Pyrroloindoline/Pyridoindoline Synthesis via C3-Dearomative Arylation/Cyclization of Tryptamine/Homotryptamine Derivatives Using Palladium-Dihydroxyterphenylphosphine Catalyst.

A palladium-dihydroxyterphenylphosphine (DHTP) catalyst was successfully applied to the dearomative C3-arylation of tryptamine derivatives with aryl nonaflates. The intramolecular cyclization of the resulting 3,3-disubstituted indolenines afforded C3a-arylated pyrroloindolines in one pot. We postulate that the formation of complexes between the lithium salts of DHTP and the tryptamine derivative is the key to promoting selective arylation at the C3-position of the indole ring. Furthermore, reactions using homotryptamine derivatives successfully provided C4a-arylated pyridoindolines.

Direct C3-Selective Arylation of N-Unsubstituted Indoles with Aryl Chlorides, Triflates, and Nonaflates Using a Palladium-Dihydroxyterphenylphosphine Catalyst.

A palladium-dihydroxyterphenylphosphine (DHTP) catalyst was successfully applied to the direct C3-arylation of N-unsubstituted indoles with aryl chlorides, triflates, and nonaflates. This catalyst showed C3-selectivity, whereas catalysts with other structurally related ligands exhibited N1-selectivity. Complex formation between the lithium salts of the ligand and the indole is assumed to accelerate the arylation at the C3 position. Reactions using 3-alkylindoles afforded 3,3-disubstituted indolenines, which can be further converted to the corresponding indoline derivatives.