Bromination of tetralin. Short and efficient synthesis of 1,4-dibromonaphthalene

Article abstract of DOI:10.1135/cccc20001791

High-temperature bromination of tetralin (1,2,3,4-tetrahydronaphthalene) with bromine resulted in benzylic biomination to give 1,4-dibromo-1,2,3,4-tetrahydronaphthalene (4) as a major product and several secondary products. Photolytic bromination of tetralin and subsequent double dehydrobromination of 1,1,4,4-tetrabromo-1,2,3,4-tetrahydronaphthalene (10) gave 1,4-dibromonaphthalene (11) as the sole product in a high yield. 1,4-Dibromonaphthalene is efficiently converted to the corresponding methoxy (12 and 13) and cyano (14 and 15) derivatives of naphthalene.

Full text of DOI:10.1135/cccc20001791

Bromination of Tetralin
1791
BROMINATION OF TETRALIN. SHORT AND EFFICIENT SYNTHESIS OF
1,4-DIBROMONAPHTHALENE
a
b
Osman ÇAKMAKa1,*, Ismail KAHVECI , Íbrahim DEMIRTAŞa2, Tuncer HÖKELEK
c
andKeith S MITH
a
Gaziosmanpaşa University, Faculty of Science, Department of Chemistry, 60100 Tokat, Turkey;
1
2
e-mail: ocakmak@gop.edu.tr, demirtas@gop.edu.tr
Hacettepe University, Department of Physics, 06532 Beytepe, Ankara, Turkey;
e-mail: merzifon@eti.cc.hun.edu.tr
Department of Chemistry, University of Wales Swansea, Swansea SA2 8PP, U.K.;
e-mail: k.smith@swansea.ac.uk
b
c
Received October 21, 1999
Accepted Septem ber 14, 2000
High -tem perature brom in ation of tetralin (1,2,3,4-tetrah ydron aph th alen e) with brom in e
resulted in ben zylic brom in ation to give 1,4-dibrom o-1,2,3,4-tetrah ydron aph th alen e (4) as
a m ajor product an d several secon dary products. Ph otolytic brom in ation of tetralin an d sub-
sequen t double deh ydrobrom in ation of 1,1,4,4-tetrabrom o-1,2,3,4-tetrah ydron aph th alen e
(10) gave 1,4-dibrom on aph th alen e (11) as th e sole product in a h igh yield. 1,4-Dibrom o-
n aph th alen e is efficien tly con verted to th e correspon din g m eth oxy (12 an d 13) an d cyan o
(14 an d 15) derivatives of n aph th alen e.
Key w ord s: Brom in e; Ph otobrom in ation ; Brom in ation ; Halogen ation ; Naph th alen es;
Tetralin ; Arom atic n ucleoph ilic substitution .
1,4-Dibrom on aph th alen e (1,4-DBN) h as becom e in creasin gly im portan t as
a triplet excitation acceptor with useful ph osph orescen t properties1. It is
also useful as a precursor for oth er 1,4-disubstituted n aph th alen e deriva-
tives such as ph en ols2, am in es3, aryl eth ers4, alkyl eth ers5 an d organ o-
m etallics6. However, in spite of th e poten tial im portan ce of 1,4-DBN,
existin g m eth ods for its preparation are n ot very practical. In con sequen ce,
on ly a very lim ited ran ge of com m ercial 1,4-disubstituted n aph th alen es is
available, an d th ey are gen erally very expen sive. Th erefore, we h ave sough t
a better syn th esis of 1,4-DBN.
Dibrom in ation of n aph th alen e with m olecular brom in e is un satisfactory,
but Yan ovskaya7 reported th e quan titative preparation of 1,4-DBN by th e
reaction of n aph th alen e with dioxan e dibrom ide, in a 1 : 2 m ole ratio, at
40 °C. However, Bayer et al.8 subsequen tly sh owed th at th is m eth od
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Cakmak et al.:
of preparation is n eith er quan titative n or specific for 1,4-dibrom o-
n aph th alen e, 1,5-dibrom on aph th alen e an d 2-brom on aph th alen e also
bein g form ed. Brom in ation of n aph th alen e with alum in a-supported cop-
per (II) brom ide appeared to be m ore prom isin g, but th e 1,4-DBN could n ot
easily be separated from th e by-products9.
High tem perature brom in ation con dition s m ay in crease th e reactivity to
en courage production of gem in al dibrom ides at ben zylic position s. In con -
n ection with our in terest in h igh tem perature brom in ation reaction s of un -
saturated system s10 we would like to exten d th e work to h ydroarom atic
h ydrocarbon s. Alth ough ben zylic brom in ation of alkylben zen es is well
kn own , it usually requires irradiation with UV ligh t in th e presen ce of a free
radical catalyst an d often gives m ixtures of products. It appeared likely,
h owever, th at tetralin could be clean ly con verted to 1,1,4,4-tetrabrom o-
1,2,3,4-tetrah ydron aph th alen e with out th e com plication of overbrom in -
ation . Th e tetrabrom ide sh ould th en be capable of un dergoin g HBr elim in a-
tion to give 1,4-DBN. We th erefore studied th is reaction an d we n ow report
a superior syn th esis of 1,4-DBN by th is approach . We h ave also clarified
som e oth er features of th e reaction an d we h ave dem on strated th e syn -
th etic utility of 1,4-DBN by usin g it as a precursor for a n um ber of oth er
com poun ds.
EXPERIMENTAL
Com m ercial reagen ts were purch ased from stan dard ch em ical suppliers an d purified to
m atch th e reported ph ysical an d spectral data. Meltin g poin ts were determ in ed on
a
Th om as–Hoover capillary m eltin g poin ts apparatus. Th e NMR spectra were recorded on spec-
trom eters operatin g at eith er 200 or 400 MHz for 1H an d 50 or 100 MHz for 13C NMR.
Ch em ical sh ifts are given in ppm (δ-scale), couplin g con stan ts (J) in Hz. All colum n ch rom a-
tograph y was perform ed on silica (60–230 m esh , Merck). TLC was carried out on Merck
0.2 m m silica gel 60 F254 an alytical alum in a plates. All brom in ation reaction s were con -
ducted in an efficien t fum e cupboard.
Th erm al Brom in ation of Tetralin
To a solution of tetralin (1; 1.00 g, 7.5 m m ol) in CCl4 (25 m l) was added a solution of bro-
m in e (2.40 g, 30.3 m m ol) in CCl4 (15 m l) an d th e m ixture was h eated un der reflux (77 °C)
for about 10 m in . Wh en th e colour of th e brom in e h ad disappeared, th e reaction was
stopped an d th e solven t was rem oved in vacuo. Th e residue was allowed to crystallise from
petroleum eth er (30 m l) in a refrigerator. 1,4-Dibromo-1,2,3,4-tetrahydronaphthalene (4; 1.36 g,
63%) was isolated, m .p. 87–89 °C (ref.11 89–93 °C). Th e dibrom ide slowly decom posed with
th e evolution of h ydrogen brom ide on stan din g at room tem perature. Th is process was
slowed by storage in a refrigerator.
Th e residue recovered from th e m oth er liquor was subjected to silica gel (90 g) colum n
ch rom atograph y, elutin g with h exan e. 1-Bromonaphthalene (2; 156 m g, 10%), naphthalene (3;
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Bromination of Tetralin
1793
135 m g, 14%), an d 1,2,4-tribromo-1,2,3,4-tetrahydronaphthalene (6; 140 m g, 5%) were eluted
successively. Recrystallisation of 6 from h exan e gave n eedle-like colourless crystals, m .p.
59–60 °C. 1H NMR (CDCl3): 2.85 (dtd, J(3a,3b) = 14.5, J(3b,2) = J(3b,4) = 6.2, J(3b,1) = 1.4, 1 H,
H3b); 3.30 (ddd, J(3a,3b) = 14.5, J(3a,4) = 9.6, J(3a,2) = 2.8, 1 H, H3a); 4.82 (m , 1 H, H2);
5.55 (dd, J(3b,1) = 1.4, J(1,2) = 2.9, 1 H, H1); 5.63 (dd, J(4,3a) = 9.6, J(4,3b) = 6.2, 1 H, H4);
7.26–7.66 (m , 4 H, aryl). 13C NMR (CDCl3): 40.2 (t), 47.2 (d), 52.1 (d), 52.8 (d), 130.9 (d),
131.5 (d), 132.9 (d), 133.1 (d), 135.2 (s), 136.6 (s). For C10H9Br3 (369) calculated: 32.56% C,
2.46% H; foun d: 31.97% C, 2.68% H.
Th en , elution of th e colum n with ch loroform gave 2-bromo-1,2,3,4-tetrahydronaphthalen-
1-ol (5; 140 m g, 8%), colourless crystals, m .p. 111–112 °C (ch loroform ) (ref.12 110 °C). 1H
NMR (CDCl3): 2.28 an d 2.51 (AB, J(3a,3b) = 13.7, 2 H, H3a an d H3b); 2.60 (s, OH); 3.00 (m ,
2 H, H4a an d H4b); 4.35 (ddd, J(2,3a) = 3.3, J(2,3b) = 9.5, J(1,2) = 7.0, 1 H, H2); 4.91 (d,
J(1,2) = 7.0, 1 H, H1); 7.60, 7.35 an d 7.14 (m ′s, 4 H, aryl). 13C NMR (CDCl3): 28.4 (t), 30.0
(t), 56.5 (d), 74.4 (d), 127.0 (d), 128.3 (d), 128.5 (d), 128.8 (d), 135.2 (s), 135.7 (s). For
C
10H11BrO (227) calculated: 52.89% C, 4.88% H; foun d: 52.67% C, 4.81% H. 1,4-Dibrom o-
1,2,3,4-tetrah ydron aph th alen e h as been prepared previously by th e reaction of
1,2,3,4-tetrah ydron aph th alen e with N-brom osuccin im ide, as reported by Djerassi11, but th e
exact stereoch em istry of th e product (cis or trans) h as n ot been determ in ed13. On th e oth er
h an d, Bloun t14 reported form ation of 1,2-dibrom o-1,2,3,4-tetrah ydron aph th alen e in about
30% yield on brom in ation of 1,2,3,4-tetrah ydron aph th alen e with brom in e with out solven t
at 95 °C. Th e differen ce presum ably arises as a result of en h an ced elim in ation of HBr from
1-brom o-1,2,3,4-tetrah ydron aph th alen e in Bloun t’s h otter an d m ore con cen trated con di-
tion s, followed by addition of brom in e to th e 1,2-dih ydron aph th alen e th us form ed.
Brom in ation of 1,2-Dih ydron aph th alen e
A solution of 1,2-dih ydron aph th alen e (8; 130 m g, 1.00 m m ol) in CHCl3 (3 m l) was treated
with brom in e (176 m g, 1.1 m m ol). After rem oval of th e solven t in vacuo, recrystallisation of
th e residue from CH2Cl2–petroleum eth er afforded trans-1,2-dibromo-1,2,3,4-tetrahydro-
naphthalene (9; 261 m g, 95%), m .p. 66 °C (ref.15 70 °C). 1H NMR (CDCl3): 7.13–7.36 (m , 4 H,
aryl H′s); 5.68 (t, 1 H, J(1,2) = J(1,3) = 1.5); 4.94–4.98 (m , 1 H); 3.20–3.30 (m , 1 H); 2.75–3.01
(m , 2 H); 2.14–2.29 (m , 1 H). 13C NMR (CDCl3): 136.5 (s), 134.9 (s), 133.3 (d), 131.2 (d),
130.9 (d), 128.7 (d), 79.7 (d), 79.1 (d), 78.4 (d), 53.6 (d), 27.2 (t), 26.5 (t).
Ph otobrom in ation of 1,2-Dibrom o-1,2,3,4-tetrah ydron aph th alen e
To a solution of 1,2-dibrom o-1,2,3,4-tetrah ydron aph th alen e (9; 145 m g, 0.50 m m ol) in
CDCl3 (0.5 m l) in an NMR tube brom in e (0.88 g, 0.55 m m ol) was added. Th e m ixture was
irradiated by a projector lam p (150 W) for 15 m in . HBr gas was rigorously evacuated durin g
th e reaction . Th e residue obtain ed after rem oval of th e solven t was recrystallised from
CH2Cl2–petroleum eth er to give 1,2,4-tribromo-1,2,3,4-tetrahydronaphthalene (6; 156 m g,
85%).
Hydrolysis of 1,2-Dibrom otetralin (9)
A solution of 1,2-dibrom o-1,2,3,4-tetrah ydron aph th alen e (9; 145 m g, 0.50 m m ol) in CHCl3
(20 m l) was m ixed with silica gel 60 (20 g) an d H2O (0.5 m l). Th e resultin g m ixture was
stirred for 2 days. Th e solution was filtered an d th e solven t was rem oved in vacuo. Th e resi-
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Cakmak et al.:
due was crystallised from CHCl3 to give trans-2-bromo-1,2,3,4-tetrahydronaphthalen-1-ol (5)
(91 m g, 80%).
Brom in ation of Naph th alen e (3)
To a refluxin g solution of n aph th alen e (3; 6.4 g, 50 m m ol) in tetrach lorom eth an e (60 m l) in
a reaction flask a solution of brom in e (17.57 g, 110 m m ol) in CCl4 (30 m l) was dropped
over 1 h . Th e reaction m ixture was stirred for an oth er 1 h at th e reflux tem perature of CCl4
(77 °C), th en cooled to room tem perature, an d th e solven t was rem oved in vacuo. On distilla-
tion of th e reaction m ixture in vacuo, 1-bromonaphthalene (2) was collected at 130 °C/10 m m Hg
to provide pure m aterial in a yield of 90% (9.31 g).
Ph otobrom in ation of 1,2,3,4-Tetrah ydron aph th alen e (1)
A solution of tetralin (3.96 g, 30 m m ol) in CCl4 (75 m l) in an in tern al type ph otoch em ical
reaction apparatus (im m ersion -well reactor, 100 m l) was cooled to 0 °C with an ice bath . A
device for absorbin g th e h ydrogen brom ide evolved was attach ed to a side arm . Th e con ten t
was irradiated by a projector lam p (150 W, cooled by run n in g water) an d stirred m agn eti-
cally wh ile a solution of Br2 (21.6 g, 135 m m ol) in CCl4 (20 m l) was added durin g 0.5 h .
Th e reaction m ixture was irradiated for 1.5 h in total. HBr was rigorously rem oved durin g
th e reaction . Th e reaction progress was m on itored by 1H NMR spectroscopy or TLC. After re-
m oval of th e solven t, th e residue was crystallised from CCl4 at 0 °C, an d was iden tified as
1,1,4,4-tetrabromo-1,2,3,4-tetrahydronaphthalene (10; 12.36 g, 92%), wh ite crystallin e m aterial,
m .p. 63 °C (decom p.) from CCl4. 1H NMR (CDCl3): 7.90 (2 H, H5, H8); 7.37 (2 H, H6, H7);
3.23 (s, 4 H, aliph atic). 13C NMR (CDCl3): 139.2 (s), 132.8 (d), 132.3 (d), 62.8 (d), 49.5 (t).
For C10H8Br4 (448) calculated: 26.82% C, 1.95% H; foun d: 26.03% C, 2.10% H. Th e
tetrabrom ide 10 slowly decom posed with evolution of h ydrogen brom ide to give
1,4-dibrom on aph th alen e on stan din g at room tem perature or at 0 °C.
1,4-Dibrom on aph th alen e
To a stirred solution of 1,1,4,4-tetrabrom o-1,2,3,4-tetrah ydron aph th alen e (10; 11.2 g, 25 m m ol)
in dry, fresh ly distilled THF (110 m l) a solution of potassium tert-butoxide (6.16 g, 55 m m ol)
in dry, fresh ly distilled THF (60 m l) was added over 20 m in . Th e resultin g reaction m ixture
was stirred m agn etically at room tem perature overn igh t. Th e m ixture was diluted with water
(100 m l) an d th e solution was extracted in to eth er (300 m l), th en th e extract was wash ed
with water an d dried with MgSO4. After rem oval of th e solven t, th e residue was filtered
th rough a sh ort silica gel colum n (30 g) (h exan e) an d recrystallised from h exan e to give clear
yellow crystals of 1,4-dibrom on aph th alen e (11; 6.79 g, 95%), m .p. 80 °C (ref.3 83–83.5 °C).
1H NMR (CDCl3): 7.62 (s, 2 H); 8.23–7.62 (AA′BB′, 4 H). 13C NMR (CDCl3): 123.1 (s), 128.3 (d),
128.7 (d), 130.6 (d), 133.4 (s). For C10H6Br2 (286) calculated: 42.00% C, 2.11% H; foun d:
42.84% C, 2.50%H.
1-Brom o-4-m eth oxyn aph th alen e (12)
Fresh ly cut sodium (460 m g, 20 m m ol) was added un der n itrogen gas to dry m eth an ol (30 m l).
W h en dissolution was com plete, th e warm solution was diluted with dry dim eth yl-
form am ide (DMF) (30 m l) followed by th e addition of vacuum -dried cuprous iodide (475 m g,
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Bromination of Tetralin
1795
2.5 m m ol). After dissolution , 1,4-DBN (11; 1.43 g, 5.0 m m ol) in dry DMF (50 m l) was added.
Th e reaction m ixture was stirred m agn etically un der a n itrogen atm osph ere at reflux (ca 90 °C).
Reaction progress was m on itored by TLC an d startin g m aterial was con sum ed with in 12 h .
After coolin g to room tem perature, H2O (50 m l) an d dieth yl eth er (100 m l) were added to
th e reaction m ixture. Th e organ ic layer was separated, wash ed with H2O (3 × 50 m l), an d
dried over MgSO4 for 1 h . Th e solven t was rem oved an d th e crude product was purified by
ch rom atograph y (SiO2, petroleum eth er). 1-Meth oxy-4-brom on aph th alen e (12; 1.16 g, 80%)
was obtain ed as a ligh t yellow oil. 1H NMR (CDCl3, 400 MHz): 4.00 (s, 3 H, OCH3); 6.68 (d,
AB, 1 H, H2); 7.65 (d, J(2,3) = 8, 1 H, H3); 7.48–7.64 (m , 2 H, H6, H7); 8.15–8.30 (m , 2 H,
H5, H8). 13C NMR (CDCl3): 57.6, 98.2, 105.0, 106.3, 123.8, 124.4, 127.0, 128.0, 129.6,
131.3, 157.2. Th is com poun d h as been prepared previously by several routes, such as
m eth ylation of th e correspon din g n aph th ol16 or brom in ation of 1-m eth oxyn aph th alen e17
.
1,4-Dim eth oxyn aph th alen e (13)
Fresh ly cut sodium (690 m g, 30 m m ol) was added un der n itrogen gas to dry m eth an ol (30
m l). Wh en dissolution was com plete, th e warm solution was diluted with dry dim eth yl-
form am ide (DMF) (30 m l) followed by th e addition of vacuum -dried cuprous iodide (950
m g, 5 m m ol). After dissolution , 1,4-DBN (11; 1.43 g, 5 m m ol) in dry DMF (50 m l) was
added. Th e reaction m ixture was stirred m agn eticaly un der a n itrogen gas atm osph ere at re-
flux (ca 90 °C) for 36 h . Reaction progress was m on itored by TLC an d startin g m aterial was
con sum ed with in 12 h to form m ain ly 1-m eth oxy-4-brom on aph th alen e (12) as assign ed by
TLC. Form ation of 1,4-dim eth oxyn aph th alen e (13) was com pleted in 36 h . After coolin g to
room tem perature, H2O (50 m l) an d dieth yl eth er (100 m l) were added to th e reaction m ix-
ture. Th e organ ic layer was separated, wash ed with H2O (3 × 50 m l), an d dried over MgSO4
for 1 h . Th e solven t was rem oved an d th e crude product was passed th rough a sh ort colum n
packed with Al2O3 (10 g). Recrystallisation from a m ixture of CH2Cl2 an d petroleum eth er
(b.p. 40–50 °C) in th e refrigerator yielded 1,4-dim eth oxyn aph th alen e (13; 752 m g, 80%) as
colourless n eedles, m .p. 76–77 °C (ref.18 86–87.5 °C). 1H NMR (CDCl3, 400 MHz): 3.94 (s,
3 H); 6.68 (s, 2 H, H2, H3); 7.47–7.51 (AA′BB′, 2 H, H6, H7); 8.18–8.22 (AA′BB′, 2 H, H5,
H8). 13C NMR (CDCl3): 57.5, 106.6, 116.2, 127.1, 128.6, 157.3.
1-Brom o-4-cyan o-n aph th alen e (14)
1,4-DBN (11; 1.43 g, 5 m m ol) dissolved in fresh ly distilled DMF (40 m l) was m ixed with dry
CuCN (0.805 g, 9 m m ol). Th e reaction m ixture was stirred m agn etically at th e reflux tem -
perature of th e solven t un der an N2 atm osph ere for 12 h . Reaction progress was m on itored
by TLC for con sum ption of th e startin g m aterial. After th e reaction m ixture h ad cooled to
room tem perature, ben zen e (40 m l) an d water (40 m l) were added. Th e m uddy m ixture was
separated by suction filtration . Th e m ud was extracted with eth er (4 × 30 m l) an d th e eth er
layers were subjected to suction filtration each tim e. Th e aqueous ph ase was extracted with
ben zen e (40 m l) an d th e com bin ed organ ic layers were wash ed with 10% aqueous FeCl3
(100 m l) an d 10% aqueous NaOH, respectively. Th e organ ic ph ase was dried over Na2SO4.
After rem oval of th e solven t, th e residue was ch rom atograph ed on a SiO2 colum n eluted
with petroleum eth er. Th e m aterial was recrystallised from dich lorom eth an e–ligh t petroleum
eth er (1 : 1, 15 m l) in a refrigerator to yield pure com poun d (810 m g, 70%), m .p. 103–104 °C.
1H NMR (CDCl3, 400 MHz): 7.74 (d, J(3,2) = 8, 1 H, H3); 7.71–7.78 (m , 2 H, H6, H7); 7.84
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Cakmak et al.:
(d, J(2,3) = 8, 1 H, H2); 8.23–8.26 (m , 1 H, H5 or H8); 8.31–8.35 (m , 1 H, H5 or H8). 13C
NMR (CDCl3): 111.0, 117.1, 126.0, 128.4, 128.5, 130.0, 130.2, 130.5, 133.1, 134.0, 134.1.
1,4-Dicyan on aph th alen e (15)
1,4-DBN (11; 1.80 g, 6.2 m m ol) dissolved in fresh ly distilled DMF (30 m l) was m ixed with
dry CuCN (1.68 g, 15 m m ol). Th e reaction m ixture was stirred m agn etically at th e reflux
tem perature of th e solven t un der an N2 atm osph ere for 20 h . Reaction progress was m on i-
tored by TLC for com pletion of form ation of th e dicyan on aph th alen e. Th e reaction m ixture
was cooled to room tem perature, an d in to it were poured ben zen e (40 m l) an d water (40 m l).
A m uddy m ixture was form ed an d th e m uddy part was separated by suction filtration . Th e
m uddy part was extracted with eth er (4 × 40 m l) an d th e eth er layers were separated from
th e m uddy part by suction filtration each tim e. Th e aqueous ph ase was extracted with ben -
zen e (30 m l) an d th e com bin ed organ ic layers were wash ed with 10% aqueous FeCl3 (100
m l) an d 10% aqueous NaOH, respectively. Th e organ ic ph ase was dried over Na2SO4. After
rem oval of th e solven t, th e crude product was ch rom atograph ed usin g a SiO2 colum n eluted
with petroleum eth er. Th e m aterial obtain ed was recrystallised from dich lorom eth an e–ligh t
petroleum eth er (1 : 1, 15 m l) in a refrigerator to yield pure com poun d 15 (890 m g, 80%),
m .p. 205–206 °C (ref.19 208 °C). 1H NMR (CDCl3): 3.94 (s, 3 H); 6.68 (s, 2 H, H2, H3);
7.47–7.651 (AA′BB′, 2 H, H6, H7); 8.18–8.22 (AA′BB′, 2 H, H5, H8). 13C NMR (CDCl3): 116.2,
117.1, 126.4, 131.4, 132.4, 133.0.
RESULTS AND DISCUSSION
In an in itial experim en t, 1,2,3,4-tetrah ydron aph th alen e (1) was subjected
to brom in ation by 4 equivalen ts of brom in e in refluxin g carbon tetrach lo-
ride for 10 m in , by wh ich tim e th e brom in e colour h ad disappeared. Th e re-
sultin g crude product was crystallised from petroleum eth er, wh ich
provided th e dibrom o com poun d 4 as th e m ajor product (63%). Th e rest of
th e m ixture was subm itted to silica gel colum n ch rom atograph y. After care-
ful repeated ch rom atograph y, followed by fraction al crystallisation , four
addition al products were isolated an d ch aracterised as 2, 3, 5, an d 6
(Sch em e 1).
In order to ch aracterise th ese products properly, an d also to provide in -
form ation about th e way h ow th ey were form ed, several addition al experi-
m en ts were con ducted. Naph th alen e (3) an d 1-brom on aph th alen e (2) were
ch aracterised by com parison with auth en tic m aterials. It appeared likely
th at 3 was form ed by elim in ation of HBr from dibrom o product 4, an d in -
deed com poun d 4 elim in ated h ydrogen brom ide spon tan eously to form
n aph th alen e both in its solid state an d in solution . Th erefore, we con -
cluded th at n aph th alen e could be form ed by double HBr elim in ation from
4 durin g th e reaction an d durin g colum n ch rom atograph y. Com poun d 2
could possibly h ave been form ed by direct brom in ation of 3 durin g th e re-
action or by double elim in ation of HBr from com poun d 5. In order to
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

Bromination of Tetralin
1797
ch eck wh eth er 2 could be produced by direct brom in ation of n aph th alen e
form in g from 4 in th e con dition s occurin g durin g th e reaction , a solution
of on e m ole equivalen t of brom in e in CCl4 was dropped to a refluxin g solu-
tion of n aph th alen e in CCl4. Th e reaction product was distilled in vacuo to
obtain pure 2 in a yield of ca 90%, th ereby dem on stratin g th e possibility
th at it could h ave been form ed in th is way.
Br
Br
Br
Br2
Br2
-HBr
1
7
8
9
SiO2
Br2
77 oC
Br
Br2/hν
CCl4
OH
Br
Br
Br
Br
Br
+
+
+
+
Br
2
3
4
5
6
Br2/CCl4
77 oC
-HBr
SCHEME 1
Th e elem en tal an alysis of com poun d 6 was in reason able agreem en t with
th e proposed tribrom ide structure (Sch em e 1). H2 sh ows a m ultiplet com -
prisin g th e couplin gs with H1, H3a, an d H3b. In sign al group at 5.63 ppm
(dd, H4) th e low couplin g (6.2 Hz) appears between H4 an d H3b, wh ile
large couplin g (9.6 Hz) H4 an d H3a. Th e m eth ylen e proton s at C3 appear as
an AB system . Th e A part, wh ich is th e sign al group of H3a, is split in to
doublets of doublets of doublets. Th e gem in al couplin g, J(3a,3b), is ca 14.5
Hz. Th e secon d doublet splittin g origin ates from couplin g to H4 (J(3a,4) =
9.6) an d th e th ird doublet (J(2,3a) = 2.8) origin ates from couplin g to H2.
Th e B part of th e AB spin system in split in to doublets of triplets of dou-
blets. Th e triplet splittin g (J = 6.2) is due to n early equal values of th e di-
h edral an gles between H3b an d H2/H4. On e of th e doublet splittin g is due
to th e gem in al couplin g (J(3a,3b)) an d th e secon d doublet splittin g (J(1,3b) =
1.4) origin ates from th e H1. Th e fact th at such lon g-ran ge couplin g exists
between H1 (δ 5.55) an d H3b is due to a W arran gem en t as con firm ed dou-
ble reson an ce experim en ts. Th e ch em ical sh ifts of th e 13C NMR reson an ces
of com poun d 6 were also con sisten t with th e expected ch em ical sh ifts.
Th erefore, th e structure of 6 was con firm ed as th at sh own in Sch em e 1.
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

1798
Cakmak et al.:
Th e elem en tal an alysis of 5 was con sisten t with its bein g a brom o alco-
h ol20. IR an alysis con firm ed th at a h ydroxy group was presen t an d th e
m eltin g poin t was th e sam e as th at reported previously for 2-brom o-
1,2,3,4-tetrah ydron aph th alen -1-ol12. Th erefore, it seem ed th at th is product
h ad been form ed by partial h ydrolysis of 1,2-dibrom o-1,2,3,4-tetra-
h ydron aph th alen e (9). Ben zylic brom ides can be h ydrolysed easily durin g
colum n ch rom atograph y to th e correspon din g brom o alcoh ols21, an d th e
reten tion of stereoch em istry probably results from in term ediate brom -
on ium ion form ation .
1
Th e H NMR spectrum 12 of brom o alcoh ol 5 sh owed th ree m ultiplets at δ
7.60, 7.35 an d 7.14 due to arom atic proton s. Th e H1 an d H2 reson an ces oc-
curred as an AB system . Th e H1 reson an ce was a doublet at δ 4.91 (J(1,2) =
7.0). Irradiation of th e sign al at δ 3.00, wh ich was assign ed to th e two pro-
ton s on C4 as a m ultiplet, sh owed th at th e sign al groups at δ 2.28 an d 2.51
belon g to proton s on C3, wh ich appear as an AB system (J(3a,3b) = 13.7).
Wh en th e H1 sign als were irradiated, th e doublet of doublets of doublets of
H2 (δ 4.35) ch an ged to a doublet of doublets (J(2,3a) = 3.3, J(2,3b) = 9.5).
Fin ally, th e h ydroxy group reson ates at δ 2.60. Th e trans-con figuration of
th e h ydroxy group an d th e brom o substituen t in th e brom o alcoh ol was as-
sign ed by X-ray crystallograph ic an alysis (Fig. 1).
Th e m olecular structure with atom -n um berin g sch em e for com poun d 5 is
sh own in Fig. 1. Th e crystallograph ic data an d th e bon d len gth s an d an gles
C7′
C6′
C7
C5′
C6
C
C8′
C9′
C8
C9
A
C5
C10
C4
O1
C1′
C2′
C10′
D
B
C1
C2
O1′
C3
Br1′
C4′
Br1
C3′
Molecule (I)
Molecule (II)
FIG. 1
Crystal structure of com poun d 5 with atom -n um berin g sch em e. Th e th erm al ellipsoids are
drawn at th e 50% probability level
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

Bromination of Tetralin
1799
are given in Tables I an d II. Th e asym m etric un it con tain s two m olecules.
Th e in term olecular close con tact between th e oxygen atom s [O1···O1′ is
2.724(8) Å] of m olecules (I) an d (II) causes a h ydrogen bon d. In m olecule
(II), th e O1′–C1′ [1.33(1) Å] an d C2′–Br1′ [1.893(9) Å] bon d len gth s are
sh orter th an in m olecule (I) but th e C2′–C3′ bon d len gth [1.68(1) Å] is ab-
n orm ally lon ger. Th e C9′–C1′–O1′ [104.3(7)°], C2′–C1′–O1′ [100.2(7) °], an d
Br1′–C2′–C1′ [99.1(6)°] bon d an gles are sm aller wh ile th e Br1′–C2′–C3′ bon d
an gle [115.5(6)°] is larger th an th e correspon din g on es [1.53(1), 2.05(1),
1.38(1) Å an d 112.1(7), 112.8(7), 114.1(6), 105.6(7)°, respectively] in
m olecule (I). The C (C5′,C6′,C7′,C8′,C9′,C10′) and A (C5,C6,C7,C8,C9,C10)
rings are planar while D (C1′,C2′,C3′,C4′,C9′,C10′) and B (C1,C2,C3,C4,C9,C10)
rin gs are n on -plan ar with m axim um deviation s of C2′ [0.266(9) Å] an d C2
[0.318(10) Å] from th e best least-squares plan es. Som e of th e dih edral an -
gles between th e best least-squares plan es of th e m olecules (I) an d (II) are
A/C = 78.0(3), B/C = 79.8(3), A/D = 73.9(3), an d B/D = 75.7(3)°. Th e C–Br
bon d len gth s an d C–C–Br bon d an gles in th e n on -plan ar rin gs an d also th e
bon d len gth s an d an gles in th e plan ar rin gs are gen erally in good agree-
m en t with th e correspon din g on es22.
It appeared likely th at com poun ds 5 an d 6 m ay h ave arised from furth er
reaction s of 1,2-dibrom o-1,2,3,4-tetrah ydron aph th alen e (9), itself form ed
from 1,2-dih ydron aph th alen e (8) followin g deh ydrobrom in ation of
1-brom o-1,2,3,4-tetrah ydron aph th alen e (7). In order to test th is possibility,
1,2-dih ydron aph th alen e (8) was reacted with m olecular brom in e in CH2Cl2
to provide trans-1,2-dibrom o-1,2,3,4-tetrah ydron aph th alen e24 (9) in n early
quan titative yield. Ph otobrom in ation of 8 with a projector lam p afforded
th e 1,2,4-tribrom o com poun d 6, wh ile h ydrolysis of 9 over silica gave th e
brom o alcoh ol 5, dem on stratin g th at th is route is in deed a possible on e for
production of th ese com poun ds. Th e un derstan din g gain ed from th is an al-
ysis of th e reaction products of th e sh ort-tim e brom in ation of tetralin in
refluxin g tetrach lorom eth an e en abled us to design better experim en ts to
provide tetrabrom otetralin .
Sim ple use of extra brom in e an d prolon ged duration of reaction at th e re-
flux tem perature of CCl4 did in deed produce tetrabrom otetralin (10), but
alon g with a large am oun t of polym eric m aterial. In order to m in im ise th e
in situ loss of HBr, wh ich was probably respon sible for in itiatin g th e pro-
duction of th e polym eric by-product, we carried out th e reaction un der
ph otolytic con dition s at low tem perature. To a solution of tetralin in CCl4
ca 4.5 m ole equivalen ts of brom in e were added wh ile th e solution was irra-
diated in tern ally with a 150 W projector lam p at 0 °C. Th e process resulted
in th e substitution of all four ben zylic h ydrogen atom s with brom in e atom s
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

1800
Cakmak et al.:
TABLE I
Crystallograph ic an d experim en tal data23 of brom o alcoh ol 5
Em pirical form ula
Form ula weigh t
Crystal colour
Crystal dim en sion s, m m
Crystal system
Lattice param eters:
a, Å
C10H11BrO
227.11
colourless
0.20 × 0.15 × 0.10
m on oclin ic
10.690(1)
b, Å
8.939(1)
c, Å
19.704(2)
β, °
95.73(1)
V, Å3
1 873.45(33)
Space group
P21/n
Z
8
Dx, g m l–1
1.61
µ(MoK), m m –1
Tem perature, K
F(000)
4.29
293
912
λ(MoKα), Å
0.71073
Residuals R; Rw
No. of reflection s used
No. of param eters
Goodn ess of fit
Min im um residual den sity, e Å–3
Maxim um residual den sity, e Å–3
Treatm en t of h ydrogen atom s
Refin em en t
0.063; 0.072
2 760
217
0.98
–0.63
0.57
Geom etric calculation
Full-m atrix least-squares (MolEN)
En raf–Non ius CAD-4 diffractom eter
CAD-4 Express Software
Mo1EN
Measurem en t
Program system
Structure determ in ation
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

Bromination of Tetralin
1801
TABLE II
Bon d distan ces (in Å) an d an gles (in °) for brom o alcoh ol 5
Atom s
Bon d distan ces
Atom s
Bon d distan ces
Br1′–C2′
Br1–C2
1.893(9)
2.05(1)
1.33(1)
1.53(1)
1.42(1)
1.55(1)
1.41(1)
1.53(1)
1.46(1)
1.52(1)
1.68(1)
1.47(1)
1.41(1)
C6′–C7′
C7′–C8′
C9–C10
C9–C1
C9–C8
C10–C4
C10–C5
C4–C3
C3–C2
C2–C1
C8–C7
C7–C6
C6–C5
1.43(2)
1.38(1)
1.35(1)
1.53(1)
1.34(1)
1.49(1)
1.41(1)
1.57(1)
1.38(1)
1.57(1)
1.41(1)
1.33(2)
1.33(1)
O1′–C1′
O1–C1
C10′–C9′
C10′–C4′
C10′–C5′
C9′–C1′
C9′–C8′
C1′–C2′
C2′–C3′
C3′–C4′
C5′–C6′
Atom s
An gles
Atom s
An gles
C9′–C10′–C4′
C9′–C10′–C5′
C4′–C10′–C5′
C10′–C9′–C1′
C10′–C9′–C8′
C1′–C9′–C8′
O1′–C1′–C9′
O1′–C1′–C2′
C9′–C1′–C2′
Br1′–C2′–C1′
Br1′–C2′–C3′
C1′–C2′–C3′
C2′–C3′–C4′
C10′–C4′–C3′
C10′–C5′–C6′
C5′–C6′–C7′
C6′–C7′–C8′
C9′–C8′–C7′
125.9(8)
117.8(8)
116.3(8)
122.0(8)
122.9(8)
115.1(8)
104.3(7)
100.2(7)
111.9(7)
99.1(6)
C10–C9–C1
C10–C9–C8
C1–C9–C8
C9–C10–C4
C9–C10–C5
C4–C10–C5
C10–C4–C3
C4–C3–C2
Br1–C2–C3
Br1–C2–C1
C3–C2–C1
O1–C1–C9
O1–C1–C2
C9–C1–C2
C9–C8–C7
C8–C7–C6
C7–C6–C5
C10–C5–C6
124.1(8)
117.1(9)
118.7(8)
120.3(8)
119.6(8)
120.0(8)
111.7(8)
114.2(9)
105.6(7)
114.1(6)
109.0(8)
112.1(7)
112.8(7)
110.3(7)
122.5(9)
120(1)
115.5(6)
116.1(7)
112.7(8)
113.4(8)
119.1(9)
122.9(9)
119.6(9)
117.6(9)
119(1)
122.2(9)
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

1802
Cakmak et al.:
to give 1,1,4,4-tetrabrom o-1,2,3,4-tetrah ydron aph th alen e (10) in h igh yield
1
(92%). Th e structure of 10 was establish ed un am biguously by its H NMR
spectrum . Th e four aliph atic proton s reson ated as a sin glet at δ 3.2. Th e aro-
m atic proton s sh owed an AA′BB′ pattern at δ 7.57 an d 8.22. An efficien t
double deh ydrobrom in ation of 10 was ach ieved by usin g 2 m ole equiva-
len ts of potassium tert-butoxide, givin g 1,4-dibrom on aph th alen e (11), iso-
lated in a yield of 95% (Sch em e 2). Th e 1H an d 13C NMR spectra sh owed
th e expected sym m etry in th e m olecule.
Br
Br
Br
Br2/hν
t-BuOK
CCl4
THF
Br
1
Br
Br
10
11
SCHEME 2
Havin g obtain ed 1,4-dibrom on aph th alen e (1,4-DBN; 11) in h igh yield by
a very con ven ien t procedure, we wish ed to dem on strate its value as a pre-
cursor of oth er useful com poun ds25. Copper-assisted n ucleoph ilic substitu-
tion s by m eth oxide an d cyan ide ion s easily an d efficien tly con verted
1,4-DBN (11) in to its m eth oxy (12 an d 13) an d cyan ide (14 an d 15) deriva-
tives as sole products (Sch em e 3).
X
Br
Nu (CH3O ,CN
)
12, X = Br, Y = OCH3
13, X = Y = OCH3
14, X = Br, Y = CN
15, X = Y = CN
Y
Br
11
SCHEME 3
1
Th e structure of n aph th alen e rests on H an d 13C NMR spectral data of 13
an d 15 in wh ich AA′BB′ system of th e arom atic proton s an d th e sin glets for
th e H2 an d H3 proton s con firm in g th e sym m etrical structures are observed.
In NMR spectra of brom ocyan ide 12 an d m eth oxybrom ide 14, H2 an d H3
proton s sh owed an AB pattern at δ 7.74, 7.84 an d δ 6.68, 7.65 with J(2,3) =
8.0, respectively.
Selectively tran sform ation of 1,4-DBN (11) in to m eth oxybrom ide 12 an d
brom ocyan ide 14 open ed up syn th esis of various cyan ide an d m eth oxy de-
rivatives of n aph th alen e due to brom o substituen t. Meth oxyn aph th alen es
h ave great syn th etic im portan ce in several poin ts, i.e., for 1,4-dim eth oxy-
n aph th alen e; in syn th esis of oth er substituted n aph th alen e derivatives26
Collect. Czech. Chem. Commun. (Vol. 65) (2000)

Bromination of Tetralin
1803
an d n atural products27, as sen sitiser28 an d electron don ors29 an d in th e
rin g-en largem en t30 with h alocarben es to ben zotropon e derivatives. Th ey
are usually prepared from h ardly accessible 1,4-dih ydroxyn aph th alen e an d,
th erefore, our m eth od appear to be m ore con ven ien t an d practical.
In con clusion , exh austive ben zylic ph otobrom in ation of tetralin , fol-
lowed by elim in ation of HBr un der basic con dition s, allows th e h igh yield
syn th esis of 1,4-dibrom on aph th alen e. Th is m eth od of syn th esis h as several
advan tages over existin g m eth ods. It begin s with a readily available startin g
m aterial, it is efficien t, an d it is applicable to large-scale work. Th e product
is a useful precursor of oth er 1,4-disubstituted n aph th alen es.
The authors are indebted to the University Research Fund of the Department of Chemistry,
Gaziosmanpasa University (grant No. 1994/2) and The Scientific and Technical Research Council of
Turkey (TUBITAK; grant No. TBAG-1322) for financial support. O. Ç. also thanks the British Council
in Turkey for supporting co-operation with the University of Wales Swansea.
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Collect. Czech. Chem. Commun. (Vol. 65) (2000)

1804
Cakmak et al.:
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