Pallabi Saikia

Carbon–Carbon Bond Cleavage Reaction: Synthesis of Multisubstituted Pyrazolo[1,5-a]pyrimidines

A new carbon-carbon bond cleavage reaction was developed for the efficient synthesis of multisubstituted pyrazolo[1,5-a]pyrimidines. This base induced reaction of 1,3,5-trisubstituted pentane-1,5-diones and substituted pyrazoles afforded good yields of the pyrazolo[1,5-a]pyrimidines.

Microwave-promoted and Lewis acid catalysed synthesis of steroidal A- and D-ring fused 4,6-diarylpyridines

The preparation of novel steroidal heterocycles containing 4,6-diaryl substituted pyridine moiety fused to the 2,3- and 16,17-positions of the steroid nucleus is described. The Michael reaction of steroidal ketones (1a, 1b and 1c) with in situ generated chalcones provided the intermediates 3,5-diaryl-1,5-dicarbonyl steroidal derivatives (4a-s). Subsequently, the intermediates 4a-s were converted to the pyridine derivatives (5a-s) by solid phase reaction with urea in presence of BF3.OEt2 as the catalyst under microwave irradiation. All the synthesized heterosteroids are new compounds and are currently being evaluated for their biological activities.

Synthesis of steroidal and nonsteroidal vicinal heterocyclic alcohols, N-(1-cycloalkenyl)heterocycles and their antibacterial studies.

A solvent free steroidal and nonsteroidal epoxide ring opening reaction by nitrogen containing heterocycles under microwave irradiation is described. Some of the epoxide ring opening compounds were converted to their corresponding N-(1-cycloalkenyl)heterocycles via an acid catalyzed dehydration reaction. The antimicrobial activities of the epoxide ring opening compounds and N-(1-cycloalkenyl)heterocyclic compounds were tested by agar diffusion assay. Compounds 6, 9-12, 24 and 27 showed moderate inhibition against the growth of pathogenic bacteria Escherichia coli, Pseudomonas syringae, Bacillus subtilis, Proteus vulgaris and Staphylococcus aureus.

Palladium mediated regioselective intramolecular Heck reaction: synthesis of 1,3,4-trisubstituted pyrazolo[3,4-b]pyridines, 3H-pyrazolo[3,4-c]isoquinolines and 3H-pyrazolo[4,3-f][1,7]naphthyridines

An efficient method was developed for the synthesis of 1,3,4-trisubstituted pyrazolo[3,4-b]pyridines, 3H-pyrazolo[3,4-c]isoquinolines and 3H-pyrazolo[4,3-f][1,7]naphthyridines via intramolecular Heck reactions of imine derivatives of β-halovinyl/aryl aldehydes and 5-aminopyrazoles. This palladium acetate catalyzed reaction afforded good yields of these pyrazolo fused compounds under thermal conditions in the presence of xantphos as the ligand.

Cascade imination, Buchwald–Hartwig cross coupling and cycloaddition reaction: synthesis of pyrido[2,3-d]pyrimidines

A novel and efficient palladium catalyzed method was developed for the synthesis of wide range of pyrido[2,3-d]pyrimidines, using readily available β-bromovinyl/aryl aldehydes and 6-amino-1,3-dialkyluracils as the starting materials with good yields. This reaction proceeds via cascade imination/Buchwald–Hartwig cross coupling/cycloaddition reactions under microwave irradiation and solvent free conditions.

An efficient route for annulation of pyrimidines to steroids and non-steroids via a base catalyzed one-pot three component reaction

A facile strategy for the synthesis of steroidal A- and D-ring fused pyrimidines has been accomplished in high yields via a one-pot reaction of steroidal ketones, aromatic aldehydes and amidine derivatives in presence of potassium tert-butoxide in refluxing ethanol. The generality of the reaction was also extended to non-steroidal ketones.

Ru(II)-Catalyzed and Ligand-Controlled C–H Activation and Annulation via 1,2-Phenyl Shift: Synthesis of Quaternary Carbon-Centered Pyrimidoindolones

A novel Ru(II)-catalyzed C-H activation and annulation reaction of N-arylpyrazol-5-ones and diaryl/arylalkyl-substituted alkynes is developed. Unlike the reported metal-catalyzed C-H activation and annulation reactions, in the present bidentate amine-ligand controlled C-H activation and annulation reaction, the annulation occurs via a 1,2-aryl shift to afford quaternary carbon-centered pyrimidoindolones.