under basic conditions at 100 °C. This reaction involves ring opening of 2-oxo-4-sec amino-5,6-dihydro-2H-benzo[h]chromene-3-carbonitrile by a carbanion generated in situ from 2-cyanomethylbenzonitrile/phenyl-acetonitrile followed by oxidative cyclization to afford the desired product. Alternatively, reaction of 6-aryl-4-sec amino-2H-pyran-2-one-3-carbonitriles and 2-cyanomethyl-benzonitrile under basic conditions provides functionalized benzo[h]quinolines. The structure of the synthesized compound was confirmed by single crystal X-ray.