Sirvi Kuupäev , alustades "2009-10-02T07:15:47Z" järgi

Filtreeri tulemusi aasta või kuu järgi

Nüüd näidatakse 1 - 1 1

Applications of mischmetal in organic synthesis
(2009-10-02T07:15:47Z) Vellemäe, Eerold
Thus, main goal of this doctoral thesis was to investigate usability of the MM as a main reagent in various applications in the organic synthesis, where MM has been activated with easily available activators with simple, reproducible and cheap procedure. During our studies we found that MM remains inert without some kind of activation prior to the reaction and trimethylsilyl chloride (TMSCl) and TiCl4 were found to be the best activators for our purposes. In the pinacol coupling of imines we demonstrated that when using MM for the pinacol coupling of imines the corresponding reaction occurred only in the THF and the presence of small amounts of water was requited for successful reaction. Without water no reaction occurred. This is an interesting fact, because in the other studies where only MM has been investigated, the water interfered the reaction. Appling MM in the Reformatsky-type reaction with azo-compounds was found that the desired reaction did not occur for any of the studied azo-substrates. Instead of the Reformatsky-type addition product complex mixtures and simple hyrdazines or their silylated forms were formed in the reaction. In our investigations of the cleavage of the Troc and Tos protective groups from the wide range of substrates we employed TMSCl/MM or TiCl4/MM system in dry THF. The removal of the Troc group was fast and very selective, even in the presence of other reactive moieties in the target molecule. We also discovered that the cleavage rate of the Troc group can be influenced by the adjacent functional groups. Similar phenomenon was also observed for the case of the Tos group. In order to cleave the Tos protecting group with the best possible results, the TiCl4 had to be used instead of the TMSCl for the MM activation. However, use of TiCl4 lowered selectivity of the reaction, leading to the cleavage of protecting groups present in the substrate alongside the Tos group. In summary, we have described several new applications of MM in several different reactions. During our work we proved that MM could be successfully applied in the organic synthesis as a main reagent without using expensive reagents.