STUDIES ON THE STABILITY AND REACTIVITY OF 2,4-HEXAHYDROXYDIPHENOYL(HHDP)-BEARING ELLAGITANNIN MONOMERIC UNIT;
ALLENYL AZIDE CYCLOADDITION CHEMISTRY APPLIED TOWARD THE SYNTHESIS OF ALKALOIDS
Open Access
Author:
Iyer, Malliga R
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
January 18, 2007
Committee Members:
Ken S Feldman, Committee Chair/Co-Chair Raymond Lee Funk, Committee Member Blake R Peterson, Committee Member Squire J Booker, Committee Member
The first synthesis of a monomeric 2,4-hexahydroxydiphenoyl (HHDP)-bearing glucopyranose ellagitannin model system was achieved. Attempts to prepare a related model system containing a 1,6-bridge on the glucose core resulted in a strain-driven tautomerization to cyclohexadienone intermediates. This project sought to answer questions relevant to the biosynthesis of geraniin family of natural products as well as address the privileged stability observed in case of 2,4-HHDP-containing natural ellagitannnin, phyllanemblinin B.
A novel cascade cyclization sequence evolving from the thermolysis of allenyl azide was developed. Incorporation of aryl or alkenyl appendages in the allene construct afforded tricyclic and bicyclic products, respectively, following cyanide trapping of the unstable imine intermediate. Azatrimethylenemethane (ATMM) diradicals were speculated to be involved in the cycloaddition/cyclization cascade. A brief survey of electronic influence on the cascade reaction was investigated.
An extension to this novel methodology was achieved by incorporating an aryl residue in the allenyl azide tether. This modification resulted in the synthesis of annealated indoles from (phenylazido)allene substrates. The proposed mechanism invokes the existence of ATMM species in the cyclization. Alternatively, the cyclization was postulated to occur through a conjugated closed shell intermediate. Further application of this methodology in the synthesis of a model system for the natural product (±)-meloscine was attempted with promising results.
