Synthesis of novel chiral bisoxazoline ligands containing 2,5-diaryl-1,3,4-oxadiazole and enantioselective cyclopropanation of styrene

Practical synthesis of chiral C₂-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.