Application of Organosilanes in [ 3 + 2 ] Annulation Approaches to Carbocyclic Compounds

Part I: The synthesis of 2-vinylindole, the parent of 2-alkenylindoles, has been achieved in three steps (70-76% yield) based on a novel allene cyclization developed in our laboratory. 2-Alkenylindoles have found use as precursors to indole and carbazole alkaloids via the Diels-Alder reaction. The key step of the synthesis involves isomerization of an arylacetylenecarbamate to an arylallenecarbamate followed by cyclization. In addition to the carbamate derivative, acetamide, and 2-methylpropanamide derivatives were explored as potential activating groups. Part II: A general [3 + 2] allenylsilane-based annulation-oxidation sequence to afford cyclopentanone derivatives has been developed. This annulation involves the addition of (alkoxy)allenylsilanes to electron-deficient olefins (allenophiles) in the presence of titanium tetrachloride to afford highly substituted cyclopentene derivatives. The cyclopentene compounds are converted to the desired cyclopentanone products via Tamao oxidation of the vinylsilane moiety. The stereochemical course of these reactions has been demonstrated to be thermodynamically controlled. (Alkyland arylthiomethyl)allenylsilanes have also been studied as potential annulation partners. A general [3 + 2] allylsilane-based annulation-oxidation sequence to afford cyclopentanol derivatives has been investigated where (aminoand tetramethylallyl)silyl derivatives were employed. Thesis Supervisor: Rick L. Danheiser Title: Professor of Chemistry