Synthesis of 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes : large and highly distorted polycyclic aromatic hydrocarbons

Merner, Bradley L. (Bradley Lawrence) (2010) Synthesis of 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes : large and highly distorted polycyclic aromatic hydrocarbons. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The synthesis of nonplanar aromatic hydrocarbons has been an area of interest for quite some time now. These distorted π-systems have fascinated the imaginations of organic chemists over the years and through extensive studies and syntheses, many important lessons on the implications of strain and aromaticity have been provided. Moreover, the chemical synthesis of monodisperse single-walled carbon nanotubes (SWCNTs) that does not involve "fullerene surgery" remains a significant challenge. This dissertation involves the synthesis of nonplanar polycyclic aromatic hydrocarbons (PAHs) - namely, 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes, which resemble large segments (about half) of (8,8) armchair SWCNTs. The work described herein focuses on new reactions of the pyrene ring system, the synthesis of new pyrenophane motifs and the exploration of the valence isomerization/dehydrogenation (VID) reaction as a means to synthesizing the most distorted π-systems contained within a cyclophane framework. -- Chapter 1: Introduction of underlying concepts involving designed molecule synthesis and seminal work on the synthesis of nonplanar aromatic hydrocarbons. Focus has been placed primarily on the synthesis of nonplanar aromatic systems that are also cyclophanes. Four general strategies towards the synthesis of cyclophanes are highlighted with an emphasis on the most powerful valence isomerization (Strategy D) approach. -- Chapter 2: Retrosynthetic analysis of the target 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes and a discussion of the early synthetic efforts to construct the teropyrene system using a four-fold functionalization approach is presented. Most of the chemistry described in this chapter led to synthetic routes that were incapable of delivering significant quantities of viable advanced intermediates of the designed targets. Also, the attempted synthesis of a modified cyclophane target is described. -- Chapter 3: Alternate disconnective analyses of the target 1,1,n,n-tetramethyl[n](2,11)teropyrenophanes, as well as model studies on the 2-tert-butylpyrene system and a novel approach to pyrenoid cyclophane systems is discussed. Several new substitution and coupling reactions of substituted pyrene derivatives were discovered during the course of this study and are presented in Chapter 3. -- Chapter 4: The synthesis of a series of 1,1, n,n-tetramethyl[n](2,11)teropyrenophanes (n=7-9) using two different synthetic routes (Routes A and B) is the main feature of this chapter. Application of a Wurtz-type coupling reaction of 1-(bromomethyl)-7-tert-butylpyrene (discovered in Chapter 3) was successful applied in the synthesis of three teropyrenophane targets. As well, the rare use of the McMurry reaction to construct [2.2]metacyclophanediene systems, a structural prerequisite for the pivotal VID reaction, is presented. Interesting structural and spectroscopic properties of 1,1,8,8-tetramethyl[8](2,11)teropyrenophane and future applications of the chemistry developed during the course of this project are also discussed.

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