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Synthesis of Structurally and Stereochemically Diverse Tetrahydropyran Structures via DDQ-Mediated Oxidative Carbon‒Hydrogen Bond Activation

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 (Unpublished)

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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.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
liu, leilel24@pitt.eduLEL24
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairFloreancig, Paul E.florean@pitt.eduFLOREAN
Committee MemberKoide, Kazunorikoide@pitt.eduKOIDE
Committee MemberWipf, Peterpwipf@pitt.eduPWIPF
Committee MemberXie, Xiang-Qunxix15@pitt.eduXIX15
Date: 30 June 2011
Date Type: Completion
Defense Date: 2 March 2011
Approval Date: 30 June 2011
Submission Date: 7 March 2011
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: (silyl)allylic; allylic; ethers; library; MnO2; oxocarbenium ion; propargylic; tertiary; vinyl
Other ID:, etd-03072011-104316
Date Deposited: 10 Nov 2011 19:32
Last Modified: 15 Nov 2016 13:36


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