Calcium- und Camphersulfonsäure katalysierte Cycloisomerisierung von Diinolen und Direkte reduktive N-Funktionalisierung von Nitroverbindungen

In this work with the topic „Calcium- and camphorsulfonic acid catalyzed cycloisomerization of diinols and direct reductive functionalization of nitro compounds” progress was made in two branches of organic chemistry. In the first part the first transition metal free cycloisomerization of readily available diinols was developed granting an efficient access to bicyclic 2H-pyranes and dienones. The transformation is enabled by a new, cooperative catalytic system, combining a simple Ca2+ catalyst with camphorsulfonic acid in the presence of benzaldehyde as a weakly Lewis-basic electron pair donor. Based on a computational DFT analysis, 1H-NMR-studys and control experiments a mechanistic proposal was developed pointing out a Z-selective isomerization of a formed allenenol intermediat via a 1,5-H-shift. Furthermore, this work provided deeper inside in the equilibrium between dienons and valence isomeric 2H-pyranes via an oxo-6π-electrocyclisation. In the second part of this work a direct reductive and general method for the selective multifunctionalization of aliphatic and aromatic nitro compounds under mild reaction conditions was successfully developed. Pointed out by detailed mechanistic studies the nitro moiety is transformed via a B2pin2 mediated twostep partial reduction to a stabilized nitronate and then to a nitrenoid, which is used in situ as the electrophilic amination reagent. Coupling of the nitrenoid with zinc organyls generates functionalized aminoboranes. The formed aminoboranes could successfully be reacted with several electrophiles enabling a selective introduction of a secondary function to the nitrogencenter. The direct harnessing of an oxidized nitrogenspecies without the detour to a reduced amine renders the process step- and redox-economically more benign in relation to established multistep approaches. Furthermore, the first oxidative functionalization of aminoboranes via a 1,2-N migration was realized. Thereby, aliphatic nitro compounds are transformed into N- and O-functionalized hydroxylamines in a single synthetic operation. Insertion of oxygen into the zinc-carbon bondof already present zincorganyls provides the necessary oxidant and circumvents the addition of explosive peroxides. Recycling of the organoboronic ester byproduct of the nitro to aminoborane transformation via a boron to zinc transmetalation keeps the amount of required zinc organyl minimal and even further increases the efficiency of the process. The presented procedure of the direct reductive N-functionalization could be further refined to the first ionic catalyst free reductive coupling of nitro and halogen compounds. In situ zinc metalation of readily available halogen compounds enabled the selective synthesis of highly functionalized aminoboranes, amines and even hydroxylamines starting from nitro compounds