Supramolecular Laboratory Chulalongkorn University (THAILAND)

Synthesis of Stilbene Crown Ether Calix[4]arenes and Their Isomerization

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AbstractAbstract

Five stilbene crown ether calix[4]arene derivatives were prepared in one step from the corresponding

bisaldehyde calix[4]arenes be McMurry coupling. The coupling reaction yielded both cis and trans

stilbenes from the o- and m-bisaldehydes. Only cis isomer however produced from the reaction of the p-isomer. The cis and trans geometry deduced from NMR and UV-VIS data ingood agreement with the spectra of model compounds, stilbene and dimethoxy stilbene. Unlike the diazobenzene crown ether calix[4]arene

derivatives, the stilbene crown ether calix[4]arene derivatives did not undergo thermal isomerization. All synthesized stilbene crown ether calix[4]arenes can photoisomerize and a photostationary state was

observed.

Supramolecular Laboratory Chulalongkorn University (THAILAND)

Synthesis of Stilbene Crown Ether Calix[4]arenes and Their Isomerization

ObjectiveObjective

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Synthesize stilbene crown ether calix[4]arenes

Study the photo-isomerization properties of the synthesized calix[4]arenes

Supramolecular Laboratory Chulalongkorn University (THAILAND)

Synthesis of Stilbene Crown Ether Calix[4]arenes and Their Isomerization

DiazobenzeneDiazobenzene

Azobenzene crown ether calix[4]arenes can isomerize between 2 geometrical isomers in the dark, at room temperature and can be catalyzed by light.

HO HO O O

O O

N NN NO O

HHO O O O

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Supramolecular Laboratory Chulalongkorn University (THAILAND)

Synthesis of Stilbene Crown Ether Calix[4]arenes and Their Isomerization

IsomerizationIsomerization

N NN

N

For azobenzene, there are two possible isomerization coordinates; 1. Twisting about the N=N double bond, and 2. in-plane inversion at one of the two nitrogen atoms.

Stilbene can not isomerize in the dark but the UV light is required to control the isomerization 4

Supramolecular Laboratory Chulalongkorn University (THAILAND)

Synthesis of Stilbene Crown Ether Calix[4]arenes and Their Isomerization

StrategyStrategy

O O O OH H HH

K2CO3, CH3CN,Bu4N+Br-

OBr

O

H

O

O HO O O

O

O O

TiCl4 / Zn THF

HHO OO O

O O

McMurry is the shortest way to synthesized stilbenefrom bisaldehyde using TiCl4 and Zn as reducing agent.

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Supramolecular Laboratory Chulalongkorn University (THAILAND)

Synthesis of Stilbene Crown Ether Calix[4]arenes and Their Isomerization

% Y i e l dC o m p o u n d

c i s t r a n sc i s : t r a n s

R a t i o

o - 1 5 7 1 0 8 5 : 1 5m - 1 2 0 8 7 3 : 2 7p - 1 5 1 0 1 0 0 : 0

Products ObtainedProducts Obtained

The m-bisaldehyde yielded 28% of the stilbene (m-1)and 20% of the corresponding pinacol by-product.The o- and p-bisbenzaldehydes gave higher yields ofstilbenes (o-1 and p-1), 67% and 51%, respectively.Both cis and trans stilbenes were obtained from thecoupling o- and m-bisbenzaldehydes but only the cisstilbene was obtained from the p-isomer. 6

Supramolecular Laboratory Chulalongkorn University (THAILAND)

Synthesis of Stilbene Crown Ether Calix[4]arenes and Their Isomerization

OrientationOrientation

The predominant of the cis- over trans-products suggests that the pre-organized structure of bisbenzaldehydes controls the geometry of products. The short ethylene glycol linkages are less likely to allow the threo orientation resulting in less trans product. This becomes more obvious for the coupling of the p-bisbenzaldehyde in which the threo orientation would be most difficult to form and no trans-isomer was observed.

Erythro Threo

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O

H

RR

O

H

R

O

HR

O

H

Supramolecular Laboratory Chulalongkorn University (THAILAND)

Synthesis of Stilbene Crown Ether Calix[4]arenes and Their Isomerization

c i s I s o m e r t r a n s I s o m e rC o m p o u n d

m a x ( n m ) c m – 1 M – 1 ) m a x ( n m ) c m – 1 M – 1 )

o - 1 2 9 2 1 9 3 2 12 9 13 3 3

3 0 1 0 62 8 4 9 2

m - 1 2 8 6 2 0 9 5 52 9 13 0 83 2 0

2 7 4 8 82 4 8 6 62 4 6 2 9

p - 1 2 8 3 1 6 6 3 2 N A N A

S t i l b e n e2 2 32 7 6

2 0 6 0 01 0 9 0 0

2 2 72 9 43 0 7

2 1 0 0 03 3 2 0 03 2 1 0 0

UV AbsorptionUV Absorption

The shorter max and lower extinction coefficients of allcis-isomers comparable to the model compounds was observed.

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Supramolecular Laboratory Chulalongkorn University (THAILAND)

Synthesis of Stilbene Crown Ether Calix[4]arenes and Their Isomerization

PhotostationaryPhotostationary

Stilbene crown ether p-tert-butylcalix[4]arenes did notisomerize under room light but readily isomerized underUV light. The photo-stationary states were observed forall isomers.

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% Isomer at photostationary stateCompound

cis-isomer trans-isomero-1 15 85m-1 70 30p-1 75 25

Supramolecular Laboratory Chulalongkorn University (THAILAND)

Synthesis of Stilbene Crown Ether Calix[4]arenes and Their Isomerization

AcknowledgementAcknowledgement

This work was supported by:

Thailand Research Fund (TRF) (PDF/13/2541)

Ministry of University Affairs (UDC39/2543)

National Science and Technology Development Agency (NSTDA) (CO-B-11-11-09-202D).

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