%A Ian Kaigh
%T Stereocontrolled Rhenium(VII) Oxide-Mediated N-Containing Heterocycle Formation
%X Piperidines are worthy synthetic targets because they are widely represented amongst pharmaceuticals and biologically active molecules in general.  Rhenium(VII) oxide has been previously used by the Floreancig group for the ionization of allylic alcohols, followed by oxygen nucleophile attack to form tetrahydropyrans.  This work further expands that methodology by utilizing protected nitrogen nucleophiles to form piperidines.  Solvent studies determined that 1,1,1,3,3,3-hexafluoroisopropanol was the most suitable solvent for these reactions.  An array of protecting groups were tested to determine viable protecting group conditions and in an attempt to develop orthogonal strategies for multiple functional group tolerance.  Time course studies elucidated the mechanism of the reaction, and the role of product equilibration.  Stereochemical assignments were complicated by the NMR peak distortion associated with the barrier to rotation in amides, which was a consequence of using protected nitrogen nucleophiles as starting materials.  This problem was overcome by using an easily cleavable protecting group, assigning the stereochemistry of the deprotected piperidine, then reprotecting the molecule with a protecting group of interest to obtain reference spectra for comparison with piperidine products obtained by cyclization of starting materials with various protecting groups of interest installed.  Several substrates were prepared, including an oxazinone which produced a bicyclic product.
%D 2020
%K Rhenium Oxide
%I University of Pittsburgh
%L pittir39532