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Chiral C2 Symmetric NHC: Synthesis and Catalytic Properties

Author: DanFengJun
Tutor: LiZhengNing
School: Dalian University
Course: Organic Chemistry
Keywords: Imidazole salt Imidazolinium salts N - heterocyclic carbenes Synthesis Catalytic Conjugate Addition Conjugate reduction
CLC: O643.36
Type: Master's thesis
Year: 2011
Downloads: 45
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Abstract


Nitrogen-containing heterocyclic carbene (NHC) and its metal complexes chemistry is a new field for the past two decades developed. NHC ligand as a novel, they can transition metal ion coordination to form stable complexes in a variety of catalytic reactions in exhibit unique charm which chiral NHC and its metal complexes in symmetric catalytic reactions play an increasingly important role, showing the important academic value. In this thesis, we designed a chelate of C2 symmetry type five, six-membered NHC's precursor, its ring oxygen atom of the substituents of the nitrogen atom with a potential ligand, may be formed after the removal of a proton multi teeth NHC ligand chelate formed when the metal coordination is likely to get a higher selectivity in catalytic asymmetric reactions. Because of their special coordination ability with traditional organic phosphine ligands in the catalytic reaction with machine phosphine ligands complementary. The following different routes the synthesized the NHC precursor imidazole having the above structural features of the salts, imidazolinium salts, tetrahydropyrimidine salt. These routes include: (1) a chiral amino alcohol (ether) the feedstock with diethyl oxalate in the reaction to form amide, and then LiAlH4 restore amide obtained diamine, and finally with ethyl orthoformate, ammonium fluoroborate (chlorinated ring closure is formed, the role of the ammonium, etc.) imidazolinium salts the seven; (2) to the amino alcohol as raw materials, with 1,2 - dibromoethane reaction diamine, and then with ethyl orthoformate, ammonium fluoroborate (ammonium chloride etc.) role ring closure forming the three kinds of imidazolinium salts; (3) lactic acid esters (or mandelic acid esters), as raw materials, phenol ether, reducing an ester to an alcohol, p-toluene sulfonylation, bromo, and finally reacted with imidazole to give the imidazole salt six; (4) phenyloxirane and imidazole in the reaction under the conditions of pressure, to give the imidazole salt of one kind; (5) for the synthesis of an amine and glyoxal carbodiimide, and then paraformaldehyde, TMSCl to ring closure, to give two kinds of imidazole salt; (6) similar to route (2), but using 1,3 - dibromoethane, to give a six-membered ring of 3,4,5,6 - tetrahydropyrimidine salt six. The reaction between the amino alcohol with glyoxal to give the bisoxazoline spiro compound, rather than not obtain the expected product diamine. The synthesis of imidazole (morpholine) salts, chelated NHC pyrimidine salt generated by deprotonation is used in catalytic reactions. Imidazole (Morpholino) salt in situ formation of diethylzinc NHC-Cu-catalyzed asymmetric conjugate addition reaction of cyclohexanone (e) ketene. Imidazoline salt, high chemical yield (99%) and reasonable ee value (78%). Use a different base, the configuration of the advantages of the product will change. Imidazole (morpholine) salt, pyrimidine salt - compound alkali-Cu (I) formed in situ is also capable of catalyzing the reduction reaction of silicon hydride reagent conjugated α, β-unsaturated ketone. The imidazolium salts formed catalyst showed good catalytic activity and selectivity enables the selectivity of the reaction was completed within 5 min, and restore only one of the carbon-carbon double bond, a nearly quantitative yield reduction product.

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CLC: > Mathematical sciences and chemical > Chemistry > Physical Chemistry ( theoretical chemistry ),chemical physics > Chemical kinetics,catalysis > Catalytic > Catalyst
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