Preparation of bicyclic boroxazolidones from aziridine-2-carboxylic esters

Abstract

Aziridine-2-carboxylic esters 1 were converted into bicyclic boroxazolidones 3 in a three-step sequence. First, the ester groups were hydrolyzed either by sodium hydroxide or with lithium hydroxide in methanol. The salts thus obtained were acidified with acetic acid or through a weakly acidic ion-exchange resin. Treatment of the zwitterionic aziridine-2-carboxylic acids 2 with triethyl-borane in hexane gave boroxazolidones 3 in high yields. Boroxazolidone 3g, obtained from optically active 1g was reconverted to the starting material by 8-hydroxyquinoline without any loss of optical activity.