[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.