Construction of C2‐Spirocyclopropyl‐Indolin‐3‐Ones through Base‐Promoted [2+1] Annulation Reaction of Indolin‐3‐ones with Bromosulfonium Salts

Abstract A simple base‐promoted [2+1] annulation of indolin‐3‐ones and bromosulfonium salts has been developed in this article. This strategy uses simple and easily prepared indolin‐3‐ones 1 as C1 synthons and bromosulfonium salts 2 as C2 synthons under mild reaction conditions, and 33 examples of C2‐spirocyclopropyl‐indolin‐3‐ones were obtained with up to 99 % yield and >20 : 1 dr.