Microwave-Assisted Group-Transfer Cyclization of Organotellurium Compounds
作者:Cecilia Ericsson、Lars Engman
DOI:10.1021/jo040155f
日期:2004.7.1
Primary- and secondary-alkyl aryl tellurides, prepared by arenetellurolate ring-opening of epoxides/O-allylation, were found to undergo rapid (3 - 10 min) group-transfer cyclization to afford tetrahydrofuran derivatives in 60-74% yield when heated in a microwave cavity at 250 degreesC in ethylene glycol or at 180 degreesC in water. To go to completion, similar transformations had previously required extended photolysis in refluxing benzene containing a substantial amount of hexabutylditin. The only drawback of the microwave-assisted process was the loss in diastereoselectivity which is a consequence of the higher reaction temperature. Substitution in the Te-aryl moiety of the secondary-alkyl aryl tellurides (4-OMe, 4-H, 4-CF3) did not affect the outcome of the group-transfer reaction in ethylene glycol. However, at lower temperature, using water as a solvent, the CF3 derivative failed to react. The microwave-assisted group-transfer cyclization was extended to benzylic but not to primary- and secondary-alkyl phenyl selenides.
Novel group transfer cyclization reactions of organotellurium compounds
作者:Lars Engman、Vijay Gupta
DOI:10.1039/c39950002515
日期:——
When irradiated in the presence of hexabutylditin, readily available O-allylated and O-prop-2-ynylated 2-hydroxyalkyl aryl tellurides undergo group transfer cyclization to afford 2, 4-disubstituted tetrahydrofuran derivatives.
Tetrahydrofuran Derivatives from Epoxides <i>via</i> Group Transfer Cyclization or Reductive Radical Cyclization of Organotellurium and Organoselenium Intermediates
作者:Lars Engman、Vijay Gupta
DOI:10.1021/jo961578n
日期:1997.1.1
undergo grouptransfer cyclization to afford 2-substituted 4-[(aryltelluro)methyl]tetrahydrofurans (cis/trans = 1/3-1/10). The aryl beta-(prop-2-ynyloxy)alkyl tellurides similarly afforded 2-substituted 4-[(aryltelluro)methylene]tetrahydrofurans with an E/Z-ratio close to unity. The beta-(allyloxy)alkyl aryl selenides and aryl beta-(prop-2-ynyloxy)alkyl selenides failed to undergo grouptransfer cyclization