R. Raghunathan

Synthesis, antimicrobial and antifungal activity of a new class of spiro pyrrolidines.

A new class of spiro pyrrolidines, dispiro[oxindole-cyclohexanone]pyrrolidines, dispiro[oxindole-tetrahydronaphthalen-1-one]pyrrolidines, dispiro[oxindole-arylidene-cyclohexanone]pyrrolidines, dispiro[oxindole-hexahydro-indazole]pyrrolidines, and spiro[butenolide]pyrrolidines, have been screened for their antibacterial and antifungal activity against ten human pathogenic bacteria and four dermatophytic fungi. They were found to have antimicrobial and antifungal activity compounds against various pathogens except Bacillus subtilis. The spiro pyrrolidinines were synthesized by the regioselective 1,3-dipolar cycloaddition reaction of azomethine ylides generated either from isatin and sarcosine or from aziridine. The azomethine ylide so generated reacted with various dipolarophiles such as 2-arylidene-cyclohexanones, 2-arylidene-tetrahydronapthalen-1-ones, 2,6-bis(arylmethylidene)cyclohexanones and 3-arylidene-5-phenyl- butenolides.

A novel entry into a new class of spiroheterocyclic framework: regioselective synthesis of dispiro[oxindole-cyclohexanone]pyrrolidines and dispiro[oxindole-hexahydroindazole]pyrrolidines

Abstract 2,6-Bis(arylmethylidene)cyclohexanones undergo a regioselective 1,3-dipolar cycloaddition reaction with the azomethine ylide derived from isatin and sarcosine by a decarboxylative route affording a series of 1-N-methyl-spiro[2.31]oxindole-spiro[3.211]611-arylmethylidenecyclohexanone-4-aryl-pyrrolidines which were further annulated to give a series of novel 1-N-methyl-spiro[2.31]oxindole-spiro[3.711](311-aryl)Δ111,711a-hexahydro-2H-indazole-4-aryl-pyrrolidines. The structures of which were established by spectroscopic techniques as well as single crystal X-ray analysis.

Synthesis of highly substituted spiropyrrolidines via 1,3-dipolar cycloaddition reaction of N-metalated azomethine ylides

Abstract 3-Arylidene-4-chromanones undergo regioselective 1,3-dipolar cycloaddition reactions with N -metalated azomethine ylides derived from aromatic aldimines of glycine methyl ester in the presence of silver acetate and triethylamine to give spiropyrrolidine derivatives in good yield. X-Ray crystal structure analysis of one of the products confirms the structure and regiochemistry of the cycloadditions.

Synthesis and antibacterial property of quinolines with potent DNA gyrase activity.

Synthesis of a series of novel tetrahydroquinoline annulated heterocycles has been accomplished by intramolecular imino and bisimino Diels-Alder reaction. These compounds were evaluated for their antibacterial activity. All the synthetic compounds, exhibited good antibacterial activity against microorganisms of which one of them 7 was found to be as active as the antibiotic ciplofloxacin and is found to have MIC value of 2.5 mg/mL against Escherichia coli.

High chemoselectivity in microwave accelerated intramolecular domino Knoevenagel hetero Diels–Alder reactions—an efficient synthesis of pyrano[3-2c]coumarin frameworks

Abstract 4-Hydroxy coumarin and its benzo-analogues undergo intramolecular domino Knoevenagel hetero Diels–Alder reactions with O-prenylated aromatic aldehydes and the aliphatic aldehyde, citronellal to afford pyrano fused polycyclic frameworks. A high degree of chemoselectivity was achieved by the application of microwave irradiation.

Synthesis of Spirooxindolo/Spiroindano Nitro Pyrrolizidines through Regioselective Azomethine Ylide Cycloaddition Reaction

Abstract Synthesis of a series of spirooxindolonitro pyrrolizidines and spiroindanonitro pyrrolizidines has been accomplished. The nonstabilized azomethine ylides generated from isatin and ninhydrin with proline reacted with nitro styrenes to regioselectively yield spirocycloadducts.

A facile entry into a new class of spiroheterocycles: synthesis of dispiro[oxindolechromanone/flavanone/tetralone]pyrroloisoquinoline ring systems

Abstract A series of novel dispiroheterocyclic systems have been synthesized by the cycloaddition of a new azomethine ylide generated by the decarboxylative route from tetrahydroisoquinoline-3-carboxylic acid and isatin with various dipolarophiles containing exocyclic double bond such as 3-arylidene-4-chromanone, 3-arylidene-4-flavanone and 2-arylidenetetrahydro-1-naphthalenone in moderate to good yield. The regio and stereochemistry of the title compounds was established by single crystal X-ray structure and spectroscopic techniques.

Regioselective Synthesis of Novel Spirooxindolo and Spiroindano Nitro Pyrrolidines Through 3+2 Cycloaddition Reaction

Abstract β‐Nitro styrene reacts with nonstabilized azomethine ylides generated from isatin/ninhydrin with sarcosine, resulting in the formation of a series of spiroxindolo nitro pyrrolidines, and spiroindano nitro pyrrolidines, respectively, in good yields. It was noted that in a one‐pot 3+2 cycloaddition reaction, the azomethine ylides generated from isatin and ninhydrin have reacted with the β‐nitro styrenes regiochemically in opposite ways.

Competition between two intramolecular domino Knoevenagel hetero Diels–Alder reactions: a new entry into novel pyranoquinolinone derivatives

Abstract 4-Hydroxy-1,2-dihydro-2-quinolinones undergo facile intramolecular domino Knoevenagel hetero Diels–Alder reactions with o-prenylated aromatic aldehydes and the aliphatic aldehyde citronellal, to afford novel pyranoquinolinone derivatives. A high degree of chemoselectivity has been achieved under microwave irradiation condition.

Stereoselective synthesis of 5-(41-azetidinyl)-proline esters via 1,3-dipolar cycloaddition reaction of N-metalated azomethine ylides

The conformationally locked s-trans enone functionality present in the (E)-3-arylidene-4-chromanones undergo regioselective 1,3-dipolar cycloaddition reaction with N-metalated azomethine ylides derived from β-lactam imines of glycine methyl ester in the presence of silver acetate to give spiropyrrolidines in moderate to good yield. The regio and stereochemistry of the cycloadducts have been established by single crystal X-ray structure and spectroscopic techniques.