《Table 2 Preparation of 1- (pyrazin-2-yl) guanidine derivatives 3》

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《"Facile Synthesis of [1,2,4]Triazolo[4,3-a]pyrazin-3-amines via Oxidative Cyclization of 1-(Pyrazin-2-yl)guanidine Derivatives"》

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a Reaction conditions described in the table were as follows:A.Guanidine carbonate（3 equiv.），K 2 CO 3（5 equiv.），NMP，130°C；B.Guanidine carbonate（3 equiv.），NaHCO 3（5 equiv.），NMP，120°C；C.A strong base NaOH（5 equiv.）was used，and the temperat

With these promising results in hand，we performed the optimization procedure of the cyclization reaction with various parameters，including temperature，solvent，and base，the results of which are provided in Table 1.From the table，we can see that the yield of 5a increases as the temperature increases from 30–45°C while maintaining the same alkali ratio and solvent（entries 1 to 4）.A further increase in temperature results in a decrease in yield（entry 5）.By changing the alkali ratio while keeping the same solvent and temperature，we observed an increasing yield trend up to a 3.1 equivalent of aq.K 2 CO 3（entries 7，4，and 8）and then a decrease in yield with a further increase in the alkali ratio（entry 9）.By replacing the solvent and base entity with those used in our aforementioned study，an unsatisfactory yield often results for 5a，with less than 20%（entries 6 and10–14）.We achieved a maximum yield of 37.4%by maintaining a 3.1 equiv.of aq.K 2 CO 3（5 mL H 2 O）in methanol at 45°C.