| Metalloporphyrins, which are recognized as a class of versatile catalysts, havegreater stability and more superior catalytic efficiency than other catalysts for theirbig conjugate π electron system, variable metal valence and the ability of axialcoordination. Among them, the chiral metalloporphyrin catalysts can directly catalyzenon-functional compounds and get some optical target products, such as epoxide,hydroxyl compound and so on. Considering sugar and sugar derivatives andporphyrins were active substance in living organism, a series of glycoconjugatedmetalloporphyrins were synthesized and used as asymmetric catalysts for theepoxidation of olefins with iodobenzene diacetate. The effect of acetylated glucosesubstituted metalloporphyrins with different structure on the epoxidation reactionswere investigated. The main contents included the following several aspects:(1)15acetylated glucose substituted porphines have been synthesized byMacdonald and Lindsey method with pyrrole and appropriate glycosylatedbenzaldehydes as raw materials. Then glycoconjugated metalloporphyrins wereprepared, respectively, from corresponding porphines and metal salt inCH2Cl2/CH3OH or DMF under reflux. All porphyrin complexes were confirmed by1H-NMR spectroscopy, UV-Vis spectroscopy and Elemental analysis.(2) The UV-Vis absorption spectrum and Fluorescence emission spectrum ofglucose substituted porphines were measured. The results showed that differentnumber of acetylated sugar groups were linked to ortho or meta or para position ofeach phenyl group of tetraphenylporphyrin and increased by1,2,3,4, the absorptionwavelength of the Soret band and Q band of UV-Vis spectrum and the maximumemission wavelength of Fluorescence spectra all exhibited1-3nm bathochromic shift,at the same time, the fluorscence quantum yield decreased. When the sa me number ofchiral groups were on the different position of meso-phenyl groups and changed fromortho position to meta to para position, the maximum absorption wavelength showed1-2nm red shift and the fluorscence quantum yield increased.(3) The influence of glycoconjugated metalloporphyrins with different structureon the styrene epoxidation was studied. The research showed that the catalyticactivity of glycosylated manganese porphyrins was superior to that of iron porphyrins.Ortho-glycosylated manganese porphyrin catalysts17,21,23and26afforded styrene epoxide with S configuration, as the number of chiral groups increased by1,2,3,4,the ee values increased from10.5%,17.8%,20.33%to24.5%. However, the meta orpara-glycosylated manganese porphyrins showed no significant asymmetric induction,a maximal enantiomeric excess of6.5%was obtained; Another interestingphenomenon was that manganese porphyrin catalysts bearing the same number ofacetylated glucose substituents at different position of each meso-phenyl group wereused to epoxidize styrene, as the location of chiral moieties changed from paraposition to meta to ortho position, the ee values also increased; Using atropoisomersof glycosylated metalloporphyrins as catalysts obtained similar ee values in theepoxidation of styrene. For example, glycosylated manganese porphyrins26had threeatropoisomers26a,26b,26c, when they were separately used as catalyst,22.0%,23.2%,24.7%ee values were obtained.(4) Upon the oxidation system of chiral metalloporphyrins-PhI(OAc)2-styrene,we expanded the substrate to styrene derivatives and studied the influence ofelectronic effect of substituents of phenyl ring and the cis-trans structure of olefins onthe enantioselective alkenes epoxidation reactions. The research indicated thatelectron-deficient olefins were efficiently epoxidized in moderate ee values, incontrast, electron-rich alkenes were epoxidized to epoxides showing lower yields andenantioselectivies; the trans-olefins epoxidation reactions obtained higher ee’s thanthat of cis-olefins. |
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