Microwave-assisted synthesis of α-hydroxy ketone and α-diketone and pyrazine derivatives from α-halo and α,α′-dibromo ketone

Article abstract of DOI:10.1016/j.tetlet.2006.10.087

A novel reaction of α-halo ketone (α-bromo and α-chloro ketone) with irradiation under microwave gave the corresponding α-hydroxyketone and pyrazine derivative in good yields. In the case of α,α′-dibromo ketone, α-diketone was obtained. This reaction affords a new, clean and convenient synthetic method for α-hydroxyketone, α-diketone, α-chloro ketone and pyrazine derivative.

Full text of DOI:10.1016/j.tetlet.2006.10.087

Tetrahedron Letters 47 (2006) 9359–9364
Microwave-assisted synthesis of a-hydroxy ketone and a-diketone
and pyrazine derivatives from a-halo and a,a0-dibromo ketone
Takamitsu Utsukihara, Hiroaki Nakamura, Masashige Watanabe and C. Akira Horiuchi*
Department of Chemistry, Rikkyo (St. Paul’s) University, Nishi-Ikebukuro, Toshima-Ku, Tokyo 171-8501, Japan
Received 28 August 2006; revised 2 October 2006; accepted 13 October 2006
Available online 13 November 2006
Abstract—A novel reaction of a-halo ketone (a-bromo and a-chloro ketone) with irradiation under microwave gave the correspon-
ding a-hydroxyketone and pyrazine derivative in good yields. In the case of a,a0-dibromo ketone, a-diketone was obtained. This
reaction affords a new, clean and convenient synthetic method for a-hydroxyketone, a-diketone, a-chloro ketone and pyrazine
derivative.
ꢀ 2006 Elsevier Ltd. All rights reserved.
In the synthesis of various natural products and phar-
macologically active compounds, a-hydroxycarbonyl
compounds are potentially valuable synthetic inter-
mediates for the preparation of a range of compounds
of biological products such as substituted 2-amino-1-
arylethanols.1
During the course of our studies, a-iodo cycloalkanones
are important as intermediates in organic synthesis,
which were synthesized in our laboratory by a new
method.9 These iodo ketones are unstable and sensitive
to light. We thus tried to obtain useful products from
these iodo compounds. In this series, we have already
shown that the photo-dehydroiodination from a-iodo-
cycloalkanones in hexane affords a,b-unsaturated
ketones as major products, accompanied by photo-
reduced products as by-products. In hexane containing
a small amount of water, the substituted product
2-hydroxycycloalkanone was also obtained.10 In our
previous letter, we found that the reaction of a-iodo-
ketone with irradiation under a high-pressure mercury
lamp gave the corresponding a-hydroxyketone in good
yields.11 However, these methods suffer some draw-
backs. The most serious of these is the use of organic
solvents and ammonium cerium(IV) nitrate for the
synthesis of a-iodoketone.
a-Hydroxyketones are usually prepared by one of the
following methods: a-hydroxylation by treatment of
their enolate forms with a molybdenum peroxide
reagent in THF–hexane at ꢀ70 ꢁC,2 transformation of
the enamine derivatives of ketones to a-hydroxy deriva-
tives by molecular oxygen,3 and a-hydroxylation of silyl
enol ethers with m-chloroperbenzoic acid,4 or with
certain other oxidizing agents.5
It is known that there has been considerable interest in
the development of direct methods for the synthesis of
a-hydroxyketones using nontoxic hypervalent iodine
reagents, which involve the following methods: reaction
of ketone with iodobenzene diacetate in the presence of
potassium hydroxide in methanol and then hydrolysis of
the dimethylacetals;6 oxidation of enol silyl ether of
acetophenone using the system iodosobenzene/boron
trifluoride etherate/water in methylene chloride at
ꢀ40 ꢁC;7 and reaction of ketones with [bis(trifluoro-
acetoxy)] iodobenzene and trifluoroacetic acid in aceto-
nitrile–water under acidic conditions.8
The use of microwaves in organic synthesis has attracted
considerable attention in recent years. It is known that
microwaves shorten the time, enhance reaction rates,
and improve product yields.12 So, we tried the reaction
of a-bromo ketone in water under irradiation with
microwaves to overcome this problem. Herein, we re-
port that the irradiation of a-bromo- 1–11, and a-chloro
alkanones 10–100 in water gave a-hydroxyketones
1a–11a.
*
The irradiation of a-bromo- 1–11 and a-chloro alka-
nones 10–100 in water at 100–160 ꢁC under microwave
Corresponding author. Tel./fax: +81 3 3985 2397; e-mail addresses:
horiuchi@rikkyo.ac.jp; cahoriuchi@nifty.com
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.10.087

9360
T. Utsukihara et al. / Tetrahedron Letters 47 (2006) 9359–9364
irradiation for 15 to 20 min gave the corresponding
a-hydroxyketones 1a–11a in good yields. These results
are summarized in Table 1.
In order to substitute the bromide into the chloride ion,
we attempted the reaction of a-bromo ketone under
microwave irradiation with NaCl solution. The reaction
of a-bromo ketones 2, 3, 4, 6, 7, 8, and 11 in 3% NaCl
solution gave the corresponding a-chloro ketone in
good yields. These results are summarized in Table 2.
As can be seen from Table 2, it was found that the reac-
tion gives preferentially a-chloro ketone by the conven-
tional method (Table 2).
As can be seen from Table 1, it was found that the
reaction gives preferentially a-hydroxyketone. Thus, in
order to discuss the reactivity of a-bromo cyclicketone,
it was compared with that of the chloro derivatives.
From these results, both a-bromo- and a-chloro ketone
showed similar reactivities. The use of microwaves was
found to significantly improve the reaction yields and
shorten the reaction time in comparison with heat con-
ditions (Schemes 1 and 2). In the case of a-bromo acyclic
ketones 12 and 13, the corresponding 3-hydroxy- 12a
and 4-hydroxy ketone 13a were obtained in 82% and
75% yields, respectively (Scheme 3).
We further developed the generality of the substituted
reaction into amino group in ammonia water. The
reaction of 2 in 7% ammonia water under microwave
irradiation gave tricyclic pyrazine 2e13 in a good yield
and in the case of some a-halo ketones (10, 200, 5, 8
and 12), the corresponding pyrazine derivatives in a
Table 1. Reaction of a-halo ketone in water under microwave or heat
Run
Substrate
n
R1
R2
R3
Reaction type
Temperature (ꢁC)
Time (min)
Product (%)
88a (47)b
1
2
3
4
5
6
7
8
9
1
1
0
0
1
1
2
2
3
3
0
0
1
1
2
2
3
3
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
MW
Heat
100
100
125
125
150
150
160
160
100
100
125
125
150
150
160
160
125
125
125
125
125
125
125
125
100
100
125
125
125
125
125
125
125
125
125
125
125
125
100
100
125
125
25
25
15
15
25
25
25
25
25
25
15
15
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
1a
1a
2a
2a
3a
3a
4a
4a
1a
1a
2a
2a
3a
3a
4a
4a
5a
5a
6a
6a
7a
7a
8a
8a
9a
9a
10a
10a
11a
11a
5a
5a
6a
6a
7a
7a
8a
8a
9a
9a
10a
10a
6 (2)
100 (62)
2 (0)
86 (80)
3 (0)
84 (66)
3 (2)
92 (49)
3 (1)
98 (71)
0 (0)
88 (79)
2 (1)
85 (70)
2 (2)
89 (88)
59 (41)
91 (76)
42 (33)
90 (80)
54 (47)
84 (74)
27 (21)
99 (90)
38 (31)
96 (82)
20 (12)
99 (81)
21 (18)
93 (88)
0 (0)
94 (78)
0 (0)
93 (85)
0 (0)
86 (83)
0 (0)
99 (88)
0 (0)
2
2
3
3
4
4
10
10
20
20
30
30
40
40
5
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
H
H
Me
Me
H
H
H
H
H
H
H
H
H
H
H
H
Me
Me
H
H
H
H
H
H
H
H
H
H
H
Me
Me
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
Me
Cl
Cl
Br
Br
OMe
OMe
H
H
H
H
H
5
6
6
7
7
8
8
9
9
10
10
11
11
50
50
60
60
70
70
80
80
90
90
100
100
H
Me
Me
H
H
H
H
H
H
H
Me
Me
Cl
Cl
Br
Br
91 (82)
0 (0)
H
Reaction conditions: Substrate (0.05 mmol) in water (3 ml) was irradiated by MW power (200 W).
a Yields were determined by GLC.
b Isolated yields.

T. Utsukihara et al. / Tetrahedron Letters 47 (2006) 9359–9364
9361
O
OH
O
O
Br
O
Microwave
H2O
X
X
R1CH2CHCR2
R1CH2CHCR2
Microwave
H2O
12: R1=Me, R2=Pr
13: R1=Et, Bnn
12a: R1=Me, R2=Pr
13a: R1=Et, Bnn
Yield: 82%
Yield: 75%
n
n
n=0-3
X=Cl, Br
1a: n=0, X=OH
2a: n=1, X=OH
3a: n=2, X=OH
4a: n=3, X=OH
1: n=0, X=Br
2: n=1, X=Br
3: n=2, X=Br
4: n=3, X=Br
1': n=0, X=Cl
2': n=1, X=Cl
3': n=2, X=Cl
4': n=3, X=Cl
Scheme 3.
O
O
Br
Br
OH
Microwave
H2O
Scheme 1.
n
n
n=1-3
14: n=1
15: n=2
16: n=3
14b: n=1
15b: n=2
16b: n=3
good yield. In the case of 4, 2-aminocyclooctanone (4f)
and, not the pyrazine derivative was obtained. These
results are summarized in Tables 3 and 4. From these
results, it is considered that a-bromo ketones are easily
converted to pyrazines via the self-condensation of
initially formed a-aminoketones. It seems that in the
O
O
Br
OH
OH
O
O
X
OH
Microwave
H2O
14c
14d
R3
R1
R3
R1
Scheme 4.
R2
R2
case of 2-aminocyclooctanone (4f), the condensation
did not occur due to the flexibility of an 8-membered
ring. As can be seen in Tables 3 and 4, it was found that
the reaction yields the corresponding pyrazine deriva-
tives by a simple and conventional method.
5: X=Br, R1=R2=R3=H
5a: R1=R2=R3=H
6a: R1=Me, R2=R3=H
7a: R1=R3=H, R2=Me
8a: R1=R2=H, R3=Me
9a: R1=R2=H, R3=Cl
10a: R1=R2=H, R3=Br
11a: R1=R2=H, R3=OMe
5': X=Cl, R1=R2=R3=H
6: X=Br, R1=Me, R2=R3=H
6': X=Cl, R1=Me, R2=R3=H
7: X=Br, R1=R3=H, R2=Me
7': X=Cl, R1=R3=H, R2=Me
8: X=Br, R1=R2=H, R3=Me
8': X=Cl, R1=R2=H, R3=Me
9: X=Br, R1=R2=H, R3=Cl
9': X=Cl, R1=R2=H, R3=Cl
10: X=Br, R1=R2=H, R3=Br
10': X=Cl, R1=R2=H, R3=Br
Moreover, it is interesting that in the case of a,a0-di-
bromo cyclicketones, a-diketones were obtained in good
yields. The reaction of a,a0-dibromo ketones 14–16 in
water gave the corresponding a-diketones 14b–16b in a
good yield. These results are summarized in Table 5.
It was found that, in view of green chemistry, this
synthetic method affords a new, clean and convenient
method for a-diketones (Scheme 4).
11: X=Br, R1=R2=H, R3=OMe
Scheme 2.
Table 2. Microwave reaction of a-bromo ketone in 3% NaCl solution
Run
Substrate
Temperature (ꢁC)
Time (min)
Hydroxy ketone
Product (%)a
Chloro ketone
Diketone
1
2
3
4
5
6
7
8
9
2
2
None
NaCl
NaCl
NaCl
NaCl
NaCl
NaCl
None
NaCl
NaCl
NaCl
75
75
100
115
115
80
100
75
75
15
15
15
14
5
25
25
80
0
1
0
43
75
74
19
93
85
0
2
3
50
4
100
120
50
25
25
6
7
8
61
1
3
1
8
48
73
91
10
11
8
11
80
75
120
50
Reaction conditions: Substrate (0.05 mmol) in NaCl solution (3 ml) and MW power (40 W) were employed.
a Yields were determined by GLC.

9362
T. Utsukihara et al. / Tetrahedron Letters 47 (2006) 9359–9364
Table 3. Microwave reaction of a-bromo ketone 2 in 7% NH3 solution
O
O
O
Br
N
OH
NH3 aq
Microwave
+
+
N
2e
2a
2c
2
Run
Temperature (ꢁC)
Time (min)
Product (%)a
2e
2a
2c
1
2
3
4
5
6
30
50
70
90
105
125
10
10
10
10
10
10
6
65
92
93
95
98
24
13
—
—
—
—
—
3
7
4
2
1
Reaction condition: Substrate (0.05 mmol) in 7% NH3 solution (5 ml), and the apparatus (DISCOVER, CEM Corporation) using microwave power
(150 W) were employed.
a Yields were determined by GLC.
Table 4. Microwave reaction of a-bromo and a-chloro ketone in 7% NH3 solution
R1
N
R2
R1
R1
O
O
7% NH3 aq
Microwave
R2
N
NH2
R2
X
4f
e
X=Br,Cl
Run
R1
R2
X
Substrate
Product (%)a
1
2
3
4
5
6
7
8
9
–CH2CH2CH2–
–CH2CH2CH2–
–CH2CH2CH2CH2–
Cl
Br
Cl
Br
Br
Br
Br
Br
Br
10
2
20
200
4
1e (88)
2e (95)
2e (90)
200e (83)
4f (70)
5e (74)
8e (74)
11e (71)
12e (50)
–CH2CH(CH3)CH2CH2–
–CH2(CH2)4CH2–
Ph
p-MePh
p-MeOPh
C3H7–
H
H
H
5
8
11
12
C2H5–
Reaction condition: Substrate (0.05 mmol) in 7% NH3 solution (5 ml) at 105 ꢁC for 10 min was irradiated by microwave.
a Yields were determined by GLC.
Table 5. Reaction of a,a0-dibromo ketone in water under microwave
ble intermediates. Moreover, it was found that the reac-
tion mixtures were converted into a-diketone under
irradiation at 125 ꢁC. From these results, it is considered
that this reaction first proceeds to substitute halogen for
a hydroxyl group, followed by dehydrobromination
occurs, and then double bond produced was isomerized.
or heata
Run Substrate Reaction Temperature Time Product
Type
(ꢁC)
(min) (%)b
1
2
3
4
5
6
14
14
15
15
16
16
MW
Heat
MW
Heat
MW
Heat
125
125
150
150
150
150
15
15
25
25
25
25
14b (87)
14b (3)
15b (87)
15b (10)
16b (60)
16b (10)
In Table 6, the microwave apparatus (DISCOVER,
CEM Corporation) was compared with that of the
unmodified domestic microwave oven NE-S330F
(National). It was found that the reaction using the
former apparatus gives higher yields and in a shorter
reaction time than the latter.
a Reaction conditions: Substrate (0.05 mmol) in water (3 ml) was
irradiated by microwave.
b Yields were determined by GLC.
In conclusion, we have developed a very clean, simple
and convenient method for the synthesis of a-hydroxy-
ketones and a-diketones. It is particularly noteworthy
that this reaction affords a new synthetic method for
a-hydroxyketones and a-diketones. Moreover, it is
interesting that we have succeeded in establishing a
In order to investigate the reaction pathway of
the a-diketone for a,a0-dibromocyclohexanone (14),
the microwave irradiation of 14 was carried out. The
reaction of 14 at 75 ꢁC gave a-diketone 14b (39%) and
2-bromo-6-hydroxycyclohexanone (14c) (61%) as unsta-

T. Utsukihara et al. / Tetrahedron Letters 47 (2006) 9359–9364
Table 6. Effects of two equipments for a-hydroxylation of a-bromo ketone
9363
Run
Substrate
Equipment
Power (W)
Time (min)
Product (%)c
1
2
3
4
5
6
2
2
2
8
8
8
Commercial microwavea
Commercial microwavea
DISCOVER (CEM)b
Commercial microwavea
Commercial microwavea
DISCOVER (CEM)b
170
700
200
170
700
200
10
10
10
43
50
10
2a (17)
2a (28)
2a (62)
8a (33)
8a (65)
8a (74)
a Reaction conditions: Substrate (0.05 mmol) in water (3 ml) was irradiated by micro wave. Commercial microwave equipments were used by NE-
S330F (National).
b Reaction conditions: Substrate (0.05 mmol) in water (3 ml) and pressure (15 bar) at 125 ꢁC were employed.
c Isolated yields.
convenient synthesis of a-chloro ketone and pyrazine
derivatives, which is more convenient than the method
used heretofore. The use of microwaves was found to
significantly improve the reaction yields and shorten
the reaction time of the key step reactions.
graphed on silica gel. Elution with hexane–ether (3:1)
gave 1,2,3,4,5,6,7,8-octahydrophenazine (2e) as a white
crystal (22 mg, 86%).
2.1. 1,2,3,4,5,6,7,8-octahydrophenazine(2e)13a–e
Mp 105–107 ꢁC; IR (KBr) 1433, 1394, 1334, 1192, 1130,
1
982, 872, and 816 cmꢀ1; H NMR (CDCl3) d = 1.4–2.2
1. Typical procedure 1: irradiation of 2-bromo cyclo-
octanone (4) by microwaves in water
(br, 8H) and 2.4–3.1 (br, 8H), 13C NMR (CDCl3)
d = 149.3, 31.6, and 22.8; MS (EI) m/z 188 (M+), 173,
160, 145, 132, 120, 94, 79, 77, and 65.
A mixture of a-bromo ketone (0.14 mmol) and water
(3 ml) was irradiated (120W) using a microwave generat-
ing equipment (DISCOVERꢂ, CEM Corporation) at
120 ꢁC for 25 min. After the irradiation was completed,
the mixture was extracted with diethyl ether (30 ml). The
ethereal solution was washed with a saturated solution
of sodium thiosulfate (2 · 2.0 ml), saturated aq NaCl
(2 · 2.0 ml) and water (2 · 2.0 ml). The ethereal solution
was dried over Na2SO4 and concentrated in a vacuum.
The resulting oil was chromatographed on silica gel.
Elution with hexane–ether (3:1) gave 2-hydroxycyclo-
octanone (4a) as a pale-yellow oil (14 mg, 70%).
Acknowledgements
This work was partially supported by Frontier Project
‘Adaptation and Evolution of Extremophile’ and a
Grant-in-Aid for Science Research (No. 18550142).
References and notes
1. (a) Corey, E. J.; Link, J. O. Tetrahedron Lett. 1990, 31,
601; (b) Corey, E. J.; Link, J. O. J. Org. Chem. 1991, 56,
442; (c) Ramachandran, P. V.; Gong, B.; Brown, H. C.
Chilrality 1995, 7, 103; (d) Elks, J.; Ganelli, C. R.
Dictionary of Drugs; Chapman and Hall, 1990, p 1160;
(e) Taggart, P.; Sutton, P.; Donaldson, R. Clin. Sci. 1985,
69, 631; (f) Wei, Z.-L.; Li, Z.-Y.; Lin, G.-Q. Tetrahedron
1998, 54, 13059.
2. (a) Vedejs, E. J. Am. Chem. Soc. 1974, 96, 5944;
(b) Vedejs, E.; Telschow, J. E. J. Org. Chem. 1976, 41,
740; (c) Vedejs, E.; Larsen, S. Org. Synth. Collect. Vol.
VII, 1990, 277; (d) Gamboni, R.; Tamm, C. Tetrahedron
Lett. 1986, 27, 3999.
1.1. 2-Hydroxycyclooctanone (4a)11b,c
Pale-yellow oil; IR (NaCl) 3475 and 1701 cmꢀ1 1H
;
NMR (CDCl3) d = 4.19 (dd, 1H, J = 1.9, 4.3 Hz,
CHOH), 3.79 (br s, 1H, CHOH), 2.71 (dt, 1H, J = 2.6,
8.5 Hz, C(O)CHH), 2.30–2.45 (m, 2H), 1.91–2.08 (m,
2H), 1.62–1.87 (m, 4H), 1.32–1.45 (m, 2H) and 0.85–
0.97 (m, 1H); 13C NMR (CDCl3) d = 217.6, 76.1, 37.4,
29.2, 28.3, 25.7, 24.8 and 22.1; MS (EI) m/z 142 (M+),
124 ([MꢀH2O]+), 113, 98, 81, 57, and 41; MS (CI) m/z
143 ([M+1]+).
3. Cuvigny, T.; Valette, G.; Larcheveque, M.; Normant, H.
J. Organomet. Chem. 1978, 155, 147.
2. Typical procedure 2: irradiation of 2-bromo cyclo-
hexanone (2) by microwave in a 7% NH3 water
4. (a) Rubottom, G. M.; Vazquez, M. A.; Pelegrina, D. R.
Tetrahedron Lett. 1974, 4319; (b) Horiguchi, Y.; Naka-
mura, E.; Kuwajima, I. Tetrahedron Lett. 1989, 30, 3323.
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Chem. Lett. 1991, 281; (b) Davis, F. A.; Sheppard, A. C.
J. Org. Chem. 1987, 52, 954.
6. Moriarty, R. M.; Hu, H.; Gupta, S. C. Tetrahedron Lett.
1981, 22, 1283.
7. Moriarty, R. M.; Duncan, M. P.; Prakash, O. J. Chem.
Soc., Perkin Trans. 1 1987, 1781.
A mixture of a-bromo ketone (0.266 mmol) and 7%
NH3 water (5 ml) was irradiated (150 W) using a micro-
wave generating equipment (DISCOVERꢂ, CEM Cor-
poration) at 120 ꢁC for 20 min. After the irradiation
was completed, the mixture was extracted with diethyl
ether (30 ml). The ethereal solution was washed with a
saturated solution of sodium thiosulfate (2 · 2.0 ml),
saturated aq NaCl (2 · 2.0 ml) and water (2 · 2.0 ml).
The ethereal solution was dried over Na2SO4 and con-
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