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Either the C2- or the C3-substituted product can be obtained with the same palladium(II) catalyst in an oxidative intermolecular alkenylation of indoles. A variety of conditions can be used for derivatization at the 3-position; however, the presence of acetic acid is required for the C2-selective process (see scheme). Further elaboration of the products by a similar CH functionalization process leads to the bisalkenylated indoles selectively.
Grimster et al. (Tue,) studied this question.