NEW STRATEGIES FOR ACCESSING ORTHO- AND PARA-QUINODIMETHANES

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Restricted (Penn State Only)
Author:
Lee, Danny
Graduate Program:
Chemistry
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
May 27, 2025
Committee Members:
Kenneth Knappenberger, Program Head/Chair
Mauricio Terrones, Outside Unit & Field Member
Ramesh Giri, Chair & Dissertation Advisor
John Asbury, Major Field Member
Lauren Zarzar, Major Field Member
Keywords:
Organic synthesis
Naphthalene
ortho-quinodimethane
Diradical
Electrocyclization
Abstract:
Naphthalene and its derivatives have played a foundational role in the development of organic chemistry, with applications found in dyes, natural products, and organic materials. Over the past century, a wide range of synthetic methods have been developed to synthesize functionalized naphthalenes through variants of the Haworth reaction, electrophilic alkyne annulation chemistry, metal catalyzed cyclizations, radical cyclizations, electrocyclizations, metatheses, the Diels-Alder reaction, and more. Among these, pericyclic reactions are the most utilized with the Diels-Alder reaction proceeding through a transient and highly reactive ortho-quinodimethane intermediate being the most widely adopted. This versatile intermediate generated through many different methods has enabled rapid access to fused and bridged ring systems under thermal, chemical, and photochemical conditions. We recently discovered a new route to generating the ortho-quinodimethane intermediate following a 6𝜋-azaelectrocyclization of 2-alkenyl aryl aldimines which can be trapped with dienophiles to form bridged bicyclic compounds, hydrogen atom sources towards natural products and pharmaceutical intermediates, nucleophiles to synthesize substituted tetrahydroisoquinolines, 4-phenyl-1,2,4-triazoline-3,5-dione for multiple annulations, or dimethyl acetylene dicarboxylate to form naphthalene-2,3- dicarboxylates following retro Diels-Alder elimination. We also explored a novel polarity mismatched 6𝜋-azaelectrocyclization of 1,2-bisarylaldimines and their reaction with dimethyl acetylene dicarboxylate to synthesize 1,4-bis(phenylamino)naphthalene-2,3-dicarboxylates. The para-quinodimethane species has also been an intriguing motif in organic materials with Thiele and Chichibabin finding diradical character in quinoidal materials in 1904 and 1907. Their open shell character and narrow HOMO-LUMO gaps make them valuable in materials science and have enhanced our knowledge of chemical bonding and aromaticity. Studies have found methods to increase diradical character, improve radical stability, and control diradical electron configuration. Yet many of these materials are synthesized through a multi-step procedure with low overall yields and limited structural variations. I have developed a new method towards p-quinoidal materials through a photochemical dibenzylation of anthracene and novel Scholl reaction proceeding through sp3 hybridized carbons to synthesize syn and anti p-quinodimethane containing materials in two steps from readily available starting materials.