We found a novel de-acylation reaction of 3-acetyl-4-bromoindole-2-carboxylate catalyzed by BF3•OEt2 at rt. This reaction proceeded with various 4-substituted 3-acetylindole-2-carboxylates, but for the 4-unsubstituted one, the 3-acetyl group was not removed under any condition. So we examined various acyl groups for the 4-unsubstituted indole-2-carboxylates. We found that a pivaloyl group is de-acylated by BF3•OEt2 at rt. Next, we examined various electrophilic substitutions of ethyl 3-pivaloylindole-2-carboxylate in order to develop a new protecting group for the 3-position of indoles. Expectedly, in bromination and nitration, the benzene-part substituted products were obtained in good yield. The products are de-acylated to give the benzene-part substituted indole-2-carboxylates by BF3•OEt2 at rt. This result shows that the pivaloyl group could be applied as a new protecting group for the C3-position of the indoles.
