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|Title:||Directed Ortho-Metalations of Benzyl Alcohols, Arenesulfonic Acids, and Thiophenol: New Methodology for Electrophilic Aromatic Substitutions and the Preparation of New Sulfuranes|
|Author(s):||Figuly, Garret Daniel|
|Department / Program:||Chemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Abstract:||Dilithio derivative I is used in the preparation of optically active monocyclic dialkoxysulfurane II and the analogous chlorosulfurane and trifluoromethanesulfonate. Examinations of the possible use
of these new optically active sulfuranes and sulfonium salts for the asymmetric synthesis of epoxides from meso-1,2-diols showed inefficient transfer of chirality from the optically active sulfur center to the carbon of the product epoxide. A racemization mechanism for II, which shows a minimum value of
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for the racemization process, is discussed. Improvements in synthetic methodology leading to new optically active chlorosulfurane III and the analogous trifluoromethane sulfonate are discussed.
The synthesis of new bromosulfuranes IV, V, and VI is^accomplished by the addition of excess aqueous hydrobromic acid^to the appropriate sulfoxide alcohol in methylene chloride. Initially^the crude reaction mixture of bromosulfurane forms a complex^equilibrium mixture including sulfonium species and sulfide species;^however, removal of excess hydrogen bromide from the reaction^mixture causes a shift in the equilibrium to form bromosulfurane^almost exclusively. When ('1)H NMR and ('13)C NMR spectral data of^the bromosulfuranes are compared to the data for covalent^chlorosulfuranes and ionic sulfonium trifluoromethane sulfonatesit is concluded that the bromosulfuranes contain highly polar, covalent, S-Br bonds.
The directed ortho-lithiation of lithium arenesulfonates to give lithium 2-lithiobenzenesulfonate and lithium 2-lithio-4-methylbenzene-sulfonate is described. Addition of electrophiles to the lithium 2-lithioarenesulfonates leads to lithium arenesulfonates substituted in the 2-position in moderate to excellent conversions. Desulfonation of the substituted sulfonates leads to moderate yields of meta-substituted toluenes when lithium 4-methylbenzenesulfonate substituted in the 2-position is desulfonated. Attempts to form sulfuranes VII and VIII were unsuccessful.
The directed ortho-lithiation of lithium thiophenolate to give S-lithio-2-lithiophenylthiol occurs in excellent yield. Addition of electrophiles to the dilithio derivative leads to thiophenols substituted in the 2-position. The preparation of triarylcarbinol IX is described. The low basicity of IX is explained as a result of the geometric constraints imposed on IX by the presence of the two large sulfur atoms introduced into the ring system.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1981.
|Date Available in IDEALS:||2014-12-13|