Synthesis of a new chiral nitrogen containing diselenide as a precursor for selenium electrophiles

Article abstract of DOI:10.1016/S0957-4166(98)00380-2

The synthesis of a new chiral nitrogen containing diselenide is described starting from (1S,2S)-1,2-diphenylethylendiamine. The electrophilic selenium species generated from this diselenide have been used for methoxyselenenylation reactions at room temper

Full text of DOI:10.1016/S0957-4166(98)00380-2

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 9 (1998) 3625–3628
Synthesis of a new chiral nitrogen containing diselenide as a
precursor for selenium electrophiles
Claudio Santi,a Gianfranco Fragale b and Thomas Wirth b,∗
aIstituto di Chimica Organica Università degli Studi, I-06123 Perugia, Italy
bInstitut für Organische Chemie der Universität Basel, St. Johanns-Ring 19, CH-4056 Basel, Switzerland
Received 1 September 1998; accepted 16 September 1998
Abstract
The synthesis of a new chiral nitrogen containing diselenide is described starting from (1S,2S)-1,2-
diphenylethylendiamine. The electrophilic selenium species generated from this diselenide have been used for
methoxyselenenylation reactions at room temperature with good yields and high diasteroselectivities. © 1998
Elsevier Science Ltd. All rights reserved.
Efficient and simple routes for the synthesis of chiral nonracemic diselenides have been de-
veloped recently.1 Nitrogen containing diselenides such as 1 can be employed in stereoselective
oxyselenenylation–elimination2 reactions using peroxodisulfates to generate the electrophilic selenium
species.3
Chiral diselenides have also been described as useful ligands in various transformations such as
diethylzinc additions to aldehydes4 as well as asymmetric hydrosilylation5 and transfer hydrogenation
reactions.6
In order to understand the role of the different reaction components on the yield and on the stereoselec-
tivity, investigations on the alkoxyselenenylation step with stoichiometric quantities of the electrophilic
selenium species have been carried out. The screening of various oxidizing agents using diselenide 1
as a precursor for stereoselective methoxyselenenylations of styrene leading to the addition product 2
clearly show that the counter ion of the selenium electrophile plays an important role in determining
the stereoselectivity as well as the rate of the reaction. Ammonium peroxodisulfate gave the highest
diastereomeric ratios with good yields after 72 h.7 Although the reaction time could be lowered with
some other oxidizing agents, the stereoselectivities decreased dramatically (Table 1).
∗
Corresponding author. E-mail: wirth@ubaclu.unibas.ch
0957-4166/98/$ - see front matter © 1998 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(98)00380-2

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Table 1
Use of different oxidants in the methoxyselenenylation of styrene with diselenide 1 at rt8,9
The conditions for the generation of aryl selenium triflates of oxygen containing diselenides10 could
not be applied to nitrogen containing diselenides like 1 because of the low solubility of the aryl selenium
triflates under the reaction conditions (−100°C). However, they can be employed in methoxyselenenyl-
ations at room temperature to afford the addition product 2 in only 35% de.
Therefore, we designed a more rigid diselenide which was assumed to give better selectivities
and shorter reaction times. The easily accessible11 and even commercially available chiral diamine
3 can be converted to the aminal 4 in quantitative yield by heating at reflux with formic acid and
formaldehyde.12 Compound 4 was then converted into a mixture of triselenide 513 and diselenide 6
(≈1:2.5) by treatment with t-BuLi and elemental selenium. Reduction of this mixture with NaBH4 was
followed by reoxidation in ammonium chloride solution to convert 5 into 6. The reaction mixture was
purified by flash chromatography and crystallization from methanol to afford diselenide 6 in 73% overall
yield.14

C. Santi et al. / Tetrahedron: Asymmetry 9 (1998) 3625–3628
3627
Table 2
Methoxyselenenylation of styrene with diselenide 6
Diselenide 6 was subsequently used for the methoxyselenenylation of styrene. The aryl selenium
triflate derived from 6 by reaction with bromine and silver triflate is soluble in a mixture of diethyl
ether and methanol at −100°C. After reaction with styrene the addition product 7 is obtained in 98%
yield with 86% de (Table 2, entry 1).
With ammonium peroxodisulfate in the presence of a catalytic amount of trifluoromethanesulfonic acid
it is possible to generate from 6 the corresponding aryl selenium sulfate at room temperature.15 Addition
to styrene yields 7 with a comparable yield and selectivity to that obtained by the triflate (Table 2, entry
2) also when the reaction is carried out at −15°C (Table 2, entry 3). The absolute configuration of the
newly generated stereocenter in 7 was assigned by HPLC analysis of 1-methoxy-1-phenylethane formed
after reductive deselenenylation of 7.
In conclusion, we have prepared a new chiral nitrogen containing diselenide containing an imidazoli-
dine moiety in a few steps. This now facilitates methoxyselenenylations of styrene with high yields and
stereoselectivities, even at room temperature.
Alkoxyselenenylations of other alkenes and selenocyclization reactions, as well as the application of
diselenide 6 in catalytic oxyselenenylation–elimination sequences are currently under investigation.
Acknowledgements
This work was supported by the Stipendienfonds der Basler Chemischen Industrie (fellowship for
G.F.), the Schweizer Nationalfonds and by Treubel-Fonds (fellowship for T.W.). We thank Professor
B. Giese and Professor M. Tiecco for generous support. This research was performed under MURST
National Project ‘Stereoselezione in Sintesi Organica. Metodologie ed Applicazioni’ (C.S.).
References
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(dd, 1H, J=1.5, 7.4 Hz), 4.10 (d, 1H, J=5.5 Hz), 3.90 (d, 1H, J=5.5 Hz), 3.74 (d, 1H, J=9.1 Hz) 3.60 (d, 1H, J=9.1 Hz),
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2H), 7.05 (ddd, 1H, J=1.5, 7.5, 7.9 Hz), 6.94 (ddd, 1H, J=1.2, 7.5, 7.9 Hz), 6.67 (dd, 1H, J=1.5, 7.5 Hz), 4.14 (d, 1H,
J=5.4 Hz), 4.00 (d, 1H, J=5.4 Hz), 3.85 (d, 1H, J=9.0 Hz) 3.80 (d, 1H, J=9.0 Hz), 2.42 (s, 3H), 2.32 (s, 3H). 13C NMR: δ
138.9, 137.6, 131.2, 130.6, 129.4, 128.3, 128.2, 128.1, 127.6, 125.5, 79.6, 78.1, 75.8, 40.1, 39.1. 77Se NMR: δ 445.8.
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