Competing concepts in CAOS

The evolution of Computer-Assisted Organic Synthesis (CAOS) is briefly reviewed. The underlying concepts and strategies of the various approaches to CAOS are compared. A status report is given on bilateral synthesis design. This requires selection of suitable starting materials from a list of available compounds according to structural features of the target by correlation of substructures, augmentation of the target molecule by co-products to yield an Ensemble of Molecules (EM) that is isomeric to the starting EM and, finally, establishment of synthesis routes that lead from the starting EM to the target EM. Despite of its apparent complexity, bilateral CAOS is a promising approach because of its combinatorial advantages.