Abstract (eng)
Heterocycles and heteroatom containing molecules in general are essential substructures of synthetically valuable compounds, such as pharmaceuticals and industrially relevant bulk and fine chemicals. Hence, their easy and atom-efficient synthesis starting from simple, commercially available precursors plays a pivotal role in modern synthetic chemistry. The borrowing hydrogen strategy (BH) and related approaches, including acceptorless dehydrogenative couplings (ADH) and oxidative dehydrogenative coupling reactions (ODC), provide outstanding opportunities for a variety of transformations of alcohols and amines, in particular the formation of new carbon-carbon or carbon-nitrogen bonds. The overall goal of this thesis was the extension of the applicability of these methods. Thus, one strategy was to identify and optimize suitable cascade reactions promoted by abundant metal catalysts in combination with organocatalysis. The first part of this research was focused on the switchable N alkylation of anilines with benzylic alcohols, catalyzed by the nitrile-ligated variant of the Knölker complex. Hence, an enantioselective one-pot, three-component condensation to form alpha-alkylamino phosphonates (yields up to 83 %, 50 % ee) was developed. For that purpose, a sequential iron-catalyzed dehydrogenative condensation was combined with a hydrophosphonylation step, promoted by a chiral BINOL-based phosphoric acid. Secondly, the reaction scope of the highly active PN3 manganese pincer complex, prepared in situ starting from the bipyridine-derived ligand bpy-6NHiPrP and Mn(CO)5Br, was extended. Thereby, on the one hand the coupling of 2-aminobenzyl alcohols with nitriles to form 2-aminoquinolines could be performed using noticeable low catalyst (1 mol%) and base loadings (10 mol%). On the other hand, the first selective synthesis of 1,2,3,4-tetrahydroquinolines (yields up to 91 %) starting from 2-aminobenzyl alcohols and secondary alcohols via homogeneous catalysis was established. The third approach comprised the synthesis, characterization and investigation of new manganese PN3-pincer complexes. Thus, a novel acyl manganese catalyst was formed upon complexation of phen-2NHiPrP with the MeMn(CO)5 metal precursor. The complex showed remarkable stability and catalytic activity under atmospheric conditions. Particularly noteworthy is the N-alkylation of aniline with benzyl alcohol under air, in which a conversion of 61 % was achieved.