Browsing by Author "Chang, Wong-Jin"

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Base Controlled Three-Component Regioselective Synthesis of 2-Imino Thiazolines and 2-Thioxoimidazolin-4-ones
(2019-04-01)
Barve, Indrajeet J.
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Chang, Wong-Jin
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Lin, Yen-Tzu
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Thikekar, Tushar Ulhas
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Sun, Chung-Ming
Base-controlled regioselective synthesis of 2-imino thiazolines and 2-thioxoimidazolin-4-ones was achieved to use a one-pot reaction between chiral amino esters, isothiocyanates, and alpha-bromoketones/alkyl halides. This three-component coupling reaction in acetonitrile provides 2-imino thiazolines, whereas the formation of 2-thioxoimidazolin-4-ones was observed under basic conditions at ambient temperature. The corresponding products were obtained in good to excellent yield with broad substrate scope. Isolation of thiourea and thiohydantoin intermediates disclosed the course of the reaction mechanism.
Microwave assisted straightforward synthetic method for benzimidazole linked quinoxalinones on soluble polymer support
(2011-03-18)
Chou, Cheng-Ting
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Yellol, Gorakh S.
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Chang, Wong-Jin
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Sun, Mei-Lian
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Sun, Chung-Ming
The simple and efficient method was developed for the synthesis of benzimidazole linked quinoxalinones on soluble polymer support using microwave conditions. The acid catalyzed condensation of 4-fluoro-3-nitrobenzoic acid with polymer immobilized o-phenylenediamine, ipso-fluoro nucleophilic substitution with various primary amines and cyclization with acetyl chloride are the key steps involved in implemented linear synthesis. In key cyclization step, the regioselective N-acylation at secondary amine with chloroacetyl chloride followed by spontaneous intramolecular ring closure through ortho-amine functionality generate the quinoxaline skeleton under microwave irradiation. The removal of polymer support and exposure of quinoxalines for auto-oxidation finally produce the benzimidazole linked quinoxalinone derivatives with high purity and yields. (C) 2011 Elsevier Ltd. All rights reserved.
Microwave-Assisted Synthesis of Tetracyclic 2,5-Diketopiperazines on a Soluble Polymer Support: A Structural Analogue of Tadalafil
(2009)
Chang, Wong-Jin
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Chanda, Kaushik
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Sun, Chung-Ming
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應用化學系
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Department of Applied Chemistry
Structural analogues of tadalafil that contain two diversity points have been synthesized from a soluble polymer support employing a Pictet-Spengler reaction using focussed microwave irradiation. Polymer-bound deprotected tryptophan reacts with various aldehydes to generate the tetrahydro-beta-carbolines on the support. Subsequently immobilized tetrahydro-beta-carboline underwent a highly efficient intramolecular N-heterocyclization in a traceless fashion from various in-situ generated alpha-alkyl and heteroalkyl amides in two steps to generate tetracyclic 2,5-diketopiperazines in high purity. All the compounds were isolated as cis and trans isomers with good yields.
Microwave-assisted traceless synthesis of hydantion-fused beta-carboline scaffold
(2007-11-26)
Yeh, Wen-Pin
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Chang, Wong-Jin
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Sun, Mei-Lian
;
Sun, Chung-Ming
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應用化學系
Multistep microwave-assisted reactions toward the synthesis of hydantoin-fused tricyclic tetrahydro-beta-carbolines on the soluble polymer support have been developed. Polymer-bound tryptophan with various aldehydes has been subjected to Pictet-Spengler reaction to obtain tricyclic beta-carboline conjugates. The terminal hydantoinyl moiety is constructed across polymer-bound beta-carbolines by the reaction with various isocyanates under microwave irradiation to form urea intermediate. Simultaneous intramolecular cyclization of urea followed by cleavage of the polymer support leads to a traceless synthesis of tetracyclic scaffolds in high yield and high purity. (c) 2007 Elsevier Ltd. All rights reserved.
Regioselective one-pot three component synthesis of chiral 2-iminoselenazolines under sonication
(2015-01-01)
Chang, Wong-Jin
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Kulkarni, Manohar V.
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Sun, Chung-Ming
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應用化學系
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Department of Applied Chemistry
A one-pot multi component reaction of selenoureas, which are in situ generated from L-amino esters and isoselenocyanates, with alpha-bromoketone under ultrasonication. Selenourea and alpha-bromoketones formed 2-iminoselenazoles through a Hantzsch selenazole-type reaction. The steric effect of the alpha-substituted bromoketones on the rate of the tandem reaction was studied to understand the reaction mechanism by isolating the key reaction intermediate, 2-iminoselenol.