STUDIES OF STERICALLY CHALLENGING POLYCYCLIC AROMATIC SYSTEMS

146 Pages·2012·4.68 MB·English

by  Grace Christine Wang

STUDIES OF
STERICALLY CHALLENGING
POLYCYCLIC AROMATIC SYSTEMS

GRACE CHRISTINE WANG

A DISSERTATION

PRESENTED TO THE FACULTY

OF PRINCETON UNIVERSITY

IN CANDIDACY FOR THE DEGREE

OF DOCTOR OF PHILOSOPHY

RECOMMENDED FOR ACCEPTANCE

BY THE DEPARTMENT OF CHEMISTRY

Advisor: Robert A. Pascal, Jr.

September 2012
© Copyright by Grace Christine Wang, 2012. All rights reserved.
ABSTRACT
For students of elementary organic chemistry, the class of molecules known as
“polycyclic aromatics” conjures up images of fused ring systems that must be flat. After all,
one of the supposed prerequisites for aromaticity is a strict alignment of p-orbitals, which
define an area of space through which electrons may orbit around parent and adjacent atoms.
However, aromatic molecular conformations are not so strictly limited as introductory
lessons might suggest. Large acenes are sensitive to both intramolecular and intermolecular
forces, making non-flat conformations, such as bowls, ribbons, and waves more common
than not. The concomitant opportunities to predict, computationally, and to determine,
experimentally, how the addition of a substituent at one position or replacement of one
moiety by another affects the lowest energy conformation are what make this vein of
synthetic organic chemistry research so exciting.
This work details three projects aimed to better understand crowded polycyclic
aromatic architectures: (i) the investigation of a three-step synthesis of
tetradecaphenylpentacene; (ii) the introduction of very bulky groups (i.e., tert-butyl and
carboranyl) into acenes by using crowded cyclopentadienones; and (iii) the development of a
method for the synthesis of a class of acenes derived from pyrene.

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ACKNOWLEDGMENTS

First, thanks to my advisor Professor Bob Pascal for taking me into his research group
and to the members of the Pascal Group. I would also like to thank the members of my thesis
committee: my second reader Professor Jeffrey Schwartz for generously giving of his time to
provide comments on this thesis, Professor Michael Hecht, Professor Marty Semmelhack,
and Professor Erik Sorensen.
At Harvard, thanks to teaching fellows Kevin Fortner, BJ Chain, Joe Young, and my
Amgen family (Paul Reider, Nick Paras, Frenel(lie) DeMorin, Natalie Stewart, Christine
Jenkins) for sparking my interest in organic chemistry. I am grateful to Professor Dave
Evans for his mentorship and for taking me into his group, where I learned from Jonathan
Scheerer, Joe Young, Matt Heuft, Travis Dunn, Drew Adams, and Jason Mulder. One of the
best parts about Harvard was the opportunity to teach, and Craig Masse, Kristen Buteau,
Greg Tochtrop, and Anneliese Franz allowed me to teach their Harvard Extension School
courses. Tim Cook always managed to provide a different perspective on most everything,
and his humor has helped me laugh through many tough days.
Thanks to Professor Dave MacMillan for convincing me to come to Princeton, and
for overseeing my initial training. Istvan Pelczer and John Eng helped me tremendously with
my research. Sallie Dunner, Kirsten Arentzen, and Meghan Krause provided invaluable
support and encouragement. Tom Graham taught me a lot about chemistry and non-
chemistry topics. Jason St. Clair provided zen perspective & insightful advice, more of
which I should have taken. Professor Michael Hecht, Professor Andy Bocarsly, and
Professor Rob L’Esperance allowed me to be a (head) teaching assistant for their courses,
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which I enjoyed immensely! I was fortunate to be a part of the Butler College community
with Master Sanj Kulkarni, Mindy Andino, Dr. Matthew Lazen, and Dr. David Stirk; fellow
RGS’s Wei Ho and Kellam Conover; and RCA’s Carrie Carpenter and Elizabeth
Hollingsworth. Clint Smith, Rebecca Strawn, Jyoti Tibrewala, Caitlin Newberry, Amanda
Tricarico, Kate Keets, Tom Umile, Andréa Granstedt, Courtney McQueen and Ely Niangar
were an amazing community of friends.
At Tulane, Mallory Cortez, Jessica Hoskins, Boyd Laurent, Dawanne-ahug Eugene
Poree, Marco Giles, and Mikey Reale welcomed me instantly. Joel Mague and Jim Bollinger
helped me tremendously with my research. Elizabeth Hamilton, Ginette Arguello, Emelina
Sanchez, Nick Altieri, Judy Weaver, Marnie Mercado, and John Drwiega helped make an
easy transition to Tulane. I gratefully acknowledge George Escher for helping me solve
many early housing problems. My last landlady, Marilyn Bernius, provided a safe and
welcoming place that has been home for three years.
Outside of the lab, I made many friends through the Touro Emergency Department
and affiliated emergency medical services. I could not have written this thesis without their
support and encouragement! Special thanks to Dr. Charlane Liles, Dr. Dean Aubin, Dr.
Philip Paulk, Dr. Elisa Arrillaga, Dr. Tim Girard, Dr. Miguel Aguilera, Dr. Nick Marney, Dr.
Neil Baum, Ronnie Landry, Stephanie Webber, Eileen Smith, Eva Morris, Chris Icamina,
Carol Borne, Glenda Cologero, Linda Lewis, Brent Dantin, Daniel Seymour, Aaron Crabtree,
Sean Cerny, Lindsey Cash, Donna Wallace, Austen Ward, Erica Brim, Patrick Frye, Angela
Hertz, Debbie Lehrmann, Claudette MacNeil, Paige McWhorter, Blake Davenport, Casey
Saavedra, Sam Santiago, Margaret Pentek, John Penton, Amber Sharber, Julia Drahn,
Wayne, Sam, and Lucien Hall, and my daily heroes at New Orleans EMS.
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Lastly, I want to thank my family. Dad and Mom always believed in me, even during
the times when I wasn’t sure whether I believed in myself. My dad took off many days from
work to help move me to Princeton, then to New Orleans, and then between apartments. My
mom has been the Jillian Michaels of my graduate school career. Thanks for being
supportive no matter what. My brother Nathan, my #1 fan when we were both little, now
loves through antagonizing and makes sure that I never take myself too seriously. I am
incredibly proud of him and all that he has accomplished (and continues to accomplish).
Christal is a better, more rounded, eight-years-younger version of me, and her fierce ambition
and growing maturity is inspiring. My youngest brother Chris is definitely my best friend in
the whole world and one of the smartest people I know. Christal and Christopher, I can’t
wait to see what amazing things you both will do! Mom, Dad, Nathan, Christal, and Chris,
this thesis is dedicated to you.
Grace

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TABLE OF CONTENTS

Chapter 1. Attempted Three-Step Synthesis of
Tetradecaphenylpentacene 1

Chapter 2. Unusual Cyclopentadienones 15

Chapter 3. Attempted Syntheses of Pyrene-Derived
Twisted Acenes 31

Chapter 4. Experimental Procedures and Spectra 48

References 136

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Chapter 1.

Attempted
Three-Step Synthesis of
Tetradecaphenylpentacene

1
The Pascal group has synthesized a variety of crowded, twisted pentacenes.1,2,3,4 Most
notable is 9,10,11,20,21,22-hexaphenyltetrabenzo[a,c,l,n]pentacene (5) prepared by a double
Diels–Alder addition of p-diphenyltetrabromobenzene (2) with phencyclone (3) to obtain the
corresponding diepoxide adduct 4, followed by titanium(III) chloride-promoted
3
deoxygenation. Pentacene 5 possesses a 144° end-to-end twist (Scheme 1). With this acene
in hand, the next logical target was tetradecaphenylpentacene (8), but Lu’s attempts to access
tetradecaphenylpentacene utilizing an analogous strategy afforded only the mono-epoxide
4
adduct 9 (Scheme 2), and this approach was abandoned.

Scheme 1. Synthesis of 9,10,11,20,21,22-hexaphenyltetrabenzo[a,c,l,n]pentacene.3

Ph
Br Br Br Br
(1) I /KIO /H SO
2 3 2 4
Br Br (2) PhI/Cu/230 °C Br Br
Ph
1 Ph
2 O n-BuLi
3 Ph
Ph Ph Ph Ph Ph Ph
n-BuLi
O O
TiCl
3
Ph Ph Ph Ph Ph Ph
5 4

2
Scheme 2. Attempted synthesis of tetradecaphenylpentacene (8).4

Ph
Ph
Ph
2 / n-BuLi O
Ph
Ph
Ph
6
X
Ph Ph Ph Ph Ph Ph Ph Ph
Ph Ph H Ph
O O O
Ph Ph H Ph
Ph Ph Ph Ph Ph Ph Ph Ph
7 9
–2O
Ph Ph Ph Ph Ph
Ph Ph
Ph Ph
Ph Ph Ph Ph Ph
8

3