Domino Route toward 1,5-Diazocines from 1,4,5,6-Tetrahydropyrimidines and Propiolic Acid Derivatives via a Ring Expansion Strategy.

1,4,5,6-Tetrahydropyrimidines react with propiolic acid esters or amides to form pseudo-three-component adducts containing a 1,5-enyne fragment. Under the action of acid or acid chlorides, these adducts undergo a domino transformation initiated by an aza-Claisen rearrangement, leading to ring expansion from a six- to an eight-membered cycle, accompanied by formal enyne metathesis. The process represents a one-pot procedure for the synthesis of 1,5-diazocines from 1,4,5,6-tetrahydropyrimidines and propiolic acid derivatives under ambient conditions, affording the products in 39-80% overall yields.