PD Research Report for the 2016 year
Name

Research group

Sunna Jung,Hamura Research Group, Graduate School of Science and Technology

Research Theme

Synthetic Study of High-Ordered Iptycene Derivatives Using Isobenzofuran
as a Reactive Platform

Research PeriodApril 1st, 2016 ~ March 31st, 2017

Research Results
Isobenzofurans are useful building blocks in synthetic chemistry having 10π-electron systems withquinoid structures. Focusing on the high reactivity toward [4+2] cycloadditions with dienophiles, our group
has developed the efficient synthetic methods and applications of highly functionalized isobenzofuran
derivatives. For example, a donor–acceptor type isobenzofuran (I), bearing both electron donating andwithdrawing groups exist in a molecule, enabling successive cycloaddition to construct polycyclic system. Inaddition, dual cycloaddition was available to lead polycycles using bis-isobenzofurans (III) as a key
intermediate by the sequencial generation of isobenzofurans from bis-epoxynaphthalenes (II). Based on theseprevious results, our interest moved on to the tris-isobenzofuran (V) bearing triptycene skeleton in the core asa three dimensional building block.
Triptycenes (IV) are the simplest member in iptycene family, having [2.2.2]bicyclooctatriene bridgeheadsystem with phenyl rings attached. The bicyclic core derives rigidity and creates prism-like geometry
involving void spaces. Supramolecular interactions, opening a substantial potentiality in crystal engineering,
host-guest complexes, molecular machines, polymers and liquid crystals.
In order to develop a novel three-dimensional π-extended molecule, our synthetic goal is synthesizing
tris-polyacene (VI) utilizing triple [4+2] cycloaddition from tris-isobenzofuran (V).
Previous Work
acceptorBrBrBrBrdonorI
R1R2OOOOOO

BrO

Br·OOOO·R1R2
bis-epoxynaphthalene (II)III
bis-isobenzofuranThis WorkOnOO
IV
triptyceneVtris-isobenzofurannn
VI
π-extended iptycene derivatives

Figure 1. Construction of polycyclic structure via isobenzofuran

The key building block, tris-isobenzofuran (4), was synthesized from hexabromotriptycene (1). Upon thetreatment of 4.0 equiv. of PhLi in toluene/THF co-solvent (conditions B), tris-epoxynaphthalene (3) wasobtained in 41% yield. Mono-isobenzofuran (5) and bis-isobenzofuran (6) was also accessible (conditions A).

Using diphenylfuran (10) instead of 2, isobenzofurans 7, 8, 9 were obtained. In this way, six different kinds oftriptycene building blocks bearing isobenzofuran motif were synthesized.
OBr

BrOO
Br

BrBr

Py

PhLi+O

THF/toluene–15 °C → rt

Br

1

Py

N N
toluenert, 3 hO41%2)

2

N N

31%

3

O
O4(tris-isobenzofuran)

Synthesized Triptycene Isobenzofurans
BrBrBrBr

BrBrOBrBrPhBrBrOBrPhO BrOO

756(mono-isobenzofuran) (bis-isobenzofuran)
PhOPhOPhPh

PhO

8Ph

Ph

Ph
PhPh

PhOO

9Ph1) Conditions A: n-BuLi (1.5 eq) in PhCl, –15 °C → rt, overnight2) Conditions B: PhLi (4.0 eq) in THF/toluene, –15 °C → rt, overnight

10Figure 2. Synthesis of triptycene isobenzofurans

Next, cycloaddition of tris-isobenzofuran (4) and anthraquinone (11) was conducted and following
aromatization in acidic conditions gave the tris-pentacenequinone (12) in 14% as a two-step yield. Furthertransformation toward pentacene derivatives was also performed. TIPS ethynyl group was added to the 12,then upon the treatment of SnCl2 and 10% HCl in THF solution gave the desired tris-pentacene (13) in 16%
yield (2 steps). Further studies toward electronic and photochemical characteristics of 13 will be studied.
1)

OO
OO

OOO

4(tris-isobenzofuran)

11O2) TsOH·H2O
toluene
70 °C, 1 hO
O

14% (2 steps)OR12(tris-pentacenequinone)
R1) TIPSLiR2) SnCl2, 10% HCl16% (2 steps)

RR

R = TIPS13(tris-pentacene)
Figure 3. Synthesis of tris-pentacenequinone and tris-pentacene
RIn conclusion, the highly reactive triptycene based isobenzofurans were synthesized and applied to thesynthesis of tris-pentacene derivative, a high-ordered iptycene derivative. We will continue our study onsupermolecular activity of this three-dimensional π-extended iptycenes as a potential organic material.

Conference Presentations(1) Sunna Jung and Toshiyuki Hamura, “Synthetic Study of High-Ordered Iptycene Derivatives Using
Isobenzofuran as a Reactive Platform”, Spring CSJ meeting, 2F1-19 (Presentation), Kanagawa, Japan, 2017,March. (English)