Immunostimulant aziridine carboxylic acid derivs. - with substits. in 2-position

Prepn. of aziridine carboxylic acid derivs. of formula (I) comprises (a) reacting aziridines (II) with a haloformate hal. CO2.R (III); (b) treating a cpd. hal. H2C.C hal.N.CO2.R HX (IV) with a dehalogenating agent; or (c) by catalytic or photochemical denitrogenation of cpds. of formulae (V) or (VI). In the formulae, X is CN, CONH2 or alkoxycarbonyl R is satd. or unsatd. alkyl opt. substd. by >=1 halo, alkoxy NH2, carbamoyloxy, cycloalkyl, OH, imido, heterocyclic gp.; or an aryl, aralkyl, aryloxyalkyl or arylthioalkyl in which the aryl gp. may be substd. by halo, alkyl, alkoxy OH, NH2, NO2, CN, acyl, alkoxycarbonyl, thioalkyl, alkylsulphonyl, phenyl or CF3; and hal is Cl or Br. Cpds. (I) (where R is not Et when X is CN), are new, and are immunostimulants for use in bacterial and viral infections. Ethyl 2-cyanoaziridine-1-carboxylate is a valuable intermediate for prepn. of the 1-carboxamide.