Browsing by Author "Dhole, Sandip"

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Catalyst-Controlled Chemodivergent Annulation to Indolo/Pyrrolo-Fused Diazepine and Quinoxaline
(2019-06-18)
Dhole, Sandip
;
Chiu, Wei-Jung
;
Sun, Chung-Ming
;
應用化學系
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Department of Applied Chemistry
Catalyst-controlled chemodivergent annulation between o-indolo anilines and diazo compounds has explored for the synthesis of indolo-fused diazepine and quinoxaline Under the Rh(III) catalyst, reaction proceeded through the free amine assisted C2-H activation followed by amidation leading to the diazepino [1,7-alpha]indole in a highly selective manner. While with Ru(II) catalyst, reaction involves formation Ru-carbene complex followed by -NH2 group insertion and cascade cyclization via metallo-ene type reaction, beta-hydride elimination to furnish the indolo[1,2-alpha]quinoxaline as the predominating product. This strategy directs modular approach towards the construction of unique indolo-fused diazepine/quinoxaline as well as pyrrolo-fused diazepine/quinoxaline scaffolds in excellent yields.
Direct Access to Dihydrobenzoimidazo[2,1-a]isoquinolines through Ruthenium-catalyzed Formal [4+2] Annulation
(2019-02-01)
Dhole, Sandip
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Sun, Chung-Ming
;
應用化學系
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Department of Applied Chemistry
A facile and straightforward synthesis of benzoimidazo[2,1-a]isoquinolines through Ru(II)-catalyzed [4+2] annulation reaction of 2-aryl benzimidazole and styrene has been explored. Tentative mechanistic studies imply the current reaction involves sequential C-C/C-N bond formation through the ortho C-H activation of 2-aryl benzimidazole followed by C-N reductive elimination. This newly developed strategy is widely applicable and tolerates various 2-arylbenzimidazole and vinyl derivatives, and allows the attractive vehicle for direct construction of diverse C6-substituated benzoimidazoisoquinoline scaffold in good yields.
Microwave Controlled Reductive Cyclization: A Selective Synthesis of Novel Benzimidazole-alkyloxypyrrolo[1,2-a]quinoxalinones
(2015-05-01)
Dhole, Sandip
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Selvaraju, Manikandan
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Maiti, Barnali
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Chanda, Kaushik
;
Sun, Chung-Ming
An efficient cascade synthesis of novel benzimidazole linked alkyloxypyrrolo[1,2-a]quinoxalinones was explored on soluble polymer support under micro-Wave irradiation. Two exclusive protocols have been developed for the partial and reductive cyclization by Controlling the microwave energy, Commencing from the smile substrate, ortho nitro, pyrrol: carboxylates, N-hydroxy pyrroloquinoxalinones were obtained by,, partial reductive cyclization (60 degrees C, 7 min), and the synthesis of pyrroloquinoxalinones was accomplished by full reductive, cyclization (85 degrees C, 12 min). This method represents the first synthesis N-hydroxy pyrroloquinoxalinones using Pd/C and ammonium formate as reducing agents: Further employing a variety Of alkyl bromides, the obtained pyrroloquinoxalinones were transformed to their corresponding O-, and N-alkylated analogues to deliver the diversified, novel molecular entities.
Regioselective Synthesis of Angular Isocoumarinselenazoles: A Benzoselenazole-directed, Site-specific, Ruthenium-catalyzed C(sp(2))-H Activation
(2018-03-01)
Dhole, Sandip
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Liao, Jen-Yu
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Kumar, Sunil
;
Salunke, Deepak B.
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Sun, Chung-Ming
The synthesis of new, angular isocoumarinselenazoles is described, which involves the construction of 2-amino benzoselenazoles and their regioselective C2N-alkylation and alkyne insertion. An expeditious and metal-free synthesis of 2-aminobenzoselenazoles by the reaction of methyl 3-amino-4-fluorobenzoate and isoselenocyanates was achieved. Further N-alkylation of the 2-aminobenzoselenazoles resulted the formation of two regioisomers with different reactivities towards the alkyne insertion. The regioselective construction of the a-pyrone ring on the benzo[1,3-d] selenazole skeleton was achieved via a ruthenium (II)-catalyzed oxidative annulation. It is clear that the selenazole nitrogen plays an important role in the observed selectivity.
Regioselective synthesis of imidazo[1,5-a]quinoxalines and methyl N-phenylbenzimidats on an ionic liquid support
(2016-01-01)
Chen, Li-Hsun
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Kao, Chih-Hsien
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Dhole, Sandip
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Barve, Indrajeet J.
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Shen, Li-Ching
An ionic liquid (IL) supported, regioselective synthesis of imidazo[1,5-a]quinoxalines and methyl N-phenylbenzimidats under microwave conditions was reported. The IL-immobilized aromatic amines were reacted with various ketones and aliphatic aldehydes using an unconventional Pictet-Spengler reaction to generate polycyclic imidazo[1,5-a]quinoxalines. Alternatively, aromatic aldehydes afforded auto-oxidized imidazo[1,5-a]quinoxalines first which further converted to novel methyl N-phenylbenzimidats unexpectedly during the cleavage of the IL-support. In the reported strategy, rapidness is achieved through microwave conditions while the IL-support assists purification by simple precipitation.
Regioselective synthesis of imidazo[1,5-a]quinoxalines and methyl N-phenylbenzimidats on an ionic liquid support
(2016-01-01)
Chen, Li-Hsun
;
Kao, Chih-Hsien
;
Dhole, Sandip
;
Barve, Indrajeet J.
;
Shen, Li-Ching
An ionic liquid (IL) supported, regioselective synthesis of imidazo[1,5-a]quinoxalines and methyl N-phenylbenzimidats under microwave conditions was reported. The IL-immobilized aromatic amines were reacted with various ketones and aliphatic aldehydes using an unconventional Pictet-Spengler reaction to generate polycyclic imidazo[1,5-a]quinoxalines. Alternatively, aromatic aldehydes afforded auto-oxidized imidazo[1,5-a]quinoxalines first which further converted to novel methyl N-phenylbenzimidats unexpectedly during the cleavage of the IL-support. In the reported strategy, rapidness is achieved through microwave conditions while the IL-support assists purification by simple precipitation.
Regioselective Synthesis of Pyranone-Fused Indazoles via Reductive Cyclization and Alkyne Insertion
(2018-03-01)
Wu, Tz-Yi
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Dhole, Sandip
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Selvaraju, Manikandan
;
Sun, Chung-Ming
;
應用化學系
A novel and efficient method for the one-pot synthesis of 2H-indazole from readily available building blocks is reported. The reaction of 2-nitrobenzylamines with zinc and ammonium formate underwent partial reduction to nitroso-benzylamine followed by an intramolecular cyclization to afford 2H-indazole via N-N bond formation. The carboxylic acid moiety of indazole was proceeded to regioselective alkyne insertion under ruthenium catalysis to form pyranone-fused indazoles. The regioselectivity is influenced by the weak coordination of indazole ring nitrogen to the metal center.
Three Component Divergent Reactions: Base-Controlled Amphiphilic Synthesis of Benzimidazole-Linked Thiazetidines and Fused Thiadiazines
(2016-10-07)
Selvaraju, Manikandan
;
Dhole, Sandip
;
Sun, Chung-Ming
;
應用化學系
;
Department of Applied Chemistry
A divergent reaction of 2-aminobenzimidazole with isothiocyanates and dihalomethanes has been developed for the selective synthesis of benzoimidazothiazetidine and benzoimidazothiadiazine. A single-pot reaction of 2-aminobenzimidazole in the presence of sodium hydride delivers benzoimidazothiazetidine, whereas triethylamine promotes the formation of benzoimidazothiadiazine via a sequential stepwise, fashion. The reaction sequence involves the initial formation of thiourea followed by regioselective nucleophilic addition and intramolecular ring-closing with dihalo electrophiles. The observed regioselectivity,of this reaction is governed by the nature of bases and the reaction sequence.