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.