%A Shelby Anderson
%T Investigation of the Addition of a Kinetic Bimolecular Fragment Coupling Step to the Re2O7-Catalyzed Transposition and Cyclization of Allylic Alcohols and Examination of the Effects of Acetonitrile
%X The Re2O7-catalyzed allylic alcohol transposition, cyclization, and trapping cascade reaction developed by the Floreancig group is a synthetically versatile reaction that has been applied to the stereoselective synthesis of tetrahydropyran rings. This work expands the Re2O7-mediated allylic alcohol transposition reaction to include a kinetically controlled bimolecular fragment coupling reaction with weak ?-silane nucleophiles to access the 2,6-trans tetrahydropyran ring systems. Expansion of the fragment coupling reaction to install quaternary centers and to prepare substrates bearing pre-existing stereocenters is accomplished and gives further insight into the mechanistic details of these reactions.
Solvent effects on the reaction are analyzed, with acetonitrile providing substantial rate enhancing effects to the reaction through stabilization of the oxocarbenium ion intermediate. Acetonitrile plays a crucial role in promoting the reaction in comparison to dichloromethane, enhancing the rate and facilitating the trapping of silane nucleophiles. This modification allows the fragment coupling reaction to be expanded to stereochemically complex products that have been previously inaccessible with Re2O7. Acetonitrile also provides improved stereocontrol in comparison to dichloromethane for trapping with substrates bearing a pre-existing stereocenter. Furthermore, acetonitrile promotes equilibration to thermodynamically favored products, further illustrating its advantages.
%D 2021
%K synthetic methodology; rhenium oxide; allylic alcohol transposition; stereoselective synthesis; tetrahydropyran ring synthesis; heterocycles; solvent effects
%I University of Pittsburgh
%L pittir40006