A facile preparation of ethanolamines by direct irradiation of some carbonyl compounds in N,N-dimethylaniline

Article abstract of DOI:10.1016/S0040-4039(01)01784-1

Direct irradiation of some carbonyl compounds in N,N-dimethylaniline, without solvent, with 300 nm UV light afforded ethanolamines as the major product in moderate yields.

Full text of DOI:10.1016/S0040-4039(01)01784-1

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 8315–8317
A facile preparation of ethanolamines by direct irradiation of
some carbonyl compounds in N,N-dimethylaniline
Sung Sik Kim,* Yoon Jung Mah and Ae Rhan Kim
Department of Chemistry, Chonbuk National University, Chonju 561-756, South Korea
Received 2 July 2001; revised 17 September 2001; accepted 21 September 2001
Abstract—Direct irradiation of some carbonyl compounds in N,N-dimethylaniline, without solvent, with 300 nm UV light
afforded ethanolamines as the major product in moderate yields. © 2001 Elsevier Science Ltd. All rights reserved.
The photoproduct was isolated by flash column chro-
matography (silica gel, 230–400 mesh) using n-hexane
and ethyl acetate as the eluent. As is clearly seen,
irradiation of carbonyl compounds in aromatic amines,
without using other solvents, can prevent the prevalent
reaction, e.g. photoreduction of carbonyl compounds
by amines. The formation of ethanolamine 2 can be
easily interpreted by the intermolecular H-abstraction
which leads to radical intermediates I and II, as shown
in Scheme 1. Some aldehydes, such as 1-naphthalde-
hyde 3, vanillin 5 and t-cinnamaldehyde 7, were also
irradiated in DMA to give the corresponding
ethanolamines such as 4, 6 and 8, respectively (Table 1).
The photochemistry of carbonyl compounds with
amines is of particular interest since it is an efficient
process for the synthesis of diols or other types of
reductive products.1–5 Photoreduction of benzophenone
by amines involves abstraction of hydrogen and leads
to benzpinacol.1,2 In the case of the photochemical
reactions of benzaldehyde with amines in methanol,
ethanolamine6,7 is produced in poor yield.3 Recently,
we found that direct irradiation of some carbonyl com-
pounds in amines, without using other solvents, over-
come a serious problem in these reactions, i.e. low
chemical yields of photoproducts and the formation of
many kinds of products.
In contrast, photoreactions of 2-dimethylaminopyridine
9 with aldehydes, such as benzaldehyde 1, resulted in
the formation of not only ethanolamine 10 (47%) but
also its oxidized products as a-aminoketone (21%).
Ethanolamines isolated here were found to be the mix-
tures of conformers except for 4 which has diagnostic
Irradiation of benzaldehyde 1 (0.1 mL, 1 mmol) in
N,N-dimethylaniline (DMA, PhNMe2, 10 mL) with 300
nm UV light (Rayonet Photochemical Reactor, Model
RPR-208) in the atmosphere of nitrogen gas for 24 h
resulted in ethanolamine 2 in 79% yield with % con-
formeric excess 46, as shown in Scheme 1 and Table 1.
When 1 (1 mmol) and DMA (2 mL, 16 mmol) were
irradiated in methanol (10 mL), the chemical yield of 2
decreased to 25%. The photoreaction of 1 (1 mmol) and
DMA (1 mmol) in methanol (10 mL) for 24 h afforded
2 only in 8% yield.
1
peaks at l 3.48 (CH2, d) and 5.60 (CH, t) in H NMR
(CDCl3). The carbon signals of CH2 and CH group
were observed at l 62.00 and 71.70, respectively.
Some ketones were also investigated in which
ethanolamines were produced as the major products
O
hν
Me
OH
Me
N
OH
+
N
Ph
H
.
Ph CH2
Ph
Ph
Ph
H
PhNMe2
.
2
1
I
II
Scheme 1.
Keywords: carbonyl compound; N,N-dimethylaniline; ethanolamine.
* Corresponding author. Tel.: (+82)63-270-3414; e-mail: hvssk@moak.chonbuk.ac.kr
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)01784-1

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S. S. Kim et al. / Tetrahedron Letters 42 (2001) 8315–8317
Table 1. Formation of ethanolamines by direct irradiation of aldehydes (1 mmol) in amines (10 mL) with 300 nm UV light
for 24 h
Ethanolamine
Aldehyde
Amine
% ce* % Yield
Structure
O
Me OH
N
1
H
2
4
PhNMe2
PhNMe2
46
79
66
Ph
O
Me OH
N
3
5
100
H
O
Ph
Ph
Ph
O
H
Me OH
N
MeO
HO
OMe
OH
H
PhNMe2
PhNMe2
6
8
26
71
Me OH
N
7
12
48
73
47
O
Me OH
N
N
N
NMe2
1
H
10
9
*: % conformeric excess.
1
(Scheme 2). When irradiated acetone 11 (1 mmol) in
DMA (10 mL) for 24 h, ethanolamine 12 was produced
in 21% yield (Scheme 2). Prolonged irradiation of 12
for 72 h gave rise to N-methyl-N-phenylethanolamine
13 in 3% yield. 1H NMR spectrum (CDCl3) shows
peaks at l 7.20–6.65 (5H), 3.75 (2H, t), 3.40 (2H, t),
2.90 (3H, s). Molecular ion peak was observed at m/e
151 in mass spectrum (EI). In order to confirm the
formation of 13, simple carbonyl compounds (1 mmol)
such as acetophenone 14 (R=Ph, R%=Me), benzophe-
none 15 (R=R%=Ph), and ethyl acetate 16 (R=Me,
R%=OEt) were irradiated in DMA (10 mL) for 24 h to
yield the same compound 13, in 57, 59 and 42% yields,
respectively, in one pot. It is interesting to note that
N-methyl-N-phenylethanolamine 13 can be produced
from direct irradiation of 14–16 without using trouble-
some gas, i.e. formaldehyde.
39 and 38% yield, respectively (Scheme 3). H NMR
spectrum (CDCl3) of 19 showed three diagnostic peaks
at l 3.40 (NCH2), 2.99 (NCH3) and 1.97 (OH). A
molecular ion peak was also observed at m/e 205 in EI
mass spectrum.
In a similar manner, a reductive photoadduct 22 as
ethanolamine was also isolated in 11% yield, when
anthraquinone 21 (1 mmol) was irradiated in DMA (10
mL) for 24 h (Scheme 4). Three peaks were observed at
l 3.58 (NCH2), 2.99 (NCH3) and 6.60 (OH) in 1H
NMR spectrum (CDCl3) of 22. On the other hand,
photoreaction of tetrachloro-1,4-benzoquinone 23 (1
mmol) with DMA (10 mL) for 24 h gave 4-(dimethyl-
amino)benzaldehyde 25 (50%) and ethanolamine 26
(10%) which was derived from DMA and 25. Irradia-
tion of 24 in DMA also afforded 25 (45%) and 26
(37%).
The photoreactions of cyclic ketones, such as cyclopen-
tanone 17 and cyclohexanone 18, in DMA also
afforded the same type of ethanolamines 19 and 20 in
In the case of 1,4-benzoquinone, 1,4-naphthoquinone
and 1,2-naphthoquinone, different type of products, i.e.
N-methyl-N-phenylaminoquinones were produced as
the major product when irradiated in DMA. In sum-
mary, we found that various ethanolamines can be
prepared easily by direct irradiation of some carbonyl
Me
N
O
OH
hν
Me
N
hν
Ph
OH
Ph
Ph
PhNMe2
12
11
13
OH
Me
N
O
hν
Ph
n
Me
N
O
O
hν
PhNMe2
n
hν
PhNMe2
OH
H
H
R
R’
PhNMe2
17: n = 1
18: n = 2
19: n = 1
20: n = 2
14 - 16
13
Scheme 3.
Scheme 2.

S. S. Kim et al. / Tetrahedron Letters 42 (2001) 8315–8317
8317
O
O
HO
Me
N
hν
Ph
O
PhNMe2
22
21
OH
O
Me
N
O
hν
X
X
X
X
hν
PhNMe2
Ph
H
PhNMe2
NMe2
Me2N
O
26
25
23 (X=Cl), 24 (X=Br)
Scheme 4.
compounds, such as aldehydes, ketones and anthra-
quinone, in aromatic amines without using other sol-
vents.
Rev. 1973, 73, 141.
2. Cohen, S. G.; Stein, N. M. J. Am. Chem. Soc. 1971, 93,
6542.
3. Kessar, S. V.; Mankotia, A. K. S.; Scaiano, J. C.; Barra,
M.; Gebicki, J.; Huben, K. J. Am. Chem. Soc. 1996,
118, 4361.
Acknowledgements
4. Groth, T.; Grotli, M.; Lubell, W. D.; Miranda, L.
P.; Meldal, M. J. Chem. Soc., Perkin Trans. 1 2000,
4258.
5. Miyasaka, H.; Kiri, M.; Morita, K.; Mataga, N.; Tani-
moto, Y. Bull. Chem. Soc. Jpn 1995, 68, 1569.
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Angew. Chem., Int. Ed. Engl. 1997, 36, 95.
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Watanabe, M. Tetrahedron 1997, 53, 4579.
This work was supported by Korea Research Founda-
tion (Grant No. KRF-2000-015-DP0305).
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