Synthesis of Novel Chiral Bisoxazoline Ligands Containing 2,5-Diaryl-1,3,4-oxadiazole and Enantioselective Cyclopropanation of Styrene

Abstract

Practical synthesis of chiral C ₂-symmetric substituted bisoxazoline ligands containing 2,5-diaryl-1,3,4-oxadiazole units was investigated. Five chiral bisoxazoline ligands containing 2,5-diphenyl-1,3,4-oxadiazole have been synthesized from 2,5-di-(o-carboxylphenyl)-1,3,4-oxadiazole and amino alcohols by methanesulfonyl chloride or p-toluenesulfonyl chloride assisted cyclization via hydroxy amide intermediate. Preliminary examination of copper complexes of new ligands as chiral catalysts in the enantioselective cyclopropanation of styrene with ethyl diazoacetate was performed. Enantioselectivities up to 35% ee and 87% ee for trans- and cis-2-phenylcyclopropanecarboxylate, respectively were observed.

Key words

bisoxazoline - oxadiazole - enantioselective cyclopropanation

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1

Visiting scholar of Wenzhou Medical College, Wenzhou 325003, Zhejiang P.R.China.

19

Crystallographic data (excluding structure factors) for the structures in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication numbers CCDC 182921 & 182922 Copies of the data can be obtained free of charge on application to CCDC 12 Union Road Cambridge CB2 1EZ UK [fax:[phone] or e-mail: [e-mail]].