The issue of stereochemical control in multicomponent reactions and glycosylation processes.

Multicomponent reactions (MCRs) are processes that show high atom and step economy; two different parts of my thesis were linked by MCRs. In the first part, levulinic acid was converted into a variety of bicyclic nitrogen heterocycles passing by an Ugi reaction. The obtained intermediate was then converted in the final product via a simple SN2 cyclization. The second part, instead, was dedicated to the obtainment of organo-catalysts structurally based on secondary and tertiary amine groups. First attempts, to get the latter in bicyclic structures, involved a starting MCR with L-prolinol, but the reaction showed low diastereoselectivity and the cyclization failed. A different strategy was aimed to obtain secondary amines and resulted to be more efficient. The involvement of a seven-membered cyclic imine, with a chiral center in C-3, in a Ugi-Joullié reaction resulted in a very diastereoselective process. Using a silyl oxy derived carboxylic acid, an Ugi adduct with a protected alcohol is obtained. Thus, an intramolecular cyclization can be performed producing the final free amine group. The obtained amine was used to perform the first catalysis tests in Michael and aldol reactions. Although no catalytic activity was detected, different reaction conditions and structures have still to been tested. Finally, the reaction mechanism in self-promoted glycosylations was investigated. They involve a trichloroacetimidate as glycosyl donor which is activated by an acceptor that contains an acid sulfonamide portion. An alcoholic function was added to the acceptor with a consecutive possible production of both O- and N-glycosides. Dissociative mechanism favors the first while an associative mechanism brings to the second. The study showed the chemoselectivity and, to some extent, the stereoselectivity of the reaction to be controlled by tuning the parameters e.g. the polarity of the solvent, the concentration of donor and acceptor and the use of additives such as lithium salts.