Abstract Sulfated zirconia and phosphotungstic acid (PWA) have been used as catalysts for the syn... more Abstract Sulfated zirconia and phosphotungstic acid (PWA) have been used as catalysts for the synthesis of some biologically potent 3,4-dihydropyrimidin-2(1H)-ones and aryl-14H-dibenzo[aj]xanthenes under solvent free conditions. Both the solid acid catalysts are ...
The synthesized porphyrin derivatives (1-7) and the free base (8) were characterized by UV-vis an... more The synthesized porphyrin derivatives (1-7) and the free base (8) were characterized by UV-vis and ABSTRACT: A modular synthetic approach for preparing a family of porphyrin appended 1,3,4oxadiazoles 9 is described. The porphyrin hydrazides are reacted with aryl aldehydes in presence of Yb(OTf) 3 as catalyst to give porphyrin hydrazones 8 which are then cyclized to porphyrin appended 1,3,4-oxadiazoles 9 using iodobenzene diacetate. Photophysical studies in CHCl 3 solvent shows that the electronic structure of the porphyrin chromophore is not greatly perturbed by the incorporation of the oxadiazole group onto the meso-phenyl ring. Efficient quenching of porphyrin fluorescence was observed in 9g with a pyridinium moiety.
The factors that affect the kinetics of the aza-Bergman cyclization of aza-enediynes (C,N-dialkyn... more The factors that affect the kinetics of the aza-Bergman cyclization of aza-enediynes (C,N-dialkynyl imines) have not previously been elucidated. Here we report our kinetic studies of the aza-Bergman reactions of a series of 6-triisopropylsilyl and 6-unsubstituted 1-phenyl-4-aryl-3-aza-3-ene-1,4-diynes in which the aryl group is phenyl, o-(methoxy)phenyl, or p-(methoxy)phenyl. These aza-enediynes are prepared as single isomers in modest yield from the corresponding 1-aryl-3-(triisopropylsilyl)propynone oximes. These aza-enediynes undergo aza-Bergman reaction followed by a rapid retro-aza-Bergman cyclization to afford beta-alkynyl acrylonitrile products. In no case are products corresponding to trapping the intermediate 2,5-didehydropyridine diradical isolated. While the rate of aza-Bergman cyclization is not greatly affected by the nature of the 4-aryl substituent, the rate is very dependent on the nature of the 6-substituent. 1-Phenyl-4-aryl-3-aza-3-ene-1,5-diynes that lack a 6-substituent undergo aza-Bergman cyclization spontaneously at 20 degrees C with first-order half-lives of 36-78 min. The effect of solvent on the kinetics of aza-Bergman cyclization of 1,4-diphenyl-3-aza-3-ene-1,5-diyne was investigated. The rate of this cyclization is solvent dependent, proceeding more rapidly in less polar solvents.
Abstract Sulfated zirconia and phosphotungstic acid (PWA) have been used as catalysts for the syn... more Abstract Sulfated zirconia and phosphotungstic acid (PWA) have been used as catalysts for the synthesis of some biologically potent 3,4-dihydropyrimidin-2(1H)-ones and aryl-14H-dibenzo[aj]xanthenes under solvent free conditions. Both the solid acid catalysts are ...
The synthesized porphyrin derivatives (1-7) and the free base (8) were characterized by UV-vis an... more The synthesized porphyrin derivatives (1-7) and the free base (8) were characterized by UV-vis and ABSTRACT: A modular synthetic approach for preparing a family of porphyrin appended 1,3,4oxadiazoles 9 is described. The porphyrin hydrazides are reacted with aryl aldehydes in presence of Yb(OTf) 3 as catalyst to give porphyrin hydrazones 8 which are then cyclized to porphyrin appended 1,3,4-oxadiazoles 9 using iodobenzene diacetate. Photophysical studies in CHCl 3 solvent shows that the electronic structure of the porphyrin chromophore is not greatly perturbed by the incorporation of the oxadiazole group onto the meso-phenyl ring. Efficient quenching of porphyrin fluorescence was observed in 9g with a pyridinium moiety.
The factors that affect the kinetics of the aza-Bergman cyclization of aza-enediynes (C,N-dialkyn... more The factors that affect the kinetics of the aza-Bergman cyclization of aza-enediynes (C,N-dialkynyl imines) have not previously been elucidated. Here we report our kinetic studies of the aza-Bergman reactions of a series of 6-triisopropylsilyl and 6-unsubstituted 1-phenyl-4-aryl-3-aza-3-ene-1,4-diynes in which the aryl group is phenyl, o-(methoxy)phenyl, or p-(methoxy)phenyl. These aza-enediynes are prepared as single isomers in modest yield from the corresponding 1-aryl-3-(triisopropylsilyl)propynone oximes. These aza-enediynes undergo aza-Bergman reaction followed by a rapid retro-aza-Bergman cyclization to afford beta-alkynyl acrylonitrile products. In no case are products corresponding to trapping the intermediate 2,5-didehydropyridine diradical isolated. While the rate of aza-Bergman cyclization is not greatly affected by the nature of the 4-aryl substituent, the rate is very dependent on the nature of the 6-substituent. 1-Phenyl-4-aryl-3-aza-3-ene-1,5-diynes that lack a 6-substituent undergo aza-Bergman cyclization spontaneously at 20 degrees C with first-order half-lives of 36-78 min. The effect of solvent on the kinetics of aza-Bergman cyclization of 1,4-diphenyl-3-aza-3-ene-1,5-diyne was investigated. The rate of this cyclization is solvent dependent, proceeding more rapidly in less polar solvents.
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Papers by Dalip Kumar