NBS-induced intramolecular annulation reactions for the divergent synthesis of fused- and spirocyclic indolines.

An NBS-induced intramolecular annulation of 3-(1 H -indol-3-yl)- N -alkoxypropanamide is described. The reactions proceed well and quickly under mild conditions with the help of a base. It was found that C2-substituents on the indole ring in 3-(1 H -indol-3-yl)- N -alkoxypropanamide have a great influence upon the reaction. By using C2-methyl- and C2-phenyl-3-(1 H -indol-3-yl)- N -alkoxypropanamide as templates, practical protocols for the divergent synthesis of fused- and spirocyclic indoline compounds were studied and established.