Synthesis and isolation of some benzo[c]tellurophenes

Full text of DOI:10.1021/jo0001030

J . Org. Chem. 2000, 65, 5413-5415
5413
Sch em e 1
Syn th esis a n d Isola tion of Som e
Ben zo[c]tellu r op h en es
Zhizhen Huang, M. V. Lakshmikantham,
Michael Lyon, and Michael P. Cava*
Department of Chemistry, The University of Alabama,
Tuscaloosa, Alabama 35487-0336
mcava@bama.ua.edu
Received J anuary 25, 2000
In tr od u ction
The highly reactive o-quinonoid heterocycles benzo[c]-
furan and benzo[c]thiophene have received much atten-
tion, both from the synthetic and the theoretical points
of view.1,2 In contrast, the unstable benzo[c]selenophene
was generated by us via a base-catalyzed selenoxide
dehydration3 but was not further examined. The genera-
tion of the unstable benzo[c]tellurophene 4 appeared only
fairly recently.4 In contrast to reports on benzo[b]tel-
lurophenes,5 which are quite stable, the o-quinonoid
benzo[c]tellurophene was found to be highly reactive.
Herein we would like to report fully on the systematic
synthesis of benzo[c]tellurophenes 4, 13, and 18, as well
as the functionalization of 4 to yield substituted 9a , 9b,
and 10.
[c]tellurophene 4 was obtained in low yield as a grayish
white solid. Reaction of 4 with N-methylmaleimide
furnished N-methylnaphthalimide (8).
Resu lts a n d Discu ssion
The functionalization of the electron-rich benzo[c]-
tellurophene 4 was studied. Direct introduction of various
electrophiles via Friedel-Crafts reactions was unsuc-
cessful as a result of the instability of the ring to acid.
However, dilithiation was achieved by reaction with
excess n-butyllithium, as evidenced by the formation of
diesters 9a and 9b and the disulfonyl derivative 10, in
60-70% yields, by quenching with the appropriate elec-
trophiles 7a , 7b, and p-toluenesulfonic anhydride, re-
spectively (Scheme 1). These diesters and the disulfonyl
derivative 10 were relatively more stable than the parent
heterocycle 4. Interestingly enough, no monosubstituted
derivatives were identified or isolated in these reactions.
1,3-Dihydro-2,2-diiodobenzo[c]tellurophene 2 can be
prepared readily by the reaction of 1,2-bis(chloromethyl)-
benzene 1 with tellurium and sodium iodide in methoxy-
ethanol.6 All attempts to eliminate the elements of
hydrogen iodide from a base catalysis met with failure.
It was found that triethylamine in refluxing benzene led
to a very low yield of 4 via dehydroiodination, the major
product being the deiodinated 5. However, replacement
of iodine in 2 by trifluoroacetate and subsequent treat-
ment of the trifluoroacetate 3 with triethylamine under
defined conditions cleanly produced benzo[c]tellurophene
4 and 1,3-dihydrobenzo[c]tellurophene 5, in a ratio of 8:1
as estimated by the NMR spectrum. Benzo[c]tellurophene
4 is relatively more stable in benzene than in more polar
solvents. Its solution in benzene can be frozen and stored
below 0 °C for several months. However, on removal of
the benzene it decomposed rapidly. The use of limited
quantities of n-butyllithium removed 1,3-dihydrobenzo-
[c]tellurophene 5, and a sample of relatively pure benzo-
Other electrophiles, such as acetyl chloride, benzoyl
chloride, cyanogen bromide, tert-butyldimethylsilyl chlo-
ride, and trifluoroacetic anhydride failed to give isolable
products with the dianion.
Attention was then focused on the synthesis of 13, a
benzo[c]tellurophene bearing an electron-withdrawing
group (NO2) on the six-membered ring. The known
4-nitro-o-xylene was converted to the dibromide 11 by
reaction with N-bromosuccinimide and light. Crude di-
bromide 11 was directly converted to the 1,3-dihydrotel-
lurophene diiodide 12 in 90% yield by reaction with
tellurium and sodium iodide in methoxyethanol (Scheme
2). Not surprisingly, dehydroiodination proved facile upon
treatment of 12 with triethylamine in refluxing benzene,
leading to the isolation of the benzo[c]tellurophene 13 by
direct crystallization of the product. Although 13 was
stable at ambient temperature and atmosphere for
several weeks, it did decompose upon prolonged exposure
to air, and it was also sensitive to acid.
(1) (a) Dean, F. M. Furans and Their Benzo Derivatives. In
Comprehensive Heterocyclic Chemistry; Katritzky, A. R., Rees, C. W.,
Eds.; Pergamon Press: Elmsford, 1984; Vol. 4, pp 531-712. (b)
Friedrichsen, W. Adv. Het. Chem. 1980, 26, 135.
(2) (a) Kellogg, R. M. Thiophenes and Their Benzo Derivatives. In
Comprehensive Heterocyclic Chemistry; Katritzky, A. R., Rees, C. W.,
Eds.; Pergamon Press: Elmsford, 1984; Vol. 4, pp 713-863. (b) Iddon,
B. Adv. Het. Chem. 1972, 14, 331.
(3) Saris, L. E.; Cava, M. P. J . Am. Chem. Soc. 1976, 98, 867.
(4) Morkved, E. H.; Lakshmikantham, M. V.; Cava, M. P. Tetrahe-
dron Lett. 1996, 37, 9149.
(5) Detty, M. R.; O’regan, M. B. Tellurium-Containing Heterocycles.
In The Chemistry of Heterocyclic Compounds; Taylor, E. C., Ed.; J ohn
Wiley & Sons, Inc.: New York, 1994; Vol. 35, pp 71-80.
(6) Ziolo, R. F.; Gunther, W. H. H. J . Organomet. Chem. 1978, 146,
245.
10.1021/jo0001030 CCC: $19.00 © 2000 American Chemical Society
Published on Web 07/27/2000

5414 J . Org. Chem., Vol. 65, No. 17, 2000
Notes
Sch em e 2
Isola tion of 4. The crude product mixture of 4 and 5 from
Sch em e 3
the bistrifluoroacetate 3 (0.92 g) in dry benzene was cooled in
an ice bath and was treated with TMEDA (0.210 g) followed by
n-BuLi; after 1.5 h the mixture was quenched with water and
worked up. The resulting oily product was dissolved in hexane
and freed of an insoluble precipitate, and the solution in hexane
was chilled (-78 °C) to give 4, mp darkens ∼55 °C and melts at
70 °C. 1H NMR (C6D6) δ: 8.84 s (2 H), 7.2 dd (2 H), 6.64 dd (2
H). MS m/e (relative intensity): 232 (M+ ,100) 230 (95%), 103
(34%).
Diels-Ald er Rea ction of 4 w ith N-Meth ylm a leim id e to
F u r n ish Na p h th a lim id e 8. A solution of benzo[c]tellurophene
(4) was prepared from 3 as above, treated with a solution of
N-methylmaleimide (0.111 g) in benzene (1 mL), refluxed for 2
h, and then stirred at 50-55 °C for 2 days. After removal of
solvent, the residue was purified by column chromatography to
give naphthalimide 8 (0.085 g. 45%). Mp 203-204 °C (lit.7 204-
205 °C). 1H NMR (CDCl3) δ: 8.31 (5.24), 8.04 (dd. J ) 6.1, 3.3
Hz, 2 H), 7.69 (dd, J ) 6.2, 3.2 Hz, 2H), 3.25 (6 H). 13C NMR
(CDCl3) δ: 168.3, 135.6, 130.5, 128.3, 128.1, 124.7, 24.4. MS m/e
(relative intensity): 211 (M+, 100).
1,3-Difu n ction a lized Ben zo[c]tellu r op h en es 9a , 9b, a n d
10. A solution of benzo[c]tellurophene 4 in benzene prepared as
above was concentrated to about 2 mL at room temperature.
This solution was diluted with THF (20 mL), and a hexane
solution of n-butyllithium (5.6 mmol, 2.5 M) was added dropwise
at -70 °C. The reaction mixture was kept at room temperature
for 1 h and recooled to -70 °C, and a solution of alkyl chloro-
formate 7a or 7b (5.6 mmol) in THF (5 mL) or p-toluenesulfonic
anhydride (4.2 mmol) in THF (30 mL) was added. The reaction
mixture was warmed to room temperature gradually and stirred
for 1 h. The resulting mixture was washed with a saturated
solution of sodium carbonate (5 mL), dried, and concentrated.
The oily residue was subjected to column chromatography (SiO2)
to obtain 1,3-dialkoxycarbonyl-substituted benzo[c]tellurophenes
9a , 9b, or 1,3-ditosyl substituted benzo[c]tellurophene 10.
1,3-Dieth oxycar bon ylben zo[c]tellu r oph en e 9a. Yield: 76%,
Finally, 5-methoxybenzo[c]tellurophene (18) was gen-
erated from the bistrifluoroacetate 17, which in turn was
made as depicted in Scheme 3. As expected, it was even
less stable than 4, precluding isolation. However, it was
characterized by NMR and was trapped by N-methyl-
maleimide to give the naphthalimide 20 by spontaneous
loss of the elements of hydrogen telluride.
Con clu sion
The elusive benzo[c]tellurophene has been synthesized
and funtionalized on the tellurophene ring via lithiation
and treatment with electrophiles. The nitro and methoxy
analogues have been made, the former being more stable
than the latter.
1
mp 153-155 °C. H NMR (CDCl3) δ: 8.48 (dd J ) 7.1 3.1 Hz, 2
H); 7.19 (dd, J ) 7.1, 3.1 Hz, 2 H), 4.40 (q, J ) 7.2 Hz, 4 H),
1.43 (t, J ) 7.1 Hz). 13C NMR (CDCl3) δ: 166.8, 151.1, 138.0,
126.7, 124.5, 61.8, 14.6. MS m/e (relative intensity): 376 (M+,
100), 374 (96) 331(61.7), 303 (89.4), 274 (20.6), 230 (22.7). HRMS
calcd for C14H4O4Te130 375.995438, found 375.994363.
Exp er im en ta l Section
Gen er a l Com m en ts. Melting points are uncorrected. THF
was freshly distilled from sodium-benzophenone. All mass
peaks containing Te are reported for Te.130
1,3-Dib e n zyloxyca r b on ylb e n zo[c]t e llu r op h e n e
9b .
1
Yield: 74%, mp 103-105 °C. H NMR (CDCl3) δ: 8.51 (dd, J )
7.1, 3.7 Hz, 2 H), 7.28-7.48 (m, 10 H). 7.21 (dd, J ) 7.0, 3.0 Hz,
2 H), 5.37 (s, 4 H). 13C NMR (CDCl)3 δ: 166.4, 151.4, 137.5,
136.0, 130.1, 128.9, 127.4, 126.9, 124.5, 67.4. MS m/e (relative
intensity): 500 (M+, 66.5), 393 (18.9). 366 (82.3), 232 (100),
191 (50.7). HRMS calcd for C24H18O4Te130 500.026738, found
500.026093
Syn th esis of 1,3-Dih yd r o-2,2-bis(tr iflu or oa cetoxy)-ben -
zo[c]tellu r op h en e 3. A mixture of 2,2-diiodo-1,3-dihydrobenzo-
[c]tellurophene 26 (4.86 g, 10 mmol) and silver trifluoroacetate
(4.42 g, 20 mmol) in benzene (200 mL) was stirred at room
temperature for 2 h. After filtration, the filtrate was concen-
trated to give 1,3-dihydro-2,2-bis(trifluoroacetoxy)-benzo[c]tel-
1,3-Dit osylb en zo[c]t ellu r op h en e 10. Yield: 61%, mp
170 °C (dec). 1H NMR (CDCl3) δ: 7.93 (d, J ) 7.2 Hz, 4 H), 7.78
(dd, J ) 7.0, 3.0 Hz, 2 H), 7.30 (d, J ) 7.2 Hz, 4 H), 7.11 (dd, J
) 7.0, 3.1 Hz, 2 H), 2.39 (s, 6 H). 13C NMR (CDCl3) δ: 153.0,
147.1, 144.8, 138.0, 130.3, 128.2, 127.2, 122.5, 21.8. MS m/e
(relative intensity): 540 (M+, 29), 262 (17.7), 218 (27.8), 139
1
lurophene 3 (4.17 g, 91%). Mp: 160 °C (dec). H NMR (C6D6) δ:
6.72 (dd, J ) 5.7, 3.3 Hz, 2 H), 6.49 (dd, J ) 5.1, 3.2 Hz, 2 H),
3.83 (s, 4 H). 13C NMR (C6D6) δ: 162.4, 161.9, 137.8, 130.2, 128.6,
116.9, 113.7, 47.8.
Ben zo[c]tellu r op h en e 4. A mixture of 1,3-dihydro-2,2-bis-
(trifluoroacetoxy)- benzo[c]tellurophene 3 (0.916 g, 2 mmol) and
triethylamine (2.02 g, 20 mmol) in degassed benzene (200 mL)
was refluxed under argon for 15 min. The resulting solution was
washed with deionized water (200 mL × 2) and dried over
sodium sulfate. Removal of solvent in vacuo at room temperature
resulted in a mixture (0.36 g) of benzo[c]tellurophene 4 and 1,3-
dihydro-benzo[c]tellurophene 5. 1H NMR (CDCl3) (4) δ: 9.34 (s,
2 H), 7.32 (dd, J ) 7.00, 3.20 Hz, 2 H), 6.72 (dd, J ) 6.72, 2.92
Hz, 2 H) and that of 5 at δ 7.2, m (2Η), 7.05m (2Η), 4.5 s (4 Η);
a comparison of the intensities of the R H in 4 (9.34 s) to the
benzylic H in 5 (4 H) at δ 4.5 showed a 8:1 ratio of 4:5, the
concentration of 4 being ∼89% in the mixture isolated in 78%
yield.
(120). HRMS calcd for
539.969774.
C
22H18O4S2Te130 539.970882, found
1,3-Dih yd r o-2,2-d iiod o-5-n itr oben zo[c]tellu r op h en e 12.
A mixture of 4-nitro-o-xylene (1.51 g, 10 mmol) and N-bromo-
succinimide (3.56 g, 20 mmol) in 1,2-dichloroethane (20 mL) was
refluxed under illumination (250 W incandescent bulb) for 20
min. The reaction mixture was washed with water (20 mL × 2)
and dried over sodium sulfate. Removal of solvent gave crude
1,2-bis(bromomethyl)-5-nitrobenzene 11 (yield 70%). The mix-
ture of the crude compound 11 (7 mmol), finely powdered
(7) Gompper, R. Chem. Ber. 1960, 93, 198.

Notes
J . Org. Chem., Vol. 65, No. 17, 2000 5415
tellurium (0.768 g, 6 mmol) and sodium iodide (3.60 g, 24 mmol)
in 2-methoxyethanol (10 mL) was refluxed for 20 min. Water
(20 mL) was added, and the resulting precipitate was filtered
and washed with water (20 mL) and ethyl ether (40 mL × 3) to
give 1,3-dihydro-2,2-diiodo-5-nitrobenzo[c]tellurophene 12 (2.90
trifluoroacetate (94.42 g, 20 mmol) in benzene (200 mL) was
stirred at room temperature for 3 h. After filtration, the filtrate
was concentrated to yield 1,3-dihydro-5-methoxy-2,2-bis(trifluo-
roacetoxy)benzo[c]tellurophene 17 (4.49 g, 92%). Mp 150 °C (dec).
1H NMR (C6D6) δ: 6.53-6.38 (m, 2 H), 6.10 (s, 1 H), 3.844 (s, 2
H), 3.839 (s, 2 H), 3.18 (S, 3 H). 13C NMR (C6D6) δ: 162.5, 162.0,
160.4, 139.5, 130.3, 129.6, 116.9, 115.0, 114.4, 113.7, 55.3, 47.6,
46.9.
Syn th esis of 5-Meth oxyben zo[c]tellu r op h en e 18. A mix-
ture of 1,3-dihydro-5-methoxy-2,2-bis(trifluoroacetoxy)benzo[c]-
tellurophene 17 (0.488 g, 1 mmol) and triethylamine (1.01 g, 10
mmol) in degassed benzene (50 mL) was stirred under argon at
50-55 °C for 2.5 h. The resulting solution was washed with
deionized water (200 mL × 2) and dried over sodium sulfate.
Removal of the solvent at room temperature gave crude 5-meth-
oxybenzo[c]tellurophene 18. 1H NMR (C6D6) δ: 8.84 (s, 1 H), 8.57
(s, 1 H), 7.00 (d, J ) 9.5 Hz, 1 H), 6.73 (d, J ) 9.7 Hz, 1 H), 6.34
(s, 1 H), 3.31 (s, 3 H), mixed with 19.
Diels-Alder Reaction of 5-Meth oxyben zo[c]tellu r oph en e
18 w ith N-Meth ylm a leim id e To F u r n ish Na p h th a lim id e
20. A solution of benzo[c]tellurophene 18 was prepared from 17
(1 mmol) as above, treated with a solution of N-methylmaleimide
(0.111 g, 1 mmol) in benzene (1 mL), and stirred at 50-55 °C
for 2 days. After removal of solvent, the residue was purified by
column chromatography to give naphthalimide 20 (0.101 g,
42%). Mp 230 °C (dec). 1H NMR (CDCl3) δ: 8.23 (s, 1 H), 8.19
(s, 1 H), 7.92 (d, J ) 9.8 Hz, 1 H), 7.41-7.27 (m, 2 H), 3.98 (s,
3 H), 3.23 (s, 3 H). 13C NMR (CDCl3) δ: 168.6, 160.3, 137.5,
131.8, 130.8, 128.9, 126.0, 124.5, 123.3, 121.8, 108.7, 55.8, 24.3.
MS m/e (relative intensity): 241 (M+, 83.5), 197 (100), 156 (37.1).
HRMS calcd for C14H11NO3 241.073893, found 241.073131.
1
g, 91%). Mp 230-232 °C. H NMR (DMSO-d6) δ: 8.25 (s, 1 H),
8.11 (d, J ) 8.5 Hz, 1 H), 7.62 (d, J ) 8.3 Hz, 1 H), 4.82 (s, 2 H),
4.80 (s, 2 H). 13C NMR (CDCl3) δ: 147.9, 146.8, 142.3, 130.6,
124.5, 122.0, 45.9.
Syn th esis of 5-Nitr oben zo[c]tellu r op h en e 13. A mixture
of 1,3-dihydro-5-nitro-2,2-diiodobenzo[c]tellurophene 12 (0.531
g, 1.0 mmol) and triethylamine (1.01 g, 10 mmol) in benzene
(50 mL) was refluxed for 40 min under argon. The resulting
mixture was washed with water (50 mL × 2), dried, and
concentrated. The residue was purified by crystallization from
Et2O/n-C5H12 to furnish 5-nitrobenzo[c]tellurophene 13 (0.17 g,
1
62%). Mp 90 °C (dec). H NMR (CDCl3) δ: 9.99 (s, 1 H), 9.53 (s,
1 H), 8.42 (s, 1 H), 7.62 (d, J ) 9.6 Hz, 1 H), 7.44 (d, J ) 9.6 Hz,
1 H). 13C NMR (CDCl3) δ: 147.9, 145.9, 134.3, 128.5, 126.9,
126.0, 123.1, 115.8. MS m/e (relative intensity): 277 (M+, 100),
275 (73), 231 (69.5), 219 (33.3), 218 (27.8), 139 (100). HRMS calcd
for C8H5NO2Te130 276.938257, found 276.936188
1,3-D ih y d r o -2,2-d iio d o -5-m e t h o x y b e n zo [c]t e llu r o -
p h en e16. A mixture of 3,4-dimethylanisole (1.36 g, 10 mmol)
and N-bromosuccinimide (3.74 g, 21 mmol) in dichloromethane
(90 mL) was refluxed under illumination (250 W incandescent
bulb) for 40 min. The reaction mixture was washed with water
(90 mL × 2) quickly and dried over sodium sulfate. Removal of
solvent resulted in the crude 1,2-bis(bromomethyl)-5-methoxy-
benzene 15 (yield 60%). The mixture of the crude compound 15
(6 mmol), finely powdered tellurium (0.384 g, 3 mmol), and
sodium iodide (3.60 g, 24 mmol) in dry methanol (15 mL) was
refluxed for 30 min, resulting in the formation of diiodide 16.
Water (30 mL) was added. After filtration, the precipitate was
washed with ethyl ether (40 mL × 3) to give 1,3-dihydro-2,2-
diiodo-5-methoxylbenzo[c]tellurophene 16 (0.960 g, 36% overall).
Ack n ow led gm en t. We thank the National Science
Foundation for a grant (CHE-961235 0) in support of
this work.
1
Su p p or t in g In for m a t ion Ava ila b le: 1H and 13C NMR
spectra for compounds 3, 9a , 9b, 10, 12, 13, 16, 17, and 20
and 1H NMR spectra for the highly labile compounds 4 and
18. This material is available free of charge via the Internet
at http://pubs.acs.org.
Mp 205 °C (dec). H NMR (DMSO-d6) δ: 7.22 (d, J ) 8.4 Hz, 1
H), 6.87 (s, 1 H), 6.84 (d, J ) 8.6 Hz, 1 H), 4.75 (s, 2 H), 4.72 (s,
2 H), 3.76 (s, 3 H). 13C NMR (DMSO-d6) δ: 158.4, 141.1, 131.3,
130.0, 113.8, 113.6, 55.4, 50.8, 50.0.
1,3-Dih yd r o-5-m eth oxy-2,2-bis(tr iflu or oa cetoxy)ben zo-
[c]tellu r op h en e 17. A mixture of 1,3-dihydro-2,2-diiodo-5-
methoxybenzo[c]tellurophene 16 (5.16 g, 10 mmol) and silver
J O0001030