Catalytic and Stoichiometric Wittig Reactions for the Synthesis of Arenes and 1,2-Dihydroquinolines
- Author(s): Zhang, Kui
- Advisor(s): Kwon, Ohyun
- et al.
In the first chapter, a phosphine-mediated multi-component reaction between o-phthalaldehydes, nucleophiles and monosubstituted allenes furnished the functionalized non-C2-symmetric naphthalenes in synthetically useful yields. Also, when the o-phthalaldehydes were reacted with 1,3-disubstituted allenes in the presence of diethylphenylphosphine, naphthalene derivatives were obtained in yields up to quantitative. The mechanism of the latter transformation is straightforward, involving aldol addition followed by Wittig olefination and dehydration. The mechanism of the former reaction has been established as a tandem γ-umpolung/aldol/Wittig/dehydration process through careful analysis of data based on the preparation of putative reaction intermediates and mass spectrometry. The current method can also be applied iteratively to prepare anthracenes and tetracenes when carboxylic acids are employed as pronucleophiles.
In the second chapter, a novel bridged [2.2.1] bicyclic phosphine oxide, devised to circumvent the burdens of waste generation and purification that are typical of Wittig olefination, has been prepared from commercially available cyclopent-3-ene-1-carboxylic acid through three steps. This new catalyst was designed based on the theoretical transition state geometry of the silane-mediated reduction of phosphine oxides. The superior performance of this novel phosphine oxide has been verified experimentally through kinetic analysis of its silane-mediated reduction, as well as catalytic Staudinger reduction, in comparison to the current bests. It has also been applied successfully in halide-/base-free catalytic γ-umpolung addition–Wittig olefinations of allenoates and 2-amidobenzaldehydes to produce 1,2-dihydroquinolines with extraordinary efficiency.