Podlesny, Erin
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Publication Chiral Binaphthoquinones: Versatile Precursors for the Synthesis of Natural Products and Ligands for Asymmetric Catalysis(2013-01-01) Podlesny, ErinThe efforts described in this dissertation initially focus on the asymmetric synthesis of axially chiral binaphtho-para- and binaphtho-ortho-quinones, followed by an exploration of their utility in natural product synthesis, development of ligands for asymmetric catalysis, and development as potential sensors. Axially chiral binaphtho-para- and in-in-binaphtho-ortho-quinones were synthesized through a concerted route involving the enantioselective coupling of a hindered 8-substituted 2-naphthol, with a diaza-cis-decalin copper catalyst developed previously by the Kozlowski group. The coupling was achieved in 62% yield and 87% ee (a single trituration produced material of >99% ee). Subsequent transformations led to an 8,8'-hydroxylated binaphthol, which was selectively oxidized to a binaphtho-para-quinone using a Co-salen catalyst or transformed to the in-in-binaphtho-ortho-quinone with o-iodoxybenzoic acid (IBX). Similarly, the out-out-binaphtho-ortho-quinone was synthesized from a 6,6'-hydroxylated binaphthol, using IBX. Binaphtho-para-quinones were used as key intermediates for the synthesis of the bisanthraquinone natural product (S)-bisoranjidiol. (S)-Bisoranjidiol was synthesized from a 6,6'-dibrominated binaphtho-para-quinone and mixed vinyl ketene acetal, through a regioselective tandem Diels-Alder/aromatization reaction. This transformation was achieved in 80% yield (~95% per transformation). The synthesis of (S)-bisoranjidiol was completed in 4% yield over 12 steps, and >99% ee. In addition, the synthesis of a reported binaphthalene tetraol natural product was achieved through reduction of an out-out-binaphtho-ortho-quinone. This synthesis led to the structural reassignment of the proposed compound to a tetrabrominated diphenyl ether. Condensation of various phenylenediamines with binaphtho-ortho-quinones led to bisbenzo[a]phenazines, which represent BINOL derivatives with electron-withdrawing groups (pyrazine ring). The in-in-bisbenzo[a]phenazines performed better than BINOL, but did not offer improvements over the electron-deficient BINOL based catalysts/ligands reported for those reactions. The bisbenzo[a]phenazines, in particular the tetrachlorinated derivatives, also displayed a series of interesting properties and colorimetric responses to various stimuli (chromism), which may lead to the development of colorimetric sensors. The properties include mechanochromism, thermochromism, solvatochromism, vapochromism, acidochromism, and fluorescence.