Synthesis and study of chemically activated biradical precursors

Citation

Dragovich, Peter S. (1993) Synthesis and study of chemically activated biradical precursors. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/p2kc-rn13. https://resolver.caltech.edu/CaltechTHESIS:11142012-144010600

Abstract

The design, synthesis and study of molecules which produce 1,4-biradical intermediates upon thermal or chemical activation is described. The preparation and cyclization behavior of (Z)-1,2,4-heptatrien-6-yne and compounds that contain the (Z)-allene-ene-yne functional group or that form it in a serial reaction sequence are discussed. Evidence is presented that supports the thermal transformation of the (Z)-allene-ene-yne functional group to an α,3-dehydrotoluene intermediate that is best described as a singlet σ,π-biradical with substantial polar character. The partitioning between polar and free radical reaction pathways in these systems is shown to be influenced by biradical substitution and by the reaction medium in which the intermediate is generated. These results are discussed with reference to electrocyclization reactions occurring within the enediyne family of natural antitumor agents.

The design, synthesis and reactivity of a system that produces a strained (Z)-enediyne moiety via the reductive activation of an anthraquinone-diacetylene conjugate in water with a flavin-based enzymatic system is described. The (Z)-enediyne thus produced is shown to undergo thermal rearrangement to form a naphthofuran product via a 1,4-dehydrobenzene biradical intermediate.

The preparation of a molecule which forms a substituted 1,6-didehydro[10]annulene intermediate by nucleophilic addition of thiol is described. This intermediate is not observed, but rearranges to form two isomeric 1,5-dehydronaphthalene biradicals as evidenced by the isolation of the corresponding aromatized products.

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