Photobromination of indane: Preparation of bromoindenones and ready access to benzo[c]fluorenone skeleton

Article abstract of DOI:10.1016/S0040-4020(01)00978-4

1,1,3,3-Tetrabromoindane and 1,1,2,3,3-pentabromoindane were efficiently synthesized by photolytic bromination of indane. Subsequent dehydrobromination of them gave the corresponding tribromo- and tetrabromoindenes, which were easily converted to the corresponding bromoindenones by silver-supported hydrolysis. Thermolysis of 3-bromoindenone gave the benzo[c]fluorenone derivative.

Full text of DOI:10.1016/S0040-4020(01)00978-4

TETRAHEDRON
Pergamon
Tetrahedron 57 <2001) 9759±9763
Photobromination of indane: preparation of bromoindenones
and ready access to benzo[c]¯uorenone skeleton
Ahmet Tutar,a,b Osman Cakmaka,p and Metin Balcib,p
aDepartment of Chemistry, Faculty of Science, Gaziosmanpasa University, 60240 Tokat, Turkey
bDepartment of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
Received 1 August 2001; accepted 12 October 2001
AbstractÐ1,1,3,3-Tetrabromoindane and 1,1,2,3,3-pentabromoindane were ef®ciently synthesized by photolytic bromination of indane.
Subsequent dehydrobromination of them gave the corresponding tribromo- and tetrabromoindenes, which were easily converted to the
corresponding bromoindenones by silver-supported hydrolysis. Thermolysis of 3-bromoindenone gave the benzo[c]¯uorenone derivative.
q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
chlorination reaction. In a previous paper, we reported the
facile formation of indenone <3) by treatment of the product
2 formed from the addition of dichloroketene to cyclo-
heptatriene <1), with base <Scheme 1).12
A rapid growth on the synthetic work of indenones has taken
place in the last three decades. Indenones are useful inter-
mediates1 in the synthesis of a variety of molecules,
including the C-nor D-homosteroid ring system,2 photo-
chromic indenone oxides,3 2,4- and 3,4-disubstituted-1-
naphtols,4 gibberellins,5 indanones6 and indenes.7
In this paper, we describe a new method leading to the
synthesis of brominated indenone derivatives which can
serve as the key compounds for the preparation of other
substituted indenone derivatives as well as for construction
of the benzo[c]¯uorenone skeleton.
A logical precursor to these compounds could be the corre-
sponding indenone. However, poor yields, irreproducibility,
or decomposition of the starting material were common
outcomes. Despite the considerable biological and synthetic
interest in indenones, the development of general and
¯exible synthetic routes to these compounds still remains
a challenging problem. Several procedures for the synthesis
of indenones and indenols have been reported.8 Mainly, two
methods have been directed towards the synthesis of inde-
none derivatives. The ®rst one1,9 is the palladium or alu-
minium chloride catalyzed addition of substituted benzoyl
chlorides to acetylenic compounds. The second method10,11
involves an intramolecular Friedel±Crafts acylation of
b-chloro-b-arylpropionyl chlorides followed by a dihydro-
2. Results and discussion
First, we focused on the development of a practical process
for the synthesis of 1,1,3,3-tetrabromoindane starting from
indane. Bromination of hydrocarbons is important process
because it leads to useful intermediates for the synthesis of a
large variety of bromoorganic compounds. Benzylic bromi-
nation requires either high temperature or irradiation with
UV light in the presence of free radical catalysts and often
gives mixtures of products. Recently, we realized that
internal irradiation of tetraline in the presence of bromine
Scheme 1.
Keywords: photobromination; bromoindenes; bromoindenones; benzo[c]¯uorene.
Corresponding authors. Tel.: 190-312-210-5140; fax: 190-312-210-1280; e-mail: ocakmak@gop.edu.tr; mbalci@metu.edu.tr
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020<01)00978-4

9760
A. Tutar et al. / Tetrahedron 57 ,2001) 9759±9763
arrangement and functionality to permit the easy introduc-
tion of one double bond to give bromoindenes, we submitted
these compounds to a dehydrobromination reaction with
1 mol of potassium tert-butoxide or thermal decomposition
without solvent at elevated temperatures <140±1508C) and
isolated 10 and 11 in high yields, respectively <Scheme 3).
The ®rst synthesis of tribromoindene 10 was reported by
Straus et al.14 According to this procedure, indene gave
the tribromide 10 in 68% yield upon treatment with KOBr
solution. Later, Proctor15 has observed the formation of
tribromide 10 as a mixture with 1,2,3-tribromoindene by
the bromination of indane with N-bromosuccinimide in
the presence of light.
Scheme 2.
provides effective benzylic bromination and gives
a,a,a0,a0-tetrabromotetraline 5 in high yield <Scheme 2).13
We describe herein the preparation of a,a,a0,a0-tetra-
bromoindane and the conversion of the photoproducts. To
a solution of indane <7) in CCl4 was added 4 equiv. bromine
while internal irradiating <150 W projector lamp) at room
temperature. The tetrabromide 8 was formed as the sole
product in high yield <95%) after 50 min irradiation. The
gem-Dibromides 8±11 are also precursors to the corre-
sponding ketones. Therefore, the bromides were subjected
to a silver ion-supported hydrolysis reaction in aqueous
acetone. Tribromoindene 10 afforded bromoindenone 1216
in 90% yield <Scheme 4).
1
structure was established easily from the simple H NMR
spectrum consisting of a AA0BB0 system in the aromatic
region and a singlet at 4.4 ppm arising from the methylenic
protons. However, prolonged irradiation of 7 resulted in the
formation of the pentabromide 9 <Scheme 3). Furthermore,
the pentabromide 9 was obtained independently by irradia-
tion of 10 in the presence of bromine.
Next, we were interested in the thermal stability of the
bromoindenone 12 derivative, since this compound contains
an antiaromatic cyclopentadienone structure. When
bromoindenone 12 was heated in a sealed tube in the
absence of solvent, two separable products were isolated.
Spectroscopic studies indicated the formation of 13 and 14
in 45 and 30% yields, respectively. The compound 1317
bearing a benzo¯uorenone structure was characterized by
After successful synthesis and isolation of polybrominated
indane derivatives 8 and 9, which have the requisite
Scheme 3.
Scheme 4.

A. Tutar et al. / Tetrahedron 57 ,2001) 9759±9763
9761
Scheme 5.
means of H and 13C NMR spectroscopic data and two-
dimensional spectral measurements <COSY, HMQC and
HMBC). For the formation of this benzo¯uorenone struc-
ture, we suggest the following mechanism. Bromoindenone
12 undergoes an intramolecular [214] cycloaddition
reaction where the cyclopentadienone structure acts as
both the diene and the dienophile as depicted in Scheme
4. The formed intermediate 15 can easily undergo HBr
elimination followed by CO extrusion to give 5-bromo-
7H-benzo[c]¯uoren-7-one 13. The isolated by-product,
2,3-dibromoindenone 14 was characterized properly.
However, its mechanism of formation is unclear.
4.2. General procedure for photobromination
1
All bromination reactions were carried out in a cylindrical
vessel with two necks attaching to a dimrot cooler and drop-
ping funnel. For the internal irradiation, a 150 W projector
lamp was used.
4.2.1. Photochemical bromination of indane ,7). A solu-
tion of bromine <8.00 g, 50 mmol) in carbon tetrachloride
<20 mL) was added to a magnetically stirred solution of
indane <1.44 g, 12.2 mmol) in CCl4 <35 mL) in a photo-
chemical reaction apparatus <60 mL) dropwise over
35 min while irradiating by 150 W projector lamp. HBr
was rigorously evacuated during the reaction. After com-
pletion of the reaction <50 min), the excess bromine and
solvent were removed at reduced pressure and at 208C, the
solid residue was crystallized from chloroform at room
temperature during two days to give colorless cubic crystals
of 1,1,3,3-tetrabromoindane <8) <5.0 g, 95%. Decomp.:
147±1508C; [Found: C, 24.79; H, 1.32. C9H10Br4 requires
C, 24.92; H, 1.39%]; nmax <KBr) 2940, 1460, 1283, 1233,
1009, 865, 761, 600, 540 cm21; dH <400 MHz, CDCl3) d
7.7±7.5 <AA0BB0, 4H, aryl), 4.4 <s, 2H, methylenic); dC
<100 MHz, CDCl3) 142.8, 131.7, 125.0, 73.2, 51.8; MS
<m/z): 430/432/434/436/438 <M1), 349/351/353/355 <M1,
2Br), 271/273/275 <M1, 22Br, 192/194 <M1, 23Br) 113
<M1, 24Br).
For further characterization of 14, we have undertaken an
independent synthesis of 14 starting from pentabromo-
indane and tetrabromoindene derivatives 9 and 11. Silver
ion supported solvolysis of 9 and 11 in aqueous acetone
solution resulted in the formation of the dibromoindenone
14 in 98% yield in both cases <Scheme 5).
3. Conclusion
A short and convenient method for the synthesis of highly
brominated indane derivatives has been developed starting
from indane. The reactions described in this paper appear to
be fairly general and provide a useful method for intro-
ducing bromine atoms into benzylic positions. Upon treat-
ment of the highly brominated indane derivatives with silver
salt in aqueous acetone, the corresponding ketones were
synthesized in high yield. Bromoindenone 12 was converted
into the benzo¯uorenone derivative 13. To the best of our
knowledge, this is the shortest synthesis of this skeleton
bearing a functional group, which can be easily replaced
by other functional groups.
4.2.2. Synthesis of 1,1,2,3,3-pentabromoindane ,9). A
solution of bromine <7.61 g, 47.6 mmol) in carbon tetra-
chloride <20 mL) was added to a magnetically stirred solu-
tion of indane <7) <1.11 g, 9.4 mmol) in 35 mL CCl4 and
irradiated as described above for 4 h. After evaporation of
the unreacted bromine and solvent at reduced pressure and
208C, the solid residue was recrystallized from methylene
chloride±hexane to give 9 <4.51 g, 88%). Decomp.: 1408C
<colorless crystals); [Found: C, 21.10; H, 0.92. C9H5Br5
requires C, 21.09; H, 0.98%]; nmax <KBr) 2934, 1460,
1252, 1198, 1178, 1024, 880, 812, 760, 599, 528 cm21; dH
<400 MHz, CDCl3) 7.7±7.5 <AA0BB0 4H, aryl), 5.3 <s, 1H,
methine); dC <100 MHz, CDCl3) d 140.7, 132.1, 125.7,
75.9, 58.3; MS m/z 512/514 <M1), 429/431/433/435/437
<M1, 2Br, 25), 351/353/355/357 <M1, 22Br, 11), 271/
273/275 <M1, 23Br, 75), 191/193 <M1, 24Br, 11), 113
<M1, 25Br, 100).
4. Experimental
4.1. General
Commercial reagents were purchased from standard chemi-
cal suppliers and puri®ed to match the reported physical and
spectral data. Thin layer chromatography was carried out on
Merck silica F254 0.255 mm plates. Classical column
chromatography was performed using Merck 60 <70±230
Mesh) silica. Melting points were determined on a
Thomas±Hoover capillary melting point apparatus.
Solvents were concentrated at reduced pressure. IR spectra
were recorded on an Jasco FT-IR 430. NMR spectra were
recorded on a Bruker instrument 400 MHz for 1H and
100 MHz for 13C NMR.
4.2.3. Synthesis of 1,1,3-tribromo-1H-indene ,10). ,a)
Thermal reaction of tetrabromide 8. A crystalline material
of 8 <1.39 g, 3.21 mmol) in a sealed glass-tube was allowed
to heat in silicon oil bath to 150±1558C for 30 min. The
elimination of HBr was observed. The dark-colored material
was ®ltered through a short column <10 g alumina) eluting
with hexane. The solvent was evaporated. The residue was
crystallized from hexane±ether <1:2, 9 mL) in a freezer to

9762
A. Tutar et al. / Tetrahedron 57 ,2001) 9759±9763
give colorless crystals, mp: 1068C <Lit. mp: 104.5±1058C)
<1.07 mg, 95%).
<25 mL acetone/5 mL H2O) was added to a stirred solution
of 1,1,3-tribromo-1H-indene <10) <2.75 g, 7.80 mmol) in
acetone <50 mL) over 5 min. The resulting mixture was
stirred magnetically at room temperature for 30 min. The
precipitated silver bromide was removed by ®ltration.
50 mL methylene chloride was added to organic phase
and washed with H2O <3£40 mL), and dried over MgSO4.
The solution was concentrated under reduced pressure.
Complete removing of the solvent should be avoided,
since the product decomposes. However, it is stable after
crystallization. Crystallization from CH2Cl2±petroleum
ether <1:1, 10 mL) in a refrigerator yielded 3-bromoinde-
none 12 <1.47 g, 90%) as yellow needles, mp 578C, <Lit
mp 57.5±588C16). nmax <KBr) 1716, 1538, 1365, 1245,
1075, 912, 762, 683, 599, 554, 413 cm21; dH <400 MHz,
CDCl3) 7.39 <dt, Jˆ7.5, 1.1 Hz, 1H), 7.34 <brd, Jˆ7.0 Hz,
1H), 7.26 <brt, Jˆ7.2 Hz, 1H) 7.12 <brd, Jˆ7.3 Hz, 1H),
6.14 <s, 1H, ole®nic); dC <100 MHz, CDCl3) 193.8, 148.6,
142.9, 133.6, 130.4, 127.34, 121.8, 121.3.
,b) Elimination of tetrabromide 8 with potassium tert-
butoxide. To a stirred solution of tetrabromide 8 <2.5 g,
5.8 mmol) in dry and freshly distilled THF <70 mL) was
added potassium tert-butoxide <0.76 g, 6.8 mmol). The
resulting reaction mixture was stirred 12 h at room tempera-
ture. The mixture was diluted with water <40 mL), the
aqueous solution was extracted with ether <60 mL), washed
with water <40£2 mL), and dried over MgSO4. After
removal of the solvent, the residue <pale-yellow oil) was
®ltered on a short silica gel column <15 g) eluted with
hexane. The product was crystallized <hexane±diethyl
ether: 1:2, 6 mL) to give pure 10 <1.67 g, 82%); [Found:
C, 30.60; H, 1.35. C9H5Br3 requires C, 30.64; H, 1.43%];
n
max <KBr) 3114, 1544, 1258, 1202, 951, 864, 780, 750, 704,
683, 647 cm21; dH <400 MHz, CDCl3) 7.7 <m, 1H), 7.4 <m,
2H), 7.3 <m, 1H), 6.85 <s, ole®nic); dC <100 MHz, CDCl3)
147.0, 139.8, 135.2, 130.0, 129.2, 124.1, 122.4, 121.1, 50.8;
MS m/z 350/352/354/356 <M1), 271/273/275 <M1, 2Br,
35), 192/194 <M1, 22Br, 15), 113 <M1, 23Br, 100).
4.2.7. Synthesis of 2,3-dibromo-1H-inden-1-one ,14). ,a)
Silver ion-promoted hydrolysis of pentabromoindane 9. A
solution of AgClO4 <5.55 g, 26.75 mmol) in aqueous
acetone <40 mL acetone/10 mL H2O) was added to a stirred
solution of 1,1,2,3,3-pentabromoindane <9) <3.15 g,
6.14 mmol) in acetone <100 mL) over 5 min. The resulting
mixture was stirred at room temperature for 30 min. The
precipitated AgBr was removed by ®ltration. To the organic
phase was added methylene chloride <60 mL) and organic
phase was washed with water <30£2 mL) and dried over
Na2SO4. After removal of the solvent, the residue was
crystallized from methylene chloride±hexane <1:1, 25 mL)
by standing in refrigerator to give 2,3-dibromo-1H-inden-1-
one <14), yellow needless, <1.75 g, 98%). mp 1208C. <Lit.
mp 1238C17).
4.2.4. Synthesis of 1,1,2,3-tetrabromo-1H-indene ,11). ,a)
Thermal dehydrobromination of pentabromide 9. Penta-
bromide 9 <1.51 g, 3.4 mmol) in a sealed glass-tube was
allowed to heat in silicon oil bath to 1208C for 30 min.
The dark-colored material was ®ltered through a short
Al2O3 <15 g) column eluted with hexane. After evaporation
of the solvent, the residue was crystallized from CH2Cl2±
hexane <1:3, 10 mL) at room temperature to give tetra-
bromoindene 11, mp 1248C <1.18 g, 93%).
,b) Base-induced elimination reaction of pentabromide 9.
To a stirred solution of pentabromide 9 <2.60 g, 5.1 mmol)
in dry and freshly distilled THF <50 mL) was added <0.66 g,
5.9 mmol) potassium tert-butoxide. The resulting reaction
mixture was stirred 12 h at room temperature. The mixture
was diluted with water <30 mL), and the aqueous solution
was extracted with ether <50 mL), washed with water
<30£2 mL), and dried over MgSO4. After removal of the
solvent, the oily residue was ®ltered on a short silica gel
column <10 g) eluted with hexane to give 11 <1.71 g, 78%);
[Found: C, 24.96; H, 0.90. C9H8Br4 requires C, 25.04; H,
0.93%]; nmax <KBr) 3048, 1460, 1238, 1171, 1118, 890, 770,
753, 692 cm21; dH <400 MHz, CDCl3) 7.7 <brd, 1H), 7.4 <m,
2H), 7.3 <m, 1H); dC <100 MHz, CDCl3) 145.9, 135.0,
133.9, 130.3, 129.1 124.8, 124.2, 120.8; 54.74; MS m/z
428/430/432/434/436 <M1), 349/351/353/355 <M1, 2Br,
25), 272/274/276 <M1, 22Br), 191/193 <M1, 23Br, 100),
113 <M1, 24Br, 71).
,b) Silver ion-promoted hydrolysis of 1,1,2,3-tetrabromo-
1H-indene 11. A solution of AgClO4 <1.27 g, 6.2 mmol) in
aqueous acetone <25 mL acetone/5 mL H2O) was added to a
solution of 1,2,3,3-tetrabromoindene <11) <1.30 g, 3.0
mmol) in acetone <100 mL) over 10 min. After stirring at
room temperature for 30 min, the precipitated AgBr was
removed by ®ltration. To the ®ltrate was added methylene
chloride <70 mL) and organic layer was washed with water
<40£2 mL) and dried over Na2SO4. After removal of the
solvent, the residue was crystallized from methylene
chloride±hexane <1:1, 25 mL) by standing in refrigerator
to give 14 <98%); [Found: C, 37.81; H, 1.45. C9H4Br2O
requires C, 37.54; H, 1.40%]; nmax <KBr) 1715, 1542,
1208, 1096, 752, 693, 657, 425 cm21; dH <400 MHz,
CDCl3) 7.39±7.35 <m, 2H), 7.45 <t, Jˆ7.5 Hz, 1H), 7.12
<d, Jˆ7.2, 1H); dC <100 MHz, CDCl3) 186.5, 146.34,
142.5, 134.4, 129.9, 129.0, 122.9, 122.4, 121.1.
4.2.5. Photobromination of 1,1,3-tribromo-1H-indene
,10). To a solution of 10 <120 mg 0.34 mmol) in CDCl3
<0.5 mL) in an NMR tube was added bromine <66 mg,
0.41 mmol). The mixture was irradiated by a projector
lamp <150 W) for 10 min. The residue obtained after
removal of the solvent was crystallized from CH2Cl2±petro-
leum ether to give 1,1,2,3,3-pentabromoindane 9 <162 mg,
93%).
4.2.8. Thermal decomposition of 3-bromo-1H-inden-1-
one ,12). Bromoindenone 12 <0.44 g) was heated in a sealed
glass-tube at 130±1358C for 5 h. The dark residue was
subjected to silica gel chromatography <40 g) eluting with
hexane. The ®rst fraction gave 14 90 mg, 30%.
The second fraction was identi®ed as 5-bromo-7H-
benzo[c]¯uoren-7-one ,13) <150 mg, 45%), mp 2208C
<Lit. mp 220±2218C17) red crystals from methylene
4.2.6. Synthesis of 3-bromo-1H-inden-1-one ,12). A solu-
tion of AgClO4 <3.60 g, 17.16 mmol) in aqueous acetone

A. Tutar et al. / Tetrahedron 57 ,2001) 9759±9763
9763
6. Zimmerman, H. E. J. Am. Chem. Soc. 1956, 78, 1168±1173.
7. Alesso, E. N.; Tombari, D. G.; Ibanez, A. F.; Iglesias, G. Y. M.;
Aguirre, J. M. Can. J. Chem. 1991, 69, 1166±1170.
8. <a) Quan, L. G.; Gevorgyan, V.; Yamamato, Y. J. Am. Chem.
Soc. 1999, 121, 3545±3546. <b) Gevorgyan, V.; Quan, L. G.;
Yamamato, Y. Tetrahedron Lett. 1999, 40, 4089±4092.
<c) Johnson, W. S.; Shellberg, W. E. J. Am. Chem. Soc.
1945, 67, 1745±1754. <d) House, H. O.; Hudson, C. B.
J. Org. Chem. 1970, 35, 647. <e) Sam, J.; Plampin, J. N.
J. Am. Chem. Soc. 1960, 82, 5205±5209. <f) Johnson, W. S.;
Shellberg, W. E. J. Am. Chem. Soc. 1945, 67, 1853.
<g) Barnes, R. A.; Kraft, E. R.; Gordon, L. J. Am. Chem.
Soc. 1949, 71, 3523±3528.
chloride; [Found: C, 66.04; H, 2.45. C17H9BrO requires C,
65.87; H, 2.52%]; nmax <KBr) 1707, 1555, 1243, 880, 745,
694 cm21; dC <400 MHz, CDCl3) 8.51 <dd, Jˆ7.2, 1.6 Hz,
1H), 8.34 <dd, Jˆ7.6, 1.5 Hz, 1H), 8.04 <s, 1H), 8.02 <d,
Jˆ7.6 Hz, 1H), 7.70 <m, 3H), 7.54 <t, Jˆ7.6 Hz, 1H) 7.34
<t, Jˆ7.4 Hz, 1H); dC <100 MHz, CDCl3) 193.5, 144.4,
142.2, 135.6, 134.7, 134.1, 131.9, 129.8, 129.6, 129.1,
129.0, 128.4, 125.2, 124.37, 124.33, 124.2, 123.5.
Acknowledgements
The authors are indebted to the Departments of Chemistry
<Gaziosmanpasa and Middle East Technical University) for
®nancial support <Grant 1997/29). A. T. thanks TUBITAK-
BAYG for a postdoctoral fellowships <1999/2000) at
METU.
9. Martens, H.; Hoornaert, G. Tetrahedron 1974, 30, 3641±3645.
10. Floyd, M. B.; Allen Jr., G. R. J. Org. Chem. 1970, 35, 2647±
2653.
11. Frank, R. L.; Eklund, H.; Richter, J. W.; Vanneman, C. R.;
Wennerberg, A. N. J. Am. Chem. Soc. 1944, 66, 1±4.
12. Zengin, M.; Dastan, A.; Balci, M. Synth. Commun. 2001, 31,
1993±1999.
References
È
13. CË akmak, O.; Kahveci, I.; DemirtasË, I.; Hokelek, T.; Smith, K.
Collect. Czech. Chem. Commun. 2000, 65, 1791±1804.
14. Straus, F.; Kollek, L.; Heyn, W. Chem. Ber. 1930, 63, 1868±
1885.
1. Larock, R. C.; Doty, M. J. J. Org. Chem. 1993, 58, 4579±
4583.
2. <a) Chatterjee, A.; Banerjee, S. Tetrahedron 1970, 26, 2599±
2608. <b) Martens, H.; Hoornaert, G. Synth. Commun. 1972, 2,
147±158.
15. Proctor, G. R. J. Chem. Soc. ,C) 1968, 2023±2025.
16. Straus, F.; KuÈhnel, R.; Haensel, R. Chem. Ber. 1933, 66,
1847±1862.
3. Ullman, E. F.; Henderson Jr., W. A. J. Am. Chem. Soc. 1966,
88, 4942±4960.
17. The synthesis of 13 has been described starting from the
7H-benzo¯uorene. However, no spectral data are reported
for the title compound see: Bolton, R. J. Chem. Res. ,S)
1977, 149.
4. Buggle, K.; Ghogain, U. N.; O'Sullivan, D. J. Chem. Soc.
Perkin Trans. 1 1983, 2075±2076.
5. House, H. O.; Larson, J. K. J. Org. Chem. 1968, 33, 448±453.