Iodide-promoted deselenylation of β-chloro-and β-oxyselenides to form alkenes and selenenyl iodides

Article abstract of DOI:10.1246/cl.2012.766

Deselenylation reaction of β-chloro-and β-oxyselenides proceeded efficiently by treatment with tetrabutylammonium iodide (TBAI) to afford alkenes in good yields. It was established that selenenyl iodides were formed in these reactions. Catalytic transformation of β-chloro-and β-oxyselenides to alkenes was also developed.

Full text of DOI:10.1246/cl.2012.766

doi:10.1246/cl.2012.766
766
Published on the web July 21, 2012
Iodide-promoted Deselenylation of ¢-Chloro- and ¢-Oxyselenides
to Form Alkenes and Selenenyl Iodides
Shohei Sase, Kazuaki Ebisawa, and Kei Goto*
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology,
2-12-1 Ookayama, Meguro-ku, Tokyo 152-8551
(Received March 21, 2012; CL-120241; E-mail: goto@chem.titech.ac.jp)
Deselenylation reaction of ¢-chloro- and ¢-oxyselenides
four equivalents of tetrabutylammonium iodide (TBAI) in
CDCl3 at 60 °C afforded cyclohexene in a good yield along
with selenenyl iodide 1 (Scheme 2). It has been suggested that
¢-chloroselenides are in equilibrium with the corresponding
seleniranium cation.8 Attack of an iodide ion to the selenium
atom of the seleniranium cation 3 is considered to result in the
formation of 1 and cyclohexene, which predominates over the
attack of a chloride ion to the carbon atom of 3 to produce the
starting material 2.
The generality of this deselenylative alkene formation was
investigated by using ¢-chloroselenides 4a-4d bearing a
phenylseleno group (Table 1). Reaction of 4a with 1.5 equiv-
alents of TBAI in CDCl3 at room temperature completed within
15 min to give stereospecifically trans-4-octene in 98% yield
(Entry 1). Its stereoisomer 4b yielded cis-4-octene in 93% yield
upon treatment with 2.5 equivalents of TBAI for 1 h (Entry 2).
In the case of 4c and 4d, deselenylation reaction proceeded
somewhat slower, but the corresponding alkenes were obtained
in good yields by increasing the amount of TBAI (Entries 3
proceeded efficiently by treatment with tetrabutylammonium
iodide (TBAI) to afford alkenes in good yields. It was
established that selenenyl iodides were formed in these
reactions. Catalytic transformation of ¢-chloro- and ¢-oxy-
selenides to alkenes was also developed.
Organoselenium compounds constitute a useful and versa-
tile class of reagents that has been widely utilized in organic
syntheses.1 Among a number of selenium-based synthetic
methodologies developed to date, alkene formation involving
release of organoselenium moieties provides an important tool
for synthetic chemistry. syn-Elimination of selenoxides is the
most common one, which proceeds under mild conditions to
form a carbon-carbon double bond stereospecifically.2 ¢-Oxy-
selenides serve as a potential alkene precursor,3 which undergo
anti-elimination upon treatment with acid,3a mesyl chloride
in the presence of amine,3b and chlorotrimethylsilane-sodium
iodide reagent.3c ¢-Chloro- and ¢-bromoselenides are also
known to lead to alkenes by the reaction with selenolate
nucleophile.4
In the course of our studies concerning biologically relevant
organoselenium intermediates,5 we have recently succeeded in
the synthesis of a selenenyl iodide (RSeI) by taking advantage of
a bowl-shaped substituent, a Bpq group (Scheme 1).6 Although
selenenyl iodides usually undergo facile disproportionation to
form diselenides and iodine,7 BpqSeI (1) was proved to have
remarkable thermal stability. In a model study of a thyroid
hormone-activating enzyme by utilizing selenenyl iodide 1, it
was suggested that selenium and iodine inherently have a high
affinity, which plays a key role in the deiodination reaction of
2,6-diiodophenol derivatives by selenols.6 It was envisioned that
their affinity could also be applied to novel deselenylation
reactions to produce alkenes. In this communication, we report
an efficient deselenylative alkene formation from ¢-chloro- and
¢-oxyselenides promoted by an iodide ion, which can be
performed with a catalytic amount of iodide source.
aIsolated yield. bEstimated by GC.
Scheme 2.
Table 1. Deselenylation of ¢-chloroselenides 4a-4d with
TBAI
To test the hypothesis that the affinity between selenium and
iodine would serve as a driving force for deselenylative alkene
formation, we first examined the reaction of ¢-chloroselenide 2
bearing a Bpq group with an iodide source. Treatment of 2 with
TBAI
/equiv
Entry
4
Time
Product
Yield/%a
1
2
3
4
4a
4b
4c
4d
1.5
2.5
5.0
6.0
15 min trans-4-octene
98
93
90
94
1 h
10 h
20 h
cis-4-octene
cyclohexene
1-octene
aEstimated by GC.
Scheme 1.
Chem. Lett. 2012, 41, 766-768
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/

767
aAll yields were estimated by GC.
Scheme 3.
Scheme 5.
aEstimated by GC.
aIsolated yield. bEstimated by GC.
Scheme 4.
Scheme 6.
Table 2. Deselenylation of ¢-oxyselenides 6a-6c with TBAI
smooth formation of the alkene. No reaction was observed upon
treatment of 6a with two equivalents of TBAI (Entry 4).
Reaction of 6a with four equivalents of TsOH¢H2O proceeded
sluggishly, affording trans-4-octene in 72% after 3 days
(Entry 5).
Catalytic deselenylation of ¢-oxyselenides 6a-6c was also
achieved to produce trans-4-octene in good to excellent yields,
although longer reaction times were necessary for these catalytic
reactions (Scheme 5).
A related alkene synthesis from ¢-oxyselenides by use of
chlorotrimethylsilane-sodium iodide reagent has been reported
by Clive et al.3c Although they suggested that HI, formed by
adventitious hydrolysis, may play a role, the reaction mechanism
was not elucidated. In the present study, the formation of a
selenenyl iodide was established by the reaction of ¢-methoxy-
selenide 7 bearing a Bpq group with TBAI in the presence
of TsOH¢H2O to produce selenenyl iodide 1 (Scheme 6).
Deselenylation of ¢-oxyselenides is considered to proceed in
a similar manner to that of ¢-chloroselenides, except that
assistance of acid is necessary for efficient generation of the
seleniranium cation intermediates from the former.
In summary, iodide has been found to promote deseleny-
lation reaction of ¢-chloro- and ¢-oxyselenides to afford alkenes
efficiently with formation of selenenyl iodides.10 A catalytic
version of the transformation has been also developed. Further
studies on application of the high affinity between selenium and
iodine to synthetic chemistry are currently in progress.
TBAI TsOH¢H2O
Entry
6
Time
Yield/%a
/equiv
/equiv
1
2
3
4
5
6a
6b
6c
6a
6a
2.0
2.0
2.0
2.0
®
4.0
4.0
4.0
®
10 min
10 min
40 min
24 h
98
98
93
n.d.b
72
4.0
3 d
aAll yields of trans-4-octene were estimated by GC. bNot
detected.
and 4).9 Besides the alkenes, diphenyl diselenide and iodine
were formed in all cases, both of which are likely to be formed
through disproportionation of phenylselenenyl iodide (PhSeI).
By taking advantage of the facile disproportionation of
PhSeI, deselenylation reaction with a catalytic amount of iodide
source was successfully developed. Since iodine can be easily
reduced to iodide ions, iodine formed through disproportiona-
tion of PhSeI would be converted to iodide ions in the presence
of appropriate reductant, which could react again with selenira-
nium cation 5 to establish a catalytic cycle (Scheme 3). Indeed,
the reaction of 4a with 20 mol % of TBAI and two equivalents of
sodium sulfite at room temperature gave trans-4-octene in 85%
yield after 2 h (Scheme 4). It is notable that this reaction can be
performed under mild conditions free from iodine.
The iodide-promoted deselenylation reaction was applicable
to ¢-oxyselenides 6a-6c with various oxy functionalities.
Reaction of 6a-6c with two equivalents of TBAI in the presence
of TsOH¢H2O at room temperature gave trans-4-octene along
with diphenyl diselenide and iodine (Table 2, Entries 1-3).
Although the reaction of 6c took somewhat longer time, all the
reactions proceeded almost quantitatively. Control experiments
performed in the absence of either TBAI or TsOH¢H2O
confirmed that the presence of both reagents is necessary for
This work was partly supported by Grants-in-Aid for the
Global COE Program for Education and Research Center for
Emergence of New Molecular Chemistry and for Scientific
Research on Innovative Areas “Molecular Activation Directed
toward Straightforward Synthesis” from the Ministry of Educa-
tion, Culture, Sports, Science and Technology, Japan.
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10 Supporting Information is available electronically on the
CSJ-Journal Web site, http://www.csj.jp/journals/chem-lett/
index.html.
Chem. Lett. 2012, 41, 766-768
© 2012 The Chemical Society of Japan
www.csj.jp/journals/chem-lett/