Synthesis Of Asymmetric 1,3-diynes With The Cul/L- Proline System Catalyzed From Bromoallene

1,3-diynes are divided into symmetric 1,3-diynes and asymmetric 1,3-diynes which have attracted widespread attention due to their unique structures, containing two conjugated triple bonds. Such compounds are not only important intermediates or raw materials in organic synthesis, but also widely present in the natural physiological active substances. Therefore, the development of efficient synthetic methods and technologies of 1,3-diynes has been a hot topic.Currently the main synthesis methods of 1,3-diynes are Glaser oxidative coupling, Cadiot-Chodkiewicz reaction, and their main raw materials are alkynes and its derivatives. It have not been reported that bromoallenes as substrates through isomerization to give asymmetric 1,3-diynes.This paper provides a new method with bromoallenes as raw materials under CuI/ L-proline catalyzed to give asymmetric 1,3-diynes.The method has mild reaction conditions, simple operation, moderate yields and the asymmetric 1,3-diyne 2a have not been reported.The optimal reaction conditions:Bromo allenes (0.2 mmol), CuI (0.04 mmol), L-proline (0.08 mmol), Cs2CO3 (0.8 mmol), DMSO (1 mL),60 ℃,4 h. Under the optimal reaction conditions the highest yield of asymmetric 1,3-diynes is 72%.This paper preliminary study and provide a possible reaction mechanism and the key steps are as follows:(1) Cuprous iodide and L-proline generate complex (2) Bromoallenes isomerize to more stable conjugated dienes structure (3) Iodine ions are oxidized to iodine, which participate in the addition of double bonds with other nucleophiles.The synthesized asymmetric 1,3-diynes (2a) is applied to synthesis pyrrole and the yield is up to 91%.