In this thesis several novel postmodifiactions of regular Ugi-4CR products have been examined. Their scope and limitations were tested both by permutating the required functionalities around the Ugi scaffold and by synthesizing compound libraries for successful permutations. The following reactions were examined: 1. Radical cyclizations of Ugi-4CR products with o-halogenoaryl and alkene substituents. The Ugi-4CR scaffold was found to be stable under radical cylization conditions with Bu3SnH but not with (Me3Si)3SiH. 2. PdII/IV catalyzed oxidative cyclization of 1,6-enynes to substituted 3-aza-bicyclo[3.1.0]hexan-2-ones. 3. Cyclizations strategies for tetrazol-Ugi-4CR products of boc-hydrazine. 4. Improved synthesis of highly substituted indazolones with improved yields and a fourth point of diversity. 5. Cyclizations of Ugi-4CR products derived from 2-azidoethylamine by a Staudinger/aza-Wittig reaction sequence. In some cases the formation of the corresponding o-amidines was observed.