A transition-metal-free, base-promoted annulation/ring-cleavage/ring-reconstruction cascade reaction: a facile access to N-protection free indole-indenones

Abstract

A one-step, transition-metal-free, base-promoted cascade reaction of 2-halogenated arylglyoxals with 2-oxindoles is reported herein, which provides a straightforward approach to structurally diverse N-protection free indole-indenones in satisfactory yields. Control experiments indicated that the geminal bisindolin-2-one intermediate played a crucial role in the downstream annulation/ring-cleavage/ring-reconstruction reaction sequence. This novel reaction not only further enriches the reactivity of indolin-2-ones as the recursive enolate anion source, but also achieves thermal-induced α-arylation of oxindoles without a transition-metal catalyst.