Swapan Dey

Multiple hydrogen bonds and tautomerism in naphthyridine derivatives

The behaviour of three 2,7-disubstituted 1,8-naphthyridines able to exhibit tautomerism has been studied by NMR in solution and in two cases in the solid state. The three derivatives studied are 2,7-dihydroxy- (1), 2-acetamido-7-amino- (3) and 2,7-diacetamido-1,8-naphthyridine (4). To explore the problem of secondary interactions, a series of complexes, with up to four simultaneous hydrogen bonds, where the monomers are generated using pyridine and 4-pyridone as building blocks, have been theoretically studied. The calculated interaction energies have been correlated with the number of hydrogen bonds and with attractive and repulsive secondary interactions. Further analysis of the electron density and orbital interactions shows that the secondary interactions, both attractive and repulsive, have a purely electrostatic origin. The X-ray structure of compounds 3 and 4 have been determined. In the solid state these compounds exist in the “diamino” tautomers with the N–H proton of the amido groups pointing towards the naphthyridine nitrogen. DFT and GIAO calculations have been essential to disentangle the problem of the structure of these compounds.

Microwave-Expedited One-Pot, Two-Component, Solvent-Free Synthesis of Functionalized Pyrimidines

The synthesis of a series of diversely substituted pyrimidines under solvent-free conditions in good yields is described. Under microwave irradiation, a variety of nucleophilic substrates containing the N–C–N unit with β-dicarbonyl compounds, ethyl cyanoacetate, malononitrile, and chalcones was cyclized to give pyrimidines. A combinatorial type approach for a one-step synthesis has been developed where a ring-closing condensation is followed by spontaneous aromatization to afford 28 functionalized and aryl/alkyl substituted pyrimidines.

Recognition of Dicarboxylic Acid by 6,6′-Dipivaloylamino-3,3′-bipyridine and the Supramolecular Solid State Locking of the Carboxyls in the anti Form

A new crystal-engineering motif has been developed where a ditopic receptor 1 having anti binding hindered pyridine pivaloylamide groups instead of normally used acetylamino groups shows a novel anti–anti hydrogen bonded polymeric supramolecular complex giving rise to hydrogen bonded stair like polymeric ribbon structure between the receptor pyridine amides and the carboxyl groups of the guest substrate (1,4-phenylenediacetic acid).