Dissertation - University Access Only
Doctor of Philosophy (PhD)
Department / School
Chemistry and Biochemistry
Despite the wide variety of chiral auxiliaries based upon the camphor skeleton which have been developed in the past two decades and the almost encyclopedic coverage of the possible vicinally disubstituted bomanes by Oppolzer's group, there has been, surprisingly, no attempt to use trans-2, 3-disubstituted bomanes as chiral auxiliaries in organic synthesis. This dissertation summarizes the results of the first systematic study of this system. MM2 molecular mechanics calculations predicted that 3-endo-benzylisobomyl propionate is the most conformationally rigid isomer of this ester and that its preferred conformation is that in which the aryl group blocks the acyl group efficiently. The required chiral 3-endo-benzylisobomeols were prepared in large quantity from enones (152) by Bouveault-Blanc reduction of the enone with sodium metal in refluxing ethanol, conversion of the mixture of stereoisomeric alcohols to the mixture of pnitrobenzoate esters, separation of the desired 2-exo-3-endo isomer (158) by fractional crystallization, and base hydrolysis of the purified p-nitrobenzoate ester. The 3-endo-(p-methoxybenzyl)isobomeol was systematically evaluated as a chiral auxiliary in the alkylation of ester enolates. It was found that, although this auxiliary does not afford a high level of diastereoselectivity in the alkylation reaction, it could be used as a chiral reagent for assigning the absolute configuration of a-methylcarboxylic acids by 1H NMR spectroscopy at 200 MHz.
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South Dakota State University
Seo, Byung-Ick, "An Evaluation of 3-endo-arlymethylisoborneols as Chiral Auxiliaries for Asymmetric Synthesis" (1995). Electronic Theses and Dissertations. 547.