Bromination of Decalin and Its Derivatives. 9. High Temperature Bromination

Article abstract of DOI:10.1021/jo9700843

Thermal and photobromination of decalin, 1, was studied, trans,cis,trans-2,5,7,9-tetrabromooctalin, 2, was obtained as the major product along with smaller amounts of bromonaphthalene derivatives. The structures of the products were determined by ¹H- and ¹³C-NMR data and single X-ray structural analysis. Bromination of the two decalin derivatives 9 and 10 results in the formation of single isomers 11 and 12, respectively. The three tetrabromides 2, 11, and 12 were shown by molecular mechanics calculations to be the most stable stereoisomer in each case. The formation of these tetrabromides under thermodynamic control is postulated.

Full text of DOI:10.1021/jo9700843

4018
J . Org. Chem. 1997, 62, 4018-4022
Br om in a tion of Deca lin a n d Its Der iva tives. 9. High Tem p er a tu r e
Br om in a tion
Arif Dastan,† M. Nawaz Tahir,‡ Dinc¸er U¨ lku¨,‡,§ Philip B. Shevlin,*,| and Metin Balci*,†,|
Department of Chemistry, Atatu¨rk University, 25240 Erzurum/ Turkiye, Department of Physics
Engineering, Hacettepe University, 06532 Beytepe, Ankara/ Turkiye, and Department of Chemistry,
Auburn University, Auburn, Alabama 36849
Received J anuary 15, 1997X
Thermal and photobromination of decalin, 1, was studied, trans,cis,trans-2,5,7,9-tetrabromooctalin,
2, was obtained as the major product along with smaller amounts of bromonaphthalene derivatives.
The structures of the products were determined by 1H- and 13C-NMR data and single X-ray
structural analysis. Bromination of the two decalin derivatives 9 and 10 results in the formation
of single isomers 11 and 12, respectively. The three tetrabromides 2, 11, and 12 were shown by
molecular mechanics calculations to be the most stable stereoisomer in each case. The formation
of these tetrabromides under thermodynamic control is postulated.
Brominations of hydrocarbons are important processes
tives were also isolated: 1,4-dibromnaphthalene (3),8 1,5-
dibromnaphthalene (4),8 1,4,6-tribromonaphthalene (5),9
and 1,4,5-tribromnaphthalene (6)9 (Scheme 1). Although
the starting material consisted of 62% cis-decalin, recov-
ered unreacted decalin consisted mainly of trans-decalin,
indicating that cis-decalin is more reactive than trans-
decalin in the bromination reaction.
because they lead to a variety of useful synthetic inter-
mediates.1 In the present investigation, we report condi-
tions under which the bromination2 of decalin, 1, and
several decalin derivatives proceeds with remarkable
regio- and stereospecifity.
Decalin 1 is a saturated bicyclic hydrocarbon which
occurs in diastereomeric cis and trans forms. Zelinsky
and Turowa-Pollak3 discovered that AlBr3-catalyzed bro-
mination of cis- and trans-decalin produced 1,2,3,5,6,7-
and 1,2,3,4,6,7-hexabromonaphthalene, respectively. The
correct structures of these molecules were determined by
McKinney4 and Ferguson.5 In 1948, Barnes6 reported the
reaction of decalin with N-bromosuccinimide and isolated
a tetrabromide whose structure was not reported. Stetter
and Tresper7 probably obtained the same product by the
bromination of decalin in liquid bromine in the presence
of catalytic amounts of hydrobromic acid. The correct
structure of this compound remained unknown.
We also investigated the light-promoted radical reac-
tion of bromine with decalin at temperatures of 50 and
10 °C using a sun lamp. Decreasing the reaction tem-
perature increased the yield of tetrabromide 2 from 32%
to 68%. The di- and tetrasubstituted naphthalene de-
rivatives were also formed under these conditions but in
lower yields.
Proton and carbon NMR studies of 2 indicated the
1
formation of a highly symmetrical compound. The H-
NMR spectrum of 2 shows two sets of signals. The
protons adjacent to bromine atoms appear as a doublet
at 5.16 ppm (J ) 2.7 Hz) and the methylene protons
appear as a multiplet at 2.10-2.60 ppm. A three-line
13C-NMR spectrum is also in agreement with the pro-
posed structure and indicates the high symmetry in the
molecule. However, on the basis of NMR data alone we
were not able to distinguish between four possible
symmetrical tetrabromides. Attempts to carry out reac-
tions (epoxidation, bromination) with the central double
bond in order to determine the structure of 2 resulted
only in unreacted starting material. Apparently steric
effects associated with the adjacent bromine atoms
preclude reaction with the central double bond. However,
the structure of tetrabromide 2 was finally determined
by X-ray analysis16 and is shown in Figure 2.
Resu lts a n d Discu ssion
Decalin (from Merck Company, 62% cis, 38% trans
isomer mixture) was heated to 150 °C and 5.0 equiv of
bromine added over a 1.5 h period. The solution was
stirred at the reaction temperature for an additional 30
min. The major product was tetrabromide 2 which was
isolated by crystallization of the reaction mixture from
hexane in a yield of 32%. After removing the unreacted
starting material, the residue was subjected to repeated
column chromatography, and four naphthalene deriva-
† Atatu¨rk University.
‡ Hacettepe University.
§ Author to whom inquiries concerning the X-ray structure should
be directed.
Since tetrabromide 2 is formally a result of sequential
allylic brominations of octalin 8, we propose that the
reaction proceeds via the free radical bromination of 1
followed by dehydrobromination to generate 8 (Scheme
2). Subsequent allylic bromination of 8 then generates
2.
| Auburn University.
X Abstract published in Advance ACS Abstracts, May 15, 1997.
(1) Hileman, B. Chem. Eng. News 1993, No. 19, 11.
(2) (a) Dastan, A.; Demir, U¨ . Balci, M. J . Org. Chem. 1994, 59, 6534.
(b) Dastan, A.; Balci, M.; Ho¨kelek, T.; U¨ lku¨, D.; Bu¨yu¨kgu¨ngo¨r, O.
Tetrahedron 1994, 50, 10555. (c) Tutar, A.; Taskesenligil, Y.; C¸ akmak,
O.; Abbasoglu, R.; Balci, M. J . Org. Chem. 1996, 61, 8297. (d) Dastan,
A.; Taskesenligil, Y.; Tumer, F.; Balci, M. Tetrahedron 1996, 52, 14005.
(3) Zelinsky, N. D.; Turowa-Pollak; M. B. Chem. Ber. 1929, 62B,
1658.
In order to test this argument, we have carried out the
bromination of 8 under the reaction conditions used for
2. This reaction also produced 2 as the only diastereo-
(4) McKinney, J .; Singh, P.; Levy, L.; Walker, M.; Cox, R.; Boben-
rieth, M.; Bordner, R. J . Agric. Food. Chem. 1981, 29, 180.
(5) Ferguson, G.; Subramanian, E. Cryst. Struct. Commun. 1977,
6, 215.
(6) Barnes, R. A. J . Am. Chem. Soc. 1948, 70, 145.
(7) Stetter, H.; Tresper, E. Chem. Ber. 1971, 104, 71.
(8) Zalkind, Y. S.; Faerman, S. B. J . Russ. Phys. Chem. Soc. 1930,
62, 1021.
(9) Salkind, J .; Belikoff, M. Chem. Ber. 1931, 64B, 955.
S0022-3263(97)00084-4 CCC: $14.00 © 1997 American Chemical Society

Bromination of Decalin and its Derivatives
J . Org. Chem., Vol. 62, No. 12, 1997 4019
Sch em e 1
Sch em e 2
ers of 2 derived from 8-Cs (two bromines axial and two
bromines equatorial). In Figure 2, we have shown the
MMX geometries of the three conformers whose energy
would be expected to differ.
An examination of the structures in Figure 2 reveals
that the conformer derived from 8-C2 with the bromines
all in the pseudoaxial position is the most stable. It is
not surprising that this conformation is the most stable
one as dipole-dipole interactions often force bromines
to be as far apart as possible. For example, 1,2-dibro-
mocyclohexane is more stable in the diaxial than in the
diequatorial conformation.12 Furthermore, gauche-in-
teractions of an axial cyclohexane substituent with an
axial hydrogen atom become more stabilizing with an
electronegative substituent. An electron rich bromine
can attract an electron deficient axial hydrogen so that
steric attraction among the axial substituents replaces
steric repulsion. The calculations also indicate that
energies of the three conformers vary inversely with the
1,3 dibromo distance, indicating that nonbonded interac-
tions dominate the energy difference between the con-
formers (Figure 2).
meric allylic tetrabromide strongly supporting the inter-
mediacy of 8 in the bromination of 1.
That an allylic tetrabromide would accumulate as the
bromination of 1 (and 8) reaction proceeds is reasonable,
as all of the allylic positions have been monobrominated,
gem dibromide formation would be sterically unfavorable,
and elimination of HBr (leading ultimately to bromo-
naphthalenes) may also be slow due to steric constraints.
The exclusive formation of 2, which is only one of the
five possible diastereomeric tetrabromides could be a
result of the fact that 2 is formed faster than the other
diastereomers (kinetic control). Alternatively, 2 may
simply be the most stable of the five possible diastereo-
meric allylic tetrabromides with sufficient time for an
initially formed mixture of allylic tetrabromides to equili-
brate (thermodynamic control).
In order to evaluate the relative stabilities of the
diastereomeric 2,5,7,9-tetrabromobicyclo[4.4.0]dec-1,6-
enes we have carried out molecular mechanics calcula-
tions with MMX force field.10 Our computational inves-
tigation of these substituted octalins started with octalin
itself. A previous MM2 study11 of 8 showed that this
molecule exists in the two conformers Cs and C2 in Figure
1 with the Cs more stable by 0.3 kcal/mol. In the present
investigation using the MMX force field, we also find the
conformers to be close in energy, but the C2 conformer
was calculated to be the more stable by 0.3 kcal/mol.
Since the allylic hydrogens in 8 are in half-chair
cyclohexenes, they are either pseudoaxial or pseudoequa-
torial (labeled A and E in Figure 1). Thus, there are two
conformers of 2 derived from 8-C2 (all bromines axial and
all bromines equatorial) and two enantiomeric conform-
If the energies of the other diastereomeric 2,5,7,9-
tetrabromobicyclo[4.4.0]dec-1,6-enes derived from 8 also
vary inversely with the 1,3 Br-Br distances, we may
expect that the diastereomer corresponding to 2, with all
of its bromines trans, would have the greatest 1,3 Br-
Br distance and hence be the most stable of the stereo-
isomers. The results of MMX calculations, shown in
Figure 3, bear out this expectation. Diastereomer 2 has
the greatest 1,3 Br-Br distance and is calculated to be
the most stable.
In order to further clarify the remarkable stereospeci-
ficity observed in these tetrabrominations, we treated
syn- and anti-octalin derivatives 9 and 10 with bromine
at high temperature (77 °C) and in both cases isolated
only one diastereomeric tetrabromide. Bromination of
914 gave exclusively 11 while 10 yielded only 1215 (Scheme
3).
(10) Gajewski, J . J .; Gilbert, K. E.; McKelvey, J . In Advances in
Molecular Modelling; Liotta, D. A., Ed.; J AI Press: Greenwhich, 1990;
vol. 2, p 65. The program used was PCWIN, V. 5.1 from Serena
Software, Bloomington, IN.
(11) Arkhipova, E. Y.; Mastryukov, V. S.; Traetteberg, M. J . Mol.
Struct. 1990, 216, 233.
(12) (a) Eliel, E. L. In Conformational Behavior of Six-Membered
Rings; J uaristi, E., Ed.; VCH: New York, 1995; p 1. (b) Abraham, R.
J .; Bretschneider, E. In Internal Rotations in Molecules; Orville-
Thomas, W. J ., Ed.; Wiley: New York, 1974; p 481.
(13) Cremer, D.; Szabo, K. J . In Conformational Behavior of Six-
Membered Rings; J uaristi, E., Ed.; VCH: New York, 1995; p 59.

4020 J . Org. Chem., Vol. 62, No. 12, 1997
Dastan et al.
F igu r e 1. Two conformers of 8.
F igu r e 3. Geometries and relative MMX energies of the five
diastereomeric 2,5,7,9-tetrabromobicyclo[4.4.0]deca-1,6-dienes.
F igu r e 2. Three possible conformers of 2 and their MMX
relative energies and the X-ray crystal structure of 2.
Sch em e 3
The assignment of the structures to 11 and 12 was
accomplished by 1H- and 13C-NMR spectral data and
NOE-measurements which were straightforward. The
1H NMR spectrum of 11 showed two sets of signals for
the methine, the cyclopropane, and the methyl protons.
The 11-line 13C NMR spectrum supports the proposed
structure and symmetry in the molecule. The syn and
anti relationship of the cyclopropyl hydrogens was con-
firmed by observation of NOE effects. Irradiation at the
resonance signal of methine protons adjacent to bromine
atoms at δ ) 5.55 caused signal enhancement at the
resonances of the adjacent cyclopropane protons at δ )
2.59 and the other cyclopropane proton at δ ) 1.63.
However, irradiation at δ ) 5.40 caused signal enhance-
ment only of the adjacent cyclopropane protons resonat-
ing at δ ) 2.75. These observations clearly indicate that
two of the bromine atoms have a syn orientation with
respect to the cyclopropane ring whereas the other two
have an anti orientation. The fact that 12 has 6 13C NMR
signals confirms the structure.
Figure 4 shows MMX-calculated geometries of these
isomers in which both have the 2-10 and 5-7 bromines
trans to one another. Table 1 shows the calculated MMX
(14) (a) Vogel, E.; Hogrefee, F. Angew. Chem., Int. Ed. Engl. 1974,
13, 735. (b) Hogrefee, F. Dissertation Thesis, University of Cologne,
1978. (c) Menzek, A.; Saracoglu, N.; Krawiec, M.; Watson, W. H.; Balci,
M. J . Org. Chem. 1995, 60, 829.
(15) Menzek, A.; Krawiec, M.; Watson, W. H.; Balci, M. J . Org.
Chem. 1991, 56, 6755.
(16) The author has deposited atomic coordinates for this structure
with the Cambridge Crystallographic Data Centre. The coordinates
can be obtained, on request, from the Director, Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge, CB2 1EZ, UK.

Bromination of Decalin and its Derivatives
J . Org. Chem., Vol. 62, No. 12, 1997 4021
Ta ble 1. Th e AM1 Ca lcu la ted Hea ts of F or m a tion a n d MMX Rela tive Ster ic En er gies in k ca l/m ol of Dia ster eom er ic
Tetr a br om id es
energies of all possible diastereomers. In each case the
diastereomer which is observed is the one calculated to
be the most stable.
Although these calculations demonstrate that the most
stable tetrabromide is formed exclusively in all cases, it
may well be that these are also the kinetically controlled
products. Once the first bromine is placed on an allylic
position, it may direct the second bromine trans to it
either three or four carbons removed. If this trans
directing effect continues as subsequent bromines are
placed on the ring, the diastereomer with all bromines
trans would result. Such a kinetically controlled trans
bromination causing the bromines to be as far as apart
as possible could result from steric effects, bromine
bridging in the radical, or a combination of these factors.
F igu r e 4. MMX calculated geometries of tetrabromides 11
and 12.
Con clu sion
These experiments demonstrate that brominations
carried out at high temperatures or photochemically,
which are unencumbered by competing ionic reactions,
can occur with remarkable stereo- and regiospecifity.

4022 J . Org. Chem., Vol. 62, No. 12, 1997
Dastan et al.
and 1,5-dibromonaphthalene 3 (1.2 g, 5%). The second fraction
was identified as tetrabromide 2 (1.92 g, total yield 48%).
Calculations and product analysis indicate that a major
factor contributing to this specifity is the steric bulk of
the bromines which dictates that products with these
atoms as far apart as possible will predominate.
P h otoch em ica l Br om in a tion of Deca lin a t 10 °C. To 4
g (0.029 mol) of decalin was added dropwise over 30 min 23.2
g (0.145 mol) bromine at 10 °C while the reaction flask was
irradiated with two 150 W sun lamps. The resulting solution
was photolyzed at the same temperature for seven days while
the temperature was controlled by an internal thermometer.
After cooling to room temperature, the formed precipitate of
tetrabromide 2 was filtered (4.5 g). After filtration of 2,
unreacted decalin (1.5 g) was removed by distillation. The
residue was treated with 10 mL of hexane and allowed to stand
one day in a refrigerator. Additional tetrabromide 2 (1.07 g)
crystallized (total 5.57 g, 68%) and the residue subjected to
silica gel (120 g) chromatography eluting with n-hexane.
Exp er im en ta l Section
Br om in a tion of Deca lin a t 150 °C. To 20 g (0.14 mol) of
decalin was added dropwise and over 1.5 h 116 g (0.72 mol)
bromine at 150 °C while stirring. The resulting solution was
stirred at the same temperature for an additional 30 min. After
cooling to room temperature, the mixture was treated with
30 mL of hexane and allowed to stand one day in the
refrigerator. Pure tetrabromide 2 (12 g, 24.5%) crystallized.
1a ,4b,5a ,8b-Tetr a br om o-1,2,3,4,5,6,7,8-octa h yd r on a p h -
th a len e (2): colorless crystals from chloroform/hexane (1:2),
The first fraction was a mixture consisting of 1,4-dibro-
monaphthalene 3 (156 mg, 3%) and 1,5-dibromonaphthalene
3 (207 mg, 4%). This ratio was determined by 1H-NMR
spectroscopy. The second fraction was identified as tetrabro-
mide 7.
1
mp 185.5-186 °C; H NMR (200 MHz, CDCl3) δ 5.16, (d, J )
2.7 Hz, H1,H4, H5, and H8), 2.10-2.60 (AA′BB′ system, 8H,
H2, H3, H6, and H7); 13C NMR (50 MHz, CDCl3) δ 135.5, 49.5,
28; MS (70 eV) m/z 375/373/371/369 (M+ - Br, 8) 293/291/289,
(M+ - 2Br, 8) 213/211, (M+ - 3Br, 27) 131/129, (M+ - 4Br,
naphthalene, 100) 128; IR (KBr, cm-1) 2995, 2905, 2835, 1423,
1335, 1200, 1170, 1000, 895, 743.
1,2,5,6-Tetr a br om on a p h th a len e (7): 261 mg (2.5%), pale
1
yellow crystals, mp 175-177 °C; H NMR (200 MHz, CDCl3)
δ 7.17 (d, A-part of AB-system, J 34 ) J 78 ) 9.0 Hz, 2H), 7.74
(d, B-part of AB-system, 2H); 13C NMR (50 MHz, CDCl3) δ
133.40, 132.87, 129.50, 125.77, 125.46; IR (KBr, cm-1) 3040,
3000, 2980, 1920, 1420, 1308, 1220, 1195, 1168, 1120, 1100,
895, 810. Anal. Calcd for C10H4Br4: C, 28.07; H, 0.91.
Found: C, 27.81; H, 0.86.
After removal of 2 by filtration, the residue was distilled to
remove unreacted decalin (5 g). The residue was subjected to
silica gel (130 g) chromatography, eluting with n-hexane. The
first fraction consisted of 1,4-dibromonaphthalene (3), 1,5-
dibromonaphthalene (4), and 1,4,6-tribromonaphthalene (5).
After evaporation of the solvent, the residue was dissolved in
methylene chloride/hexane and allowed to stand in a refrigera-
tor causing 5 to crystallize.
1,4,6-Tr ibr om on a p h th a len e (5): 1.98 g (5%), yellow crys-
tals, mp 86-87 °C (lit. 86-87 °C9); 1H NMR (200 MHz, CDCl3)
δ 8.36, (d, J 57 ) 1.9 Hz, 1H, H5), 8.04 (d, J 78 ) 9.0 Hz, 1H, H8),
7.65 (d, J 78 ) 9.0 Hz, 1H, H7), 7.58 (m, 2H, H2 and H3); 13C
NMR (50 MHz, CDCl3) δ 134.29, 132.02, 131.91, 131.53,
130.88, 130.36, 129.98, 123.47, 122.95, 121.67.
After removal of 5 by filtration, the residue was analyzed
by 1H-NMR spectroscopy which showed a mixture of 1,4-
dibromonaphthalene (4.35 g, 14%) and 1,5-dibromonaphtha-
lene (3.11 g, 10%). After repeated column chromatography
(silica gel, hexane), both isomers were isolated as pure
compounds.
Br om in a tion of syn -Dim eth yl Tetr a cyclo[5.5.0.03,5.09,11]-
d od ec-1(7)en e-4,10-d ica r boxyla te a t 77 °C. Compound 9
(1 g, 3.62 mmol) was dissolved in 25 mL of CCl4 in a 50 mL
two-necked flask equipped with reflux condenser and inlet
glass tube touching the bottom of the reaction flask. The inlet
glass-tube was connected to a 25 mL round-bottomed flask
which contained 13 g (81.25 mmol) of bromine. Bromine vapor,
obtained by heating of the flask to 100 °C, was transferred
directly into CCl4 solution at a temperature of 77 °C over 10
min while stirring magnetically. The reaction mixture was
refluxed for 1 h. After cooling of the reaction mixture to 10
°C, tetrabromide 11 precipitated and was removed by filtra-
tion. The solvent was evaporated, and 50 mL of CH2Cl2 and
75 mL hexane were added. The CH2Cl2/hexane solution was
allowed to stand for 15 h at 20 °C. Tetrabromide 11 that
crystallized was removed by filtration. Colorless crystals from
CHCl3/ether: mp 186-187 °C; (1.41 g, 63%) 1H NMR (200
MHz, CDCl3) δ 5.45 (m, 2H), 5.40 (m, 2H), 3.77 (s, 3H), 3.70
(s, 3H), 2.75 (m, 2H), 2.59 (m, 2H), 1.89 (t, J ) 4.9 Hz, 1H),
1.63 (t, J ) 4.0 Hz, 1H); 13C NMR (50 MHz, CDCl3) δ 172.33,
170.93, 131.23, 53.09, 52.89, 47.53, 43.57, 35.17, 32.26, 27.19,
24.89.
Br om in ation of a n ti-Dim eth yl Tetr acyclo[5.5.0.03,5.09,11]-
d od ec-1(7)en e-4,10-d ica r boxyla te a t 77 °C. Compound 10
(5 g, 18.1 mmol) in 250 mL of CCl4 was brominated using the
procedure described above. The solvent was removed, and 50
mL CH2Cl2 and 75 mL hexane were added. The CH2Cl2/
hexane solution was allowed to stand for 15 h at 20 °C.
Tetrabromide 12 was removed by filtration. Colorless crystals
(8.01 g, 75.0%) from CHCl3/ether: 1H NMR (200 MHz, CDCl3)
δ 4.94 (m, 4H), 3.70 (s, 6H), 2.58 (m, 4H), 1.72 (t, J ) 4.05 Hz,
2H); 13C NMR (50 MHz, CDCl3) δ 170.99, 129.79, 52.87, 43.16,
27.89, 24.53.
1,4-Dibr om on a p h th a len e (3): pale yellow crystals, mp
80-81 °C (lit. 81-82 °C8); 1H NMR (200 MHz, CDCl3) δ 8.26-
7.61 (AA′BB′ system, 4H, H5), 7.61 (s, 2H, H2 and H3); 13C NMR
(50 MHz, CDCl3) δ 133.37, 130.57, 128.65, 128.25, 123.09.
1,5-Dibr om on a p h th a len e (4): pale yellow crystals, mp
1
128-129 °C (lit. 131 °C8); H NMR (200 MHz, CDCl3) δ 8.21
(d, J ) 8.1 Hz, 2H), 7.83 (d, J ) 7.0, 2H), 7.41 (t, 2H); 13C
NMR (50 MHz, CDCl3) δ 133.51, 131.38, 127.89, 127.79,
123.52.
The second fraction isolated was 1,4,5-tribromonaphthalene
(6). 1,4,5-Tr ibr om on a p h th a len e (6): 1.2 g (3%), yellow
1
crystals, mp 80-81 °C (lit. 85-86 °C14); H NMR (200 MHz,
CDCl3) δ 8.36, (dd, J 78 ) 8.5 Hz, J 68 ) 1.2 Hz, 1H, H8), 8.01
(dd, J 67 ) 7.5 Hz, 1H, H6), 7.77 (d, J 23 ) 8.1 Hz, 1H,), 7.60 (d,
1H), 7.38 (dd, 1H, H7); 13C NMR (50 MHz, CDCl3) δ 138.29,
137.24, 137.16, 137.02, 132.76, 130.94, 129.63, 125.61, 122.17,
121.53.
As the third fraction, 3.72 g of tetrabromide 2 was isolated
(total yield 32%).
P h otoch em ica l Br om in a tion of Deca lin a t 50 °C. To
20 g (0.14 mol) of decalin was added dropwise over 1 h 116 g
(0.72 mol) of bromine at 50 °C while the reaction flask was
irradiated with two 150 W sun lamps. The resulting solution
was photolyzed at the same temperature for five days while
the temperature was controlled by an internal thermometer.
After cooling to room temperature, the mixture was treated
with 30 mL of hexane and allowed to stand one in day in a
refrigerator. Tetrabromide 2 (16 g, 43%) crystallized. After
filtration of 2, unreacted decalin (8.6 g) was removed by
distillation and the residue subjected to silica gel (130 g)
chromatography eluting with n-hexane. The first fraction was
a mixture consisting of 1,4-dibromonaphthalene 3 (1.9 g, 8%)
Ack n ow led gm en t. The authors are indebted to the
Department of Chemistry and Atatu¨rk University for
financial support, State Planning Organization of Tur-
key (DPT) for purchasing a 200 MHz NMR (Ataturk
University) and CAD4 diffractometer under Grant DPT/
TBAG1 (Hacettepe University), and N. Saracoglu for
providing us with NOE experiment results. M.B thanks
the Fulbright Scholarship Board for a Fulbright grant
(1996/1997 Auburn University, AL).
J O9700843