eprintid: 6450 rev_number: 5 userid: 6 dir: disk0/00/00/64/50 datestamp: 2011-11-10 19:32:07 lastmod: 2016-11-15 13:36:55 status_changed: 2011-11-10 19:32:07 type: thesis_degree metadata_visibility: show contact_email: lel24@pitt.edu item_issues_count: 0 eprint_status: archive creators_name: liu, lei creators_email: lel24@pitt.edu creators_id: LEL24 title: Synthesis of Structurally and Stereochemically Diverse Tetrahydropyran Structures via DDQ-Mediated Oxidative Carbon‒Hydrogen Bond Activation ispublished: unpub divisions: sch_as_chemistry full_text_status: public keywords: (silyl)allylic; allylic; ethers; library; MnO2; oxocarbenium ion; propargylic; tertiary; vinyl abstract: The 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ)-mediated oxidative carbon¨Chydrogen bond cleavage of allylic ethers has been studied. The generated ¦Á,¦Â-unsaturated oxocarbenium ions can be captured by appended enol acetate nucleophiles to stereoselectively provide cis-2,6-disubstituted tetrahydropyrones. Alkenes with a wide assortment of substitution patterns undergo oxidative cyclizations efficiently, and commonly encountered functional groups on either side of the ether linkage are well tolerated.The scope of this method has successfully been expanded to (silyl)allylic and propargylicethers. The generated vinylsilane-substituted tetrahydropyrans are versatile precursors for a wide range of functional group interconversions and stereocontrolled additions. The cyclization of(silyl)allylic ethers proceeds efficiently to generate cis-2,6-disubstituted tetrahydropyrones with excellent stereocontrol, and therefore is preferable for target-oriented syntheses. The cyclization of propargylic ethers results in a mixture of cis- and trans-2,6-disubstituted tetrahydropyrones, and it is applicable in diversity-oriented syntheses.Two models of the geometries of 1,1-disubstituted oxocarbenium ions (A) and the conformations of oxocarbenium ions that contain a tertiary stereocenter (B) have been designed. Both models have been applied to highly stereoselective syntheses of tetrahydropyrans containing tertiary ethers.DDQ-catalyzed oxidative cyclizations for tetrahydropyran synthesis have been achievedby using MnO2 as an inexpensive and environmentally benign terminal oxidant. This catalytic system is also applicable to other commonly encountered DDQ-mediated reactions, such as PMB ether cleavages and dehydrogenations. The products are quite easy to purify, and the yields are comparable with the corresponding reactions using stoichiometric DDQ. date: 2011-06-30 date_type: completed institution: University of Pittsburgh refereed: TRUE etdcommittee_type: committee_chair etdcommittee_type: committee_member etdcommittee_type: committee_member etdcommittee_type: committee_member etdcommittee_name: Floreancig, Paul E. etdcommittee_name: Koide, Kazunori etdcommittee_name: Wipf, Peter etdcommittee_name: Xie, Xiang-Qun etdcommittee_email: florean@pitt.edu etdcommittee_email: koide@pitt.edu etdcommittee_email: pwipf@pitt.edu etdcommittee_email: xix15@pitt.edu etdcommittee_id: FLOREAN etdcommittee_id: KOIDE etdcommittee_id: PWIPF etdcommittee_id: XIX15 etd_defense_date: 2011-03-02 etd_approval_date: 2011-06-30 etd_submission_date: 2011-03-07 etd_access_restriction: immediate etd_patent_pending: FALSE assigned_doi: doi:10.5195/pitt.etd.2011.6450 thesis_type: dissertation degree: PhD committee: Paul E. Floreancig (florean@pitt.edu) - Committee Chair committee: Kazunori Koide (koide@pitt.edu) - Committee Member committee: Peter Wipf (pwipf@pitt.edu) - Committee Member committee: Xiang-Qun Xie (xix15@pitt.edu) - Committee Member etdurn: etd-03072011-104316 other_id: http://etd.library.pitt.edu/ETD/available/etd-03072011-104316/ other_id: etd-03072011-104316 citation: liu, lei (2011) Synthesis of Structurally and Stereochemically Diverse Tetrahydropyran Structures via DDQ-Mediated Oxidative Carbon‒Hydrogen Bond Activation. Doctoral Dissertation, University of Pittsburgh. (Unpublished) document_url: http://d-scholarship-dev.library.pitt.edu/6450/1/liulei03022011.pdf