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28th March 2018 @ 09:35

Method:

2-chloro-6-(2-hydrazinyl(2-hydroxybenzylidene))pyrazine (134 mg, 0.54 mmol, 1.00 equiv.) was dissolved in dry DCM (30 mL) forming an orange solution. Diacetoxyiodobenzene (174 mg, 0.54 mmol, 1.00 equiv.) was added and the solution stirred at room temperature under an inert atmosphere for approximately 3.5 hours upon which it slowly turned a dark red colour. TLC analysis showed the reaction had not reached completion, so the solution was heated to ~35 ˚C for ~1 hour forming a near black solution. The solution removed from stirring and exposed to the atmosphere overnight, forming a pale yellow solution. The solution was quenched with saturated aqueous Na2CO3 solution (20 mL) and extracted with DCM (2 × 10 mL). The combined organic layers were washed with saturated brine solution (20 mL), dried over MgSO4, filtered and concentrated to give a crude product as a brown oil. The crude product was analysed by 1H NMR and what was thought to be the desired product was purified by flash column chromatography (EtOAc) and isolated as a brown oil (7 mg). NMR analysis of this sample showed no presence of any product, only many peaks due to impurities and was therefore inconclusive as to the identity of the product.


Attached Files
22nd March 2018 @ 16:25

Method:

2-chloro-6-(2-hydrazinyl(benzylidene))pyrazine) (40.0 mg, 0.172 mmol, 1.0 equiv.) was dissolved in dry dichloromethane (15 mL) forming a yellow solution. Diacetoxyiodobenzene (PIDA) (55.4 mg, 0.172 mmol, 1.0 equiv.) was then added and the solution was stirred at room temperature under nitrogen for approximately 16 hours. After this time, the reaction mixture was exposed to air and analysed by TLC (1:1 EtOAc: PET ether) showing a clear product peak. The reaction mixture was quenched by the addition of a saturated aqueous solution of sodium hydrogen carbonate (~15 mL). Aqueous layers were separated and then extracted with DCM (2 x 15 mL). The organic layers were combined and washed with brine (1 x 20 mL), dried with MgSO4, filtered and evaporated in vacuo, yielding the crude product as a fine yellow powder (22.5 mg, 56.5%). The crude product was characterised using 1H NMR and IR. The product was purified using a silica column and the pure product (yellow solid) was obtained in vacuo (19.7 mg, 49.5%). The product was characterised by 1H NMR, 13C NMR, DEPT 90 + 135, GC-MS and IR.


Attached Files
22nd March 2018 @ 14:50

Method:

2-chloro-6-(2-hydrazinyl(4-bromobenzylidene))pyrazine) (C) (100.2, 0.322 mmol, 1.0 equiv) was dissolved in dry dichloromethane (15 mL) forming a pale yellow solution. Diacetoxyiodobenzene (PIDA) (114 mg, 0.354 mmol, 1.1 equiv) was then added and the solution was stirred at room temperature under nitrogen for approximately 16 hours. After this time, the reaction mixture was exposed to air and analysed by TLC (pure EtOAc) showing a clear product peak as well as some residual PIDA. The reaction mixture was quenched by the addition of a saturated aqueous solution of sodium hydrogen carbonate (~15 mL). Aqueous layers were separated and then extracted with DCM (2 x 15 mL). The organic layers were combined and washed with brine (1 x 20 mL), dried with MgSO4, filtered and evaporated in vacuo, yielding the crude product as pale yellow crystals (69.6 mg, 70.2%). The crude product was characterised using 1H NMR, 13C NMR, DEPT 90 + 135, GC-MS and IR. The purified product was isolated using a silica plug since TLC showed the presence of the product and PIDA with significant separation.


Attached Files
22nd March 2018 @ 14:49

Method:

2-chloro-6-hydrazinopyrazine (A) (100.00 mg, 0.70 mmol, 1.00 equiv.) was dissolved in EtOH (10 mL) forming a bright yellow solution, to which 4 bromobenzaldehyde (B) (141 mg, 0.76 mmol, 1.1 equiv.) was added. The reaction was stirred for a further 3.5 hours and was monitored by TLC. During this time, a yellow precipitate formed. The reaction mixture was filtered under vacuum to give 2-chloro-6-(2-hydrazinyl(4-bromobenzylidene))pyrazine) as a yellow powder (111.3 mg, 51.6%) which was characterised by IR and 1H NMR.TLC of the showed the reaction had gone to completion.


Attached Files
22nd March 2018 @ 14:45

Method:

2-chloro-6-hydrazinopyrazine (202.0 mg, 1.39 mmol, 1.00 equiv.) was partially dissolved in EtOAc (30 mL) forming a yellow solution before addition of 2-hydroxybenzaldehyde (0.2 mL, 1.92 mmol, 1.2 equiv.). The reaction was heated under reflux under a Dean-Stark trap for 1 hour, darkening the solution slightly, however no water was collected in the trap. After 1 hour at reflux, a TLC of the reaction mixture revealed that the reaction had reached completion. The solvent was removed in vacuo giving an orange powder which was shown to contain 2-hydroxybenzaldehyde, desired product, and an unknown side product. The powder was recrystallized from boiling ethanol to give yellow needle like crystals (123 mg). The crystals were analysed by NMR and IR spectroscopy and mass spectrometry to determine that they were salicylaldehyde azine formed by a side reaction with free hydrazine impurities in the 2-chloro-6-hydrazinopyrazine. The filtrate was therefore collected and concentrated in vacuo giving an orange powder (209 mg) analysed by NMR and IR spectroscopy to contain 2-chloro-6-(2-hydrazinyl(2-hydroxybenzylidene))pyrazine and salicylaldehyde azine in a 2:1 molar ratio.


Attached Files