In Situ Assembled Boronate Ester Assisted Chiral Carboxylic Acid Catalyzed Asymmetric Trans-Aziridinations

We developed herein a new chiral
Brønsted acid catalyst which
is composed of two independent organic molecules, a chiral diol, and
2-boronobenzoic acid. In situ formation of a boronate ester was utilized
as a key process to generate an active catalyst. This boronate ester
assisted chiral carboxylic acid catalyst was successfully applied
to the trans-aziridination of N-Boc and N-benzyl imines with N-phenyldiazoacetamide. This
is the first catalyst to achieve high enantioselectivities using N-benzyl imines.