Sterically Controlled Ru(II)-Catalyzed Divergent Synthesis of 2‑Methylindoles and Indolines through a C–H Allylation/Cyclization Cascade

A ruthenium-catalyzed
synthesis of 2-methylindole was accomplished
via a C–H allylation/oxidative cyclization cascade. Strategically,
β-hydride elimination from the σ-alkyl-Ru intermediate
has been suppressed by steric hindrance from a remote position. Hence,
2-methylindolines from the corresponding ortho-substituted
anilines were achieved via protodemetalation in lieu of β-hydride
elimination under a modified reaction condition. This mild intermolecular
annulation cascade proceeds smoothly by a redox-neutral ruthenium
catalyst without stoichiometric metal oxidants, such as silver­(I)
or copper­(II) salts, providing excellent functional group tolerance.