Synthesis of Chiral C2-Symmetric Methylene- and Boron-Bridged Bis(imidazolines)

Abstract

A series of C 2-symmetric boron-bridged bis(imidazolines) was obtained by lithiation of 2-imidazolines and subsequent reaction with dialkyl- or diarylhaloboranes. The corresponding 2-imidazolines were prepared by an efficient four-step sequence starting from N-tert-butoxycarbonyl-protected α-amino acids. C 2-Symmetric methylenebis(imidazolines) were readily synthesized from chiral diamines by condensation with diethyl malonimidate. The bis(imidazolines) were used as ligands in the enantioselective cyclopropanation of styrene and allylic oxidation of cyclic alkenes.