CONVERSION OF AZIRIDINE-2-CARBOXYLIC ESTERS INTO 2H-AZIRINE-2-CARBOXYLIC ESTERS

Aziridine-2-carboxylic esters 1 were converted into 2H-azirine-2-carbo xylic esters 4 in two steps. Treatment of 1 with tert-butyl hypochlori te in ether gave smooth N-chlorination. Reaction of N-chloroaziridines 2 with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or 1,4-diazabicyclo[2 .2.2]octane (DABCO) gave 2H-azirine-2-carboxylic esters 4 in moderate yields, with concomitant formation of aziridines 1. Aziridines 1 could readily be N-brominated with N-bromosuccinimide. Treatment of N-bromo aziridines 3 with base, however, did not lead to azirine formation. N- Halogenated aziridines 2, and 3 exist as mixtures of invertomers, whic h slowly interconvert in solution.