Li, Minyan

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Organic Chemistry
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  • Publication
    Functionalization Of 2-Azaallyl Anions, Radicals And Benzylic Chloromethyl-Coupling Polymerization
    (2017-01-01) Li, Minyan
    C-C bond forming reactions, under either metal catalyzed or metal free conditions, are mainstay in the construction of functionalized molecules in organic synthesis. Disubstituted methylamines are highly valuable small molecule pharmaceuticals which are widely applied in the treatment of human disease. To date, traditional synthesis of such amines requires significant effort of synthesizing pre-functionalized reagents. This dissertation describes an innovation in the construction of disubstituted methylamines via the umpolung functionalization of 2-azaallyl anions and radicals. In chapter 1, umpolung synthesis of diarylmethylamines via palladium-catalyzed arylation of 2-azaallyl anion intermediates is introduced. 2-Azaallyl anion coupling partners include 1,1,3-triaryl-2-azaallyl anions and 1,3-diaryl-2-azaallyl anions. The key to success is the advancement of NIXANTPHOS-based catalysts that enabled the arylation of aryl bromides and more challenging aryl chlorides to be conducted under mild conditions. Moreover, the identification of hindered silylamide bases ensures that products of the arylation were not deprotonated or isomerized. In chapter 2, we address the regioselectivities in the α- and γ-arylation of azapentadienyl anions. The regioselectivity was achieved by controlling the reductive elimination of the Pd-azapentadienyl intermediates using two distinct catalysts. These methods provide the first divergent synthesis of allylic amine and enamine derivatives. In chapter 3, we presented an innovative concept that 2-azaallyl anions could behave as organic super-electron-donors. Such unique behavior was illustrated in (i) generation of 2-azaallyl radicals from single-electron-transfer (SET) between 2-azaallyl anions and neutral ketimines, which then coupled with vinyl bromides; (ii) generation of 2-azaallyl radicals from SET of 2-azaallyl anions with aryl and alkyl electrophiles, which then captured aryl and alkyl radicals to form C–C bonds. The transition-metal-free vinylation, arylation and alkylation of 2-azaallyls make possible the synthesis of high-value functionalized amine derivatives in good to excellent yields. In chapter 4, a new polymerization method named benzylic-chloromethyl-coupling polymerization (BCCP) is introduced. BCCP is catalyzed by sulfenate anions, which promote an umpolung polycondensation via step-growth propagation cycles involving sulfoxide intermediates. This protocol represents a very rare example of an organocatalyst that links monomers by C=C double bonds after each enchainment.