Novel formation of 1,2,4-triselenolanes by the reaction of tert-butylarylmethylenetriphenylphosphoranes with elemental selenium

Article abstract of DOI:10.1016/S0040-4039(01)00592-5

Reaction of tert-butylarylmethylenetriphenylphosphoranes with elemental selenium afforded the corresponding 1,2,4-triselenolanes (1), 1,3-diselenetanes (4), and triphenylphosphine selenide. Triselenolanes 1 were formed from selenation of 4, which may suggest a stepwise selenation of selenoketones.

Full text of DOI:10.1016/S0040-4039(01)00592-5

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 42 (2001) 3881–3883
Novel formation of 1,2,4-triselenolanes by the reaction of
tert-butylarylmethylenetriphenylphosphoranes with elemental
selenium
Kentaro Okumaa,b,* and Tomoaki Kubotaa
aDepartment of Chemistry, Fukuoka University, Jonan-ku, Fukuoka 814-0180, Japan
bAdvanced Materials Institute, Fukuoka University, Jonan-ku, Fukuoka 814-0180, Japan
Received 28 February 2001; revised 2 April 2001; accepted 6 April 2001
Abstract—Reaction of tert-butylarylmethylenetriphenylphosphoranes with elemental selenium afforded the corresponding 1,2,4-
triselenolanes (1), 1,3-diselenetanes (4), and triphenylphosphine selenide. Triselenolanes 1 were formed from selenation of 4, which
may suggest a stepwise selenation of selenoketones. © 2001 Elsevier Science Ltd. All rights reserved.
1,2,4-Triselenolanes (1) are one of the cyclic poly-
selenides. The rich literature on 1,2,4-trithiolanes (2)1
oddly contrasts with the few reports on the formation
of 1,2,4-triselenolanes (1).2,3 In our and Erker’s previ-
ous reports, the formation of selones (3) by the reaction
of phosphorus ylides with elemental selenium was
described.4,5 In some cases, 1,3-diselenetanes (4) were
isolated by dimerization of selenoketones.6 Only the
reported example of 1,2-diselenolanes was observed in
the reaction of selenobenzophenone (3a) with cyclopen-
tadiene.7 Recently, we have reported the synthesis of
cis- and trans-1,2,4-trithiolanes (2) by the reaction of
pivalophenones with tetraphosphorus decasulfide and
the thermal isomerization between the isolated
stereoisomers of trithiolanes 2 (Scheme 1).8
to afford pale yellow crystals (1a) along with 2,4-di-
tert-butyl-2,4-bis(p-methoxyphenyl)-1,3-diselenetane 4a
(24%), and triphenylphosphine selenide (75%).
Mass spectroscopy of 1a has shown that we are dealing
with [4a+Se], which is formally a [3+2] cycloaddition
1
product. Its H NMR spectrum suggests two tert-butyl,
and two methoxy protons along with aromatic protons.
Careful investigation of the above result suggested that
the structure of 1a was 3,5-di-tert-butyl-3,5-bis(p-
methoxyphenyl)-1,2,4-triselenolane 1a (36%).10 Reac-
tion of the ylide derived from tert-butyl(p-phen-
oxyphenyl)methyltriphenylphosphonium fluoroborate
with elemental selenium was carried out in a similar
manner to give the corresponding 1b (42%) and 4b
(26%) (Scheme 2).
These results prompted us to investigate the reaction of
phosphorus ylides with elemental selenium as a practi-
cal method for the formation of cyclic polyselenides.
This report offers the first practical synthesis of 1.
In the case of 1,2,4-trithiolane both cis and trans iso-
mers were obtained, whereas in the case of selenium
analogs only one isomer was isolated.11
A refluxing suspension of elemental selenium (3 atom
equiv.) and the ylide, prepared from tert-butyl(p-
Ar
methoxyphenyl)methyltriphenylphosphonium
tetra-
S
fluoroborate and butyllithium in toluene, turned into a
bright green suspension of tert-butyl(p-methoxy-
phenyl)selenoketone.9 After 30 min, the reaction mix-
ture was cooled to room temperature. After standing
for 15 h, the suspension changed to pale green. The
resulting mixture was chromatographed over silica gel
Ar
S
S
S
S
O
S
Ar
Ar
+
Ar
S
S
S
P4S10
+
Ar
Ar
Scheme 1.
* Corresponding author.
0040-4039/01/$ - see front matter © 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4039(01)00592-5

3882
K. Okuma, T. Kubota / Tetrahedron Letters 42 (2001) 3881–3883
R
R
R
Se
Se
Se
PPh3
+
Se Se
+
(Se)n
4a: R=MeO
4b: R=PhO
R
1a: R=MeO
1b: R=PhO
R
+ Ph3P=Se
Scheme 2.
Ar
Ar
PPh3
Ar
Se
Se
Se
Ar
Se
Se
Se
Ar
+
(Se)n
1
3
6
Scheme 3.
Ar
Ar
PPh3
Se
Se
H
O
H
+
(Se)n
H
7
Scheme 4.
Thus, the reaction might proceed through a stepwise
selenation of selenopivalophenones (Scheme 6).
We first proposed that triselenolanes 1 were formed by
the cycloaddition of selenocarbonyl Se–selenides (6)
and selenoketones by analogy of their sulfur analogs
(Scheme 3).
Previously, 1,2,4-triselenolanes were prepared by desele-
nation of bis[tris(trimethylsilyl)methyl triselenide2 or by
the reaction of diketone dihydrazone with Se2Cl2.3
However, to our knowledge, there is no report on the
formation of 1,2,4-triselenolanes from phosphorus
ylides. The present method is very simple and only
requires commercially available butyllithium, elemental
selenium, and phosphonium salts prepared by a two-
step reaction from commercially available 4-
phenoxypivalophenone.
However, a trapping reaction of this intermediate 6 by
using norbornadiene resulted in the formation of
selenopivalophenone–norbornadiene cycloadduct
7
(Scheme 4). Attempted reaction of the ylide with ele-
mental selenium and dimethyl acetylenedicarboxylate
led to a similar product. These results suggested that
the intermediate of these reactions was only the corre-
sponding selone 3. At present, we have no evidence for
the formation of 6.
cat. Ph3P or Ph3P=Se
4a
+ Sen
1a
Actually, when 1,3-diselenetane 4a was treated with
elemental selenium in the presence of a catalytic
amount of triphenylphosphine or triphenylphosphine
selenide in refluxing toluene, 1,2,4-triselenolane 1a was
obtained in 37% yield (Scheme 5). The reaction of 1a
with norbornadiene in refluxing toluene also afforded
the adduct 7 (38%), which is identical with the cycload-
duct obtained in the reaction of the ylide and elemental
selenium in the presence of norbornadiene.
toluene, reflux
Ar
Se
Se
7
Se
Ar
Scheme 5.

K. Okuma, T. Kubota / Tetrahedron Letters 42 (2001) 3881–3883
3883
Ar
Se
Se
Ar
Se
Ar
3
4
+ Sen
or
Ar
1
Se
Se
Se
Se
Se
(Se)n
Se
(Se)n Se
Scheme 6.
Tokitoh and co-workers reported the deselenation of
cyclic polyselenides by triphenylphosphine to afford the
1,3-diselenetane at room temperature.12 In our case,
deselenation of triselenolanes 1 was also successful by
using triphenylphosphine in refluxing benzene to give
the corresponding diselenetane. Diselenetane was also
obtained in refluxing toluene.
Chem. Lett. 1994, 2283; (b) Back, T. G.; Dyck, B. P.;
Parvez, M. J. Org. Chem. 1995, 60, 703.
7. Okuma, K.; Kaneko, I.; Ohta, H.; Yokomori, Y. Hetero-
cycles 1990, 31, 2107.
8. Okuma, K.; Shibata, S.; Koga, Y.; Shioji, K.; Yokomori,
Y. Chem. Commun. 2000, 1535.
9. The formation of selenoketone was confirmed by its 13C
NMR signal of CꢂSe (275.3 ppm).
1a+Ph3Pꢀꢀꢀꢀꢀꢀꢀꢀꢁ4a+Ph3PꢂSe
10. All new compounds gave satisfactory analytical data.
Selected spectral data: Compound 1a: yellow crystals, mp
benzene, reflux
In summary, we have found that phosphonium ylides
react with elemental selenium to afford 1,2,4-tri-
selenolanes 1, which are also formed by the reaction of
1,3-diselenetanes 4 with elemental selenium and a cata-
lytic amount of triphenylphosphine.
1
128–129°C; H NMR (400 MHz, CDCl3): l 1.30 (s, 9 H,
tert-Bu), 3.70 (s, 3 H, OMe), 6.52 (d, 2H, J=8.8 Hz,
p-MeOC6H4), 7.53 (d, 2H, J=8.8 Hz, p-MeOC6H4); 13C
NMR (100 MHz, CDCl3): l 29.60 (tert-Bu), 43.68 (C-
Me3), 54.95 (MeO), 94.71 (Se-C-Se), 110.79, 132.33,
134.54, 157.25 (Ar); 77Se NMR (CDCl3): l 690.84,
729.15. Compound 1b: yellow crystals, mp 116–117°C; 1H
NMR (400 MHz, CDCl3): l 1.33 (s, 9 H, tert-Bu), 6.65
(d, 2H, J=8.8 Hz, PhOC6H4-), 6.86 (d, 2H, J=8.0 Hz,
PhO), 7.05 (t, 1H, J=8.0 Hz, PhO), 7.28 (t, 2H, J=8.0
Hz, PhO), 7.59 (d, 2H, J=8.8 Hz, PhOC6H4). Compound
4a: yellowish green crystals, mp 203–204°C; 1H NMR
(400 MHz, CDCl3): l 1.00 (s, 9 H, tert-Bu), 3.71 (s, 3 H,
OMe), 6.52 (d, 2H, J=8.8 Hz, p-MeOC6H4), 7.45 (d, 2H,
J=8.8 Hz, p-MeOC6H4); 13C NMR (100 MHz, CDCl3):
l 26.75 (q, tert-Bu), 39.03 (s, Se-C, with 77Se Satellite),
39.78 (s, C-Me3), 54.95 (q, MeO), 94.71 (s, Se-C-Se),
110.79 (d), 132.33 (d), 134.54 (s), 157.25 (s); 77Se NMR
(CDCl3): l 780.40. Compound 7: colorless crystals, mp
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