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o‐Diaminobenzene derivatives react smoothly with ortho‐esters in the presence of 0.5 mol% of Yb(OTf)3 under solvent‐free conditions to afford the corresponding benzimidazole derivatives in good to excellent yields. In addition, Yb(OTf)3 can be easily recovered almost quantitatively from the aqueous layer after the reaction was completed, and it could be reused with no loss of activity.
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Wang et al. (2004) studied this question.
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