Preparation of new chiral bisoxazoline ligands for the catalytic asymmetric intramolecular cyclopropanation of α-diazo-β-keto phenyl sulfone to afford a useful bicyclo[3.1.0]hexane derivative

Herein we describe the preparation of novel chiral bisoxazoline ligands with various substituents at the bisoxazoline linkage, for use in the catalytic asymmetric intramolecular cyclopropanation (CAIMCP) of α-diazo-β-keto phenyl-5-hexenyl sulfone to afford a simple, but useful, bicyclo[3.1.0]hexane derivative. The enantioselectivity of the CAIMCP of α-diazo-β-keto phenyl-5-hexenyl sulfone was improved and a product with 84% ee was obtained using 30 mol % of the catalyst, which was prepared in situ by CuOTf and the new bisoxazoline ligand with two 3,5-di-tert-butylbenzyl groups at the bisoxazoline linkage. The product was obtained in enantiomerically pure form by a single crystallization, enabling its use as a chiral building block.