Functional groups are prerequisites for the assembly of building blocks to more elaborate structures for research work in the life sciences field. Functionalization can be most conveniently and efficaciously accomplished by generating an organometallic deriv. of the arom. or heterocyclic starting material and subsequently treating it with the electrophile of choice. The presence of heterosubstituents facilitates immensely the introduction of the metal (by permutational halogen/metal or hydrogen/metal interconversion) and at the same time enables a perfect control of the desired regioselectivity as will be illustrated by typical examples selected from the indole, pyrazoles, pyridine and quinoline fields.