A convenient synthesis of conjugated ω-arylpolyenals via Wittig reaction with (1,3-dioxan-2-yl-methyl)triphenylphosphonium bromide/sodium hydride

Article abstract of DOI:10.1081/SCC-120015766

Commercially available reagent, (1,3-dioxan-2-yl-methyl)triphenylphosphonium bromide, sodium hydride and a catalytic amount of 18-crown-6 has proven efficient system for vinylic extension of ω-arylpolyenals.

Full text of DOI:10.1081/SCC-120015766

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A Convenient Synthesis of Conjugated ω-Arylpolyenals
via Wittig Reaction with (1,3-Dioxan-2-yl-
methyl)triphenylphosphonium Bromide/Sodium
Hydride
a
a
a
a
Damian Plażuk , Izabela Janowska , Arkadiusz Kłys , Asia Hameed & Janusz Zakrzewski
a
a
Department of Organic Chemistry, University of Łódź, Łódź, Narutowicza 68, Poland
Published online: 17 Aug 2006.
To cite this article: Damian Plażuk , Izabela Janowska , Arkadiusz Kłys , Asia Hameed & Janusz Zakrzewski (2003): A
Convenient Synthesis of Conjugated ω-Arylpolyenals via Wittig Reaction with (1,3-Dioxan-2-yl-methyl)triphenylphosphonium
Bromide/Sodium Hydride, Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic
Chemistry, 33:3, 381-385
To link to this article: http://dx.doi.org/10.1081/SCC-120015766
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Õ
SYNTHETIC COMMUNICATIONS
Vol. 33, No. 3, pp. 381–385, 2003
A Convenient Synthesis of Conjugated
v-Arylpolyenals via Wittig Reaction with
1,3-Dioxan-2-yl-methyl)triphenylphosphonium
Bromide/Sodium Hydride
(
Damian Pla z_ uk, Izabela Janowska, Arkadiusz Klys, Asia Hameed,
and Janusz Zakrzewski*
Department of Organic Chemistry,
University of Lodz´ , Lodz´ , Narutowicza 68 Poland
´ ´
ABSTRACT
Commercially available reagent, (1,3-dioxan-2-yl-methyl)triphenyl-
phosphonium bromide, sodium hydride and a catalytic amount
of 18-crown-6 has proven efficient systemfor vinylic extension of
o-arylpolyenals.
Key Words: Aldehyde; Unsaturated aldehyde; o-Arylpolienal;
Wittig reaction.
*
Correspondence: Janusz Zakrzewski, Department of Organic Chemistry,
University of Lo
6
´
dz
´
, 90-136 Lo
´
dz
´
, Narutowicza 68 Poland; Fax: þ4842-
786583; E-mail: janzak@krysia.uni.lodz.pl.
3
81
DOI: 10.1081/SCC-120015766
Copyright & 2003 by Marcel Dekker, Inc.
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com

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3
82
Pla z_ uk et al.
Conjugated o-arylpolyenals 1 attract interest as starting materials for
synthesis of conjugated molecules displaying unusual electronic, optical
or magnetic properties such as a,o-disubstituted polyenes 2 and ‘‘push–
pull’’ polyenes 3 for the second-order nonlinear optics (Sch. 1).
[
1–4]
Among various synthetic methods leading to 1 particularly interest-
ing seems the stepwise vinylic extension of aromatic aldehydes via Wittig
reaction with 1,3-dioxolan-2-yl-methylenephosphoranes (generated from
1,3-dioxolan-2-yl-methylphosphonium salts 4a–b and a base), followed
by acidic hydrolysis of the dioxolane function (Sch. 2):
[
5–9]
[
5]
Cresp, Sargent and Vogel used in this reaction (1,3-dioxan-2-yl-
methyl)triphenyl-phosphonium bromide 4a and lithium me thoxide in
N,N-dimethylformamide (DMF) or methanol. They obtained the pro-
ducts of the vinylic extension of aromatic aldehydes such as 4-nitrobenzal-
dehyde or piperonal in relatively good yields (68 and 58%, respectively).
[
6]
Later Spangler and McCoy used 4a and sodiumethoxide in DMF to
extend a,b-unsaturated aldehydes in which the carbonyl function was
strongly deactivated by electron-withdrawing substituents such as
4-(N,N-dimethylamino)cinnamaldehyde and 4-methoxycinnamaldehyde
but obtained only ‘‘vanishingly small’’ yields of the products. They
[
6]
[7]
and others used in these cases the more reactive salt 4b, which gave
the corresponding extended aldehydes in 71 and 79%. Compound 4b was
Scheme 1.
Scheme 2.

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v-Arylpolyenals
383
Table 1. Products 1 obtained fromtheir containing ( n ꢀ 1) olefinic bonds
precursors by Wittig reaction with 4b/NaH (ꢁ4 mole equiv.)/18-crown-6.
Entry
Product
Ar
n
Yield (%)
1
2
3
4
5
6
7
8
9
1a
1a
1b
1c
1c
1d
1e
1f
4-Me N–C H –
2
2
3
1
1
2
3
1
2
92
54
2
2
2
6
6
6
4
4
4
a
4-Me
4-Me
N–C
N–C
H
H
–
–
65
85
Ferrocenyl
Ferrocenyl
Ferrocenyl
Ferrocenyl
4-Pyridyl
b
37
82
92
89
58
1g
4-Pyridyl
a
In the presence of 1 mole equiv. of NaH.
In the absence of 18-crown-6.
b
[
8,9]
also used in extension of strongly deactivated o-ferrocenyl polyenals
but the experimental details of these reactions are lacking.
In this paper we report that 4a reacts with aldehydes (including
strongly deactivated conjugated ones) in the presence of an excess of
sodiumhydride ( ꢀ4 mole equiv.) and a crown ether to give extended alde-
hydes in good yields. A list of the products 1 obtained fromtheir shorter,
containing (n ꢁ 1) ethylenic bonds precursors is shown in Table 1.
This procedure gives high yield of the extended products in the case
of 4-(N,N-dimethylamino)cinnamaldehyde (Entry 1, 92% compare with
[
6]
7
2% reported using 4b ), ferrocenylpolyenals (Entries 4–6) and 4-
pyridinecarboxyaldehyde (Entry 8). Lower, but still acceptable yields of
the extended products were observed in reactions with 5-(4-N,N-
dimethylaminophenyl)-2,4-pentadienal (Entry 3) and 3-(4-pyridyl)-pro-
penal (Entry 9). An excess of NaH, as well as the presence of 18-
crown-6 is necessary, otherwise the yields significantly drop down
(
Entries 2 and 5).
The above data indicate that the phosphorane formed from 4a is
sufficiently reactive toward the aldehyde function in o-arylpolyenals
and gives high yields of the extended products even with aldehydes
considered as strongly deactivated (e.g., o-ferrocenylpolyenals).
The lack of reactivity of 4a under conditions employed by Spangler
[6]
and McCoy can be explained assuming that there was no efficient
formation of the corresponding phosphorane. In our opinion there
must be some steric inhibition of deprotonation of 4a in comparison

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84
Pla z_ uk et al.
ꢂ
with 4b (e.g., compare ‘‘cone angles’’ of PPh and PBu , 145 and 132 ,
3
3
[10]
respectively ). The use of an excess of NaH extends its reactive surface
and the presence of the crown ether facilitates the transport of the ions into
solutions. These two facts ensure efficient deprotonation of 4a under
employed reaction conditions.
[
6]
In conclusion, we have found that despite earlier statement 4b can be
used in Wittig extension of polyenals when an excess of NaH and a catalytic
amount of 18-crown-6 is used for generation of the corresponding
phosphorance. An advantage of 4a over 4b is its stability and commercial
availability (Aldrich).
EXPERIMENTAL
General Procedure
To a stirred, argon-flushed solution of aldehyde (1.2 mmol), 4a (1.0 g,
.4 mmol) and 18-crown-6 (c.a. 5 mg) in THF (15 mL), NaH (120 mg,
mmol) was added in one portion. After 2 h stirring at r.t. the same amount
2
5
of NaH was added and the stirring was continued overnight. The reaction
mixture was quenched with water (Caution: exothermic reaction, external
cooling required), the extracted with ether (3 ꢃ 50mL). After evaporation
of ether, the residue was dissolved in the mixture of THF (50 mL) and
20% HCl (20mL), stirred 2 h at r.t., alkalized with 10% NaOH and
extracted with dichloromethane (5 ꢃ 50mL). Drying (Na SO ), solvent
2
4
removal and chromatography (SiO /chloroform) afforded the product.
2
Compounds 1a–g were identified by comparison with authentic sam-
[6,8,9] 1
ples.
H NMR (200 MHz, CDCl , d): Ia: 9.56 (d, 1H, J ¼ 8.0 Hz),
3
7
.41 (d, 2H, J ¼ 8.9 Hz), 7.26 (dd, 1H, J ¼ 15.0 Hz and J ¼ 10.2 Hz), 6.96
(
d, lH, J ¼ 15.2 Hz), 6.82 (dd, 1H, J ¼ 15.3 Hz and J ¼ 10.2 Hz), 6.69
(
d, 2H, J ¼ 8.8 Hz), 6.18 (dd, 1H, J ¼ 15.0 Hz and J ¼ 8.0 Hz), 3.03 (s, 6H).
Ib: 9.54 (d, 1H, J ¼ 8.1 Hz), 6.39–7.42 (m, 9H), 6.13 (dd, 1H, J ¼ 6.8 Hz,
J ¼ 8.2 Hz), 3.00 (s, 6H). Ic: 9.55 (d, J ¼ 8.0 Hz, 1H), 7.42 (d, J ¼ 15.6 Hz,
1
H), 6.34 (dd, J ¼ 15.6 Hz and J ¼ 8.0 Hz, 1H), 4.55 (s, 2H), 4.51 (s, 2H),
.16 (s, 5H). Id: 9.56 (d, J ¼ 8.0 Hz, 1H), 7.16 (dd, J ¼ 15.1 Hz and
4
J ¼ 11.2 Hz, 1H), 6.89 (d, J ¼ 15.2 Hz, 1H), 6.59 (dd, J ¼ 15.1 Hz and
J ¼ 10.9 Hz, 1H), 6.15 (dd, J ¼ 15.1 Hz and J ¼ 7.8 Hz, 1H), 4.49 (s, 2H),
4
.28 (s, 2H), 4.16 (s, 5H). Ie: 9.57 (d, J ¼ 8.1 Hz, 1H), 7.15 (dd, J ¼ 15.0 Hz
and J ¼ 11.0 Hz, 1H), 6.74 (dd, J ¼ 11.4 Hz and J ¼ 10.0 Hz, 1H), 6.64
d, J ¼ 9.9 Hz, 1H), 6.50 (dd, J ¼ 14.7 Hz and J ¼ 10.7 Hz, 1H), 6.41 (dd,
J ¼ 11.6 Hz and J ¼ 10.0 Hz, 1H), 6.17 (dd, J ¼ 15.2 Hz and J ¼ 8.2 Hz,
(

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v-Arylpolyenals
385
1
H), 4.45 (s, 2H), 4.37 (s, 2H), 4.14 (s, 5H). If: 9.78 (d, J ¼ 7.4 Hz, 1H), 8.72
(
d, J ¼ 6.0 Hz, 2H), 7.45 (d, J ¼ 15.4 Hz, 1H), 7.43 (d, J ¼ 6.0 Hz, 2H), 6.85
(
dd, J ¼ 7.4 Hz and J ¼ 15.4 Hz, 1H). Ig: 9.68 (d, J ¼ 8.0 Hz, 1H), 8.64 (d,
J ¼ 6.5 Hz, 2H), 7.35 (m, 2H), 7.23 (d, J ¼ 6.5 Hz, 2H), 6.85 (d, J ¼ 15.1 Hz,
1H), 6.38 (dd, J ¼ 8.0 Hz, J ¼ 15.1 Hz, 1H).
ACKNOWLEDGMENT
The financial support by the Polish State Committee for Scientific
Research (Grant 3T09 A 027 16) is gratefully acknowledged.
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10. Komiya, S. Synthesis ofOrganometallic Compounds —A Practical
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Received in the Netherlands January 7, 2002

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