Yi Wen-bin
2007
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Journal
Fine chemicals
Abstract
2-(n-Propyl)-4-methyl-6-methoxycarbonylbenzimidazole(Ⅰ) is an important intermediate of telmisartan pharmaceutical.Methyl 3-methyl-4-butyrylamino-5-aminobenzoate was efficiently converted into Ⅰ in fluorous biphasic system(FBS) without acetic acid.It was found that Yb(OPf)3 and C10F18 were the best catalyst and fluorous solvent respectively for the reaction.Yield of Ⅰ could be up to 94% at 80 ℃ for 2 h with x(Yb(OPf)3)=0.3%.By simple phase separation,the fluorous phase containing only the catalyst could be directly reused next time.Based on 19F NMR and UV-Vis and GC-MS data,no loss of catalyst or fluorous solvent to the organic phase can be detected,and no organic compounds can be found in the fluorous phase.There is no significant difference between the UV-Vis spectra of the initial and recovered fluorous phases,indicating that Yb(OPf)3 is recovered unaltered after the condensation reaction.The catalyst was completely(99%) recovered as determined by atomic emission spectrometry.The fluorous phase containing only catalyst can be reused up to ten times with only a slight decrease in yields from 94% to 90%.