New Mechanisms for Turnover and Functionalization in the Platinum Initiated Cyclization of Polyenes Public Deposited

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  • March 19, 2019
Creator
  • Geier, Michael
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • The replication of nature's ability to convert acyclic polyenes to polycycles has long been the target of synthetic chemists. Progress has been made through manipulation of both substrate and initiator to achieve products of increasing complexity. While significant advances have been made, the abilities of the synthetic chemist pale in comparison to that of nature. In an effort to bridge this gap, several areas have been explored. Current synthetic methods for the synthesis of C3-oxygenated polycycles rely upon pre-installation of the oxygen functionality. Development of a catalytic scheme for the generation of several C3-oxygenated polycycles using molecular oxygen as the oxygen source has been achieved. This scheme proceeds through a unique Pt(III) intermediate which undergoes homolytic cleavage of the Pt-C bond before interception of the alkyl radical. Application of a (CNC)Pt2+ pincer complex to the cyclization of polyene substrates has resulted in a remarkably efficient cycloisomerization. Where phosphine ligated Pt complexes have proven remarkably stable toward oxidation, rapid Pt-alkyl protodemetallation was observed. This complex was particularly effective in initiating cyclization of the more challenging alkene terminating substrates, forming up to four rings and five stereocenters in a single step. Extension of this cycloisomerization methodology to substrates which proceed through secondary carbocations has allowed for a unique opportunity to study the nature of polycyclization reactions experimentally. Through selective substrate demethylation, a concerted yet highly asynchronous process was uncovered, revealing a process highly dependent on the stability of the A ring. En route to exploration of new methods for oxygenation of the C-3 position, an opportunity for the fundamental study of reductive elimination from Pt(IV) complexes arose. Under standard conditions, reactions of a Pt(II) organometallic complex with electrophilic halonium reagents resulted in stereoretentive reductive elimination. Addition of the appropriate anion to these reactions resulted in a switch in the mechanism of reductive elimination, forming the invertive halogenation products.
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  • In Copyright
Advisor
  • Schauer, Cynthia
  • Brookhart, Maurice
  • Gagne, Michel
  • Nicewicz, David
  • Templeton, Joseph
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2014
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  • Chapel Hill, NC
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