N ‐Phenacylpyridinium Salts‐Involved Formal Cyclization Reactions to Access Spiro[cyclopropane‐1,3'‐indolines]

ABSTRACT

A novel formal (2 + 1) cyclization reaction between iminoindoline‐derived alkenes and N‑phenacylpyridinium salts has been developed to enable the efficient assembly of spiro[cyclopropane‐1,3'‐indolines] with excellent yields. A related one‐pot formal (1 + 1 + 1) cyclization reaction among iminoindolines, aldehydes, and N‑phenacylpyridinium salts has also been designed to construct the same spiroskeletons efficiently. The mild reaction conditions, the broad scope of substrates, and the promising scale‐up potential embody the synthetic superiority of these two processes.