The present invention relates to a process for linking two molecules by means of a Diels Alder reaction with inverse electron requirement (DARinv), comprising the following steps: reaction of a (a) triazine or tetrazine with one or more electron-attracting substituents on the ring as a diene component, the electron-attracting substituents being selected from: COOR C(O)NR2 CX3 (X=halogen) halogen CN SO2—R or SO3—R PR2 wherein R═H, alkyl, aryl, heterocycle, which in turn may be substituted, where appropriate, with alkyl, OH, SH, halogen, aryl, heterocycle, nitro, carboxyamido or amine group. —heterocyclic rings having 1, 2 or 3 N, O or S atoms with a ring size of 5 or 6 ring members, which are substituted with at least one carboxyl, sulfonic acid or phosphone group with (b) an isolated double bond or triple bond in a (hetero)carbocyclic ring or an isolated olefinic double bond or triple bond in a linear or branched hydrocarbon chain which may also contain heteroatoms, where appropriate, as a dienophile component.