?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=http%3A%2F%2Fd-scholarship-dev.library.pitt.edu%2F6450%2F&rft.title=Synthesis+of+Structurally+and+Stereochemically+Diverse+Tetrahydropyran+Structures+via+DDQ-Mediated+Oxidative+Carbon%E2%80%92Hydrogen+Bond+Activation&rft.creator=liu%2C+lei&rft.description=The+2%2C3-Dichloro-5%2C6-dicyano-1%2C4-benzoquinone+(DDQ)-mediated+oxidative+carbon%C2%A8Chydrogen+bond+cleavage+of+allylic+ethers+has+been+studied.+The+generated+%C2%A6%C3%81%2C%C2%A6%C3%82-unsaturated+oxocarbenium+ions+can+be+captured+by+appended+enol+acetate+nucleophiles+to+stereoselectively+provide+cis-2%2C6-disubstituted+tetrahydropyrones.+Alkenes+with+a+wide+assortment+of+substitution+patterns+undergo+oxidative+cyclizations+efficiently%2C+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%2C6-disubstituted+tetrahydropyrones+with+excellent+stereocontrol%2C+and+therefore+is+preferable+for+target-oriented+syntheses.+The+cyclization+of+propargylic+ethers+results+in+a+mixture+of+cis-+and+trans-2%2C6-disubstituted+tetrahydropyrones%2C+and+it+is+applicable+in+diversity-oriented+syntheses.Two+models+of+the+geometries+of+1%2C1-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%2C+such+as+PMB+ether+cleavages+and+dehydrogenations.+The+products+are+quite+easy+to+purify%2C+and+the+yields+are+comparable+with+the+corresponding+reactions+using+stoichiometric+DDQ.&rft.date=2011-06-30&rft.type=University+of+Pittsburgh+ETD&rft.type=PeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=http%3A%2F%2Fd-scholarship-dev.library.pitt.edu%2F6450%2F1%2Fliulei03022011.pdf&rft.identifier=++liu%2C+lei++(2011)+Synthesis+of+Structurally+and+Stereochemically+Diverse+Tetrahydropyran+Structures+via+DDQ-Mediated+Oxidative+Carbon%E2%80%92Hydrogen+Bond+Activation.++Doctoral+Dissertation%2C+University+of+Pittsburgh.++++(Unpublished)++