which are important for obtaining cationic liposomes for gene therapy. The most common methods for the synthesis of urethanes are the reaction between chloroformates and amines'O and the Curtiusrearrangement of acyl azides," followed by reaction of the isocyanates with alcohols. The route involving the reaction of chlorofoxmates with amines has been improved by the use of N-ca rbakoxy imids~J* easily obtained