Facile access to organotellurium heterocycles by nitration of bis(3,5-dimethylphenyl) ditelluride

Article abstract of DOI:10.1002/jhet.5570420210

Efficient access to bis(nitrophenyl) ditellurides was developed and their utility for the preparation of novel nitrogen-containing organotellurium heterocycles demonstrated. The nitration of diphenyl ditellurides resulted in their oxidation to benzenetell

Full text of DOI:10.1002/jhet.5570420210

March 2005
243
Facile Access to Organotellurium Heterocycles by Nitration of
Bis(3,5-Dimethylphenyl) Ditelluride
1
1
2
Prabodhika R. Mallikarachy, Harry O. Brotherton, Frank R. Fronczek,
1*
and Thomas Junk
1
Department of Chemistry, University of Louisiana at Monroe, Monroe, Louisiana 71209
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70903
2
Received March 4, 2004
Efficient access to bis(nitrophenyl) ditellurides was developed and their utility for the preparation of novel
nitrogen-containing organotellurium heterocycles demonstrated. The nitration of diphenyl ditellurides
resulted in their oxidation to benzenetellurinic acids, followed by nitration in ortho or meta positions relative
to tellurium. Nitration of bis(3,5-dimethylphenyl) ditelluride furnished bis(3,5-dimethyl-2-nitrophenyl)
ditelluride, which was elaborated into 2,4,6-trimethylbenzotellurazole and (Z)-2-methoxycarbonylmethyl-
ene-3,4-dihydro-3-oxo-2H-benzo-1,4-tellurazine, the first reported 3,4-dihydro-2H-benzo-1,4-tellurazine.
This compound, as well as 2,4,6-trimethyltellurazolium (4-dicyanomethylene-cyclohexa-2,5-
dienylidene)cyanoacetate were characterized by x–ray crystallography.
J. Heterocyclic Chem., 42, 243 (2005).
with respect to the tellurinic acid moiety despite its elec-
tron-withdrawing properties. Thus, nitration of bis-(3,4-
dimethoxyphenyl) ditelluride followed by partial reduction
in the presence of chloride has been reported to generate 1-
chloro-5,6-dimethoxybenzo[2,1,3]oxatellurazole-N-oxide,
shown in Figure 1 [10].
Introduction.
In analogy bis-(2-nitrophenyl) diselenides, bis(2-
nitroaryl) ditellurides are expected to offer convenient
access to various nitrogen-containing organotellurium het-
erocycles [1]. Bis(2-nitroaryl) ditellurides and their deriv-
atives are of interest as potential precursors to substituted
tellurazoles [2-4], polymethine dyes [5], and as organotel-
lurium ligands [6]. Only one example of this class of com-
pounds has been reported, however. Bis(2-nitrophenyl)
ditelluride was prepared in two steps, starting with 2-
lithionitrobenzene and benzyltellurocyanate [7].
Benzyltellurocyanate is light sensitive and 2-lithioni-
trobenzene is unstable above -100 °C, giving this approach
a somewhat limited scope. More recently, the authors
reported the synthesis of bis(2-nitrophenyl) ditelluride
from 2-nitrophenylboronic acid [8]. Bis(2-nitrophenyl)
ditellurides cannot be accessed by reacting 2-nitrohaloben-
zenes with the ditelluride anion, due to the strongly reduc-
ing properties of tellurium-containing anions of types
Figure 1. 1-Chloro-5,6-dimethoxybenzo[2,1,3]oxatellurazole-N-oxide
This indicates that the regioselectivity of nitration of
aryltellurinic acids may not be as predictable as that of the
corresponding sulfonic acids due to the formation of prod-
ucts with Te-O coordination. 1-Chloro-5,6-dimethoxy-
benzo[2,1,3]oxatellurazole-N-oxide formally can be
regarded as 4,5-dimethoxy-2-nitrophenyl-tellurium chlo-
ride; in fact, 2-nitroaryltellurinic acids and their deriva-
tives tend to be heterocyclic in nature [13]. It seemed
plausible that 2-nitroaryltellurinic acids can be prepared
from appropriately substituted diphenyl ditellurides by a
one-pot oxidation-nitration procedure, thereby offering
improved access to organotellurium heterocycles.
The synthesis of six-membered Te-N heterocycles is
challenging and has been limited to that of phenotellu-
razines [14,15]. Thus, the preparation of benzo[1,4]thi-
azines by condensation of α-halocarbonyl compounds with
2-aminobenzenethiols cannot be adapted to generate the
corresponding benzotellurazines due to reductive dehalo-
genation of the α-halocabonyl compound by tellurolate
anions [16]. Consequently, the condensation of 2-amino-
benzenetellurols with dimethylacetylenedicarboxylate was
investigated as a possible entry point to six-membered
-
2-
2-
RTe , Te and Te in general [9]. Instead, other synthetic
2
strategies are required for the preparation of organotel-
lurium heterocycles such as tellurazoles and tellurazines.
These include their synthesis from organomercury precur-
sors [2], by reduction of oxatellurazolium salts [3], by
reduction of 2-azophenyltellurium halides [10], by photo-
stimulated telluromethylation [11], and access via 2-nitro-
phenylboronic acids [8]. All of these have limited scope or
utilize relatively inaccessible precursors. Other Te-N hete-
rocycles such as 1,4-benzotellurazines also should be
accessible via bis(2-nitroaryl) ditellurides, but remain
largely unknown to date.
Treatment of diaryl ditellurides with nitric acid invari-
ably leads to oxidation of the ditelluride moiety before ring
substitution [12]. Further nitration of the resulting aryltel-
lurinic acids, however, has not been investigated in much
detail. Evidence exists for the feasibility of ortho nitration

244
P. R. Mallikarachy, H. O. Brotherton, F. R. Fronczek, and T. Junk
Vol. 42
mL) and extracted with CH Cl (3 x 50 mL). The solvent was
Te-N heterocycles, in analogy to that reported for 2-
aminobenzenethiol [17]. The conversion of bis(3,5-
dimethyl-2-nitrophenyl) ditelluride to derivatives of ben-
zotellurazole and (Z)-3,4-dihydro-3-oxo-2H-benzo-1,4-tel-
lurazine as shown in Schemes 1 and 2 did indeed proceed
smoothly.
2
2
removed and the residue crystallized by addition of ethanol (15
mL) and chilling in an ice bath. Recrystallization from ethanol
furnished 8.82 g (73%) of red needles; mp 50-52 °C; ir: 2915,
-1
1
1597, 1563, 1458, 1036, 987, 837, 786, 602 cm ; H nmr
(CDCl ): δ 2.13 (s, 3H, -CH ), 2.15 (s, 3H, -CH ), 6.85 (s, 1H,
3
3
3
13
phenyl), 7.38 (s, 2H, phenyl); C nmr (CDCl ): δ 21.14, 130.22,
135.64, 138.77;
3
125
Te (CDCl ): δ 415.1; ms: m/z 571 (11), 468
3
Scheme 1
(39), 338 (20), 212 (100). This compound underwent slow oxi-
dation while in solution.
Anal. Calcd. for C
H Te : C, 41.28; H, 3.90. Found: C,
16 18 2
40.91; H, 4.02.
Bis(3-nitrophenyl) ditelluride (2).
A round bottom flask with magnetic stirring was charged with
concentrated sulfuric acid (20 mL), submersed in an ice bath, and
benzenetellurinic acid nitrate (5.0 g, 17.69 mmol) prepared accord-
ing to the literature [18] was slowly added in approx. 0.2 g batches.
The mixture was stirred at ambient temperature for 12 h and subse-
quently poured over crushed ice (50 g). Crude 3-nitrobenzenetel-
lurinic acid precipitated and was collected by filtration. Without
drying, this was suspended in water (50 mL) and reduced by
adding sodium metabisulfite (4.0 g, 21.0 mmol) and stirring for 12
Synthesis of 2,4,6-trimethylbenzotellurazole 6
Scheme 2
h at ambient temperature. The product was extracted with CH Cl
2
2
(2 x 25 mL). Crystallization from ethanol furnished 2.98 g (68%)
dark red crystals. The product was identical to a sample prepared
by a previously published procedure [8].
Synthesis of (Z)-2-methoxycarbonylmethylene-3,4-dihydro-3-oxo-2H-
benzo-1,4-tellurazine 7
Bis(3,5-dimethyl-2-nitrophenyl) ditelluride (3).
A round bottom flask with magnetic stirring was charged with
powdered bis(3,5-dimethylphenyl) ditelluride (1) (6.0 g, 12.89
mmol). The flask was submersed in an ice bath and 70% nitric
acid (12.0 mL, 254 mmol) slowly added using a pipette (Caution!
Copious evolution of nitrous oxides). Any remaining lumps
were broken up with a glass rod. After completed oxidation, con-
centrated sulfuric acid (16 mL) was slowly added with cooling to
keep the temperature of the mixture below 50 °C. The mixture was
stirred overnight and then diluted with ice water (100 mL) and
ethanol (5 mL). Excess acid was buffered by addition of sodium
acetate until pH >4, followed by reduction with sodium metasulfite
(8.0 g, 42 mmol). A blood-red precipitate formed (possibly due to
formation of an oxatellurazolium salt), which gradually gave way
to a brown precipitate upon stirring for 8 h at ambient temperature.
Solids were collected on a Büchner funnel, washed with approxi-
mately water (50 mL) and dissolved in CH Cl (50 mL). Insoluble
EXPERIMENTAL
Hydrochloric acid, nitric acid, sulfuric acid and sodium
metabisulfite were obtained from Fisher Scientific. Dimethyl
acetylenedicarboxylate was purchased from Acros. All other
reagents were purchased from Aldrich Chemical Company and
used as received. Melting points were recorded using an elec-
trothermal EM-6 apparatus, and are not corrected. Nuclear mag-
netic resonance spectra were recorded on a Jeol Eclipse 300 MHz
spectrometer. Mass spectrometry was performed on a Finnigan
Mat GCQ mass spectrometer under 70 eV electron impact condi-
tions with direct probe inlet. Infrared spectra were recorded with
the multiple internal reflectance (MIR) technique on a Perkin
Elmer Paragon FTIR spectrometer. Elemental analyses were per-
formed by Gailbraith Laboratories and in-house on an Exeter
Analytical CE-440 Elemental Analyzer.
2
2
matter (mostly elemental tellurium) was removed by filtration and
the solvent evaporated. Recrystallization from ethyl acetate fur-
nished 5.4 g (75%) of orange crystals; mp 168-170 °C; ir 2928,
Bis(3,5-dimethylphenyl) ditelluride (1).
1
1590, 1558, 1505, 1296, 840; H nmr (CDCl ): δ 2.27 (s, 3H, -
A 250 mL round bottom flask equipped with a magnetic stirrer
and reflux condenser was charged with 1-bromo-3,5-dimethyl-
benzene (10.0 g, 62 mmol), magnesium turnings (1.8 g, 74
mmol) and anhydrous tetrahydrofuran (80 mL). The mixture was
heated until no more magnesium dissolved (approx. 1 h) and then
chilled to 0 °C in an ice bath. Tellurium powder (200 mesh, 7.92
g, 75 mmol) was added, the mixture removed from the ice bath
and stirred vigorously. Most tellurium powder went into solution
within 30 min. The mixture was then exposed to air by removing
the reflux condenser and leaving the neck of the flask uncovered.
Stirring was continued overnight to assure complete oxidation of
the intermediate tellurolate. The mixture was then diluted with
ice water (100 mL), acidified with 36% hydrochloric acid (10
3
CH ), 2.52 (s, 3H, -CH ), 7.03 (s, 1H, phenyl), 7.80 (s, 1H,
3
3
13
phenyl); C nmr (CDCl ): δ 21.08, 21.22, 107.98, 133.48, 135.13,
138.72, 143.82, 148.91; Te nmr (CDCl ): δ 532.8; ms: m/z 556
3
125
3
(20), 430 (24), 359 (59), 264 (100).
Anal. Calcd. for C
H N O Te : C, 34.58; H, 2.88; N, 5.06.
16 16 2 4 2
Found: C, 34.45; H, 2.90; N, 5.04.
4-tert-Butyl-3-nitrophenyl tellurium tribromide (4).
A round bottom flask with magnetic stirring was charged with
of powdered bis(4-tert-butylphenyl) ditelluride (2.0 g, 3.83
mmol), prepared according to Haller and Irgolic's procedure [19].
The flask was immersed in an in an ice bath and 70% nitric acid

March 2005
Facile Access to Organotellurium Heterocycles by Nitration
245
(4.0 mL 63 mmol) was then slowly added (Caution! Copious
evolution of nitrous oxides). Any remaining lumps were broken
up with a glass rod. The mixture was stirred overnight after
which it had turned into an off-white paste. Acetonitrile (10 mL)
was added and precipitated crude tellurinic acid nitrate collected
by filtration. This crude product was added to an ice-cold mix-
ture of 70% nitric acid (3 mL, 23.5 mmol) and concentrated sul-
furic acid (6 mL). The mixture was stirred overnight and then
heated to 50 °C for one hour in a water bath. It was diluted with
water (150 mL), buffered to pH >4 with sodium acetate, and
reduced by adding of sodium metabisulfite (6.0 g, 31.5 mmol)
and stirring for 12 h at ambient temperature. The product was
dimethylphenyl) ditelluride (5) (1.0 g, 2.02 mmol) in THF (10
mL), acetic anhydride (20 mL) and 50% hypophosphorous acid
(2.0 mL, 38.5 mmol). The mixture was heated at reflux for 15
min, after which time its color had changed from dark brown to
yellow-gray. The mixture was diluted with water (100 mL), neu-
tralized with sodium bicarbonate and solid material collected by
filtration. This was dissolved in CH Cl (10 mL), byproducts
2
2
removed by flash chromatography (1.5 × 5 cm column, 200 mesh
silica gel, CH Cl ) and the solvent removed by evaporation.
2
2
Treatment of the remaining orange oil with methanol (2 mL) and
chilling in an ice bath induced crystallization. (In some
instances, crystallization was achieved with difficulty and seed-
ing or extensive refrigeration became necessary).
Recrystallization from methanol at -20° C produced 0.40 g
(36%) of product as pale yellow solid; mp 42-44° C; ir 2915,
extracted with CH Cl (2 x 20 mL) and the solvent removed by
2
2
evaporation. All efforts to crystallize bis(4-tert-butyl-3-nitro-
phenyl) ditelluride failed; consequently, the crude ditelluride was
taken up in carbon tetrachloride (10 mL) and converted to 4-tert-
butyl-3-nitrophenyl tellurium tribromide by adding a 50% solu-
tion of bromine in carbon tetrachloride until the color of the solu-
tion changed from red to lemon-yellow. The product precipitated
as a yellow microcrystalline solid, yield 3.10 g (74%). An ana-
lytical sample was obtained by recrystallization from acetic acid;
mp 210-212 °C (with partial decomposition); ir: 2962, 2525,
1
1599, 1560, 1543, 1429, 1286, 1120, 845, 776, 735, 558; H nmr
(CDCl ): δ 2.34 (s, 3H, 2-CH ), 2.74 (s, 3H, phenyl-CH ), 2.84
3
3
3
(s, 3H, phenyl-CH ), 7.02 (s, 1H, phenyl), 7.48 (s, 1H, phenyl);
3
13
C nmr (CDCl ): δ 20.92, 21.19, 30.79, 129.22, 129.25, 129.28,
134.74, 135.04, 157.81, 166.84; Te nmr (CDCl ): δ 911.1; ms:
3
125
3
m/z 275 (75), 234 (21), 103 (95). 77 (100).
Anal. Calcd. for C
H NTe: C, 44.02; H, 4.07; N, 5.12.
10 11
1
1532, 1365, 1060, 823, 662; H nmr (DMSO-d ): δ 1.37 (s, 9H),
Found: C, 43.98; H, 4.13; N, 4.95.
6
7.80 (d, 1H, phenyl), 8.53 (m, 1H, phenyl), 8.74 (m, 1H, phenyl);
ms: m/z 466 (26, M -Br), 387 (100), 372 (52).
(Z)-2-Methoxycarbonylmethylene-3,4-dihydro-3-oxo-2H-benzo-
1,4-tellurazine (7).
+
Anal. Calcd. for C
H Br NO Te: C, 22.02; H, 2.22. Found:
10 12 3 2
A round bottom flask with stirring and reflux condenser was
charged with bis-(2-amino-3,5-dimethylphenyl) ditelluride (5)
(100 mg, 0.20 mmol), dimethyl acetylenedicarboxylate (85 mg,
0.60 mmol), THF (2 mL) and methanol (3 mL). To this solution
was added 50% hypophosphorous acid (50 mg, 0.76 mmol), fol-
lowed by 37% hydrochloric acid (50 mg, 18.5 mmol). The mix-
ture was stirred and heated to reflux for 10 min, then diluted with
water (20 mL). Solids were collected by filtration, taken up in
C, 22.16; H 2.42.
Bis(2-amino-3,5-dimethylphenyl) ditelluride (5).
Bis(3,5-dimethyl-2-nitrophenyl) ditelluride (3) (0.50 g, 0.90
mmol) was suspended in absolute ethanol (30 mL) and the mix-
ture was magnetically stirred and heated to 90 °C. Sodium boro-
hydride was slowly added and the mixture warmed until the color
of the mixture faded. An additional 3 (4.5 g) was then added in
batches of approximately 100 mg, followed each time by as much
sodium borohydride as necessary for complete discoloration. No
effort was made to control the temperature of the reaction mix-
ture, resulting in boiling and considerable loss of ethanol by
evaporation. In total, 3 (5.0 g, 9.0 mmol) was reduced with
sodium borohydride (6.02 g, 159.1 mmol). The resulting solu-
tion was diluted with water (200 mL) and the mixture stirred for
48 h in an open beaker to assure complete oxidation of the tel-
lurol to the ditelluride. The product was collected by filtration,
CH Cl (10 mL) and chromatographed on a 0.8 × 4 cm column
2
2
(neutral alumina, CH Cl followed by CH Cl -acetonitrile 10:1
2
2
2
2
v/v). A small quantity of light yellow material eluted before the
main fraction, which was collected as an orange band.
Recrystallization from nitromethane furnished 33 mg (24%) of
product as pale yellow crystals; mp 226-228 °C (with darkening
and partial decomposition); ir: 2924, 2360, 1639, 1546, 1304,
1
1204; H nmr (CDCl ): δ 2.26 (s, 3H, phenyl-CH ), 2.36 (s, 3H,
3
3
phenyl-CH ), 3.87 (s, 3H, -OCH ), 6.90 (a, 1H, =CH), 7.16 (s,
3
3
13
dissolved in CH Cl (50 mL), insoluble matter removed by filtra-
1H, phenyl), 7.93 (1H, NH); 8.23 (1H, phenyl); C nmr
2
2
tion and the solvent removed by evaporation on a water bath at 60
ºC under an aspirator vacuum. Crystallization from ethanol pro-
duced 3.8 g (85%) of product as orange crystals; mp 138-139 °C;
(CDCl ): δ 13.37, 15.52, 39.89, 79.06, 94.31, 94.80, 98.56,
3
125
98.97, 100.69, 101.66, 118.96, 128.64;
Te nmr (CDCl ): δ
3
656.0; ms: m/z 361 (56), 231 (100), 172 (63).
1
ir 3402, 3330, 2921, 2851, 1614, 1470, 1234, 862; H nmr
Anal. Calcd. for C H NO Te: C, 43.51; H, 3.65; N, 3.90.
13 13 3
(CDCl ): δ 2.12 (s, 3H, -CH ), 2.14 (s, 3H, -CH ), 4.03 (2H,
NH), 6.84 (s, 1H, phenyl), 7.39 (s, 1H, phenyl); C nmr
Found: C, 43.73; H, 3.71; N, 3.65.
3
3
3
13
2,4,6-Trimethyltellurazolium (4-dicyanomethylenecyclohexa-
2,5-dienylidene)cyanoacetate (8).
(CDCl ): δ 18.99, 20,00, 96.11, 121.21, 128.23, 133.70, 141.29,
3
125
146.18;
Te nmr (CDCl ): δ 271.6; ms: m/z 496 (15), 375 (28),
3
Solutions of 2,4,6-trimethyl-benzotellurazole (6) (300 mg, 1.1
mmol) and 7,7,8,8-tetracyanoquinodimethane (225 mg, 1.1
mmol) in acetonitrile (5 mL) each were combined in a glass vial
and set aside for slow open-air evaporation over approx. 5 days.
The mixture gradually darkened and approximately 40 mg of
metallic-blue crystals formed. Several well-formed crystals were
manually separated from oily byproducts and collected for x-ray
crystallography. Attempts to isolate the product in analytically
pure form were unsuccessful.
240 (100). The compound has a pronounced tendency to undergo
decomposition in solution and usually is contaminated with
traces of elemental tellurium.
Anal. Calcd. for C
H N Te : C, 38.74; H, 4.04; N, 5.65.
16 20 2 2
Found: C, 38.50; H, 3.82; N, 5.44.
2,4,6-Trimethylbenzotellurazole (6).
A round bottom flask with magnetic stirring and reflux con-
denser was charged with a solution of bis(2-amino-3,5-

246
P. R. Mallikarachy, H. O. Brotherton, F. R. Fronczek, and T. Junk
Vol. 42
Tellurium Expulsion from Bis(2-amino-3,5-dimethylphenyl)
ditelluride.
unexpected results. The formation of several well-formed crys-
tals of 8 appears to have resulted from partial hydrolysis of
TCNQ under open-air conditions [21]. No attempt was made to
optimize the preparation of 8 as its sole purpose was the charac-
terization of the benzotellurazole structure by X-ray crystallogra-
phy. The structure of 8 can be compared to that of 2-phenylben-
zotellurazole 9 (Figure 2), the only benzotellurazole derivative
for which structural parameters have been reported [22]. Table 1
summarizes selected properties for both compounds. The Te-C1
and Te-C3 bond lengths are within the normal ranges of those
typically observed for sp and sp carbon-tellurium bonds,
respectively. The angles C1-Te-C8 are similar to that of 80.3°
previously reported for tellurophene [23]. The 2,4,6-benzotellu-
razolium cation was found to be essentially planar, with a mean
standard deviation from planarity for all non-hydrogen atoms of
0.017 Å.
A round bottom flask with magnetic stirring and reflux con-
denser was charged with a solution of bis(2-amino-3,5-
dimethylphenyl) ditelluride (5) (0.5 g 1.0 mmol) in 37%
hydrochloric acid (10 mL) The mixture was heated at reflux for
2 h. The reaction mixture was diluted with water (20 mL) and
precipitated solids removed by filtration. The filtrate was neu-
tralized with sodium carbonate solution and extracted with
CH Cl (2 × 10 mL). Rotary evaporation produced a pale yellow
2
2
3
2
oil (211 mg), which was analyzed by GC-MS. Comparison with
authentic material indicated the formation of 3,5-dimethylaniline
as the only major product. No semivolatile organic tellurium
compounds were observed.
Results and Discussion.
The nitration of diphenyl ditelluride and bis(4-tert-
butylphenyl) ditelluride did not produce benzo[2,1,3]oxatellu-
razole N-oxides in analogy to that of bis(3,4-dimethoxy-
phenyl) ditelluride. Instead, meta-nitrated products were iso-
lated exclusively. Clearly, potential Te-O coordination in the
product and moderate steric hindrance in para position did not
impose the desired regioselectivity. While meta nitrated
diaryl ditellurides are of potential interest for the preparation
of macrocyclic organotellurium compounds, they clearly are
not suited for the synthesis of tellurazoles and tellurazines. In
contrast, blockage of both meta positions resulted in ortho
nitration without evidence for the formation of a para isomer.
Temperatures in excess of 50 °C during nitration were found
to result in increased tellurium-carbon bond fission. No satis-
factory conditions could be found for the reduction of bis(3,5-
dimethyl-2-nitrophenyl) ditelluride (3) directly to bis(2-
amino-3,5-dimethylphenyl) ditelluride (5). Instead, the com-
plete reduction of 3 to 2-amino-3,5-dimethylbenzenetellurol
was followed by air oxidation to 5. The use of hypophospho-
rous acid in excess to counteract atmospheric re-oxidation was
found to be more convenient than work under inert atmos-
phere. The acid sensitivity of 5 is noteworthy in light of
acidic conditions used in subsequent cyclizations. Clearly,
exposure of this compound to acids has to be kept as brief as
possible. Indeed, tellurium expulsion appears to be a major
side reaction inherently limiting the yields of 6 and 7 under
acidic conditions.
Compound
8
9
Te–C1 bond length, Å
Te–C3 bond length, Å
C1–N bond length, Å
C1-Te-C3 bond angle
2.06(2)
2.08(2)
1.30(3)
80.1(5)
2.12
2.08
1.29
78.6
Table 1. Selected structural parameters for the 2,4,6-benzotel-
lurazolium cation in 8 as compared to those published for 2-
phenylbenzotellurazole 9. Indexing follows that in Figure 2
Figure 2. ORTEP plot of 2,4,6-trimethyltellurazolium cyano-(4-
Spectroscopy.
dicyanomethylene-cyclohexa-2,5-dienylidene)-acetate 8.
In accordance with those of other benzotellurazoles [2], the
mass spectrum of 6 featured a strong molecular ion cluster. Other
intense ions correspond to the loss of acetonitrile and to tellurium
elimination. The Te shift of 6 indicates significant deshielding
of tellurium and is very similar to those measured for other ben-
Molecular Structure of (Z)-2-Methoxycarbonylmethylene-3,4-
dihydro-3-oxo-2H-benzo-1,4-tellurazine (7).
125
Well-formed crystals of 7 were obtained by slow evaporation
of a solution in DCM. Each unit cell contains two molecules of
nearly identical geometry, one of which is shown in Figure 3.
Bond lenghts of 1.413(2) Å for the C2-N1 bond and 2.0954(2) Å
for the C1-Te distance resemble the molecular geometry of phe-
notellurazine, for which average lengths of 1.40 Å and 2.10 Å
were reported for the C-N and C-Te bonds, respectively [14]. In
contrast to benzotellurazine, however, 7 was found to be planar
with a mean standard deviation from palanrity of 0.072 Å for all
non-hydrogen atoms. The angle C1-Te-C4 of 93.38(6)° is signif-
icantly larger that those found in benzotellurazoles.
zotellurazoles [2]. Deshielding is less pronounced for 7, the
Te shift of which is typical of that expected for organotel-
lurium(II) compounds [20].
125
Molecular Structure of the 2,4,6-Trimethylbenzotellurazolium
Cation
Several attempts to obtain crystals of 6 suitable for X-ray crys-
tallography were unsuccessful, due to the pronounced tendency
of this compound to form disordered crystals of poor quality.
Consequently, the preparation of a 1:1 adduct of 6 with 7,7,8,8-
tetracyanoquinodimethane (TCNQ) was attempted, with

March 2005
Facile Access to Organotellurium Heterocycles by Nitration
247
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Figure 3. ORTEP plot of (Z)-2-methoxycarbonylmethylene-3,4-dihydro-
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Acknowledgments.
We wish to express our gratitude to Dr. Pia. R. Alburquerque
for her assistance in this study.
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