Novel oxidative ring opening reaction of 1H-isotellurochromenes to bis(o-formylstyryl) ditellurides

Article abstract of DOI:10.3390/molecules15031466

The oxidation of 1-unsubstituted or 1-phenyl-1H-isotellurochromenes with m-chloroperbenzoic acid (mCPBA) in CHCl₃ resulted in a ring opening reaction to produce as the sole products the corresponding o-formyl or benzoyl distyryl ditellurides, which were also produced by the hydrolysis of the 2-benzotelluropyrylium salts readily prepared from the parent isotellurochromene.

Full text of DOI:10.3390/molecules15031466

Molecules 2010, 15, 1466-1472; doi:10.3390/molecules15031466
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molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Novel Oxidative Ring Opening Reaction of 1H-Isotelluro-
chromenes to Bis(o-formylstyryl) Ditellurides
Haruki Sashida 1,*, Hirohito Satoh 1, Kazuo Ohyanagi 2 and Mamoru Kaname 1
1
Faculty of Pharmaceutical Sciences, Hokuriku University, Kanagawa-machi, Kanazawa 920-1181,
Japan; E-Mail: m-kaname@hokuriku-u.ac.jp (M.K.)
2
Faculty of Pharmacy, Institute of Medical, Pharmaceutical and Health Sciences, Kanazawa University,
Kakuma-machi, Kanazawa 920-1192, Japan; E-Mail: ohyanagi@p.kanazawa-u.ac.jp (K.O.)
* Author to whom correspondence should be addressed; E-Mail: h-sashida@hokuriku-u.ac.jp;
Tel.: +81-76-229-6211; Fax: +81-76-229-2781.
Received: 5 January 2010; in revised form: 2 February 2010 / Accepted: 5 March 2010 /
Published: 9 March 2010
Abstract: The oxidation of 1-unsubstituted or 1-phenyl-1H-isotellurochromenes with
m-chloroperbenzoic acid (mCPBA) in CHCl3 resulted in a ring opening reaction to produce as
the sole products the corresponding o-formyl or benzoyl distyryl ditellurides, which were also
produced by the hydrolysis of the 2-benzotelluropyrylium salts readily prepared from the
parent isotellurochromene.
Keywords: isotellurochromene; mCPBA oxidation; 2-benzotelluropyrylium salt; distyryl
ditelluride
1. Introduction
The preparation and investigation of the reactions of new tellurium-containing heterocycles have lately
attracted increasing interest in the fields of both heterocyclic [1–3] and organotellurium chemistry [4–8].
We have been studying the syntheses and reactions of the novel tellurium- or selenium-containing
heterocyclic compounds over the past twenty years. Our synthetic strategy [9,10] for the preparation of

Molecules 2010, 15
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these compounds is based on the intramolecular cyclization of the tellurol or selenol moieties to a triple
bond. As a part of our continuing studies, we have previously reported the successful synthesis of the
isotellurochromenes
as
the
precursors
for
the
preparation
of
the
novel
2-benzotelluropyrylium salts [11,12]. In addition, the 1H-isotellurochromenes were found to transform
into the 1,2-dihydro-2-metalanaphthalenes via (E)-o-(2'-lithiovinyl)benzyllithium generated by a
tellurium-lithium exchange reaction [13]. In this study, an investigation of the oxidation of the
isotellurochromenes is described as an extension of the known reactivity of these compounds.
There are several reports concerning the oxidation of mono and benzene ring fused six-membered
heterocycles containing a chalcogen atom. The selenium dioxide oxidation of 4H-thiopyrans [14] and 4H-
selenopyrans [14] produces a ring contraction to give hiophenes and selenophenes, respectively. The
oxidation of dihydro-2H-selenopyrans [15] with sodium periodate is also known to produce selenophenes.
Furthermore, the oxidation of thiochromenes [16], selenochromenes [16] and tellurochromenes [17] by
selenium dioxide, trityl perchlorate or K2CrO7 produced the corresponding 2-formylbenzo[b]-thiophenes,
-selenophenes and -tellurophenes, respectively. Whereas the isothiochromenes [18,19] are easily oxidized
by mCPBA to afford the thermally stable normal S-oxide products, a similar oxidation of the highly
substituted isoselenochromenes [20] produces the corresponding benzo[b]selenophene derivatives as the
main product. These facts prompted us to investigate the oxidation of the isotellurochromenes 1.
2. Results and Discussion
When tert-butylisotellurochromene 1a was oxidized with 1.2 equiv. of mCPBA in CHCl3 at 0 °C, the
starting material immediately disappeared, and the bis(o-formylstyryl) ditelluride 2a was obtained in 83%
yield as the sole product after the usual work up. The structure of the ditelluride 2a was characterized by
NMR, IR and mass spectroscopy. The low-mass spectrum of this compound suggested the ditelluride
molecular formula based on the molecular ion at m/z = 634 (130Te) and the expected isotope pattern for
Te2. In addition, the HRMS of 2a showed the same exact molecular formula. Similarly, the
1-nonsubstituted 2b, alkyl 2c-g and phenyl 2h derivatives were also obtained in moderate to good yields.
These results are summarized in Table 1 (entries 1-8). The double bond in the products 2 was proven to
1
have a (Z)-stereochemistry by the vicinal coupling constant (J = 10 Hz) in the H-NMR spectra of the
nonsubstituted derivative 2b. A similar mCPBA oxidation of the 1-substituted isotellurochromenes 1 was
examined (entries 9, 10). The 1-phenylisotellurochromene 1i [21] was oxidized to give the bis(o-
benzoylstyryl) ditelluride 2i in 80% yield, while the similar oxidation of the 1-methyl isochromene 1j [21]
resulted in decomposition to afford a complex mixture without any characterized products. The significant
differences in the product yield according to whether or not the 1-substituent is a methyl group cannot be
clearly explained at the present time. The structure of the products 2 including the geometry of the styryl
moiety was finally determined by an X-ray crystallographic analysis using the tert-butyl derivative 2a.

Molecules 2010, 15
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Table 1. Oxidation of isotellurochromenes 1 with mCPBA.
R1
Te
R1
mCPBA
2
Te
C
R2
R2
O
2
1
Entry
Product
R1
R2
H
H
H
H
H
H
H
Yield (%) Appearance (mp, °C)
1
2
3
4
5
6
7
8
9
2a
2b
2c
2d
2e
2f
2g
2h
2i
t-Bu
H
Me
n-Pro
n-Bu
83
43
57
60
70
83
62
67
80
0
orange prisms, 140–143
orange prisms, 95–97
orange oil
orange oil
orange oil
orange oil
orange oil
orange oil
orange oil
1-cyclohexenyl
n-Oct
Ph
t-Bu
t-Bu
H
Ph
Me
10
2j
---
The telluroxides 3, which are presumed to be produced by the oxidation of the isotellurochromene 1
with mCPBA in this reaction, were too unstable to isolate. The oxidation of 1a with mCPBA, followed by
treatment with Ac2O resulted in a Pummerer-type rearrangement to afford 1-acetoxy-isotellurochromene
4a as a pale yellow oil, together with a small amount of the ditelluride 2a. The hydrolysis of the acetoxy
derivative 4a with NaHCO3 aq. produced the ditelluride 2a in almost quantitative yield.
In addition, the ditellurides 2a and 2b could be obtained in high yields by the hydrolysis of the
2-benzotelluropyrylium tetrafluoroborates 5 [15], which had previously been prepared by the treatment of
-
the isotellurochromenes 1 with triphenylcarbenium tetrafluoroborate (Ph3C+ BF4 ) in MeNO2 in almost
quantitative yields. The initial intermediates 6 were produced by the nucleophilic attack of water at the C-
1 position of the telluropyrylium cation 5, and then oxidized to give 2. The ditelluride 2a was easily
converted to the tellulium trichloride 8 by fission of the Te-Te bond by sulfuryl chloride in benzene in
quantitative yield.
A plausible mechanism for the formation of the ditellurides 2 from the isotellurochromenes 1 and
2-benzotelluropyrylium salts 5 is outlined in Figure 1. The telluroxides 3 generated by the oxidation of the
isotellurochromenes 1 rearranged to afford the 1-hydroxyisochromenes 6 by a Pummerer-type reaction.
The intermediate 6 undergoes ring opening with migration of the hydroxy proton to form the vinyltellurol
7. The resulting tellurol tautomer 7 is immediately oxidized by mCPBA or air to give the distyryl
ditelluride 2.
In summary, the oxidation of the isotellurochromenes with mCPBA resulted in the unprecedented ring-
opening reaction to give the bis[o-formyl(benzoyl)-α-styryl] ditellurides in moderate to good yields. The

Molecules 2010, 15
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reaction might proceed through a Pummerer-type reaction via the telluroxides. Further detailed studies of
this reaction, an expanding the applications and selenium analogues are now in progress.
Figure 1. Reaction conditions and a plausible mechanism.
R
R
R
ii
i
Te
Te
Te
OAc
O
1
4
3
iii
iv
R
R
R
v
TeH
+
Te
Te
BF4
CHO
-
O
H
7
5
6
[O]
R
R
Te
TeCl3
vi
2
CHO
CHO
2
8
Reagents and Conditions: i, mCPBA, CHCl3, 0 °C to room temp., ii, Ac2O, room temp., iii, 5% NaHCO3,
-
room temp., iv, Ph3C+ BF4 , MeNO2, room temp., v, H2O, room temp. vi, SO2Cl2, benzene, room temp.
3. Experimental
Melting points were measured on a Yanagimoto micro melting point hot stage apparatus and are
uncorrected. IR spectra were determined with a Horiba FT-720 spectrometer. Mass spectra (MS) and
HRMS were recorded on a JEOL SX-102A instrument. NMR spectra were determined with a JEOL ECP-
500 (500 MHz) spectrometer in CDCl3 using tetramethylsilane as internal standard and J values are given
in Hz. Microanalyses (MT-5) were performed in the Microanalytical Laboratory in this Faculty. The
starting materials, isotellurochromenes (1) were prepared by the literature method [12].
Oxidation of 3-tert-butylisotellurochromene (1a) with mCPBA: formation of (Z)-bis(o-formyl-α-tert-
butylstyryl) ditelluride (2a): mCPBA (70%, 296 mg, 1.2 mmol) was added to a solution of 3-tert-
butylisotellurochromene (1a, 302 mg, 1.0 mmol) in dry CHCl3 (10 mL) at 0 °C and the mixture was

Molecules 2010, 15
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stirred at room temperature for 1h. After addition of sat. NaHCO3 aq. (10 mL), aqueous mixture was
extracted with CH2Cl2 (50 mL x 3). The organic layers were washed with brine (30 mL × 2), dried
(MgSO4) and evaporated. The resulting residue was chromatographed on silica gel using n-hexane-
CH2Cl2 (2:1) as an eluent to give pure 2a (263 mg, 83%), dark red prisms, mp 140-143 °C (from acetone-
hexane); MS m/z (%) : 634, 632, 630, 628 (1, 2, 2, 1, M+), 187 (100), 145 (33), 115 (22). IR (KBr) cm-1
1
1690 (C=O); H-NMR (500 MHz, CDCl3) δ 1.24 (18H, s, t-Bu × 2), 6.88 (2H, s, Ph-CH=C- × 2), [7.20
(2H, d, J = 7.6 Hz), 7.36 (2H, dd, J = 7.7, 7.7 Hz), 7.47 (2H, ddd, J = 7.7, 7.6, 1.4 Hz), 7.80 (2H, dd,
J = 7.7, 1.4 Hz) Ph-H], 10.06 (2H, s, CHO × 2). 13C-NMR (125 MHz, CDCl3) δ 30.7 (q), 41.3 (s) 127.5
(d), 128.3 (d), 131.6 (d), 133.5 (s), 133.6 (d), 134.6 (s), 138.0 (s), 144.4 (s), 191.5 (s); HRMS m/z Calcd
for C26H30130Te2: 634.0374. Found: 634.0352.
Acknowledgements
A part of this work was supported by a Grant-in-Aid for Scientific Research from The Ministry of
Education, Culture, Sports, Science and Technology of Japan (No. 19590022).
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Appendix 1
This paper constitutes Part 28 in the ‘Studies on Tellurium-Containing Heterocycles’, For Part 27:
Sashida, H.; Nakabayashi, S.; Kaname, M., Minoura, M. 2-Substituted Isotellurochromenium Salt
Derivatives: Preparations, Structures, Spectroscopic Properties. Heterocycles 2010, 80, 1339–1352.

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Appendix 2
The details of the X-ray data of bis(o-formylstyryl) ditelluride 2a will be reported in a full paper that
will appear in the near future.
Sample Availability: Samples of the compounds 1,2 are available from the authors.
© 2010 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland. This
article is an open-access article distributed under the terms and conditions of the Creative Commons
Attribution license (http://creativecommons.org/licenses/by/3.0/).