Pd-Catalyzed Dearomative Carboxylation of Indolylmethanol Derivatives.

By using a new catalytic system (PdCl2[P( n-Bu)3]2 in combination with ZnEt2), various 3-indolylmethanol derivatives were successfully carboxylated with CO2 (1 atm) via dearomatization of the indole nucleus, affording 3-methyleneindoline-2-carboxylates. In contrast, carboxylation of 2-indolylmethanol derivatives afforded unexpected doubly carboxylated products, which are useful synthetic precursors for biologically active compounds.