A convenient synthesis of isotellurazoles via deoxygenation of isotellurazole Te-oxide oligomers by using a combination of Ph3P/I2

Article abstract of DOI:10.3987/COM-17-13773

Ynones and ynals bearing a variety of substituent were converted into isotellurazole Te-oxide oligomers through a convenient procedure via formation and ring closure of β-(N,N-dimethylcarbamoyltellurenyl)alkenyl ketones or aldehydes, and the subsequent co

Full text of DOI:10.3987/COM-17-13773

HETEROCYCLES, Vol. 94, No. 10, 2017
1931
HETEROCYCLES, Vol. 94, No. 10, 2017, pp. 1931 - 1939. © 2017 The Japan Institute of Heterocyclic Chemistry
Received, 26th June, 2017, Accepted, 19th July, 2017, Published online, 1st August, 2017
DOI: 10.3987/COM-17-13773
A
CONVENIENT SYNTHESIS OF ISOTELLURAZOLES VIA
DEOXYGENATION OF ISOTELLURAZOLE Te-OXIDE OLIGOMERS
BY USING A COMBINATION OF Ph3P/I2
Yusuke Taneichi, Kazuaki Shimada,* and Toshinobu Korenaga
Department of Chemistry and Biosciences, Faculty of Science and Engineering,
Iwate
University,
Morioka,
Iwate
020-8551,
Japan;
E-mail:
shimada@iwate-u.ac.jp
Abstract – Ynones and ynals bearing a variety of substituent were converted into
isotellurazole Te-oxide oligomers through a convenient procedure via formation
and ring closure of -(N,N-dimethylcarbamoyltellurenyl)alkenyl ketones or
aldehydes, and the subsequent conversion of A into the corresponding
isotellurazoles B was carried out efficiently by treating with Ph3P/I2 under a rather
mild reaction condition.
Recently, hetero Diels-Alder reactions have been widely recognized as one of the most effective methods
for the syntheses of various heterocycles, and especially, the thermal reactions of higher-row
chalcogenazoles and isochalcogenaozles have been of great interest in line with the synthetic potentiality
of these compounds,1,2 and especially isotellurazoles having a tellurium-bridged cisoid heterodiene along
with a weak carbon-tellurium and nitrogen-tellurium bonds and the enhanced ring strain of the ring
systems involving a tellurium atom with a large atomic radius. However, the synthetic methods of
isotellurazoles have been strictly limited because of the difficulty in the preparation of suitable precursors.
In the course of our synthetic research work on the synthesis of higher-row chalcogen-containing
heteroaromatic compounds, we have previously reported a preparation of isoselenazoles and
isotellurazoles through a four-step procedure starting from ynones and bis(N,N-dimethylcarbamoyl)
diselenide or ditelluride, respectively.3 Especially, isotellurazole Te-oxides were formed in all cases by
treating -(N,N-dimethylcarbamoyltelluro)alkenyl ketones with NH2OSO3H, and deoxygenation of those
products required the treatment with Ph3P at rather high reaction temperature. In addition, treatment of
isotellurazole Te-oxides with a variety of acetylenic dienophiles for hetero Diels-Alder reaction just gave
substituted pyridines in much lower yields as the cycloadducts in all cases along with the formation of
several byproducts in contrast to the cases using isotellurazoles as heterodienes.4 Recently, Vargas-Baca

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HETEROCYCLES, Vol. 94, No. 10, 2017
reported the unique tetrameric and/or hexameric macrocyclic structures of 4 for isotellurazole Te-oxides
(isotellurazole N-oxides) obtained through the similar procedure,5 and this result suggested the disfavor in
the synthetic use of isotellurazole Te-oxide oligomers 4 as the heterodienes for hetero Diels-Alder
reaction in contrast to isotellurazoles. Through the requirement for the use of isotellurazoles 5 as reactive
heterodienes for the synthesis of azafluorenone alkaloid skeletons, we attempted the modification of our
previous procedure involving the deoxygenation of isotellurazole Te-oxide oligomers 4 by applying the
combination of Ph3P with an electrophilic activator in line with the previous reports on deoxygenation of
epoxides and sulfoxides.6 Finally, we found a novel and efficient procedure for deoxygenation of
isotellurazole Te-oxide oligomers 4 by treating with Ph3P and I2, and in this paper we would like to report
the details of the efficient and convenient preparation of mono- and disubstituted isotellurazoles 5
involving the synthetic scope and limitation.
Isotellurazole Te-oxide oligomers 4 were at first prepared through a three-step procedure starting from
bis(N,N-dimethylcarbamoyl) ditelluride (1) [(1) NaBH4 (2.2 equiv.), (2) ynone or ynal 2 bearing a variety
of substituents at R1 and an alkyl group or hydrogen atom for R2, (3) NH2OSO3H (3.0 equiv.)], and
compounds 4 were subsequently subjected to deoxygenation by treating with Ph3P at high temperature in
a sealed tube in order for the preparation of authentic isotellurazoles 5.3 Our previous attempts for
deoxygenation of isotellurzole Te-oxide oligomers 4 by using NaBH4 reduction, Luche reduction, or the
treatment of NH2NH2•H2O were not successful at all except for the treatment with Ph3P under the
condition of high temperature in a sealed tube. Furthermore, isotellurazole Te-oxide oligomer 4b bearing
two alkyl substituents at the R1 and R2 positions was unexpectedly inactive toward Ph3P reduction under
the similar condition even after the prolonged reaction time, and this phenomenon just limited the
synthetic use of isotellurazoles.
Table 1. Preparation of Isotellurazole Te-Oxide Oligomers 4
Ynone 2
Yield (%)
R1
R2
3
4
C6H5
Me
Me
Me
94 (3a)
75 (3b)
92 (3c)
81 (4a)a
74 (4b)
98 (4c)
n-C4H9
t-C4H9

HETEROCYCLES, Vol. 94, No. 10, 2017
1933
n-C4H9
C6H5
H
H
H
91 (3d)
69 (3e)
93 (3f)
46 (4d)
75 (4e)
64 (4f)
Me
aSee reference 3.
When a toluene solution of isotellurazole Te-oxide oligomer 4a was treated with Ph3P (2.2 equiv.) at
refluxing temperature for 168 h, the corresponding isotellurazole 5a was obtained as a sole product in
moderate yield. However, the same reaction performed under 0 °C to room temperature only afforded the
recovery of substrate 4a. On the other hand, the reaction condition was dramatically improved by adding
I2 (1.2 equiv.) to the reaction mixture, and the starting compound 4a underwent facile deoxygenation to
afford isotellurazoles 5a in medium yield even at 0 °C within one or two hours. After the attempts of
optimization of the reaction condition, the yield of 5a was finally raised up to 82% by treating Ph3P (2.0
equiv.) and I2 (1.0 equiv.), and the method was applicable to deoxygenation of other isotellurazole
Te-oxide oligomers 4b-f bearing a variety of R1 and R2 substituents involving aryl group, alkyl groups,
and hydrogen. It is noteworthy that the combination of Ph3P-CBr4 and Ph3P-TiCl4 was also effective for
deoxygenation of 4. However, in the cases applying the combination of Ph3P-BF3•OEt2, substrate 4a was
quantitatively recovered after the usual quenching procedure using an aqueous NaHCO3 solution. All the
results of deoxygenation of isotellurazole Te-oxide oligomers 4 by the combination of Ph3P and an
electrophilic activator are summarized in Table 2.
Table 2. Synthesis of Isotellurazoles 5 by Treating Isotellurazole Te-Oxide Oligomers 4 with Ph3P and an
Additive
Substrate / 4
Ph3P
(equiv.)
1.1
Additive
Solvent
Condition
Yield of 5
(%)
R1
R2
(equiv.)
Temp (°C)
Time (h)
4
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
C6H5
Me
Me
Me
Me
Me
Me
Me
Me
-
-
CHCl3
toluene
CCl4
100
1
168
2
91 (5a)a
59 (5a)
33 (5a)
48 (5a)
16 (5a)
50 (5a)
82 (5a)
0b
4a
4a
4a
4a
4a
4a
4a
4a
2.2
reflux
2.0
-
reflux
1.2
CBr4 (1.2)
CBr4 (1.0)
I2 (1.2)
I2 (1.0)
BF3•OEt2 (1.0)
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
0
0
0
0
0
1
2.0
2
1.2
2
2.0
2
2.0
2

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HETEROCYCLES, Vol. 94, No. 10, 2017
C6H5
Me
Me
Me
Me
Me
H
2.0
2.2
1.2
2.0
2.0
2.0
2.0
2.0
TiCl4 (1.0)
-
CH2Cl2
toluene
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CHCl3
0
1
48
1
51 (5a)
0c
4a
4b
4b
4b
4c
4d
4e
4f
n-C4H9
n-C4H9
n-C4H9
t-C4H9
n-C4H9
C6H5
reflux
CBr4 (1.2)
I2 (1.0)
I2 (1.0)
I2 (1.0)
I2 (1.0)
I2 (1.0)
0
0
43 (5b)
91 (5b)
73 (5c)
66 (5d)
69 (5e)
80 (5f)
3
rt
12
0.5
2
-50
0
H
Me
H
0
1
aCarried out in a sealed tube. See reference 3c. bSubstrate 4a was quantitatively recovered after the usual
workup procedure. cStarting isotellurazole oxide oligomer 4b was recovered.
Vargas-Baca recently reported that isotellurazole Te-oxide oligomers 4 undergo equilibration among a
few oligomers in the solution, and therefore the monomeric forms of 4 are assumed to behave as the key
intermediates for deoxygenation. The plausible reaction pathway of the deoxygenation of isotellurazole
Te-oxide oligomers 4 could then be summarized as shown in Scheme 1 involving three step reactions: the
primary reaction of Ph3P-I2 complex with 4 forming intermediates A, subsequent nucleophilic attack of
iodide ion to the tellurium atom of A, and the final attack of Ph3P to the iodine atom of intermediates B
forming isotellurazoles 5 in an analogous manner to that of deoxygenation of sulfoxides.6 This pathway
requires two molar amounts of Ph3P and one molar amount of I2 for deoxygenation of 4, which would be
consistent with the experimentally optimized ratio of these reagents.
Scheme 1. Plausible Pathway for Deoxygenation of Isotellurazole Te-Oxide Oligomers 4
It is assumed that the deoxygenation step would be accelerated by the facile fragmentation of
isotellurazole Te-oxide oligomers 4 through the reaction with iodophosphonium ion (Ph3P+-I) with the
oxygen atom of monomeric isotellurazole Te-oxides 4 (n = 1) in the reaction mixture as well as the facile

HETEROCYCLES, Vol. 94, No. 10, 2017
1935
elimination of Ph3P=O from the in situ generated intermediates A to form intermediates B through the
-
strong Te+•••I interaction between the tellurium atom of A and iodide ion. However, all attempts to carry
1
out the direct observation of plausible intermediates A or B through a H NMR monitoring of the
deoxygenation of 4 using Ph3P-I2 in a NMR tube was unsuccessful.
In conclusion, we could find a new procedure for deoxygenation of isotellurzole Te-oxide oligomers 4 by
using the combination of Ph3P and I2. We have already reported that isotellurazoles undergo hetero
Diels-Alder reaction to afford substituted pyridines under rather mild conditions, and further synthetic
application of alkyl-substituted isotellurazoles for the construction of polycyclic alkaloid skeletons are
under way in our laboratory.
EXPERIMENTAL
1
The melting points were determined with a Barnstead International MEL-TEMP. H NMR spectra were
recorded on a Bruker DRX-400P (400 MHz) or Bruker AVANCE III 500 (500 MHz) spectrometer, and
the chemical shifts of the 1H NMR spectra are given in  relative to internal tetramethylsilane (TMS). 13C
NMR spectra were recorded on Bruker DRX-400P (101 MHZ) AVANCE III 500 (126 MHZ). 125Te
NMR Spectra were recorded on Bruker AVANCE III 500 (158 MHZ), and the chemical shifts of the
125Te NMR are given in  relative to Ph2Te2 ( = 421 ppm). Mass spectra were recorded on a JEOL
JMS-700T mass spectrometer with electron-impact ionization or electrospray ionization. High resolution
mass spectra (HRMS) were also recorded on a JEOL JMS-700T spectrometer. IR spectra were recorded
for thin film (neat) or KBr disks on a JASCO FT/IR-7300 spectrometer. Elemental analyses were
performed using a Yanagimoto CHN corder MT-5.
Starting Materials. Bis(N,N-dimethylcarbamoyl) ditelluride (1) was prepared from elemental tellurium,
sodium metal or sodium hydride, and N,N-dimethylformamide (DMF) according to our previous previous
paper.3a,7 Ynones and ynals (2) were prepared through Friedel-Crafts type acylation of terminal acetylenic
compounds or oxidation of substituted propargyl alcohols according to the previous papers.7 All other
chemicals used in this study were commercially available.
A Typical Procedure for Preparation of Isotellurazole Te-Oxide Oligomers 4 from
Bis(N,N-dimethylcarbamoyl) Ditelluride (1) and Ynones 2. To DMF or EtOH solution of
bis(N,N-dimethylcarbamoyl) ditelluride (1, 398 mg, 1.00 mmol) was added EtOH solution (5 mL) of
NaBH4 (84 mg, 2.2 mol amt.) at -50 °C, and the reaction mixture was then treated with ynone 2 (2.2 mol
amt.) at -50 °C to rt for 7 h. The reaction was quenched with aqueous NH4Cl solution, and the reaction
mixture was extracted with CH2Cl2. The organic layer was washed twice with water and was dried over
anhydrous Na2SO4 powder. The organic solvent was removed in vacuo, and the residual crude products
were subjected to column chromatography on silica gel to obtain Te-alkenyl

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HETEROCYCLES, Vol. 94, No. 10, 2017
N,N-dimethyltellurocarbamates 3 in high to moderate yields as yellow oil. Then, MeOH solution (10 mL)
of compounds 3 was treated with hydroxylamine-O-sulfonic acid (3.0 mol amt.) at reflux for 1 h. The
reaction mixture was cooled to room temperature and was quenched with saturated aqueous NaHCO3
solution, and the reaction mixture was subjected to suction filtration to obtain isotellurazole Te-oxide
oligomers 4 as main products besides a small amount of isotellurazoles 5.3c
4a (R1 = C6H5, R2 = Me): Pale yellow powder, mp 210.5-211.4 °C (decomp.) (Lit.,3c 210.3-211.8 °C
(decomp.)).
4b (R1 = n-C4H9, R2 = Me): Yellow needles, mp 131.8-132.5 °C; IR (KBr) 2954, 2927, 2900, 2868, 2855,
1575, 1475, 1464, 1426, 1374, 1232, 1139, 1092, 887, 829, 718, 579 cm-1; 1H NMR (500 MHz, CDCl3) 
0.89 (3H, t, J = 7.5 Hz), 1.36 (2H, sext, J = 7.5 Hz), 1.62 (2H, quint, J = 7.5 Hz), 2.10 (3H, s), 2.80 (2H, t,
13
J = 7.5 Hz), 7.09 (1H, s); C NMR (126 MHz, CDCl3)  14.1 (q), 16.0 (q), 22.5 (t), 34.1 (t), 36.1 (t),
124.8 (d), 155.7 (s), 156.9 (s); 125Te NMR (158 MHz, CDCl3)  1607. Anal. Calcd for C8H13NOTe: C,
36.01; H, 4.91; N, 5.25%. Found: C, 36.00, H; 4.90; N, 5.28%.
4c (R1 = t-C4H9, R2 = Me): Pale Yellow Powder, mp 217.0-217.5 °C (decomp.); IR (KBr) 2952, 2908,
2866, 1564, 1465, 1363, 1125, 967, 897, 697, 451 cm-1; 1H NMR (500 MHz, CDCl3)  1.41 (9H, s), 2.14
13
(3H, s), 7.00 (1H, s); C NMR (126 MHz, CDCl3)  16.1 (q), 32.3 (q), 41.5 (s), 122.5 (d), 155.6 (s),
168.1 (s). (Lit.,5c 180-185 °C (decomp.), IR (KBr) 2953, 2912, 2865, 1565, 1466, 1424, 1389, 1370, 1361,
1
1337, 1243, 1231, 1202, 1125, 1030, 1001, 967, 896, 842, 828, 794, 760, 756, 697 cm-1; H NMR (500
13
MHz, CDCl3)  6.96 (1H, s), 2.17 (3H, s), 1.42 (9H, s); C DEPTq NMR (125.8 MHz, CD2Cl2)  16.0,
32.1, 41.5, 122.7, 156.4, 168.9. HRMS calcd. for C8H14ON129Te: m/z 270.0138 (M+-H). Found: m/z
270.0122.)
4d (R1 = n-C4H9, R2 = H): Yellow oil; MS (m/z) 255 (M+; bp, 130Te), 253 (M+; 92%, 128Te), 251 (M+;
56%, 126Te), 250 (M+; 22%, 125Te), 249 (M+; 14%, 124Te), 247 (M+; 7%, 122Te); IR (neat) 2954, 2868,
2857, 1561, 1477, 1103, 1081, 744 cm-1; 1H NMR (500 MHz, CDCl3)  0.90 (3H, t, J = 7.5 Hz), 1.38 (2H,
sext, J = 7.5 Hz), 1.63 (2H, quint, J = 7.5 Hz), 2.86 (2H, t, J = 7.5 Hz), 7.12 (1H, d, J = 4.0 Hz), 8.31 (1H,
13
d, J = 4.0 Hz); C NMR (126 MHz, CDCl3)  14.1 (q), 22.4 (t), 34.1 (t), 36.3 (t), 120.9 (d), 148.3 (d),
159.8 (s); 125Te NMR (158 MHz, CDCl3)  1639. HRMS Calcd for C7H11NOTe: m/z 254.9903. Found:
m/z 254.9902.
4e (R1 = C6H5, R2 = H): Pale yellow powder, mp 217.8-218.1 °C (decomp.); MS (FAB+, m/z) 274 (M+-1;
130Te, 29%), 272(M+-1; 128Te, 18%); IR (KBr) 1658, 1618, 1399, 1305, 1098, 1021, 836, 718, 694 cm-1.
Anal. Calcd for C9H7NOTe: C, 39.63; H, 2.59; N, 5.14%. Found: C, 39.62; H, 2.70; N, 5.13%.
4f (R1 = Me, R2 = H): Grayish powder, mp 203.4-203.7 °C (decomp.); IR (KBr) 1563, 1479, 1139, 1103,
1037, 801, 732 cm-1; 1H NMR (500 MHz, CDCl3)  2.55 (3H, s), 7.12 (1H, d, J = 3.5 Hz), 8.32 (1H, dd, J

HETEROCYCLES, Vol. 94, No. 10, 2017
1937
= 3.5, 1.5 Hz); 13C NMR (126 MHz, CDCl3)  23.5 (q), 122.1 (d), 148.9 (d), 154.3 (s); 125Te NMR (157
MHz, CDCl3)  1654. HRMS Calcd for C4H5NOTe: m/z 212.9433. Found: m/z 212.9432.
A Typical Procedure for Deoxygenation of Isotellurazole Te-Oxide Oligomer 4a (R1 = C6H5, R2 =
Me) by Treating with Ph3P and I2. A CH2Cl2 solution of Ph3P (183 mg, 0.698 mmol, 2.0 equiv.) was
treated with I2 (89 mg, 0.349 mmol, 1.0 equiv.) at 0 °C for 30 min, and then isotellurazole Te-oxide
oligomer 4a (R1 = C6H5, R2 = Me, 100 mg, 0.349 mmol) was treated with the reaction mixture at 0 °C for
3 h. The reaction was then quenched by addition of saturated aqueous Na2SO3 solution, and the reaction
mixture was extracted with CHCl3. The organic layer was washed with water and was dried over
anhydrous Na2SO4 powder. After removing the organic solvent in vacuo, the crude product was subjected
to purification by using column chromatograph on silica gel to isolate isotellurazole 5a (77 mg, yield
82%) as pale yellow solid.
5a (R1 = C6H5, R2 = Me): Pale yellow needles, mp 147.6-148.0 °C (Lit.,2b,3c 147.5-148.0 °C).
5b (R1 = n-C4H9, R2 = Me): Pale yellow oil; MS (m/z) 253 (M+; bp, 130Te), 251 (M+; 93%, 128Te), 249
(M+; 57%, 126Te), 248 (M+; 22%, 125Te), 247 (M+; 14%, 124Te), 245 (M+; 7%, 122Te); IR (neat) 2954, 2862,
1
1552, 1454, 1328, 831 cm-1; H NMR (500 MHz, CDCl3)  0.95 (3H, t, J = 7.5 Hz), 1.44 (2H, sext, J =
7.5 Hz), 1.66 (2H, quint, J = 7.5 Hz), 2.43 (3H, s), 2.96 (2H, td, J = 7.5 Hz, 1.0 Hz), 7.62 (1H, t, J = 1.0
13
Hz); C NMR (126 MHz, CDCl3)  14.1 (q), 22.3 (t), 23.2 (q), 34.5 (t), 38.4 (t), 128.9 (d), 171.8 (s),
182.4 (s); 125Te NMR (158 MHz, CDCl3)  1610. HRMS calcd for C8H13NTe: m/z 253.0110. Found: m/z
253.0110.
5c (R1 = t-C4H9, R2 = Me): Colorless needles; mp 55.5-56.0 °C; MS (m/z) 253 (M+; bp, 130Te), 251 (M+;
92%, 128Te), 249 (M+; 56%, 126Te), 248 (M+; 22%, 125Te), 247 (M+; 14%, 124Te), 245 (M+; 8%, 122Te); IR
(KBr) 2955, 2923, 2854, 1552, 1455, 1361, 1317, 833, 712, 565 cm-1; 1H NMR (500 MHz, CDCl3)  1.39
13
(9H, s), 2.42 (3H, s), 7.60 (1H, s); C NMR (126 MHz, CDCl3)  25.9 (q), 33.8 (q), 39.8 (s), 132.7 (d),
176.8 (s), 188.5 (s); 125Te NMR (158 MHz, CDCl3)  1642; HRMS Calcd for C8H13NTe: m/z 253.0110.
Found: m/z 253.0106.
5d (R1 = n-C4H9, R2 = H): Colorless needles; mp 44.5-45.0 °C; MS (m/z) 239 (M+; bp, 130Te), 237 (M+;
91%, 128Te), 235 (M+; 58%, 126Te), 234 (M+; 22%, 125Te), 233 (M+; 15%, 124Te), 231 (M+; 8%, 122Te); IR
1
(KBr) 2928, 2881, 2863, 1548, 1461, 1444, 1418, 1246, 792, 532 cm-1; H NMR (500 MHz, CDCl3)
0.95 (3H, t, J = 7.5 Hz), 1.45 (2H, sext, J = 7.5 Hz), 1.68 (2H, quint, J = 7.5 Hz), 3.03 (2H, td, J = 7.5,
1.0 Hz), 7.64 (1H, dt, J = 2.0, 1.0 Hz), 9.71 (1H, d, J = 2.0 Hz); 13C NMR (126 MHz, CDCl3)  13.9 (q),
22.4 (t), 36.0 (t), 36.5 (t), 134.8 (d), 168.5 (d), 176.9 (s); 125Te NMR (158 MHz, CDCl3)  1677; HRMS
Calcd for C7H11NTe: m/z 238.9954. Found: m/z 238.9953.
5e (R1 = C6H5, R2 = H): Pale yellow Powder, mp 134.8-135.5 °C; IR (KBr) 1534, 1441, 1420, 1261, 815,
751, 684, 565, 407 cm-1; 1H NMR (400 MHz, CDCl3)  7.39-7.41 (3H, m), 7.48-7.50 (2H, m), 8.03 (1H,

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HETEROCYCLES, Vol. 94, No. 10, 2017
s), 9.95 (1H, s); 13C NMR (101 MHz, CDCl3)  127.9 (d), 129.4 (d), 129.5 (d), 132.2 (d), 138.1 (s), 169.3
(d), 173.1 (s). Anal. Calcd for C9H7NTe: C, 42.10; H, 2.75; N, 5.46%. Found: C, 42.08; H, 2.90; N,
5.46%.
5f (R1 = Me, R2 = H): Colorless needles; mp 99.0-99.5 °C (decomp.); MS (m/z) 198 (M++1; bp, 130Te); IR
1
(KBr) 1549, 1433, 1253, 1128, 796 cm-1; H NMR (500 MHz, CDCl3)  2.75 (3H, d, J = 1.0 Hz), 7.62
13
(1H, dq, J = 2.0, 1.0 Hz), 9.68 (1H, d, J = 2.0 Hz); C NMR (126 MHz, CDCl3)  22.0 (q), 137.1 (d),
168.1 (s), 168.4 (d); 125Te NMR (158 MHz, CDCl3)  1712. HRMS calcd for C4H6NTe: m/z 197.9562
(M+H+). Found: m/z 197.9563.
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