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Chapter 3 Synthesis of trisubstituted pyrazoles/isoxazoles 3.8 Experimental section Thin-layer chromatography was accomplished on 0.2-mm precoated plates of silica gel G60 F 254 (Merck). Visualization was made with UV light (254 and 365nm) or with an iodine vapor. IR spectra were recorded on a FTIR-8400 spectrophotometer using DRS prob. 1 H (300 MHz), 1 H (400 MHz), 13 C (75 MHz) and 13 C (100 MHz) NMR spectra were recorded on a Bruker AVANCE II spectrometer in CDCl 3 and DMSO. Chemical shifts are expressed in δ ppm downfield from TMS as an internal standard. Mass spectra were determined using direct inlet probe on a GCMS-QP 2010 mass spectrometer (Shimadzu). Solvents were evaporated with a BUCHI rotary evaporator. Melting points were measured in open capillaries and are uncorrected. General synthesis of 3-cyclopropyl-3-oxo-N-arylpropanamide (3a-o). A mixture containing the primary amine (1a-h, 10 mmol), methyl 3- cyclopropyl-3-oxopropanoate (2, 10 mmol), and catalytic amount of sodium or potassium hydroxide (10 %) in toluene (50 mL) was reflux at 110 o C for the approximately 12-15 h. The reaction was monitored by TLC. After completion of reaction, the solvent was removed under vaccuo and the solid or oil was crystallized from methanol which afforded pure products. General synthesis of ketene dithioacetals (4a-o). A 100mL conical flask equipped with magnetic stirrer and septum was charged with a solution of 3-cyclopropyl-3-oxo-N-arylpropanamide (3a-o, 10 mmol) in DMF (10 mL). Dried K 2 CO 3 (20 mmol) was added and the mixture was stirred for 2 h at room temperature. CS 2 (10 mmol) was added and the mixture was stirred for an additional 2 h at room temperature. Methyl iodide (20 mmol) was added at 0-5 o C and the mixture was stirred for 4 h at room temperature. The reaction was monitored by TLC. After completion, the mixture poured into water (40 mL). The precipitated crude product was purified by filtration followed by crystallization from EtOH. When the product was oil, the organic phase was extracted with Et 2 O (3 × 10 mL). The combined organic extracts were washed with H 2 O (2 × 10 mL), dried (MgSO 4 ), and concentrated in vaccuo to afford ketene dithioacetals directly used for the next step. Department of Chemistry <strong>Saurashtra</strong> university, Rajkot-360005 101
Chapter 3 Synthesis of trisubstituted pyrazoles/isoxazoles General procedure for the synthesis of trisubstituted pyrazoles5a-o. ‣ Conventional method: A 25mL conical flask equipped with magnetic stirrer and septum was charged hydrazine hydrate (15 mmol) and various ketene dithioacetals (3a-o, 10 mmol) and heated up to 75-85 o C for appropriate times (Table-1). After completion of the reaction, the reaction mixture was allowed to come to room temperature and add cold water (50 mL). The separated suspension was filtered, washed with water, dried and crystallized from methanol to afford analytically pure products with 80-90% yield. ‣ Microwave assisted method: A one neck flat bottom flask charged with the hydrazine hydrate (15 mmol), and various ketene dithioacetals 3a-o (10 mmol), was heated at 90 o C under microwave irradiation for appropriate time (Table-1). After completion of the reaction, the reaction mixture was allowed to attain room temperature and added cold water (50 mL). The suspension was filtered, washed with water, dried and crystallized from methanol to afford analytically pure products with 85-95% yield. General procedure for the synthesis of trisubstituted isoxazoles6a-o. ‣ Conventional method: A 25mL conical flask equipped with magnetic stirrer and septum was charged with hydroxyl amine hydrochloride (15 mmol), potassium hydroxide (15 mmol) and various ketene dithioacetals (3a-o, 10mmol) and heated up to 75-85 o C for appropriate times (Table-1). After completion of the reaction, the reaction mixtures were cooled to room temperature and add cold water (50 mL). The separated solid was filtered, washed with water, dried and crystallized from methanol to afford analytically pure products with 80-90% yield. ‣ Microwave assisted method: A one neck flat bottom flask charged with hydroxyl amine hydrochloride (15 mmol), potassium hydroxide (15 mmol) and various ketene dithioacetals 3a-o (10 mmol) and reaction mixture heated at 90 o C under microwave irradiation for appropriate time (Table-1). After completion of the reaction, the reaction mixture was allowed to come to room temperature and add cold water (50 mL). The separated solid was filtered, washed with water, dried and crystallized from methanol to afford analytically pure products with 85-95% yield. Department of Chemistry <strong>Saurashtra</strong> university, Rajkot-360005 102
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Saurashtra University Re - Accredit
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Statement under O.Ph.D.7 of Saurash
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I am thankful to FIST/DST and SAP/U
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Chapter 4 Synthesis and Characteriz
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Chapter - 1 Palladium Catalyzed Syn
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Chapter 1 Synthesis of functionaliz
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Chapter - 2 Synthesis and Biologica
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Chapter 2 Synthesis of substituted
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Chapter 6 Synthesis of benzodiazepi
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pyrazole derivative were faster and
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Conferences participated 1. “15 t
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