An efficient bromination of alkenes using cerium(IV) ammonium nitrate (CAN) and potassium bromide

Article abstract of DOI:10.1016/S0040-4020(01)00712-8

Bromination of alkenes using a combination of potassium bromide and cerium(iv) ammonium nitrate (CAN) in a two phase system consisting of water and dichloromethane affords the corresponding dibromides in excellent yield. The reaction most likely involves the addition of the bromine radical generated from bromide ion by CAN and subsequent formation of the dibromide.

Full text of DOI:10.1016/S0040-4020(01)00712-8

TETRAHEDRON
Pergamon
Tetrahedron 57 .2001) 7417±7422
An ef®cient bromination of alkenes using ceriumꢀIV) ammonium
nitrate ꢀCAN) and potassium bromide
Vijay Nair,a,p Sreeletha B. Panicker,a Anu Augustine,a Tesmol G. George,a Siji Thomasa
and M. Vairamanib
aOrganic Chemistry Division, Regional Research Laboratory ꢀCSIR), Trivandrum 695019, India
bIndian Institute of Chemical Technology, Hyderabad 500 007, India
Dedicated with best wishes to Professor James P. Kutney on the occasion of his 70th birthday.
Received 5 December 2000; revised 12 June 2001; accepted 5 July 2001
AbstractÐBromination of alkenes using a combination of potassium bromide and cerium.iv) ammonium nitrate .CAN) in a two phase
system consisting of water and dichloromethane affords the corresponding dibromides in excellent yield. The reaction most likely involves
the addition of the bromine radical generated from bromide ion by CAN and subsequent formation of the dibromide. q 2001 Elsevier
Science Ltd. All rights reserved.
1. Introduction
of the variety of reagents available for bromination, lack of
selectivity and unwanted side reactions continue to be
problems. In this context a search for mild, selective and
easy-to-handle reagents assume importance.
Recently, C±C bond forming reactions mediated by
cerium.IV) ammonium nitrate .CAN) have been the subject
of considerable interest.1 Less attention however has been
paid to the use of CAN in C-heteroatom bond formation
despite the report of CAN mediated addition of azide to
alkenes by Trahanovsky as early as 19712 and subsequent
exploitation of the reaction in the synthesis of aminosugars
by Lemieux et al.3 Very recently we have observed the
ef®cient thiocyanation of styrenes and indoles using
NH4SCN and CAN.4±5 We have also reported the conver-
sion of cinnamates to a-azidocinnamtes, cinnamic acids to
b-azido styrenes6 and styrenes to phenacyl azides and
phenacyl thiocyanates.7 It appeared that a similar strategy
would be applicable for the bromination of alkenes without
the direct use of bromine. The bromination of alkenes is an
important organic transformation and it is worthy of note
that protection and deprotection of double bonds via
bromination±debromination strategy is ®nding increasing
application in organic synthesis.8 A number of protocols
are available to achieve the bromination of alkenes.9±13
Very recently, Fraser-Reid has reported the bromination
of alkenyl glycosides using a combination of LiBr and
CuBr2.14
2. Results and discussion
Against the background presented above, we have carried
out a detailed investigation aimed at the bromination of
various alkenes and our results are presented in this paper.
Our studies were initiated by the treatment of styrene with
potassium bromide and CAN in a two-phase system consist-
ing of water and dichloromethane. A facile reaction
occurred and the dibromide 2 was isolated in 91% yield
.Scheme 1).
Mechanistically, by comparing the redox potentials of
Br2/Br and Ce .IV)/Ce .III)16,17 it is reasonable to assume
that bromide ion is undergoing oxidation to bromine radical
by CAN and subsequent addition of the latter to the double
bond producing a benzylic radical followed by trapping with
another bromine radical .vide infra for a detailed dis-
cussion). A number of styrenes were subjected to similar
reaction conditions and in all the cases, the dibromides were
The bromination of alkenes using hydrobromic acid and
tert-butyl hydroperoxide has also been reported.15 In spite
Keywords: cerium compounds; bromination; dibromide.
Corresponding author. Tel.: 191-471-490-406; fax: 191-471-491-712;
e-mail: gvn@csrrltrd.ren.nic.in
p
Scheme 1. .i) CAN, KBr, H2O, CH2Cl2, rt, 30 min.
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020.01)00712-8

7418
V. Nair et al. / Tetrahedron 57 ꢀ2001) 7417±7422
Table 1. Bromination of styrenes
Entry
Substrate
Reaction conditions
Product
Yield .%)
1
2
3
4
4-Methylstyrene .3)
4-Chlorostyrene .5)
b-Methylstyrene .7)
2-Vinylnaphthalene .9)
CAN, KBr, H2O,
CH2Cl2, rt, 35 min
CAN, KBr, H2O,
CH2Cl2, rt, 20 min
CAN, KBr, H2O,
CH2Cl2, rt, 30 min
CAN, KBr, H2O,
CH2Cl2, rt, 45 min
1,2-Dibromo-.4-methyl)-phenyl ethane .4)
1,2-Dibromo-.4-chloro)-phenyl ethane .6)
1,2-Dibromo-1-phenyl propane .8)
67
85
90
95
1,2-Dibromo-1-naphthyl ethane .10)
Table 2. Bromination of alkenes
Entry
Substrate
Reaction conditions
Product
Yield .%)
1
2
3
4
Cyclohexene .11)
Allylbenzene .13)
1-Octene .15)
CAN, KBr, H2O,
CH2Cl2, rt, 20 min
CAN, KBr, H2O,
CH2Cl2, rt, 20 min
CAN, KBr, H2O,
CH2Cl2, rt, 35 min
CAN, KBr, H2O,
CH2Cl2, rt, 20 min
1,2-Dibromocyclohexane .12)
1,2-Dibromo-3-phenyl propane .14)
1,2-Dibromooctane .16)
65
65
51
82
1-Hexene .17)
1,2-Dibromohexane .18)
Table 3. Bromination of a,b-unsaturated carbonyl compounds
Entry
Substrate
Reaction conditions
Product
Yield .%)
1
2
3
4
Methyl cinnamate .19)
CAN, KBr, H2O,
CH2Cl2, rt, 50 min
CAN, KBr, H2O,
CH2Cl2, rt, 20 min
CAN, KBr, H2O,
CH2Cl2, rt, 20 min
CAN, KBr, H2O,
CH2Cl2, rt, 20 min
2,3-Dibromo-3-phenyl methyl propanoate .20)
78
80
81
95
3,4-Dimethoxy
ethylcinnamate .21)
Benzylidene acetone .23)
2,3-Dibromo-3-.30,40-dimethoxy)-phenyl ethyl propanoate .22)
3,4-Dibromo-4-phenyl butan-2-one .24)
Chalcone .25)
2,3-Dibromo-1,3-diphenyl propan-1-one .26)
obtained in excellent yields. The results are summarized in
Table 1.
CAN underwent selective bromination yielding the
dibromide 30 .Scheme 3).
In order to assess the generality of the reaction, CAN
mediated bromination was carried out with some repre-
sentative alkenes and also with some a,b-unsaturated
carbonyl compounds. In all the cases, the corresponding
dibromides were obtained in high yields. Tables 2 and 3
summarize the results.
In view of the facility and ease with which alkenes under-
went CAN mediated bromination, it was of interest to
explore the applicability of this reaction to acetylenes.
With this objective, a number of acetylenes were treated
under the reaction conditions used for the bromination of
alkenes. The vicinal dibromoalkenes were obtained in
excellent yields and the results are presented in Table 4. A
mixture of isomers was obtained in one case and the ratio of
the isomers was determined by GC±MS.
Since radical reactions are chemoselective in nature, it was
of interest to probe the chemoselectivity of the CAN
mediated bromination. When the allyl phenyl ether 27 was
treated with KBr and CAN in a two-phase system consisting
of water and dichloromethane under the reaction conditions
described previously, the dibromide 28 was obtained in 75%
yield .Scheme 2).
In order to gain an insight into the effect of solvent in these
reactions, the reaction of styrene with potassium bromide
and CAN in various solvents was studied. Interestingly, the
product obtained was the nitrato bromide and phenacyl
bromide .Scheme 4).
The isomeric compound 29 also on treatment with KBr and
Scheme 2. .i) CAN, KBr, H2O, CH2Cl2, rt, 30 min.
Scheme 3. .i) CAN, KBr, H2O, CH2Cl2, rt, 30 min.

V. Nair et al. / Tetrahedron 57 ꢀ2001) 7417±7422
7419
Table 4. Bromination of acetylenes .reaction conditions: KBr, CAN, H2O,
CH2Cl2, rt, 30 min)
and dichloromethane is necessary for the reaction to occur.
In the absence of a two-phase system, dibromide is not
isolated. The success of the reaction may be attributed to
the fact that the bromine radicals generated by CAN will be
predominantly distributed in the organic phase along with
the alkene, thus facilitating the bromination, whereas the
oxidant will remain in the aqueous phase; its limited contact
with the substrate will minimize the possibility of unwanted
side reactions.
Entry 31 a±d
R1
R2
32 a±d .E/Z) Yield .%)
1
2
3
4
31a
31b
31c
31d
H
Ph
H
Ph
Ph
100/0
80/20
80
94
79
75
.CH2)5CH3 100/0
.CH2)2CH3 .CH2)2CH3 100/0
3. Mechanistic consideration
Although the mechanistic details of the reactions are far
from clear, a rationalization can be made as follows.
There is enough circumstantial evidence to suggest that
bromide ion can be oxidized to bromine radical by CAN.
A comparison of the oxidation/reduction potential of Br2/Br
and Ce.IV)/Ce.III) systems .1.6 for Ce.III)/Ce.IV) and
1.03 V for Br/Br2) also lends credence to this postulate.
Therefore it is reasonable to assume that the bromination
reported herein proceeds via a mechanistic pathway
Scheme 4. .i) CAN, KBr/LiBr, Solvent, rt.
Table 5. Effect of solvent in bromination reactions
Entry
Solvent
33 .Yield, %)
34 .Yield, %)
Reaction conditions
1
2
3
4
Aq. methanol
Aq. acetonitrile
Acetonitrile±acetic acid
tert-Butanol
48
35
12
10
25
35
68
65
CAN, KBr, rt, 2 h
CAN, KBr, rt, 1 h
CAN, LiBr, rt, 3 h
CAN, LiBr, rt, 6 h
involving bromine radical. Conceivably, bromine radical
generated by the oxidation of bromide ions can add to the
alkene to give a secondary radical. The latter can either
undergo oxidation to produce the cation, which on attack
by another bromide ion can give the product; or the benzylic
radical can be trapped by a bromine radical itself. A third
possibility that needs to be considered is the reaction of
the secondary radical with molecular bromine, that may
be formed by the radical combination, leading to the
dibromide.
Scheme 5. .i) CAN, LiBr, MeCN, Argon, rt, 2 h.
The results are presented in Table 5.
When the reaction was carried out in a deoxygenated
atmosphere, as expected, no keto product was formed;
instead the nitrato bromide was formed exclusively
.Scheme 5).
The formation of the nitrato bromide and/or the phenacyl
bromide in methanol and in acetonitrile .Schemes 4 and 5)
can also be explained by invoking the transformations of the
benzylic radical. The benzylic radical can give rise to the
nitrato bromide by ligand transfer or it can be trapped by
molecular oxygen producing a peroxy radical, which is
It is noteworthy that a two phase system consisting of water
Scheme 6.

7420
V. Nair et al. / Tetrahedron 57 ꢀ2001) 7417±7422
further transformed to the hydroperoxide. The hydro-
peroxide can undergo fragmentation giving the keto
bromide.
5.2.1. 1,2-Dibromo-1-ꢀ4-methyl)-phenyl ethane 4.
4-Methylstyrene .236 mg, 2 mmol) on treatment with potas-
sium bromide .500 mg, 4.2 mmol) and CAN .2.56 g,
4.6 mmol) in a two phase system of water and dichloro-
methane afforded .372 mg, 67%) the dibromide 4 as viscous
The exclusive formation of the nitrato bromide in a
deoxygenated atmosphere lends support to the postulate
that the genesis of the keto product involves the incorpora-
tion of molecular oxygen. A schematic representation of the
mechanistic pathway is given below. .Scheme 6).
1
liquid. IR .neat): 1613, 1512, 1438, 1135, 818 cm21; H
NMR: 7.25 .d, 2H, ArH, Jˆ7.8 Hz), 7.16±7.13 .d, 2H,
ArH, Jˆ7.8 Hz), 5.09 .dd, 1H, CHBr, Jˆ5.5, 10.4 Hz),
4.05±3.95 .m, 2H, CH2Br), 2.35 .s, 3H, CH3); 13C NMR:
138.94, 135. 57, 129.43, 127.45, 50.84, 34.86, 21.22; HRMS
calcd for C9H10Br2, 275.9149. Found .M1) 275.9161,
.M114) 279.9130.
It may be pointed out that a mechanistic postulate involving
the intermediacy of bromine radical may be preferred over
the one involving the bromonium ion proposed by Asakura
et al.18 Indirect support for a radical mechanism is rendered
by the lack of solvent incorporation, in the case of reactions
carried out in methanol and acetonitrile. A cationic species
resulting from the addition of bromonium ion is likely to be
quenched by the solvent under these conditions.
5.2.2. 1,2-Dibromo-1-ꢀ4-chloro)-phenyl ethane 6.
4-Chlorostyrene .138 mg, 1 mmol) on treatment with potas-
sium bromide .250 mg, 2.1 mmol) and CAN .1.26 g,
2.3 mmol) in a two phase system of water and dichloro-
methane afforded .254 mg, 85%) of the dibromide as low
melting, pale yellowsolid. IR .neat) nmax: 1484, 1091, 1023,
890 cm 21.1H NMR: 7.30 .s, 4H, ArH), 5.08±5.03 .m, 1H,
CHBr), 4.03±3.87 .m, 2H, CH2Br); 13C NMR: 137.02,
134.86, 128. 99, 128.96, 49.44, 34.57; HRMS calcd for
C8H7Br2Cl2, 295.8603. Found .M1) 295.8612, .M114)
299.8588.
4. Conclusion
In conclusion, we have encountered an ef®cient route to the
synthesis of 1,2-dibromides in a two-phase system.
Evidently, the present procedure offers a mild and experi-
mentally simple alternative to the one using bromine, which
is toxic, corrosive and expensive. In addition, it appears that
the newcombination of reagents will ®nd application in the
chemoselective bromination of multifunctional compounds.
Since the solvent plays an important role in these reactions,
suitable selection of the solvent leads to the product of
choice. It may be emphasized that, by using the combination
of potassium bromide and CAN it is possible to convert
styrene into a variety of products such as dibromoalkane,
phenacyl bromide and the nitratobromide.
5.2.3. 1,2-Dibromo-1-phenyl propane ꢀ8) ꢀmixture of
isomers).8 b-Methylstyrene .118 mg,1 mmol) on treatment
with potassium bromide .250 mg, 2.1 mmol) and CAN
.1.26 g, 2.3 mmol) in a two phase system of water and
dichloromethane afforded .250 mg, 90%) of the dibromide
as a viscous liquid.
5.2.4. 1,2-Dibromo-1-naphthyl ethane 10. Vinylnaphtha-
lene .154 mg, 1 mmol) on treatment with potassium
bromide .250 mg, 2.1 mmol) and CAN .1.26 g, 2.3 mmol)
in a two phase system of water and dichloromethane
afforded .298 mg, 95%) of the dibromide as colorless crys-
tals, recrystallized from dichloromethane±hexane mixture,
mp 56±588C; IR .neat) nmax: 1452, 1371, 1141, 996,
5. Experimental
1
761 cm21; H NMR: 7.88±7.81 .m, 4H, ArH), 7.51±7.48
5.1. General methods
.m, 3H, ArH), 5.30 .dd, 1H, CHBr, Jˆ7, 9.3 Hz), 4.14±4.08
.m, 2H, CH2Br); 13C NMR: 135.74, 133.59, 132.98, 129.11,
128.25, 127.83, 127.48, 126.90, 126,69, 124.41, 51.29, 34.
72; HRMS calcd for C12H10Br2, 311.9149. Found .M1)
311.9134, .M114) 315.9096.
1H and 13C NMR spectra were recorded at 300 MHz NMR
instrument. Chemical shifts are reported relative to TMS
.1H) and CDCl3 .13C) as the internal standards. Mass spectra
were recorded under EI/HRMS. Column chromatography
was performed on silica .100±200 mesh). All the solvents
were distilled prior to use. Alkenes were purchased and or
prepared. The CAN was purchased from Aldrich Co. and
was used without further puri®cation.
5.2.5. 1,2-Dibromo cyclohexane 12. Cyclohexene .410 mg,
5 mmol) on treatment with potassium bromide .1.0 g,
10.1 mmol) and CAN .6.3 g, 11.5 mmol) in a two phase
system of water and dichloromethane afforded .786 mg,
65%) of the dibromide as a viscous liquid.12
5.2. General procedure for the preparation of 1,2-
dibromide 213
5.2.6. 1,2-Dibromo-3-phenyl propane 14. Allyl benzene
.118 mg, 1 mmol) on treatment with potassium bromide
.250 mg, 2.1 mmol) and CAN .1.26 g, 2.3 mmol) in a two
phase system of water and dichloromethane afforded
.180 mg, 65%) of the dibromide as colorless oil. IR .neat)
To a solution of styrene .104 mg, 1 mmol) in dichloro-
methane .10 mL) was added KBr .250 mg, 2.2 mmol) and
a solution of CAN .1.26 g, 2.3 mmol) in water .10 mL) at
room temperature and stirred. After completion of the reac-
tion, the dichloromethane layer was separated washed with
brine and dried over sodium sulfate. The solvent was
removed and the residue was crystallized from dichloro-
methane±hexane mixture to afford white crystals .240 mg,
91%), mp 74±768C, data consistent with the literature.
n
max: 2995, 1809, 1600, 1494, 1580, 1445 cm21; 1H NMR:
7.33±7.27 .m, 5H, ArH), 4.36±4.30 .m, 1H, CH2Br), 3.83±
3.78 .m, 1H, CH2Br), 3.63±3.45.m, 3H), 3.11 .dd, 1H,
Jˆ7.7, 14.4 Hz; 13C NMR: 136.74, 129.52, 128.49,127.
20, 52.24, 41.92, 35.89; HRMS calcd for C9H10Br2, 275.
9149. Found .M1) 275.9152, .M114) 279.9123.

V. Nair et al. / Tetrahedron 57 ꢀ2001) 7417±7422
7421
5.2.7. 1,2-Dibromo octane 16.12 1-Octene .500 mg,
4.5 mmol) on treatment with potassium bromide .1.1 g,
9.3 mmol) and CAN .5.7 g, 10.35 mmol) in a two phase
system of water and dichloromethane afforded .624 mg,
51%) of the dibromide as viscous liquid.12
130.52, 114.33, 69.04, 46.99, 32.99, 26.24.HRMS calcd
for C11H12O2Br2, 333.9204. Found .M1) 333.9194,
.M114) 337.9173.
5.2.14. ꢀ2,3-Dibromo)allylꢀ2-acetoxy)phenyl ether 30.
Allylphenyl ether .174 mg, 1 mmol) on treatment with
potassium bromide .250 mg, 2.1 mmol) and CAN .1.26 g,
2.3 mmol) in a two phase system of water and dichloro-
methane afforded .267 mg, 79%) of the dibromide as color-
less viscous liquid IR .neat) nmax: 1676, 1595, 1483, 1452,
1290, 1159 cm21.1H NMR: 7.73 .d, 1H, ArH Jˆ7.5 Hz),
7.43 .m, 1H, ArH), 7.03 .t, 1H, ArH Jˆ7.4 Hz), 6.93 .d,
1H, ArH, Jˆ8.3 Hz), 4.49 .broad triplet, 3H, OCH2, CHBr),
3.90 .broad triplet, 2H, CH2), 2.67 .s, 3H, CH3);13C NMR:
190.70, 156.92, 133.52, 130.69, 128.70, 121.57, 112.51,
69.71, 46.98, 32.15, 32.06; HRMS calcd for C11H12Br2O2;
333.9204. Found .M1) 333.9200, .M114) 337.9176.
5.2.8. 1,2-Dibromo hexane 18.12 1-Hexene .170 mg,
2 mmol) on treatment with potassium bromide .500 mg,
4.2 mmol) and CAN .2.5 g, 4.6 mmol) in a two phase
system of water and dichloromethane afforded 82%
.450 mg) of the dibromide as colorless viscous liquid.
5.2.9. 2,3-Dibromo-3-phenylmethyl propanoate 20.15
Methyl cinnamate .162 mg, 1 mmol) on treatment with
potassium bromide .250 mg, 2.1 mmol) and CAN .1.26 g,
2.3 mmol) in a two phase system of water and dichloro-
methane afforded .250 mg, 78%) of the dibromide as
colorless crystals, recrystallized from dichloromethane±
hexane mixture, mp 114±1168C.
5.2.15. 1,2-Dibromo-1-phenyl ethene 32a.15 Phenylacetyl-
ene .102 mg, 1 mmol) on treatment with potassium bromide
.250 mg, 2.1 mmol) and CAN .1.26 g, 2.3 mmol) in a two
phase system of water and dichloromethane afforded
.210 mg, 80%) of the dibromoethene as a 2:3 mixture of
E and Z isomers.
5.2.10. 2,3-Dibromo-3-ꢀ3,4-dimethoxy)-phenylethyl pro-
panoate 22. Cinnamyl ester .236 mg, 1 mmol) on treatment
with potassium bromide .250 mg, 2.1 mmol) and CAN
.1.26 g, 2.3 mmol) in a two phase system of water and
dichloromethane afforded .316 mg, 80%) of the dibromide
as light yellowcrystals, recrystallized from dichloro-
5.2.16. 1,2-Dibromo-1,2-diphenylethene 32b.15 Diphenyl-
acetylene .178 mg, 1 mmol) on treatment with potassium
bromide .250 mg, 2.3 mmol) and CAN .1.26 g, 2.3 mmol)
in a two phase system of water and dichloromethane
afforded .317 mg, 94%) of the dibromoethene as mixture
of E and Z isomers.
methane±hexane mixture, mp 102±1048C; IR .KBr) nmax
:
1738, 1600, 1513, 1463, 1369, 1331, 849, 801 cm21.1H
NMR 6.99±6.81 .m, 3H, ArH), 5.31 .d, 1H, CHBr,
Jˆ11.7 Hz), 4.79 .d, 1H, CHBr, Jˆ11.7 Hz), 4.36 .q, 2H,
OCH2, Jˆ7 Hz), 3.92 .s, 3H, OCH3), 3.90 .s, 3H, OCH3),
1.39 .t, 3H, CH3, Jˆ7.1 Hz); 13C NMR: 167.70, 149.91,
149.27, 129.98, 120.98, 110.89, 110.69, 62.53, 55.95,
55.86, 51.57, 47.37, 13.98; HRMS calcd for C13H16Br2O4;
392.933. Found .M1) 392.9325.
5.2.17. 1,2-Dibromo-1-hex-1-ene 32c.15 1-Hexyne .82 mg,
1 mmol) on treatment with potassium bromide .250 mg,
2.1 mmol) and CAN .1.26 g, 2.3 mmol) in a two phase
system of water and dichloromethane afforded .194 mg,
79%) of the dibromoethene as a 2:1 mixture of E and Z
isomers.
5.2.11. 3,4-Dibromo 4-phenyl butan-2 one 24.13 Benzyl-
idene acetone .146 mg, 1 mmol) on treatment with potas-
sium bromide .250 mg, 2.3 mmol) and CAN .1.26 g,
2.3 mmol) in a two phase system of water and dichloro-
methane afforded .252 mg, 81%) of the dibromide as
colorless crystals, recrystallized from dichloromethane±
hexane mixture, mp 118±1208C.
5.2.18. 3,4-Dibromo-4-octyne 32d.15 4-Octyne .110 mg,
1 mmol) on treatment with potassium bromide .250 mg,
2.1 mmol) and CAN .1.26 g, 2.3 mmol) in a two phase
system of water and dichloromethane afforded .202 mg,
75%) of the dibromide as colorless liquid.
5.2.12. 2,3-Dibromo-1,3-diphenylpropan-1-one 26.6
Chalcone .208 mg, 1 mmol) on treatment with potassium
bromide .250 mg, 2.1 mmol) and CAN .1.26 g, 2.3 mmol)
in a two phase system of water and dichloromethane
afforded .351 mg, 95%) of the dibromide as colorless
crystals, recrystallized from dichloromethane±hexane
mixture, mp 156±1588C.
5.2.19. 1-Nitrato-1-phenyl-2-bromoethane ꢀ34) and
1-bromoacetophenone ꢀ33). Styrene .104 mg, 1 mmol)
on treatment with potassium bromide .250 mg, 2.1 mmol)
and CAN .1.26 g, 2.3 mmol) in the solvent .methanol,
acetonitrile, acetic acid±acetonitrile mixture or tert-
butanol) for 1±6 h, after work up and puri®cation afforded
the nitrato bromide 34 as pale yellowviscous liquid and
phenacylbromide 33 as colorless solid. 1-Nitrato-1-phen-
yl-2-bromoethane .34) IR .neat) nmax: 1645, 1489, 1452,
5.2.13. ꢀ2,3-Dibromo)allylꢀ4-acetoxy)phenyl ether 28.
Allyl phenyl ether .174 mg, 1 mmol) on treatment with
potassium bromide .250 mg, 2.1 mmol) and CAN .1.26 g,
2.3 mmol) in a two phase system of water and dichloro-
methane afforded .250 mg, 75%) of the dibromide as color-
less crystals, recrystallized from dichloromethane±hexane
mixture, mp 44±468C; IR .neat) nmax: 1680, 1604, 1506,
1363, 1251, 1174, 831, 581 cm21 1H NMR: 7.92 .d, 2H
ArH, Jˆ8.2 Hz), 6.95 .d, 2H, ArH, Jˆ8.2 Hz), 4.43
.broad triplet, 3H, OCH2, CHBr), 3.89 .d, 2H, CH2Br),
2.54 .s, 3H, CH3). 13C NMR: 195.97, 161.58, 131.09,
1
1278, 1209, 855 693 cm±1; H NMR: 7.39 .brs, 5H, ArH),
5.97 .dd, 1H, CHONO2, Jˆ8.3 Hz, 5.1 Hz), 3.69±3.53 .m,
2H, CH2Br); 13C NMR: 135.21, 129.82, 129.07, 126.60,
83.82, 30.41; HRMS calcd for C8H8BrNO3; .M1),
244.9687. Found 244.9694, .M112) 246.9662. 1-Bromo
acetopheneone .33)19 mp 46±488C; IR .neat) nmax: 1682,
1
1451, 1276, 1195, 1108, 997, 752 cm21; H NMR: 8.01 .t,
2H, ArH, Jˆ 7.2 Hz),7.69 .t, 2H, ArH Jˆ7.3 Hz), 7.61 .d,
ArH Jˆ7.6 Hz), 4.44 .s, 2H, CH2).

7422
V. Nair et al. / Tetrahedron 57 ꢀ2001) 7417±7422
8. Ranu, B. C.; Guchhait, S. K.; Sarkar, A. Chem. commun. 1998,
2113 and references cited therein.
Acknowledgements
9. House, H. O. In Modern Synthetic Reactions, 2nd ed., W. A.
Benjamin: Melno Park, California, 1972; p. 422.
10. Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis;
Wiley: NewYork, 1967; vol. 1, p. 967.
S. B. P., A. A. and T. G. G. thank the CSIR, NewDelhi for
Research Fellowships. S. T. thanks The American Cynamid
Co. .Agricultural Division), USA for ®nancial assistance.
Thanks are also due to Ms Soumini Mathewfor NMR
spectral data and Mr Robert Philip for GC±MS data. The
authors thank Professor Michael Schmittel, University of
Siegen for helpful discussion.
11. Berthelot, J.; Benammar, Y.; Lange, C. Tetrahedron Lett.
1991, 33, 4135.
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J. Chem. Soc., Perkin Trans. 1 1994, 1667 and references cited
therein.
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