Studies On Metalloporphyrins Catalyzed Oxidation Reactions And Asymmetric Catalysis Using Chiral N-Heterocyclic Carbenes

Catalytic oxidation and asymmetric catalysis have attracted intensive interest from both organic chemists and industry. This thesis includes two parts: (1) A series of porphyrins and metalloporphyrins were synthesized and evaluated for their catalytic oxidation activity;(2) A series of chiral N-heterocyclic carbenes (NHC) and their transitional metal complexes were designed and synthesized, and their applications in catalyzed asymmetric reactions were investigated. The research results are summarized as follows:1. A new method for the selective oxidation of saturated hydrocarbons to ketones using the Fe(TPP)Cl/chloramine-T/O₂ system has been developed. It was found that chloramine-T (0.5 equiv) combining with oxygen as oxidant could selectively convert benzyl and allyl methylenes into ketones using Fe(TPP)Cl (5 mol%) as catalyst at room temperature in CH₃CN. This system is also efficient to the oxidation of alcohols. Compared with the published methods, our procedure has some advantages, such as high selectivities and very mild reaction conditions.2. Ten porphyrins and metalloporphyrins linked with stable nitroxyl radials were synthesized, and evaluated for the catalyzed epoxidation of olefins, the catalyzed oxidation of sulfides to sulfoxides, and the catalyzed oxidation of alcohols to aldehydes or ketones. It was found that manganese porphyrins linked with stable nitroxyl radials could selectively oxidized sulfides and alcohols using NaOCl as the oxidant to give sulfoxides and aldehydes or ketones, respectively.3. Three chiral N-heterocyclic carbenes derived from the naturally occurred podophyllotoxin were synthesized. They coordinated with [(η³-allyl)Pd(Br)]₂ to obtain NHC-Pd-allyl complexes, which were stable to water and air. The structure of NHC-Pd-allyl complexes was unambiguously established by X-ray single crystal analysis. These chiral NHC and NHC-Pd-allyl complexes were found to be able to catalyze the substitution reaction of allylic compounds, giving high conversions and enantioselectivities (up to 82% e.e.). It was also found that the chiral NHC combined with Rh₂(OAc)₄ could catalyze the addition of phenylboronic acid to 4-bromobenzaldehyde with moderate enantioselectivity (40%e.e.).4. Three chiral N-heterocyclic carbenes derived from cinchonine were synthesized. They coordinated with [(η³-allyl)Pd(Br)]₂ to give NHC-Pd-allyl complexes. These chiral NHC were found to be able to catalyze the substitution reaction of allyliccompounds, giving moderate enantioselectivities (51% e.e.).