Transannular Cyclization of Dehydrobenzo[12]annulene Induced by

Nucleophilic Attack

Tobe 　 LabAyumi Yoshizaki

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Contents• Introduction - π-Conjugated compounds Application Frame-work Dibenzoindacene • Motivation• Experiments & Results• Future Work• Summary

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π-Conjugated compounds 2D π-conjugated compounds have attracted attention

as organic semiconductors.　　

N=1 N=2 N=3 N=4 N=5 N→∞Ethylene

・・・

Allyl Radical Butadiene

E

Energy bands of olefins

3

Pentadienyl Radical

Application

Pentacene has already been put to practical use in thin-film transistor. But, it unfortunately is prone toward oxidative degradation.

There is demand for alternative, acene-like topologies.

Pentacene

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Frame-work 　• Acenes 　 condensed benzene ring in a line

• Dibenzopentalene

• Dibenzoindacene

Attractive Structural Motifs

Pentalene

Indacene

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Dibenzoindacene

• Antiaromatic (20 π-electorons)• p-Xylylene core• More resistant to degrade acenes It does not possess any internal s-cis diene linkage.　　　　　　　　　

　 Fully conjugated dibenzoindacenes are extremely rare.

p-Xylylene

s-cis diene

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Benzene(4n+2) π

The Hückel Rule• Aromatic (4n+2) π-electrons (n = 0, 1, 2, 3, …)• Antiaromatic (4n) π-electrons (n = 0, 1, 2, 3, …)

Cyclic π-Conjugated Polyene

Ex

1,3-Cyclobutadiene(4n) π

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Example １ of Dibenzoindacene

• Transannular Cyclization is induced by Iodine, electrophilic.

• Tetraiodides These rapidly oxidized to the corresponding diones

upon exposure to air.

R

R

R

R

I2, PhHR

R

R

R

I

I

I

I

R

R

R

R

I

I

O

O

T. M. Swager, et al. J. Org. Chem. 1994, 59, 1294-1301.

R = H, Decane, DodecaneTetraiodides

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R

R

R

R

I2, PhHR

R

R

R

I

I

I

I

R

R

R

R

I

I

O

O

TIPSA, CuI[PdCl2(PPh3)2]

iPr2NH, THF60 °C

R

R

R

R

O

O TIPS

TIPS

1. TIPSCCLi THF, 0 °C2. H3O+

R

R

R

R

TIPS

TIPS

TIPS

TIPS

OH

HO

SnCl2

toluene, 80 °CR

R

R

R

TIPS

TIPS

TIPS

TIPS

Example 2 of Dibenzoindacene• The Synthesis of Stable DibenzoindacenesMultiple Steps

M. M. Haley, et al. Angew. Chem. Int. Ed. ASAP

1 : R = H2 : R = Decane

2 or 3 months

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Electronic Absorption Spectra

pentacene

2

1

M. M. Haley, et al. Angew. Chem. Int. Ed. ASAP 10

BuO

BuO

OBu

OBu

1. BuLi2. BuI

BuO

BuO

Bu

OBu

OBu

BuO

BuO

Bu

Bu

Bu

1. BuLi2. BuI

OBu

OBuBuBu

Motivation• The dibenzoindacene (tetraiodides) synthesized in a

single step is unstable.• Multiple steps are required to synthesize the stable

one.

• For easy synthesis, a short-step synthesis rout is required.

• I have studied to synthesize a dibenzoindacene with transannular cyclization.

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Bu Li

Bu Bu

Bu

Me

1. BuLi, THF, -78 °C2. MeI

BuLi, THF, -78 °C MeI

MeI

Transannular 　 Cyclization

J.Otera, et al. Chem. Lett. 2008, 37, 1296-1297. 12

Synthesis of Dehydrobenzo[12]annulene

HO

HO

BuBr, K2CO3

DMF

BuO

BuO

I2, H5IO6

EtOH

BuO

BuO

I

I

TMS

BuO

BuO

TMS

TMSA,Pd(PPh3)4, CuI

Et3N

Cu(OAc)2• H2O

pyridine/MeOH/THF

K2CO3

MeOH/THF

BuO

BuO OBu

OBu

BuO

BuO

96% 98%

86%

36% (2 steps)

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Dehydrobenzo[12]annulene

BuO

BuO OBu

OCH2CH2CH2CH3

12

H

3 4 5

Identification by NMR

1

2 3 45

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BuO

BuO OBu

OBu1. BuLi2. BuI

BuO

BuO

Bu

OBu

OBu

Bu

THF

34%

Transannular Cyclization of Dehydrobenzo[12]annulene

Various reaction conditions were investigated. （ concentration of material, equivalent of BuLi, reaction time, reaction temperature ）

Reaction conditions were optimized.

3

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Identification by NMRBuO

BuO

CH2C3H7

OCH2C3H7

OBu

CH2C3H7

H

H

H

H3

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Future Work 1

BuO

BuO

Bu

OBu

OBu

BuO

BuO

Bu

Bu

Bu

1. BuLi2. BuI

Bu

THF

Bu

OBu

OBu

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• I will study reaction conditions for the next transannular cyclization.

• Then I will mesure its physical properties, and tune them by using other reagents instead of BuLi and BuI.

Future Work ２• Bergman Cycloaromatization

OH

OHPhH

70 °C, 4 h

OH

OH+

OH

OH

OH

OH

OH

OH

ΔPhH

W. M. Dai, et al. J. Am. Chem. Soc. 1992, 114, 7360-7371.

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Future Work ２• Bergman Cycloaromatization of 3

BuO

BuO

Bu

OBu

OBuBu

PhH70 °C

OBu

OBu

BuO

BuO

Bu

Bu

OBu

OBu

BuO

BuO

Bu

Bu

PhH70 °C

OBu

OBu

BuO

BuO

Bu

Bu

OBu

OBu

BuO

BuO

Bu

Bu

+

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Summary

• Dibenzoindacene are rare fully conjugated species.

• The reaction conditions for transannular cyclization of dehydrobenzo[12]annulene were optimized.

• Future works are transannular cyclization of the next step and bergman cycloaromatization to synthesize π-conjugated compounds with short-steps.

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