Detail The development of asymmetric catalytic reactions and application to synthesis Bibliografi Author: Schaus, Scott Edward ; Jacobsen, Eric N. (Advisor) Topik: CHEMISTRY; ORGANIC Bahasa: (EN )    ISBN: 0-599-64063-4     Penerbit: Harvard University Press     Tahun Terbit: 2000     Jenis: Theses - Dissertation Fulltext: 9960514.pdf (0.0B; 0 download) Abstract The hydrolytic kinetic resolution of racemic 1,2-terminal epoxides with water, catalyzed by a chiral (salen)Co(III)OAc complex, provides access to both enantiopure 1,2-terminal epoxides and enantioenriched 1,2-diols. The reaction scope has been investigated, and a procedure for practical access to recovered epoxides (>99% ee) and enantioenriched 1,2-diols has been determined. The krel or each substrate has been calculated by enantiomeric excess measurement at low conversion of the epoxide. The robust nature of the catalyst allows for its reisolation at the end of the experiment and subsequent use in multiple kinetic resolution reactions. The procedure developed provides practical access to chiral building blocks that had not been previously available.* The asymmetric hetero-Diels-Alder reaction of aldehydes and 1-methoxy-3-[(trimethylsilyl)oxy]-1,3-butadiene is catalyzed by chiral (salen)Cr(III) complexes. Optimization of the metal counterion, ligand and the reaction conditions allowed for the production of the corresponding dihydropyranones in optically active form employing 2 mole% of the catalyst. Some of the products were recrystallized to enantiomeric purity. Investigation of the reaction indicated the sole presence of the [4+2] cycloaddition product, independent of a Mukaiyama aldol intermediate.* The total synthesis of muconin has been completed by the efficient assembly of chiral building blocks. The completion of the synthesis illustrates the utility of the hydrolytic kinetic resolution (HKR) of terminal epoxides catalyzed by a chiral (salen)Co(III) complex and the asymmetric (salen)Cr(III) catalyzed hetero-Diels-Alder condensation of 1-methoxy-3-[(trimethylsilyl)oxy]-1,3-butadiene with aldehydes. The introduction of four of the eight stereocenters from readily accessible chiral building blocks makes the outlined synthesis easily amenable to stereochemical and structural analogs.* The ring opening of epoxides with TMSCN is catalyzed by lanthanide salts. The ring opening of chiral 1,2-terminal epoxides with TMSCN was successfully accomplished using 5 mole% LaCl3·6H2O in THF at room temperature. The asymmetric ring opening of meso-epoxides with TMSCN catalyzed by (pybox)YbCl3 complexes was accomplished in good enantioselectivities (83–92% ee) to yield the β-trimethylsilyloxy nitrile ring-opened products. The reaction exhibits a second-order dependence on catalyst concentration and first-order dependence on epoxide concentration. The qualitative and kinetic evidence indicates the possibility of a bimetallic pathway.* *Please refer to dissertation for diagrams. Opini Anda Klik untuk menuliskan opini Anda tentang koleksi ini! Lihat Sejarah Pengadaan  Konversi Metadata   Kembali

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