Allylation reactions of aromatic aldehydes and ketones with lithium in THF under ultrasonic irradiation

Article abstract of DOI:10.3184/030823407X198320

The allylation reactions of aromatic aldehydes and ketones were carried out in 69-90% yield using Li-THF system under ultrasound irradiation at r.t. for 40 min. The reactions of the same system with stirring gave homoallyl alcohols in 49-67% yield at r.t.

Full text of DOI:10.3184/030823407X198320

162 RESEARCH PAPER
MARCH, 162–163
JOURNAL OF CHEMICAL RESEARCH 2007
Allylation reactions of aromatic aldehydes and ketones with lithium in
THF under ultrasonic irradiation
Yan-Jiang Biana*, Jian-You Zhanga, Ji-Tai Lib
aDepartment Of Chemistry, Langfang Normal College, Hebei, Langfang 065000, P. R. China
bCollege of Chemistry and Environmental Science, Hebei University, Baoding 071002, P.R China
The allylation reactions of aromatic aldehydes and ketones were carried out in 69–90% yield using Li–THF system
under ultrasound irradiation at r.t. for 40 min. The reactions of the same system with stirring gave homoallyl alcohols
in 49–67% yield at r.t. for 4 h.
Keywords: ultrasound irradiation, allylation, lithium
Carbon–carbon bond formation is the essence of organic
In order to optimise the conditions we screened the reaction
synthesis. A powerful method for constructing carbon–
of benzaldehyde with allyl bromide in a variety of Li–THF
carbon bond is the allylation reaction between an allyl
halide and carbonyl compounds.1 Metals such as tin,2-6
indium,7 samarium,8 gallium,9 yetterbium,10 manganese,11
magnesium,12 zinc,13-18 have been found to be effective for
such transformations. However, there were always difficulties
due to long reaction times or reduction reactions.
reaction systems (Table 1). From the results in Table 1,
the optimum reaction conditions are benzaldehyde: allyl
bromide: Li = 1:3:8, time: 40 min. In order to demonstrate the
positive effect of ultrasound irradiation on the reaction, the
same reaction in entry (a–i) (Table 2) also has been studied
under stirring.
Ultrasound has increasingly been used in organic synthesis.
Many metal-mediated organic reactions have been accelerated
under ultrasound.19-23 A search of the literature revealed
that no report has appeared on the results of the allylation
reactions using lithium to date. Herein, we report the results of
the allylation reactions of aromatic aldehydes and ketones by
Li with stirring or under ultrasound irradiation respectively.
As shown in Table 2, the allylation reaction was carried
out under ultrasonic irradiation giving higher yield. For
example, benzaldehyde (1a), furfural (1c) and piperonal (1e)
reacted with allyl bromide in Li–THF system giving nearly
quantitative yields of the corresponding homoallylic alcohols
(2a, 2c, 2e) under ultrasonic irradiation for 40 min. In the case
of stirring for 4 h, the yields of the corresponding homoallylic
Table 1 Optimisation of the allylation reaction of C6H5CHO mediated by Li in THF under ultrasonic irradiation with various conditions
Entry
Reaction system
THF/ml
Time/min
Isolated yield/%
1
2
Benzaldehyde:allyl bromide:Li = 1:1:1
Benzaldehyde:allyl bromide:Li = 1:2:1
Benzaldehyde:allyl bromide:Li = 1:3:1
Benzaldehyde:allyl bromide:Li = 1:4:1
Benzaldehyde:allyl bromide:Li = 1:3:2
Benzaldehyde:allyl bromide:Li = 1:3:4
Benzaldehyde:allyl bromide:Li = 1:3:6
Benzaldehyde:allyl bromide:Li = 1:3:8
Benzaldehyde:allyl bromide:Li = 1:3:9
Benzaldehyde:allyl bromide:Li = 1:3:8
4
4
4
4
4
4
4
4
4
4
40
40
40
40
40
40
40
40
40
50
41
53
3
62
4
62.4
75
5
6
79
7
88
8
90
9
90.2
90.3
10
Isolated yield based on the substrate; THF: 4 ml; ultrasound irradiation: 40KHz: temperature: r. t.
Table 2 The allylation reactions of aromatic aldehydes and ketones mediated by Li in THF under ultrasound irradiation or stirring
OH
C
O
C
Li/THF
u.s.
CH2
CH
CH2
R1
CH2
R2
CH
CH2
R2
Br
R1
1 (a-h)
2 (a-h)
Entry
Substrate
Isolated yield/%
Rf*
Stirring (4 h)
Ultrasound (40 min)
1a
1b
1c
1d
1e
1f
C6H5CHO
4-ClC6H4CHO
Furfural
66
66
54
49
67
59
56
57
90
83
90
75
89
81
70
69
0.61
0.59
0.52
0.68
0.53
0.50
0.81
0.68
Cinnamaldehyde
3,4-(OCH2O)C6H3CHO
4-CH3OC6H4CHO
C6H5COC6H5
1g
1h
C6H5COCH3
Isolated yield based on the substrate; Ultrasound irradiation time for 40 min and stirring for 4 h.
aEluant: petroleum ether: diethyl ether (V:V) = 1:1
* Correspondent. E-mail: bianyanjiang@126.com
PAPER: 06/4482

JOURNAL OF CHEMICAL RESEARCH 2007 163
2d:24 Oil; 1H NMR: δH 2.02 (1H, s), 2.40–2.50 (2H, m), 4.32–4.44
(1H, t), 5.14–5.26 (2H, m), 5.78–5.88 (1H, m), 6.60–6.72 (1H, m),
7.18–7.40 (5H, m). MS m/z (%): 174 (M+). IR (KBr) ν 3400, 1642,
988 cm-1.
alcohols were only 66, 54 and 67% respectively. The data
indicates that the reaction time is reduced and the yields are
improved under ultrasound irradiation condition. In order to
examine the effects of the carbonyl group of ketone, we choose
benzophenone (1g) and acetophenone (1h) as substrates.
It was found that the corresponding products were obtained
respectively in 70 and 69% yield under ultrasound irradiation.
We infer that the steric hindrance around the carbonyl group
may inhibit the allylation reactions.
Based on these results, we have demonstrated that
ultrasound irradiation can markedly speed up the allylation
reaction of aromatic aldehydes and ketones with Li–THF
system. The main advantage of the present procedure is the
higher yield and the shorter reaction time. This new approach
has considerable practical value due to its efficiency and
simplicity.
2e:24 Oil; 1H NMR: δH 2.40 (t, J = 6.4 Hz, 2H), 2.49–2.60 (br, 1H),
4.56 (t, J = 6.4 Hz, 1H), 5.08 (m, 1H), 5.10 (m, 1H), 5.68–5.76 (m,
1H), 5.90 (s, 2H), 6.68–6.74 (m, 2H), 6.80 (s, 1H). MS m/z (%): 192
(M+). IR (KBr) ν 3420, 1192, 990 cm-1.
2f:24 Oil; 1H NMR: δH 2.43 (q, J = 6.6 Hz, 2H), 2.79–2.86 (br, 1H),
3.76 (s, 3H), 4.61 (t, J = 6.6, 1H), 5.04–5.09 (m, 1H), 5.08–5.12 (m,
1H), 5.72–5.82 (m, 1H), 6.82 (d, J = 8.8, 2H), 7.21 (d, J = 8.8, 2H).
MS m/z (%): 178 (M+). IR (KBr) ν 3410, 1191, 991.
2g:24 Oil; 1H NMR: δH 2.48–2.72 (s, 1H), 3.12–3.40 (d, 2H), 5.12–
5.58 (d, 2H), 5.68–6.02 (m, 1H), 6.96–7.80 (m, 10H). MS m/z (%):
224 (M+). IR (KBr) ν 3505, 1196, 994.
2h:24 Oil; 1H NMR: δH 1.23–1.42 (s, 3H), 1.48–1.73 (s, 1H), 2.26–
2.60 (d, 2H), 4.62–5.08 (d, 2H), 5.16–5.69 (m, 1H), 6.86–7.39 (m,
5H). MS m/z (%): 162 (M+). IR (KBr) ν 3430, 1192, 990.
The project was supported by Natural Science Foundation
of Hebei Province (B2006000969), Science and Technology
Foundation of Hebei Province (04213041) and Science
Foundation of Hebei Lang Fang Normal College (200602).
Experimental
Liquid substrates were distilled before use. IR spectra were recorded
on a Bio-Rad FTS-40 spectrometer (KBr). MS spectra were
determined on anAEI MS-50 SD90 spectrometer (EI, 70 eV). 1H NMR
spectra were measured on VXR-300S spectrometer (300 MHz) by
using CDCl3 as solvent and TMS as internal standard. Sonication
was performed in a Shanghai SK8200LH ultrasonic cleaner (with a
frequency of 40k Hz and a nominal power 500W; Shanghai Kudos
Ultrasonic Instrument Co., Ltd). The reaction flask was located at the
maximum energy area in the cleaner, where the surface of reactants
is slightly lower than the level of the water. The reaction temperature
was controlled by addition or removal of water from ultrasonic bath.
A50 ml Pyrex flask was charged with the desired aldehyde or ketone
(1 mmol), allyl bromide (3 mmol), lithium (8 mmol) and THF(4 ml).
The mixture was irradiated in the water bath of an ultrasonic cleaner
in air at 25–30°C for 40 min (or stirring 4 h). After the completion
of the reaction, the resulting suspension was filtered to remove
the Li. The filtrate was extracted with ethyl acetate (3 × 10 ml).
The combined organic layers were washed with saturated aqueous
NaHCO3 solution and brine, dried over anhydrous magnesium sulfate
for 12 h. Ethyl acetate was evaporated under reduced pressure to give
the crude product, which was separated by column chromatography
on silica (200–300 mesh), eluted with a mixture of petroleum ether
and diethyl ether. All the products were identified by their IR, MS,
1H NMR, spectral data.
Received 12 February 2007; accepted 13 March 2007
Paper 07/4482
doi:10.3184/030823407X198320
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4.57 (t, J = 6.6 Hz, 1H), 5.05–5.08 (m, 1H), 5.10 (m, 1H), 5.68–5.72
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PAPER: 06/4482