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 C2spirocyclopropyl-indolin-3-ones were obtained with up to 99 % yield and > 20 : 1 dr.