Highly Efficient Ultrasound Promoted Synthesis of 2-phenylquinoxaline in Glycerol- Water

Introduction: Quinoxalines show diversified applications in the field of medicinal chemistry. Materials and Methods: Therefore, we have designed a highly efficient, environmentally benign and one-pot protocol for the synthesis of 2-phenylquinoxaline from the reaction of Acetophenone, N-bromosuccinimide and 1,2-phenylenediamine under ultrasound irradiation in glycerol-water. Results and Discussion: We observed that, although the reaction efficiently completed in all of these solvents, the use of glycerol-water with different ratios gives consistently higher yields (89–94%) and decreases reaction times. Conclusion: The main advantages of this protocol are that it is a green method, avoids the use of toxic catalysts and volatile organic medium and the product is obtained with excellent yield. </jats:sec

Environmentally Benign PEG-OSO3H-Catalysed Ultrasound Promoted Cascade Synthesis of Furocoumarins in Water

Background: For the green synthesis of furocoumarins in water, PEG-OSO3H was used as a recyclable catalyst for the one-pot synthesis in water. To avoid the use of toxic lachrymators and unstable phenacyl bromides, we prepared them in-situ and directly condensed with 4-hydroxycoumarins. Objective: PEG-OSO3H was found to be an efficient and reusable catalyst for the microwave irradiated one-pot synthesis of 3-Aryl-furo[3,2-c]coumarins in PEG-water as a greener reaction medium. This method was found to be rapid, simple, eco-friendly and obtained relatively higher yield than other reported methods. Methods: Aromatic ketones (5 mmol), NBS (5mmol) were added in the solution of PEG-OSO3H (10 mol%) in 10 ml water and irradiated under ultrasound at 80-85°C. Then, the solution of 4- hydroxycoumarin (5 mmol) and the solution of acetic acid and ammonium acetate (1 ml) were added into it. The reaction mass was further irradiated for 3 min. From the reaction mixture, ethyl acetate (3 x 10ml) was extracted and the combined ethyl acetate phase was concentrated under reduced pressure to obtain corresponding 3-Aryl-furo[3,2-c]coumarins. The aqueous layer was reused for the next reactions. Results: It was observed that electrons withdrawing groups (-NO2,-F etc.) on the benzene ring of aromatic ketones increased the rate of reactions as well as the yield of the products. The IR spectrum of compound 4a showed prominent peaks at 1737cm-1C=O stretching for lactone. 1H NMR of compound 4c showed characteristic singlets for –CH3 of methoxy group at 3.94 ppm. The above spectral data confirmed the structure of the compound. The 13C NMR spectrum of 4b also showed the peaks of CH3, at 23.25 ppm. Conclusion: PEG-OSO3H has been found to be an efficient and reusable catalyst for the microwave irradiated one-pot synthesis of 3-Aryl-furo[3,2-c]coumarins in PEG-water as a greener reaction medium. This method found to be rapid, simple, eco-friendly and obtained relatively higher yield than other reported methods. </jats:sec

Microwave-promoted One-pot Synthesis of Imidazo[1,2-a]pyridines in Lemon Juice

Objective: A simple and highly efficient microwave-promoted procedure for the synthesis of imidazo[1,2-a]pyridine derivatives from the reaction of aromatic ketones, N-bromosuccinimide, and 2-aminopyridines in lemon juice was designed. The main advantages of this protocol, such as clean reaction profile, mild reaction condition, high yield, and minimum reaction time, were compared to other previously developed methods. Method: A mixture of aromatic ketones (1a-m) (0.005 m), N-bromosuccinimide (NBS) (0.005 m), and lemon juice (10 ml) was irradiated by microwave at 400-watt power at 85°C, and the formation of α- bromoketones was monitored by Thin Layer Chromatography (TLC). After completion of α-bromination, 2-aminopyridines (0.005 m) was added to the reaction mixture and it was further irradiated at the same reaction condition. After completion of the reaction, the reaction mass was poured in ice-cold water, the solid product obtained was filtered, washed with cold water, and recrystallized from aqueous ethanol. Result: In the present investigation, we have developed an environmentally benign, easy, and highly efficient one-pot procedure for the synthesis of 2-phenylimidazo [1, 2-a] pyridines from the reaction of aromatic ketones, N-bromosuccinimide, and 2-aminopyridines in lemon juice as a natural acid catalyst and solvent under microwave irradiation. This new protocol offers very attractive features such as minimum reaction time, clean reaction profile, mild reaction condition, and green aspects such as avoid poisonous catalyst, hazardous solvents, ease of the work-up procedure, and higher yield. Conclusion: In the present investigation, we have developed an environmentally benign, easy, and highly efficient one-pot procedure for the synthesis of 2-phenylimidazo [1, 2-a] pyridines from the reaction of aromatic ketones, N-bromosuccinimide, and 2-aminopyridines in lemon juice as a natural acid catalyst and solvent under microwave irradiation. This new protocol offers very attractive features such as minimum reaction time, clean reaction profile, mild reaction condition, and green aspects such as no need for a poisonous catalyst and hazardous solvents, ease of work-up procedure, and higher yield. </jats:sec

Withdrawal Notice: Ionic Liquid Mediated Synthesis of Schiff bases Bearing Thiazole and Indole Moieties

The article has been withdrawn at the request of the authors and editor of the journal "Current Organic Synthesis." Bentham Science apologizes to the readers of the journal for any inconvenience this may cause. The Bentham Editorial Policy on Article Withdrawal can be found at https://benthamscience.com/editorial-policies-main.php Bentham Science Disclaimer: It is a condition of publication that manuscripts submitted to this journal have not been published and will not be simultaneously submitted or published elsewhere. Furthermore, any data, illustration, structure or table that has been published elsewhere must be reported, and copyright permission for reproduction must be obtained. Plagiarism is strictly forbidden, and by submitting the article for publication the authors agree that the publishers have the legal right to take appropriate action against the authors, if plagiarism or fabricated information is discovered. By submitting a manuscript, the authors agree that the copyright of their article is transferred to the publishers if and when the article is accepted for publication. </jats:sec

Synthesis of novel antimicrobial 7-But-2-ynyl-1-(substituted-benzyl)-3-methyl-8-morpholin-4-yl-1H -purine-2,6-diones

In this study, we synthesized 7-But-2-ynyl-3-methyl-8-morpholin-4-yl-3,4,5,7-tetrahydro-purine-2,6-diones from 8-Bromo-7-but-2-ynyl-3-methyl-3,4,5,7-tetrahydro-purine-2,6-dione and morpholine using lithium hydroxide and DMSO as a medium. We further coupled 7-But-2-ynyl-3-methyl-8-morpholin-4-yl-3,4,5,7-tetrahydro-purine-2,6-dione with different halo compounds to obtain various derivatives. These synthesized compounds were then tested for their antimicrobial activities against S. aureus, B. subtilis, S. typhi, and E. coli

Synthesis of 3-methyl-4H-benzo[b][1,4]thiazine-2-carboxylates Using CAN as a Catalyst and Its Conversion Into Guanidines

Background: 1,4-benzothiazine carboxylates show wide application in the field of medicinal chemistry. Therefore, we have designed convenient and efficient method for the synthesis of 1,4-benzothiazine carboxylates. Objective: Synthesis of 1,4-benzothiazine carboxylates and its guanidines by simple and facile method using efficient catalyst. Methods: Derivatives of 1,4-benzothiazine carboxylates were synthesized by cyclocondensing β- keto esters with 2-aminobenzenethiols using CAN as a catalyst at room temperature. 1,4-benzothiazine carboxylate, condensed with guanidine hydrochloride in the presence of sodium methoxide in DMF to obtained new 3-substituted-l-4H-benzo[b][1,4]thiazine-2-carboxyguanidines (88-91%). Results: All the products were obtained with good to excellent yields within 40 min. Here, CAN oxidizes aminothiophenol into disulfide and then nucleophilic attack of enolic form of β-ketoesters on the disulphide and 1, 4-benzothiazine acetates, were obtained with good yields. Conclusion: We have designed convenient and efficient method for the synthesis of 1,4-benzothiazine carboxylates. Most remarkable features of this cyclocondensation such as use of efficient catalyst and non-volatile solvent under mild reaction condition to obtain excellent yield. </jats:sec