In the field of organic chemistry, the development of new catalytic methods for the synthesis of complex molecules from simple precursors is a top priority. The main focus of this thesis concerns the diastereoselective synthesis of heterocyclic compounds using main group elements as Lewis acid catalysts.

The first part of this thesis deals with an annulation reaction of nitrones with oxiranes, aziridines, and thiiranes using Al(III) or In(III) catalysts. From this protocol, 1,4,2-dioxazinanes, 1,2,4-oxadiazinanes, and 1,4,2-oxathiazinanes were obtained in moderate to high yields with excellent diastereoselectivity. The transformation was found to be stereospecific and proceed via an S_N2-mechanism.

The second and third parts concern the development of In(III)-catalyzed annulation of carbonyl compounds, amines, and alkynyl enones. InBr₃ was found to be an efficient catalyst for the activation of alkynyl enones in a multicomponent reaction with aldehydes and amines. The method affords cyclopenta[c]furans in high yields and in good to excellent diastereomeric ratios. Bicyclo[3.n.1]alkenone derivatives were formed via a double Michael addition reaction of cyclic ketones, amines, and alkynyl enones, in the presence of InCl₃. The utility of these protocols was also demonstrated by sequential transformations.

In the fourth part, AgOTf and CuI were found to be efficient catalysts for the activation of pyridine-substituted enynes towards enamines, providing indolizine derivatives in high yield and good diastereomeric ratios.

In the last part of the thesis, 1,2-aminoarylation of γ,δ-unsaturated oxime esters with arylboronic acids using Ni catalysis is discussed. The protocol demonstrates the potential of Ni-catalysts for the generation of iminyl radicals to furnish functionalized pyrroline derivatives. The utility of this protocol was exemplified by transforming the pyrroline products to the corresponding pyrrole and pyrrolidine derivatives. 

The nitrogen atom plays a unique role in organic chemistry. It is abundantly found in organic materials and is responsible for the activity of many biologically relevant compounds. In this thesis, nitrosoarenes and keto- and pyridyl-substituted enynes are used as convenient starting materials for the selective synthesis of nitrogen-containing compounds.

Nitrosoarenes are versatile compounds that can undergo a broad range of reactions. The nature of the nitroso group is significantly different from that of related nitrogen-based functional groups and this can be used as an advantage in the development of new methodology. In the first part of this thesis, the para-selective halogenation of nitrosoarenes with copper(II) halides as halogenating reagents is explored. The one-pot transformation of the products to the corresponding nitroarenes and anilines is demonstrated. The use of nitrosoarenes for radical N-perfluoroalkylation is presented in the next chapters. N-Perfluoroalkylation is a relatively new field and only a limited number of reagents and substrates have been employed so far. In this thesis, the stable and convenient Langlois reagent was used to achieve selective N-trifluoromethylation of nitrosoarenes to obtain the corresponding hydroxylamines. Longer perfluoroalkyl chains were investigated as well, but the less stable products were defluorinated to form hydroxamic acid derivatives. These products could be reduced to yield perfluoroalkyl amides.

Keto- and pyridyl-substituted enynes are starting materials designed to undergo cyclization reactions in the presence of a metal catalyst and a nucleophile. This offers the possibility to obtain a variety of more complex molecular structures in a single step. In the second half of the thesis, the reaction between these starting materials and enamines is explored. A range of cyclopenta[c]furans were synthesized in good yields and with high diastereoselectivities from alkynyl enones and enamines with InBr₃ as the catalyst. The enamines were formed in situ in a multicomponent reaction. Pyridyl-substituted enynes are the pyridine analogues of alkynyl enones and were found to form polycyclic indolizines in the reaction with cyclic enamines with AgOTf as a catalyst. Good yields and high to excellent diastereoselectivities were obtained. When the reaction was performed with in situ-generated enamines, different indolizine derivatives were obtained.