An efficient reagent for the monobromination of 1,3-diketones and b-ketoesters
59
Table 1 Selective a-monobromination of active methylene compounds using ethylenebis(N-methylimidazolium)ditribromide (EBMIDTB)
a
b
a
Entry
Substrate
Product
Time/min
Yield/%
M.p/°C
1
2
3
4
5
6
7
8
9
PhCOCH
2
COPh
PhCOCHBrCOPh
CH COCHBrCOCH
PhCOCHBrCOCH
2-Br-cyclohexane-1,3-dione
2-Br-5,5-Me -cyclohexane-1,3-dione
20
20
20
20
20
40
30
40
40
90
90
90
90
85
80
90
95
85
90
85
85
50
50
50
91–93 [18, 45]
–
CH
3
COCH
2
COCH
3
3
3
PhCOCH
2
COCH
3
3
32–33 [18]
168–170 [46]
174–176 [47]
115–118 [48]
Oil [49]
Cyclohexane-1,3-dione
5,5-Me -cyclohexane-1,3-dione
2
2
Indane-1,3-dione
2-Br-indane-1,3-dione
2-Me-cyclopentane-1,3-dione
2-Br-2-Me-cyclohexane-1,3-dione
CH
PhCOCH
EtOCOCH
3
COCH
COOEt
COOEt
2
COOEt
CH
3
COCHBrCOOEt
Oil [50]
2
PhCOCHBrCOOEt
EtOCOCHBrCOOEt
NCCHBrCOOEt
NCCHBrCN
Oil [51]
10
11
12
a
2
Oil [52]
NCCH
NCCH
2
COOEt
Oil [53]
2
CN
64–65 [54]
1
All of the products were identified by comparing melting point and H NMR with those of authentic samples reported in literature
b
Yields refer to isolated products
3
causing ring brominations. We believe that 2 provides an
excellent complement to other reagents for this transfor-
mation such as NBS.
completion of the reaction as monitored by TLC, 15 cm
water were added to the reaction mixture, which was then
3
extracted with dichloromethane (2 9 25 cm ). The com-
bined organic layer was dried (Na SO ). After filtration,
2
4
the solvent was evaporated, and the residue was purified
by filtration through a short silica gel column (eluent:
n-hexane and ethyl acetate). The spectroscopic data for the
known products compared well with the reported data.
Experimental
Melting points were measured on Electro Thermal 9100.
1
NMR spectra were recorded at 500 MHz for H and 125
1
3
MHz for C with BRUKER DRX500. Elemental analysis
was done with PERKIN ELMER 2-2400 and the obtained
results agreed favourably with the calculated values.
Acknowledgment We are thankful to the Research Council of
Mazandaran University for the partial support of this work.
References
Ethylenebis(N-methylimidazolium) ditribromide
(
A mixture of 4.85 g N-methylimidazole (58.5 mmol) and 2.3
2, C H Br N )
10 16 6 4
1
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2. Erian AM, Sherif SM, Gaber HM (2003) Molecules 8:793
2
3
cm 1,2-dibromoethane (26.6 mmol) was stirred in 40 cm
3
3
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DMF at 120 °C for 2 h. After cooling the mixture, a white
solid formed, which was filtered off, washed with diethyl
4
5
3
ether (2 9 20 cm ), and dried under vacuum. This solid was
3
dissolved in 40 cm acetic acid. To this mixture was added
3
dropwise a solution of 2.3 cm Br (43.75 mmol) in 20 cm
3
6
7
2
n-hexane The resulting orange solid was collected by filtra-
tion, washed with diethyl ether, and dried under vacuum to
1
give 10.4 g 2. Mp 103–105 °C; H NMR (500 MHz, DMSO-
8. Stotter PL, Hill KA (1972) Tetrahedron Lett 40:4067
. Karimi S, Grohmann KG (1995) J Org Chem 60:554
9
d ): d = 3.80 (s, 2CH ), 4.62 (s, 2CH ), 7.36 (pseudo t,
6
3
2
1
0. Bateson JH, Quinn AM, Southgate R (1986) J Chem Soc Chem
Commun 1151
11. Curran DP, Bosch E, Kaplan J, Newcomb M (1989) J Org Chem
54:1826
2
H-imi), 7.65 (pseudo t, 2H-imi), 8.94 (s, 2H, NCHN) ppm;
1
3
C NMR (125.76 MHz, DMSO-d ): d = 37.0 (CH ), 49.4
6
3
(
CH ), 123.2 (imi-C), 124.9 (imi-C), 138.0 (NCHN) ppm.
2
1
1
2. Coats SJ, Wasserman HH (1995) Tetrahedron Lett 36:7735
3. Yang D, Yan Y, Lui B (2002) J Org Chem 67:7429
General procedure for a-monobromination
of a b-dicarbonyl compound with 2
14. Das B, Venkateswarlu K, Mahender G, Mahender I (2005) Tet-
rahedron Lett 46:3041
1
5. Meshram HM, Reddy PN, Sadashiv K, Yadav JS (2005) Tetra-
hedron Lett 46:623
To a stirred solution of 1 mmol b-dicarbonyl compound in
1
6. Meshram HM, Reddy PN, Vishnu K, Sadashiv K, Yadav JS
(2006) Tetrahedron Lett 47:991
3
1
0 cm acetonitrile was added 0.5 mmol 2 at 0–5 °C. After
123