"Preparation of benzoenyne -allenes, enyne -isocyanates and enyne -carb" by Hongbin Li

Semester

Spring

Date of Graduation

2002

Document Type

Dissertation

Degree Type

PhD

College

Eberly College of Arts and Sciences

Department

Chemistry

Committee Chair

Kung K. Wang.

Abstract

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.

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