An optically active N-protected azetidine-2-carboxylic acid (5) can be produced by preparing an optically active 4-amino-2-halobutyric acid (3) by halogenating an optically active 3-hydroxy-2-pyrrolidinone (1) with inversion of configuration to prepare an optically active 3-halo-2-pyrrolidinone (2) followed by hydrolysis or by halogenating an optically active 4-amino-2-hydroxybutyric acid ester (6) with inversion of configuration to prepare an optically active 4-amino-2-halobutyric acid ester (7) followed by hydrolysis or by halogenating the compound (6) with inversion of configuration to prepare the compound (7), cyclizing the same to prepare the compound (2) followed by hydrolysis, further cyclizing the compound (3) followed by treating the reaction product with an amino group-protecting agent. The thus-obtained compound (5) can be improved its optical purity further by recrystallization ##STR00001##

Compounds of formula (I), wherein A is an unsubstituted or substituted aromatic or non-aromatic, monocyclic or bicyclic heterocyclic radical wherein a ring nitrogen atom may have been replaced by a group ##STR2## R.sub.1 is hydrogen or C.sub.1 -C.sub.3 alkyl; R.sub.2 is hydrogen or C.sub.1 -C.sub.3 alkyl; R.sub.3 is hydrogen, an unsubstituted or substituted C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.6 cycloalkyl C.sub.2 -C.sub.6 alkenyl or C.sub.2 -C.sub.6 alkynyl group, or C(.dbd.O)--R.sub.5, R.sub.5 is C.sub.1 -C.sub.4 alkyl C.sub.1 -C.sub.4 alkoxy, an unsubstituted or substituted phenyl, phenoxy or benzyloxy group, or N(R.sub.6).sub.2, each R.sub.6, independently of the other, is hydrogen, C.sub.1 -C.sub.4 alkyl or unsubstituted or substituted phenyl, X is CH--NO.sub.2, N--CN or N--NO.sub.2 and n is from 1 to 3, in free form or in salt form, and, where appropriate, tautomers of those compounds and the salts thereof, can be used as agrochemical active ingredients and can be prepared in a manner known per se.

Compounds of formula: ##STR1## wherein A is an unsubstituted or substituted aromatic or non-aromatic, monocyclic or bicyclic heterocyclic radical wherein a ring nitrogen atom may have been replaced by a group ##STR2## R.sub.1 is hydrogen or C.sub.1 -C.sub.3 alkyl; R.sub.2 is hydrogen or C.sub.1 -C.sub.3 alkyl; R.sub.3 is hydrogen, an unsubstituted or substituted C.sub.1 -C.sub.6 alkyl, C.sub.3 -C.sub.6 cycloalkyl, C.sub.2 -C.sub.6 alkenyl or C.sub.2 -C.sub.6 alkynyl group, or C(.dbd.O)--R.sub.5, R.sub.5 is C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, an unsubstituted or substituted phenyl, phenoxy or benzyloxy group, or N(R.sub.6).sub.2, each R.sub.6, independently of the other, is hydrogen, C.sub.1 -C.sub.4 alkyl or unsubstituted or substituted phenyl, X is CH--NO.sub.2, N--CN or N--NO.sub.2 and n is from 1 to 3, in free form or in salt form, and, where appropriate, tautomers of those compounds and the salts thereof, can be used as agrochemical active ingredients and can be prepared in a manner known per se.

Compounds of formula ##STR1## wherein A is an unsubstituted or substituted aromatic or non-aromatic, monocyclic or bicyclic heterocyclic radical wherein a ring nitrogen atom may have been replaced by a group ##STR2## R.sub.1 is hydrogen or C.sub.1 -C.sub.3 alkyl; R.sub.2 is hydrogen or C.sub.1 -C.sub.3 alkyl; R.sub.3 is hydrogen, an unsubstituted or substituted C.sub.1 -C.sub.3 -C.sub.6 alkyl, C.sub.6 cycloalkyl, C.sub.2 -C.sub.6 alkenyl or C.sub.2 -C.sub.6 alkynyl group, or C(.dbd.O)--R.sub.5, R.sub.5 is C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, an unsubstituted or substituted phenyl, phenoxy or benzyloxy group, or N(R.sub.6).sub.2, each R.sub.6, independently of the other, is hydrogen, C.sub.1 -C.sub.4 alkyl or unsubstituted or substituted phenyl, X is CH--NO.sub.2, N--CN or N--NO.sub.2 and n is from 1 to 3, in free form or in salt form, and, where appropriate, tautomers of those compounds and the salts thereof, can be used as agrochemical active ingredients and can be prepared in a manner known per se.

This invention relates to a method of using compounds selected from those of the following formula: ##STR1## wherein R.sup.1 is hydrogen, alkyl or alkenyl; R.sup.2 is hydrogen, alkyl, cycloalkyl or mononuclear aryl or R.sup.1 and R.sup.2, taken together with the carbon atom to which they are attached, form a cycloalkyl or cyloalkoxyalkyl; R.sup.3 is hydroxy, alkyl, alkoxycarbonyl, hydroxy lower alkyl or a radical of the formula: --C(.dbd.Y)NR.sup.4 R.sup.5 wherein R.sup.4 is hydrogen, alkyl, or alkenyl, R.sup.5 is alkyl, alkenyl carbalkoxy, or mononuclear aryl, or R.sup.4 and R.sup.5 may be joined together with the nitrogen atom to which they are attached to form a 5- to 7-membered heterocyclic ring having from 1 to 3 hetero atoms; Y is O or S; X is alkyl, alkoxycarbonylalkyl or cyano; m is an integer of 0 to 2 and n and n' are integers each having a value of 1 to 2 and the dotted line indicates an optional carbon to carbon double bond, compositions containing said compounds as insect repellents and to novel compounds.