Novel Strategies For The Synthesis Of N-heterocyclic Carben Precursor Imidazolinium Salts And Their Applications

N-heterocyclic carbens (NHCs) have been found extensive applications in catalytic asymmetric synthesis probably due to their high stability, easy preparation and high efficiency. As a kind of most common NHCs, imidazolidin-2-ylidenes have been receiving more and more attention on their novel synthetic methodologies and catalytic activity. This thesis mainly introduced our novel strategies for the synthesis of N-heterocyclic carbene precursor heterocycle salts. The thesis mainly includes:1. The properties, development history, and common synthetic methods of NHCs and their applications in catalysis were reviewed;2. A new method using formamidine and epoxide to prepare a-amidino alcohols was explored and developed for the facile preparation of imidazolinium salts by triflic anhydride mediated intramolecular cyclisation. A range of backbone-substituted, chiral or achiral imidazolinium salts were synthesised and then characterized by NMR, HRMS, optical rotation, X-ray single crystal diffraction and HPLC etc. The mechanism was proposed to explain the experimental phenomenons such as regioselectivity;3. Further research was carried out to find another way for the preparation of backbone-multisubstituded imidazolinium salts. The synthetic methodologies were convenient and versatile for the preparation of various backbone-substituted imidazolinium salts by triflic anhydride mediated intramolecular cyclisation. The products were characterized by NMR, HRMS and X-ray single crystal diffraction etc. Based on the previous theory and our observation, the mechanism was aslo proposed to explain the experimental phenomenons such as regioselectivity and stereoselectivity;4. The preliminary test was carried out to exanmine the application of backbone-mono substituted N-heterocyclic carben precursor imidazolinium salts in catalysis.