Eninole in Calcium-katalysierten Cycloisomerisierungsreaktionen und Bor-vermittelte elektrophile Aminierung von Nitroverbindungen

During this work experiments on two different fields in organic chemistry were carried out. In the first field, concerning cycloisomerisation reactions, the synthesis of complex structures out of simple 1,6-enynols was achieved with the help of a calcium catalyst developed in the Niggemann group. Based on a previously published calcium catalyzed cyclopropanation reaction, the equilibrium between a homoallenyl cation and his cyclopropyl congener was exploited. In a first project the homoallenyl cation was intercepted with different aldehydes to yield dihydro pyranes. Mechanistic studies allowed to propose two possible mechanistic scenarios for this transformation. In a second project the vinyl cation present in the cyclopropyl congener was stabilized via the introduction of an adjacent ether function. This allowed reaction of the vinyl cation with water as a nucleophile, yielding highly substituted cyclopentane derivatives. A strong influence of different groups on the reactivity of the enynol starting material was observed. After modification of the enynol substrates, the reaction of the homoallenyl cation with different nucleophiles was enabled. That is how the synthesis of exocyclic allenes was realized in another project. All of the mentioned reactions provide a greener and more sustainable alternative to previously know transition metal catalyzed reactions. The second field was concerned with the electrophilic amination of nitroarenes. In a first project, aromatic nitro compounds were transformed to functionalized amines via the reaction with a B2pin2-zinc organyl system. A two step partial reduction of the nitro moiety, lead to the formation of a nitronate and then a nitrenoid. This nitrenoid was used as electrophilic amination reagent for zinc organyls, yielding aminoboranes. These could be reacted with different electrophiles. Exhaustive mechanistic studies were carried out using in situ 11B-NMR and control experiments. A great variety of nitroaromatics, zinc organyls and electrophiles could be used for this reaction. In a second project, the reaction principle was transferred to aliphatic nitro compounds. The intermediacy of highly reactive nitroso compounds which are in equilibrium with the corresponding oxime and often entangled in side reactions was avoided. That is how also aliphatic nitro compounds could be converted to functionalized amines in high yields for the first time. The scope of nitro compounds and zinc organyls was broad for the aliphatic nitro compounds as well. In a third project the aminoboranes synthesized from nitroaromatics were reacted with carbenoids, yielding formanilides in low yields