Reaction of Some Dibromomethyl-Substituted Cyclohexadienones with Molecular Bromine

Article abstract of DOI:10.1023/A:1025589614195

4-Dibromomethyl-4-methyl-2,5-cyclohexadienone and its 2- and 3-methyl-substituted derivatives react with an equimolar amount of molecular bromine in carbon tetrachloride, yielding vinyl bromination products at the α-position with respect to the carbonyl g

Full text of DOI:10.1023/A:1025589614195

Russian Journal of Organic Chemistry, Vol. 39, No. 3, 2003, pp. 361 367. Translated from Zhurnal Organicheskoi Khimii, Vol. 39, No. 3, 2003,
pp. 393 399.
Original Russian Text Copyright
2003 by Gavrilova, Gavrilov, Krut’ko, Butin.
Dedicated to Full Member of the Russian Academy of Sciences
I.P. Beletskaya on Her Jubilee
Reaction of Some Dibromomethyl-Substituted
Cyclohexadienones with Molecular Bromine
G. V. Gavrilova, A. A. Gavrilov, D. P. Krut’ko, and K. P. Butin
Faculty of Chemistry, Moscow State University, Vorob’evy gory, Moscow, 119899 Russia
e-mail: butin@org.chem.msu.su
Received July 29, 2002
Abstract 4-Dibromomethyl-4-methyl-2,5-cyclohexadienone and its 2- and 3-methyl-substituted derivatives
react with an equimolar amount of molecular bromine in carbon tetrachloride, yielding vinyl bromination
products at the -position with respect to the carbonyl group. The reaction of 4-dibromomethyl-3,4-dimethyl-
2,5-cyclohexadienone with a large excess of bromine, apart from the vinyl bromination product, gives the
corresponding 3-bromomethyl and 3-dibromomethyl derivatives. 4-Dibromomethyl-2,4-dimethyl-2,5-cyclo-
hexadienone takes up bromine molecule at the C2 C3 double bond.
During the last three decades, geminal dihalo-
methyl-substituted cyclohexadienones (Auvers ketones
[1, 2]) have been successfully used in the synthesis of
pharmaceuticals [3, 4], tropones [5], tropovalene [6],
and spirans [7]. These transformations involve the
carbonyl group and the dihalomethyl moiety. The
reactivity of endocyclic double bonds conjugated with
the carbonyl group has been studied to a considerably
lesser extent. It is known [8] that concentrated sulfuric
acid does not react at the double C C bonds but
reversibly protonates the carbonyl oxygen atom.
Hydrogen adds to the unsaturated bonds in the pres-
ence of catalysts [3, 9]. 4-Dichloromethyl-4-methyl-
2,4-cyclohexadienone reacts with molecular chlorine
or bromine to give the corresponding 2-halo ketones
[10]. Reactions of halogens with cyclohexadienones
having a dibromomethyl group were not studied.
The results of recent studies have shown that
brominated cyclohexadienones are natural pharmaco-
phores. For example, Latrunculia marine sponge
produces previously unknown pentacyclic derivatives,
discorhabdins [11, 12], whose high biological activity
was believed to originate just from the presence of
cyclohexadienone fragment in their molecules. Bio-
logically active 2-(1-hydroxy-4-oxo-2,5-cyclohexadi-
enyl)acetamide was isolated from Aplisina fistularis
sponge [13, 14].
strates were 4-dibromomethyl-3,4-dimethyl-2,5-cyclo-
hexadienone (I), 4-dibromomethyl-2,4-dimethyl-2,5-
cyclohexadienone (II), and 4-dibromomethyl-4-
methyl-2,4-cyclohexadienone (III). A mixture of
appropriate ketone and molecular bromine was kept
for a certain period at room temperature in the dark.
The products were isolated by thin-layer chromatog-
raphy; their structure was established on the basis of
1
the H and 13C NMR (including selective double-
resonance experiments), IR, and UV spectra, and
elemental analyses.
Below are considered some general relations ob-
1
served in the H and 13C NMR spectra of the com-
pounds under study, which should facilitate signal
assignment and structure determination. In the 1H
NMR spectra of all these compounds, the CHBr2
proton signal appears in a stronger field ( 5.6
5.9 ppm) than signals from the olefinic ring protons.
In some cases, singlets in the downfield region of the
spectrum were assigned to olefinic, dibromomethyl,
or bromomethylene fragments by measurement of the
1
direct proton carbon coupling constants. The JCH
value for the CHBr2 group is about 180 Hz, which is
greater by 10 15 Hz than the corresponding coupling
1
constant for olefinic protons. The JCH value for the
BrCH group is 145 146 Hz. Also, couplings through
four bonds (W-coupling) were observed between
protons in positions 2, 6 and 3, 5, respectively:
4JHH = 1.5 3 Hz. The chemical shifts of olefinic
In the present work we examined reactions of
Auvers ketones with molecular bromine. The sub-
1070-4280/03/3903-0361$25.00 2003 MAIK Nauka/Interperiodica

362
GAVRILOVA et al.
Scheme 1.
Yield, %
Ratio I:Br2
Reaction time, h
I
IV
V
VI
1:1
1:25
1:25
24
24
48
16
65
8
18
25
55
98
Scheme 2.
Yield, %
Ratio II:Br2
Reaction time, h
II
VII
VIII+IX
1:1
1:25
24
48
2
87
Traces
Traces
79
Scheme 3.
Yield, %
Ratio III:Br2
Reaction time, h
III
X
XI
1:1
1:25
1:25
24
24
48
1.4
74
12
14
64
96
protons located in the -position with respect to the
carbonyl group were always smaller by 0.5 1 ppm
than those of the -protons. Replacement of the
-hydrogen atom by bromine leads to further down-
field shift of the -proton signal (by about 0.5 ppm).
Some specific features of the 13C NMR spectra can
also be noted. The presence of bromine in the -posi-
tion relative to the carbonyl group induces an upfield
shift (by 7 ppm) of the carbonyl carbon signal and
a downfield shift (by 3 ppm) of the C4 signal. The
13C chemical shifts of the methyl and dibromomethyl
groups almost do not change. The assignment of the
13C NMR signals of product mixtures was performed
with account taken of their relative intensities.
In the initial period, the reaction was slow; later on,
evolution of hydrogen bromide was observed, and the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 3 2003

REACTION OF SOME DIBROMOMETHYL-SUBSTITUTED CYCLOHEXADIENONES
363
Scheme 4.
reaction became much faster. The structure of the
products obtained from compounds I III and their
yields (depending on the reactant ratio and reaction
time) are given in Schemes 1 3. It is seen that the
reaction with methyl-substituted cyclohexadienones
initially occurs at the unsubstituted C5 C6 bond and
that bromine replaces hydrogen in the -position with
respect to the carbonyl group. In the presence of
excess bromine and on increasing the reaction time,
the substituted C2 C3 bond is involved. Here, com-
pound I (which can be enolized with participation of
the 3-methyl group) gives rise to hydrogen replace-
ment product at the methyl group, while nonenolizable
ketone II takes up bromine molecule at the substituted
double bond to give compound VIII which then
undergoes bromination at the methyl group with
formation of bromomethyl derivative IX.
Let us consider in more detail initial bromination
of the unsubstituted double bond. Dienones are
Michael substrates to which bromine addition may be
either electrophilic or nucleophilic, depending on fine
details of the alkene structure and reaction conditions.
The fact that the addition of bromine occurs first at
the unsubstituted double bond cannot be interpreted
in terms of electrophilic mechanism. Also, it is hardly
consistent with radical mechanism which cannot be
ruled out (although the reactions were carried in the
dark), for some amount of oxygen is always present
in the system. Hence we presume that the mechanism
of bromine addition at the C5 C6 bond is nucleo-
philic. Nucleophilic addition of bromine at the C5 C6
bond of I could occur by the action of hydrogen
tribromide as shown in Scheme 4. Although in the
initial period the reaction solution contains no hydro-
gen tribromide (only Br2 is present), it is generally
assumed that molecular bromine always contains
an admixture of HBr (HBr3) due to the presence of
traces of water and other impurities. Micro amounts
of HBr3 initiate nucleophilic addition of bromine
to the unsubstituted C5 C6 bond, and subsequent
elimination of hydrogen bromide (most probably,
according to the E1cb mechanism) gives product IV
together with an appreciable amount of HBr. In such
a way, the process becomes autocatalytic, as in the
addition of bromine to acrylic acid derivatives in
acetic acid [15].
Compound IV is a much less reactive Michael
substrate, as compared to I, since donor effect of
lone electron pair on the bromine atom considerably
reduces the positive charge on the -carbon atom,
induced by the carbonyl group. Therefore, nucleo-
philic addition stops after introduction of only one
bromine atom.
Unlike the C5 C6 bond, the reaction at the C2 C3
bond gives no hydrogen replacement product at C2,
and the bromination occurs exclusively at the allylic
position, i.e., at the 3-methyl group. It is commonly
believed that allylic bromination is a radical process
[16, 17]. In fact, in many cases, this reaction is very
sensitive to radical initiators and inhibitors, and it
does not occur in the absence of at least traces of
radical initiator. As applied to the reaction under
study, the mechanism of allylic bromination may be
trivial: it may be a secondary process initiated by
hydrogen bromide which is released during primary
autocatalytic nucleophilic bromination at the unsub-
stituted C5 C6 bond. Therefore, the formation of
an appreciable amount of dienol form XII of the
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 3 2003

364
GAVRILOVA et al.
Scheme 5.
-methyl- , -unsaturated ketone is highly probable.
VIII/IX by thin-layer chromatography. According to
the 1H NMR data, the ratio VIII:IX is 2.62.
A plausible mechanism of this reaction includes
initial electrophilic addition at the substituted double
bond, elimination of hydrogen bromide, and secon-
dary nucleophilic or electrophilic bromine addition to
the newly formed exocyclic double bond (Scheme 6).
The latter reacts with bromine at the exocyclic double
bond as shown in Scheme 5. These scheme explains
the formation of products V and VI (see Scheme 1).
However, compound XIII having no bromine atoms
in the ring is not formed. This means that allylic
bromination of initial substrate I occurs at a much
lower rate than nucleophilic addition at the unsub-
stituted double bond.
Thus, molecules of the examined substrates possess
both electrophilic and nucleophilic reaction centers.
The transformation of electrophilic double bond into
nucleophilic is achieved by introduction of a methyl
group. In the molecule of compound III, which has
no methyl group at the double bonds, both these
bonds are electrophilic. Therefore, the reaction of III
with excess bromine yields 2,6-dibromo-4-dibromo-
methyl-4-methyl-2,5-cyclohexadienone (XI, see
Scheme 3) as a result of double addition of nucleo-
philic brominating agent.
To conclude, it should be emphasized that the
mechanism of bromine reactions with unsaturated
compounds remains an interesting matter of further
studies and discussions. Michael substrates could take
up bromine according to either electrophilic or nucleo-
philic mechanism. Here, even such a factor as the
presence of a methyl group at the C C bond may be
crucial. The substrates examined in the present work
contain two double bonds conjugated to carbonyl
group, i.e., two idependent Michael systems. The
unsubstituted C C bond reacts with bromine follow-
The bromination of II also begins with nucleo-
philic addition at the unsubstituted double bond to
give product VII. Excess bromine reacts further at
the substituted double bond, affording polybrominated
derivatives VIII and IX (Scheme 1). Their structure
1
was established on the basis of the H and 13C NMR
spectra. The signals were assigned with account taken
of their relative intensities and proton-coupled 13C
1
NMR spectra; the coupling constants JCH for the
CHBr2 and CHBr groups were deduced from the
13C satellites, 178 and 145 146 Hz, respectively.
Unfortunately, we failed to separate product mixture
Scheme 6.
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REACTION OF SOME DIBROMOMETHYL-SUBSTITUTED CYCLOHEXADIENONES
365
ing the nucleophilic substitution pattern, with hydro-
gen replacement at the -position relative to the
carbonyl group. The reaction of bromine with the
other, methyl-substituted double bond, follows the
electrophilic mechanism, finally leding to allylic
substitution product (with substrate I) or electrophilic
addition product (compound II). Compound III has
a symmetric structure with two equivalent Michael
systems; both double bonds therein have no methyl
substituents, so that they react according to the
nucleophilic mechanism.
product was isolated by steam distillation. mp 60
61 C (from petroleum ether). Yield 4.6 g (20%).
UV spectrum, max: 236 nm (log 4.00). IR spectrum,
1
1
, cm : 1620, 1645, 1670. H NMR spectrum, d,
ppm (J, Hz): 1.48 s (3H, 4-Me); 1.95 d (3H, 2-Me,
4JHH = 1.2); 5.67 s (1H, CHBr2); 6.38 d (1H, 6-H,
3JHH = 10.0); 6.71 m (1H, 3-H); 6.92 d.d (1H, 5-H,
4
3JHH = 10.0, JHH = 3.2). 13C {1H} NMR spectrum,
C, ppm: 16.04 (2-Me); 24.46 (4-Me); 47.35 (C4);
51.06 (CHBr2); 130.27 (C6); 137.15 (C2); 144.63
(C3); 149.09 (C5); 185.43 (C O). Found, %: C 37.02;
H 3.30. C9H10Br2O. Calculated, %: C 37.16; H 3.17.
EXPERIMENTAL
Reaction of 4-dibromomethyl-3,4-dimethyl-2,5-
cyclohexadienone (I) with molecular bromine
(Scheme 1). a. Reactant ratio 1:1. A mixture of 0.1 g
(0.34 mmol) of dienone I and 0.054 g (0.34 mmol)
of bromine in 5 ml of carbon tetrachloride was kept
for 24 h at room temperature in the dark. The mixture
was evaporated, and the residue was subjected to
chromatographic separation using benzene ether (1:1)
as eluent. Fractions with Rf 0.25, 0.45, and 0.65 were
collected. The first fraction (Rf 0.25) contained initial
dienone I. Yield 0.016 g. mp 121 C (reprecipitation
from benzene with hexane).
1
The H and 13C NMR spectra were recorded on
a Varian VXR-400 spectrometer at 25 C using CDCl3
as solvent and tetramethylsilane as internal reference.
The IR spectra were obtained on a UR-20 instrument
from samples dispersed in mineral oil. The UV
spectra were measured on a Specord M-40 spectro-
photometer from solutions in ethanol. The progress of
reactions was monitored by TLC on Silufol UV-254
plates. Preparative separation of product mixtures was
performed by TLC on silica gel (Silpearl UV-254)
applied to 250 250-mm glass plates.
2-Bromo-4-dibromomethyl-4,5-dimethyl-2,5-
cyclohexadienone (IV). Rf 0.45. Yield 0.082 g.
mp 125 C (reprecipitation from chloroform with
4-Dibromomethyl-4-methyl-2,5-cyclohexadienone
(III) was synthesized by the procedure reported in [1].
Its spectral parameters were in agreement with the
data of [18].
hexane). UV spectrum:
249 nm (log 4.00).
max
1
IR spectrum, , cm : 1610, 1660, 1675. 1H NMR
4-Dibromomethyl-3,4-dimethyl-2,5-cyclohexadi-
enone (I). Bromoform, 17.4 ml (0.2 mol), was added
over a period of 30 min to a mixture of 10 g
(0.081 mol) of 3,4-dimethylphenol and 20 g (0.5 mol)
of NaOH in 180 ml of H2O under vigorous stirring at
57 C. The mixture was heated for 4 h, and the precip-
itate was filtered off, washed with two portions of
petroleum ether, and dried. The product was subjected
to column chromatography on SiO2 using CHCl3 as
eluent. Yield 7.1 g (30%). mp 130 C (from benzene);
spectrum, , ppm (J, Hz): 1.50 s (3H, 4-Me); 2.03 d
4
(3H, 5-Me, J = 1.2); 5.78 s (1H, CHBr2); 6.29 q (1H,
4
6-H, J = 1.2); 7.61 s (1H, 3-H). 13C {1H} NMR
spectrum, C, ppm: 18.59 (5-Me); 24.92 (4-Me);
48.61 (CHBr2); 53.36 (C4); 126.90 (C2); 128.12 (C6);
149.66 (C3); 158.22 (C5); 178.18 (C O). Found, %:
C 28.69; H 2.28. C9H9Br3O. Calculated, %: C 28.95;
H 2.41.
2-Bromo-5-bromomethyl-4-dibromomethyl-4-
methyl-2,5-cyclohexadienone (V). Rf 0.65. Yield
0.028 g. mp 101 C (reprecipitation from chloroform
published data [19]: mp 132 C. UV spectrum:
max
1
231 nm (log 4.18). IR spectrum: (C O) 1670 cm .
with hexane on cooling). UV spectrum:
253 nm
1H NMR spectrum, , ppm (J, Hz): 1.47 s (3H,
1
max
(log 4.01). IR spectrum, , cm : 1600, 1630, 1670.
4
4-Me); 2.03 d (3H, 3-Me, J = 1.2); 5.87 s (1H,
1H NMR spectrum, , ppm (J, Hz): 1.66 s (3H,
3
1
CHBr2); 6.19 m (1H, 2-H); 6.46 d.d (1H, 6-H, J =
4-Me); 4.13 (2H, CH2Br, AB system, J = 12.4);
4
3
10.0, J = 1.6); 7.18 d (1H, 5-H, J = 10.0). 13C NMR
5.89 s (1H, CHBr2); 6.73 s (1H, 6-H); 7.55 s (1H,
1
3-H). 13C {1H} NMR spectrum, C, ppm: 25.12
(4-Me); 26.61 (CH2Br); 48.06 (CHBr2); 53.45 (C4);
spectrum, C, ppm (J, Hz): 18.70 q (3-Me, JCH
=
1
129); 24.83 q (4-Me, J = 132); 49.77 d (4-CHBr2,
1J = 180); 49.90 s (C4); 129.58 d (C2 or C6, 1J = 165);
126.55 (C2); 131.90 (C6); 149.70 (C3); 154.94 (C5);
178.13 (C O). Found, %: C 23.80; H 1.85.
C9H8Br4O. Calculated, %: C 23.89; H 1.76.
130.77 d (C6 or C2, J = 167); 149.47 d (C5, J =
1
1
163); 157.80 s (C3); 185.19 s (C O).
4-Dibromomethyl-2,4-dimethyl-2,5-cyclohexadi-
enone (II) was synthesized in a similar way. The
b. Reactant ratio 1:25. The reaction of 0.1 g
(0.34 mmol) of ketone I with 1.44 g (9 mmol) of
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 39 No. 3 2003

366
GAVRILOVA et al.
1
bromine was carried out as described above in a.
Three products with Rf 0.45, 0.65, and 0.82 were
isolated. The product with Rf 0.45 (0.01 g) was
2-bromo-4-dibromomethyl-4,5-dimethyl-2,5-cyclo-
hexadienone (IV), and that with Rf 0.65 (0.04 g) was
2-bromo-5-bromomethyl-4-dibromomethyl-4-methyl-
2,5-cyclohexadienone (V).
2-Bromo-4,5-bis(dibromomethyl)-4-methyl-2,5-
cyclohexadienone (VI). Rf 0.82. Yield 0.12 g.
mp 184 C (reprecipitation from THF with hexane at
1JCH = 178); 59.25 d (CHBr, JCH = 146); 61.47 s
(C6); 122.23 s (C3); 148.39 d ( CH, JCH = 170);
1
181.54 s (C O).
1
Ketone IX. H NMR spectrum, , ppm (J, Hz):
1.82 s (3H, 4-Me); 4.07 d and 4.53 d (1H, CH2Br,
2JHH = 10.2); 5.79 s (1H, CHBr); 5.88 s (1H, CHBr2);
7.65 s (1H, CH). 13C NMR spectrum, C, ppm
1
(J, Hz): 20.82 q (4-Me, JCH = 133); 35.56 t (CH2Br,
1JCH = 162); 51.46 s (C4); 54.41 d (CHBr2, JCH
=
1
176); 54.70 d (CHBr, JCH = 145); 63.37 s (C6);
1
low temperature). UV spectrum:
260 nm (log
max
1
1
1
122.23 s (C3); 149.83 d ( CH, JCH = 170);
4.01). IR spectrum, , cm : 1610, 1630, 1650. H
NMR spectrum, , ppm (J, Hz): 1.68 s (3H, 4-Me);
5.81 s (1H, 4-CHBr2); 6.22 s (1H, 5-CHBr2); 7.28 s
178.93 s (C O).
Reaction of 4-dibromomethyl-4-methyl-2,5-
cyclohexadienone (III) with molecular bromine
(Scheme 3). a. Reactant ratio 1:1. A mixture of 0.1 g
(0.36 mmol) of dienone III and 0.056 g (0.36 mmol)
of bromine in 5 ml of carbon tetrachloride was kept
for 24 h at room temperature in the dark. The solution
was evaporated, and the oily residue was dissolved in
ether. The solution was washed with a 10% solution
of sodium acetate, dried over Na2SO4, and evaporated,
and the residue was subjected to chromatographic
separation using benzene petroleum ether (4:1) as
eluent. Fractions with Rf 0.17, 0.37, and 0.64 were
collected. The fraction with Rf 0.17 contained un-
reacted ketone III.
(1H, 6-H); 7.40 s (1H, 3-H). 13C {1H} NMR spec-
trum, C: 24.19 (Me); 30.87 (5-CHBr2); 46.65
(4-CHBr2); 53.08 (C4); 126.50 (C2); 134.04 (C6);
148.54 (C3); 158.80 (C5); 178.22 (C O). Found, %:
C 20.36; H 1.26. C9H7Br5O. Calculated, %: C 20.33;
H 1.31.
Reaction of 4-dibromomethyl-2,4-dimethyl-2,5-
cyclohexadienone (II) with molecular bromine
(Scheme 2). a. Reactant ratio 1:1. The reaction was
carried out as described above for dienone I. The
products were separated by chromatography using
petroleum ether ether (4:1) as eluent. A fraction
with Rf 0.23 was collected. It contained 0.11 g of
2-bromo-4-dibromomethyl-4,6-dimethyl-2,5-cyclo-
hexadienone (VII). mp 99-100 C (reprecipitation
2-Bromo-4-dibromomethyl-4-methyl-2,5-cyclo-
hexadien-1-one (X). Rf 0.37. Yield 0.095 g. mp 63
64 C (reprecipitation from chloroform with hexane).
250 nm (log 4.01). IR spectrum,
, cm : 1600, 1640, 1665. H NMR spectrum,
from chloroform with hexane in the cold). UV spec-
UV spectrum:
1
max
trum:
236 nm (log 4.14). IR spectrum, , cm :
1
1
max
,
1
1620, 1650, 1665. H NMR spectrum, , ppm (J, Hz):
1.52 s (3H, 4-Me); 2.01 d (3H, 6-Me, JHH = 1.6);
ppm (J, Hz): 1.55 s (3H, 4-Me); 5.60 s (1H, CHBr2);
4
3
3
6.50 d (1H, 6-H, J = 10.0); 6.99 d.d (1H, 5-H, J =
10.0, J = 3.2); 7.41 d (1H, 3-H, J = 3.2). 13C NMR
5.66 s (1H, CHBr2); 6.74 m (1H, 5-H); 7.38 d (1H,
4
4
4
3-H, JHH = 2.8). 13C {1H} NMR spectrum, C, ppm:
1
spectrum, C, ppm (J, Hz): 24.32 q (4-Me, J = 132);
48.67 d (CHBr2, J = 177); 50.81 s (C4); 126.48 s
1
16.78 (6-Me); 24.30 (4-Me); 49.72 (CHBr2); 50.11
(C4); 126.44 (C2); 136.17 (C6); 144.78 (C5); 149.29
(C3); 178.61 (C O). Found, %: C 28.87; H 2.26.
C9H9Br3O. Calculated, %: C 28.95; H 2.41.
(C2); 128.89 d (C6, J = 168); 149.41 d and 149.49 d
1
(C3, C5, 1J = 167); 177.68 s (C O). Found, %:
C 26.66; H 1.86. C8H7Br3O. Calculated, %: C 26.74;
H 1.94.
b. Reactant ratio 1:25. From the reaction mixture
we isolated a mixture of two brominated compounds,
2,5,6-tribromo-4-dibromomethyl-4,6-dimethyl-2-
cyclohexenone (VIII) and 2,5,6-tribromo-6-bromo-
methyl-4-dibromomethyl-4-methyl-2-cyclohexenone
(IX) at a ratio of 2.62:1 (Rf 0.8, eluent petroleum
ether ether, 2:1). Yield 0.181 g.
2,6-Dibromo-4-dibromomethyl-4-methyl-2,5-
cyclohexadienone (XI). Rf 0.64. Yield 0.22 g.
mp 165 C (from chloroform); published data [19]:
mp 165-166 C (from methylene chloride). UV spec-
264 nm (log 4.16). IR spectrum, , cm :
1600, 1630, 1670. H NMR spectrum, , ppm (J, Hz):
1
trum:
max
1
1
1.60 s (3H, 4-Me); 5.72 s (1H, CHBr2); 7.45 s (2H,
Ketone VIII. H NMR spectrum, , ppm (J, Hz):
1.83 s (3H, 4-Me); 2.15 s (3H, 6-Me); 4.85 s (1H,
3-H, 5-H). 13C {1H}: 24.13 (4-Me); 47.65 (CHBr2),
CHBr2); 7.55 s (1H, CH). 13C NMR spectrum,
,
53.14 (C4); 123.77 (C2, C6); 149.74 (C3, C5); 171.85
(C O). Found, %: C 21.86; H 1.25. C8H6Br4O. Cal-
culated, %: C 21.91; H 1.36.
ppm (J, Hz): 20.44 q (4-Me, JCH = 133); 29.81 Cq
1
1
(6-Me, JCH = 133); 51.85 s (C4); 54.82 d (CHBr2,
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REACTION OF SOME DIBROMOMETHYL-SUBSTITUTED CYCLOHEXADIENONES
367
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