Date of Graduation
Eberly College of Arts and Sciences
Kung K. Wang.
The thionyl chloride-induced cascade cyclization of enediynyl propargylic alcohols provides an efficient synthetic route to 11H-benzo[ b]fluoren-11-ols and related compounds. The simplicity of the synthetic sequence and the mildness of the reaction condition make this pathway especially attractive. Interestingly, in certain cases the intramolecular [2+2] cycloaddition reaction of the chlorinated benzoenyne-allene intermediates occurred preferentially to form 1H-cyclobut[a]indenes. Competition from the intramolecular [2+2] cycloaddition reaction could be avoided with the non-chlorinated benzoenyne-allenes, providing direct access to novel polycyclic aromatic hydrocarbons. Several indeno-fused 4,5-diarylphenanrenes were synthesized by a consecutive C2-C6 cyclization of a symmetrical benzoenyne-allene. The formal Diels-Alder reaction involving a C2-C6 cyclization reaction followed by a radical-radical coupling reaction of the benzannulated enyne-allenes is key to the efficient assembly of the phenanthrene system. The buttressing effects due to the indeno-fused rings and the two tert-butyl groups at the 1- and 8-positions are responsible for increasing the activation barrier for the helix inversion of the resulting 4,5-diarylphenanthrenes.;Thermolysis of enyne-isocyanates represents a new way of generating biradicals and/or zwitterions from unsaturated molecules having nitrogen and oxygen atom in the conjugated system. Due to the ring strain, cycloaromatization of cyclopentene-based enyne-isocyanates and enyne-carbodiimides underwent predominately C 2-C7 cyclization pathway. The existence of intramolecular decay routes for the initially formed biradicals or zwitterions made these cyclization reactions essentially useful, leading to a variety of polycyclic heterocycles.
Li, Hongbin, "Preparation of benzoenyne -allenes, enyne -isocyanates and enyne -carbodiimides and their applications in the synthesis of polycyclic aromatic hydrocarbons and heterocycles" (2002). Graduate Theses, Dissertations, and Problem Reports. 1595.