ISSN print edition: 0366-6352 ISSN electronic edition: 1336-9075 Registr. No.: MK SR 9/7 Published monthly

Synthesis of unsymmetric 1,3-diynes from bromoallenes using the catalysis of CuI and amino acid

Wenfang Jiang, Guanghua Shao, Ying Liu, and Xin Du

College of Chemistry, Dalian University of Technology, Dalian, China

E-mail: yingliu1013@ipe.edu.cn

Received: 25 June 2019  Accepted: 14 October 2019

Abstract:

Unsymmetric 1,3-diynes were synthesized by using bromoallenes as the starter substrates over the catalysts of CuI and amino acid. l-Proline was chosen as the amino acid as a suitable ligand of CuI. Inorganic bases, especially Cs₂CO₃, obviously facilitated the reaction. After screening the reaction solvents, such as CH₂Cl₂, DMF, Et₂O, C₆H₅CH₃, THF, CH₃CN, DMSO and CH₃C(O)CH₃, DMSO was chosen as the best reaction solvent, and within the solvent, the yield of unsymmetric 1,3-diynes could achieve the good value of 72%. Under optimum conditions of CuI/l-proline, Cs₂CO₃ and DMSO, bromoallenes with methyl-, bromo- or chloro-groups in the para-position of aromatic rings gave more than 61% yields of unsymmetric 1,3-diynes. When bromoallenes had the ortho- or meta-bromine groups, the reaction failed and there were no products. The mechanism of formation of unsymmetric 1,3-diyne was also proposed as both processes of isomerization and subsequent elimination, which were catalyzed by the coupling of CuI with l-proline.

Graphic Abstract:

Scheme 1 Graphic abstract for the synthesis of unsymmetric 1,3-diynes

Keywords: Bromoallenes; Unsymmetric; 1,3-Diynes; CuI/amino acid

Full paper is available at www.springerlink.com.

DOI: 10.1007/s11696-019-00962-z

Chemical Papers 74 (4) 1367–1373 (2020)