[1+5] Cyclization of Indoline‐Derived Azadienes with 1,3,5‐Triazinanes: An Efficient Protocol for the Synthesis of Indoline‐Spiro‐Hexahydropyrimidines

An unprecedented formal [1+5] cyclization of indoline‐derived azadienes with 1,3,5‐triazinanes has been realized, providing a facile access to biologically important indoline‐spiro‐hexahydropyrimidines with good to excellent yields (up to 99% yield). Different from previous reports, this is the first study that indoline‐derived azadienes could participate in cyclizations as one‐atom synthons. This methodology is also distinguished by not involving any additive or catalyst, readily available starting materials, wide range of substrate applicability, operational simplicity and simultaneously reassembling two C‐N and two C‐C bonds in one‐step reaction.