Date of Award
Doctor of Philosophy (PhD)
Chemistry & Biochemistry
This dissertation describes the development of new cascade reactions for the synthesis of quaternary carbons bearing additional proximal hindrance. The general reaction design principles are described which include the in-situ generation of a vicinal di-π system capable of undergoing a charge-accelerated [3,3]-sigmatropic rearrangement facilitated by the cleavage of a weak heteroatom-heteroatom bond. Also described is a practical route for the synthesis of N-vinyl nitrones that utilizes a 1,4-conjugate elimination as the key step. The reaction of an N-vinyl nitrone and a disubstituted ketene to form all-carbon quaternary centers is also detailed. Mechanistic studies provide evidence that the reaction proceeds by a pericyclic cascade reaction involving an initial [3 + 2] dipolar cycloaddition followed by two consecutive [3,3]-sigmatropic rearrangements. An asymmetric version of this reaction based on a chiral auxiliary approach is also described. Finally, a new method for the synthesis of oxindoles containing a quaternary carbon at the 3-position is described. This novel method proceeds via the copper triflate-mediated reaction of a phenyl-hydrazine and a ketene.
Michael, Ryan Edward, "New Methods for the Synthesis of All-Carbon Quaternary Centers via the Reactions of N-Vinyl Nitrones and Phenyl Hydrazines with Ketenes" (2013). Chemistry & Biochemistry Graduate Theses & Dissertations. 100.