Synthesis of 1,2,4-ditellurazolidines by oxidative ring contraction of 2H,6H-tetrahydro-1,5,3,7-ditelluradiazocines

Article abstract of DOI:10.1246/cl.2000.870

Synthesis of novel five-membered cyclic ditellurides, 4-aryl-1,2,4-ditellurazolidines was achieved by treating 3,7-diaryl-2H,6H-tetrahydro-1,5,3,7-ditelluradiazocines with oxidizing agents or by aerobic exposure. The oxidative ring contraction of the heterocycles was assumed to proceed through formation and subsequent fragmentation of bicyclic ditellura dications.

Full text of DOI:10.1246/cl.2000.870

870
Chemistry Letters 2000
Synthesis of 1,2,4-Ditellurazolidines by Oxidative Ring Contraction of
2H,6H-Tetrahydro-1,5,3,7-ditelluradiazocines
Yuji Takikawa,* Takamasa Yoshida, Yutaka Koyama, Kazuto Sato, Yuko Shibata,
Shigenobu Aoyagi, Kazuaki Shimada, and Chizuko Kabuto†
Department of Chemical Engineering, Faculty of Engineering, Iwate University, Morioka, Iwate 020-8551
†Instrumental Analysis Center for Chemistry, Faculty of Science, Tohoku University, Sendai, Miyagi 980-8578
(Received April, 27, 2000; CL-000403)
Synthesis of novel five-membered cyclic ditellurides, 4-
no significant changing (broad singlet) from 20 °C to 80 °C
range. Thus, the ∆G‡ value for the conformational interconver-
sion of 1e was estimated as 54.4 kJ/mol. The dynamic conforma-
tional feature of 1e was similar to those of 2a (X=Se, R=Ph),2,3,5
and the crown-type conformation was suggested for 1 (X=Te).
However, all attempts for X-ray crystallographic analysis of 1a–e
were not successful. All the results are shown in Table 1.
aryl-1,2,4-ditellurazolidines was achieved by treating 3,7-
diaryl-2H,6H-tetrahydro-1,5,3,7-ditelluradiazocines with oxi-
dizing agents or by aerobic exposure. The oxidative ring con-
traction of the heterocycles was assumed to proceed through
formation and subsequent fragmentation of bicyclic ditellura
dications.
Recently, tellurium-containing heterocycles are of great
interest in their synthetic potentiality as the precursors of vari-
ous heterocycles and the substrates for electroconductive mate-
rials. However, the lack of convenient synthetic methods of
cyclic polytellurides has impeded the structural and synthetic
studies except for some limited cyclic ditellurides.1 During our
studies on cyclic chalcogenoamino acetals, we reported an
oxidative ring contraction of 2H,6H-tetreahydro-1,5,3,7-diselena-
diazocines A (X=Se) to form 1,2,4-diselenazolidines C (X=Se)
via dications B (X=Se).2 It was expected that oxidation of telluri-
um analogues A (X=Te) would cause ring contraction to give
cyclic ditellurides C (X=Te) through a similar process via B
(X=Te).3 Along with such expectation, we started the study on
2H,6H-tetrahydro-1,5,3,7-ditelluradiazocines A (X=Te). In this
paper, we would like to describe a synthesis and the structural
features of A (X=Te) as well as the conversion into 1,2,4-ditel-
lurazolidines C (X=Te) by treating with an oxidizing agent or
by aerobic exposure.
Subsequently, a CH2Cl2 solution of 1 was treated with air,
O2 gas, or an oxidizing agent (1 mol amount) at –78 °C or at
R.T. to give 1,2,4-ditellurazolidines 3 as deep purple crystals in
good yields. When the oxidation of 1 was carried out by aero-
bic exposure, the formation of 1,3,5-triarylhexahydro-1,3,5-tri-
azines 58,9 was accompanied with 3 as main byproducts. The
1
physical data of the products including the MS, IR, H NMR,
Treatment of an aqueous or an ethanolic solution of a pri-
mary arylamine (1 mol amount) with formalin (10 mol amounts)
and NaTeH (3 mol amounts)4 at room temperature (R.T.) in an
Ar atmosphere according to the reported methods2,5 afforded
2H,6H-tetrahydro-1,5,3,7-ditelluradiazocines (1a–e) as greenish
yellow solids. There found no products originated from
NaTeH-reduction of formaldimines,4b,6 and, in all cases, 1,2,4-
ditellurazolidines 3 were obtained as main byproducts due to aer-
obic oxidation of 1 during the usual workup and purification.
The 1H NMR and 13C NMR spectral patterns of 1 measured at 25
°C were quite similar to those of sulfur and selenium analogues
and 13C NMR spectra, as well as the elemental analysis data,
were fully consistent with the structures of 3 and 5.8
Especially, the UV–Vis spectra of 3 showed characteristic two
absorptions at about 685 and 565 nm regions due to the n–σ*
transition of Te–Te bonds,1f,1j and the patterns of the UV–Vis
spectra were different from those of common dialkyl or diaryl
ditellurides. The structural determination of 3 was achieved
finally by X-ray crystallographic analysis of 3e (R=p-FC6H4),
and the ORTEP drawing of 3e was shown in Figure 1.10 All the
oxidation reactions of 1 are shown in Table 2.
It was assumed that 3 were formed from 1 through oxida-
tive ring contraction via ditellura dications B (X=Te) as shown
in Scheme 1. The formation of 5 was also explained by the
reaction including the formation and trimerization of
formaldimines9 D generated from the counterparts of B (X=Te).
1
A (X=S, Se) in all respects.7 The dynamic H NMR measure-
ment of 1e (R=p-FC6H4) in toluene-d8 at –10 °C exhibited a cou-
ple of broad doublet signals assigned to the geminal methylene
protons. The signal showed the coalescence point at 10 °C and
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
871
It is noteworthy that the conversion of 1a into 3a by aerobic
exposure underwent much faster than that of selenium analogue
2a into 4a due to the lower oxidation potential of tellurium
atoms of 1 than that of the selenium analogues of 2 and the con-
formational preference for transannular Te–Te interaction
which might accelerate the formation of dication B (X=Te)3e,3f
by oxidation. The calculated intramolecular Te–Te atomic dis-
tance of 1a for the most favored crown-like conformation was
estimated to be 3.606 Å from MM2, and the estimated value
was much smaller than the sum of the van der Waals radii of
tellurium atoms (4.0 Å).11
In conclusion, 1,2,4-ditellurazolidines 3 were synthesized
by oxidation of 2H,6H-tetrahydro-1,5,3,7-ditelluradiazocines 1.
Further attempts for the conversion of 3 into various tellurium-
containing heterocycles are in progress in our laboratory.
This work was partially supported by Grant-in-Aid for
Scientific Research (No. 09650946) from the Ministry of
Education, Science, Sports, and Culture.
References and Notes
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Selected NMR spectral data for the methylene signals of A. A
1
(X=S, R=C6H5): H NMR (CDCl3) δ = 5.10 (8H, br.s); 13C NMR
1
(CDCl3) δ = 56.5(t). A (2a, X=Se, R=C6H5): H NMR (CDCl3) δ
= 5.10 (8H, br.s); 13C NMR (CDCl3) δ = 51.3 (t). A (1a, X=Te,
R=C6H5): 1H NMR (CDCl3) δ = 5.12 (8H, br.s); 13C NMR
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8
9
Physical data of 1, 3, and 5 are available as the supplementary
materials.
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10 X-ray crystallographic data for 3e: Deep green needle, tetragonal,
I41/a(#88), a = 18.699(5), c = 11.820(5) Å, V = 4132(2) Å3, Z = 16,
Dcalc= 2.522 g/cm3, µ(Mo Kα) = 56.10 cm–1, R = 0.027, RW = 0.027.
11 MM2 calculation of 1a was carried out by using CS Chem3D Pro
Ver. 3.5 on the Macintosh.