In this book main approaches toward construction of complex polycyclic core structures of biomolecules are discussed. Successful implementation of the chosen strategies for the synthesis of symbioimines and platencine is shown. A Lewis acid induced intramolecular Diels-Alder (IMDA) reactions are used as the key steps in the formation of symbioimine and (+)-neosymbioimine iminium alkaloids. The enantioselective total synthesis of (+)-neosymbioimine was accomplished in 18 steps from (-)-(S)-citronellol utilizing an organocatalytic -oxidation. All double bonds of Diels-Alder substrate were made in a stereoselective manner by Wittig-type reactions. A concise formal synthesis of platencin was based on an efficient oxygen-mediated palladium-catalyzed cycloalkenylation to form a bicyclo[3.2.1]octane, and a deoxygenative rearrangement of tosylhydrazone to construct the bicyclo[2.2.2]octane in 17.5 % total yield for 13 steps from commercially available compounds.