Visible light photocatalyzed direct conversion of aryl-/heteroarylamines to selenides at room temperature

Article abstract of DOI:10.1021/ol500567t

A novel strategy for the direct conversion of aryl- and heteroarylamines to selenides has been developed via diazotization of amines with tert-butyl nitrite in neutral medium followed by reaction with diaryl/diheteroaryl/dialkyl diselenides in one pot under photocatalysis at room temperature in the absence of any metal. This reaction is also applied for the synthesis of tellurides. The selenylation of heteroarylamine by this protocol is of much significance because of the difficulty in diazotization of these molecules by a standard diazotization method in acid medium.

Full text of DOI:10.1021/ol500567t

Letter
pubs.acs.org/OrgLett
Visible Light Photocatalyzed Direct Conversion of Aryl-/
Heteroarylamines to Selenides at Room Temperature
Debasish Kundu, Sabir Ahammed, and Brindaban C. Ranu*
Department of Organic Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Kolkata 700032, India
S
* Supporting Information
ABSTRACT: A novel strategy for the direct conversion of aryl-
and heteroarylamines to selenides has been developed via
diazotization of amines with tert-butyl nitrite in neutral medium
followed by reaction with diaryl/diheteroaryl/dialkyl diselenides
in one pot under photocatalysis at room temperature in the
absence of any metal. This reaction is also applied for the
synthesis of tellurides. The selenylation of heteroarylamine by this
protocol is of much significance because of the difficulty in diazotization of these molecules by a standard diazotization method in
acid medium.
he applications of photoredox catalysis in organic
synthesis has received considerable interest in recent
chemoselectivity. The aryl diazonium fluoroborates have also
been employed for the synthesis of diaryl selenides by
transition-metal-free coupling with diaryl diselenides under
microwave irradiation,9a by ball-milling,9b and by conventional
methods in the presence of hypophosphorus acid (Scheme
2).9c However, the major limitation of these processes using
T
years.1 One of the important applications is toward the
formation of aryl radicals which has made light-mediated
aromatic substitution a powerful alternative to widely employed
metal-catalyzed reactions.2 These photocatalyzed reactions in
the presence of suitable photosensitizers involve a single-
electron-transfer process, and the primary merits of these
reactions are a metal-free protocol and mild generation of aryl
radicals at room temperature.
Scheme 2. Transition-Metal-Catalyst-Free Reaction To
Form a C−Se Bond Using Diazonium Salts
The organoselenides have received continued interest
because of their presence as structural motifs in a variety of
molecules of biological, pharmaceutical, and material interest.3
They are also used as catalysts4 and useful intermediates5 in
organic reactions. Thus, a number of methods have been
developed for their synthesis.6 One of the widely accepted and
efficient practices is the transition-metal-catalyzed C−Se bond
formation by the coupling of aryl hadies/boronic acids/triflates
and selenol/PhSeNa/diphenyl diselenide (Scheme 1).7 These
diazonium fluoroborates is toward the synthesis of heteroaryl
selenides as heteroarylamines such as pyridinyl- and quinolinyl-
amines are difficult to diazotize because of their tendency to
form salt during diazotization in acidic medium.10 A similar
difficulty is also encountered in the reaction of 2-ethynylanilines
which form cinnolones readily during diazotization.11 Needless
to say, conversion of these amines to selenides was not
addressed in any of these procedures.9
Scheme 1. Transition-Metal-Catalyzed Cross-Coupling
Reactions To Form a C−Se Bond
To overcome these drawbacks, we report here a novel
protocol for the synthesis of aryl/heteroaryl selenides from
t
aryl/heteroarylamines using BuONO and diaryl/diheteroaryl/
dialkyl selenides in one pot at room temperature under
photocatalysis in absence of any metal and base (Scheme 3).
Although a couple of reports on visible light photocatalyzed C−
S bond formation involving diazonium ion appeared recently
(Scheme 4)8f,h there is no report on C−Se bond formation
from anilines in one pot.
reactions are usually performed at a higher temperature for a
relatively long period. Recently, aryldiazonium salts have
attracted much attention as an important source of aryl
radicals, and they have been employed successfully for a variety
of aryl substitution reactions.8 In fact, aryl diazonium salts
particularly fluoroborates become an attractive alternative to
aryl halides and triflates because of their ease of preparation
from readily available amines and better reactivity with high
To standardize the reaction conditions, a series of experi-
ments were performed under varying reaction parameters such
Received: February 21, 2014
Published: March 12, 2014
© 2014 American Chemical Society
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Letter
Thus, in a general experimental procedure a mixture of amine
(0.5 mmol), diaryl diselenide (0.5 mmol) BuONO (0.6
Scheme 3. Visible Light Photocatalyzed Direct One-Pot
Synthesis of Organoselenides from Aryl- and
Heteroarylamines
t
mmol), and eosin Y (0.01 mmol) in DMSO (2 mL) was
stirred under blue-LED light at room temperature for 2 h
(TLC). After evaporation of DMSO, standard workup by
extraction with ethyl acetate followed by column chromatog-
raphy over silica gel provided the pure product. A wide range of
diversely substituted aryl- and heteroarylamines underwent
reactions with diaryl diselenides by this procedure to produce
the corresponding selenides. The products obtained from
arylamines are outlined in Scheme 5 and those with
Scheme 4. Recent Developments on C−S Bond Formation
under Visible Light Photocatalysis
Scheme 5. Visible Light Photocatalyzed Synthesis of Diaryl
a
Selenides
as additive, organocatalyst, solvent, and time for a representa-
tive reaction of 4-aminoacetophenone and diphenyl diselenide.
Among a variety of solvents and organocatalysts studied, eosin
Y as a single-electron-transfer agent in DMSO produced the
best result under the blue-LED light (Table 1, entry 2). The
a
Table 1. Standardization of Reaction Conditions
b
entry
photocatalyst
solvent
DMSO
additive
time (h) yield (%)
10
1
2
3
4
5
6
7
8
9
eosin Y
eosin Y
eosin Y
eosin Y
eosin Y
eosin Y
eosin Y
eosin Y
[Ru(bpy)3]Cl2
eosin Y
DMSO
DMF
tBuONO
tBuONO
tBuONO
tBuONO
tBuONO
tBuONO
tBuONO
tBuONO
tBuONO
tBuONO
tBuONO
tBuONO
2
2
90
30
CH3CN
1,4-dioxane
toluene
Xylene
THF
2
70
a
25
30
16
16
16
18
18
6
trace
Reaction conditions: amine (1.0 mmol), diselenide (1.0 mmol),
tBuONO (1.1 mmol), eosin Y (0.01 mmol), DMSO (2.0 mmol), blue
LED, 2 h. 3 h. 4 h.
b
c
trace
80
DMSO
DMSO
DMSO
DMSO
DMSO
b
heteroarylamines in Scheme 6. Both electron donating
(−OMe, −O-allyl) and electron withdrawing (−COMe,
−CN, −CF3, −NO2) groups at all positions of the aromatic
ring are compatible with these reactions. The dinitro-
substituted phenyl phenyl selenide (Scheme 5, 3d), which is
of great potential for biological activity,12 has been easily
prepared by this procedure. A series of substituted aryl
heteroaryl and diheteroaryl selenides have been efficiently
obtained from the corresponding anilines (Scheme 6) by this
protocol. This is of much interest to pharmaceutical industries
as these compounds are of considerable importance for
biological screening.13 Several heterocyclic units such as
pyridinyl, quinolinyl, and thiazolyl anilines, which do not
provide selenides by the conventional procedures using
diazonium fluoroborates,8f,9 have been successfully employed
in this selenylation reaction (Scheme 6). 2-Ethynylanilines that
produce cinnolones via a diazotization reaction11 are readily
converted to the corresponding 2-alkynylaryl selenides by this
protocol (Scheme 7).
10
11
12
13
fluoroscene
22
rose bengal
6
trace
a
Reaction conditions: amine (0.5 mmol), diselenide (0.5 mmol),
b
additive (1.1 mmol), photocatalyst (0.01 mmol), blue LED. Reaction
was carried out in the absence of light.
reaction did not proceed in the absence of either blue-LED or
eosin Y (Table 1, entries 10 and 11). Although [Ru(bpy)3]Cl2
too serves as SET agent in this reaction (Table 1, entry 9) less
expensive eosinY becomes obvious choice in place of highly
expensive ruthenium catalyst. Other SET reagents such as Rose
Bengal or fluoroscein (Table 1, entries 12 and 13) failed to
produce satisfactory results. Although CH3CN is considerably
effective (Table 1, entry 4), in other polar solvents such as
DMF, 1,4-dioxane, and THF much lower yields were obtained
(Table 1, entries 3, 5, and 8). Nonpolar solvents like toluene
and xylene did not initiate the reaction at all (Table 1, entries 6
and 7). The reaction did not proceed in the absence of
tBuONO (Table 1, entry 1).
This strategy is also applied for the synthesis of unsym-
metrical bis-selenides and selenosulfides starting from nitroani-
lines (Scheme 8) and diaryl and aryl heteroaryl tellurides from
the corresponding anilines (Scheme 9).
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mentioned earlier, very recently two similar procedures under
photocatalysis have been reported for C−S bond formation.8f,h
One of these8f involved a two-step procedure using preformed
diazonium fluoroborate, although the other one8h presents a
direct conversion of anilines to sulfides using thiols and Ru
catalyst. However, they are primarily concerned with C−S bond
formation, and only one reaction for the synthesis of aryl
selenide was addressed in the two-step procedure.8f Thus, the
present procedure of C−Se bond formation is quite different,
presenting an efficient and general procedure for a one-pot
conversion of anilines including heteroaryl- and 2-ethynylaryl-
amines to selenides and tellurides.
Scheme 6. Visible Light Photocatalyzed Synthesis of
Heteroaryl Selenides
a
Most likely, the reaction occurs by the interaction of the
aryldiazonium ion, generated in situ, with the diphenyl
diselenide under visible light. A reaction pathway is outlined
in Scheme 10 in accordance with the previous reports.8 Aryl
Scheme 10. Possible Reaction Pathway for Visible Light
Photocatalyzed Synthesis of Organochalcogenides from
Anilines
a
Reaction conditions: heteroarylamine (1.0 mmol), diselenide (1.0
t
mmol), BuONO (1.1 mmol), eosin Y (0.01 mmol), DMSO (2.0
mmol), blue LED, 2 h. 3 h.
b
Scheme 7. Visible Light Photocatalyzed One-Pot Synthesis
of 2-Ethynyl Aryl Selenides from 2-Ethynylamines
diazonium ion undergoes reduction by photoactivated eosin Y,
and the resulting aryl radical interacts with diaryl diselenide to
produce a trivalent selenide radical B which is stabilized by aryl
and selenium moiety. The radical B then leads to intermediate
C via one-electron oxidation by eosin Y radical cation, which
undergoes cleavage to provide the product. The involvement of
radical pathway is confirmed by arrest of the reaction in
presence of TEMPO (radical quencher) and THF (radical
trapper).
Scheme 8. Visible Light Photocatalyzed Synthesis of Bis-
Selenide and Selenosulfide Starting from Nitroanilines
To conclude, an efficient and general method for the one-pot
conversion of aniline to selenide at ambient conditions under
photocatalysis is developed. This procedure avoids isolation
and handling of hazardous diazonium salt and use of any metal.
The reaction tolerates a broad range of functionalities, and
more significantly heteroaryl- and 2-ethynylanilines are
successfully converted to the corresponding selenides in this
procedure, which were not addressed in earlier reports.8f,9 This
protocol is also employed for the synthesis of tellurides. We are
not aware of any procedure for direct conversion of anilines to
selenides and tellurides in one-pot at room temperature under
visible light, and thus, this is the first report of this reaction
using a green protocol.
Scheme 9. Visible Light Photocatalyzed Synthesis of
Tellurides
ASSOCIATED CONTENT
* Supporting Information
■
In general, the reactions are clean and high yielding. The
reactions are performed at room temperature in neutral
reaction medium, which makes the procedure compatible
with a wide range of functionalities and heteroarylanilines. As
S
Typical experimental procedure and characterization data of all
1
products and copies of their H NMR and 13C NMR spectra.
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Organic Letters
Letter
Chem., Int. Ed. 2013, 52, 7860. (i) Xiao, T.; Dong, X.; Tang, Y.; Zhou,
L. Adv. Synth. Catal. 2012, 354, 3195.
This material is available free of charge via the Internet at
http://pubs.acs.org.
(9) (a) Kundu, D.; Ahammed, S.; Ranu, B. C. Green Chem. 2012, 14,
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(10) Wang, X.; Xu, Y.; Mo, F.; Ji, G.; Qiu, D.; Feng, J.; Ye, Y.; Zhang,
S.; Zhang, Y.; Wang, J. J. Am. Chem. Soc. 2013, 135, 10330.
(11) Dey, R.; Chatterjee, T.; Ranu, B. C. Tetrahedron Lett. 2011, 52,
461.
AUTHOR INFORMATION
Corresponding Author
■
*E-mail: ocbcr@iacs.res.in.
Notes
The authors declare no competing financial interest.
(12) Engman, L.; Cotgreave, I.; Angulo, M.; Taylor, C. W.; Paine-
Murrieta, G. D.; Powis, G. Anticancer Res. 1997, 17, 4599.
(13) (a) Matsho, M.; Ogino, T.; Tsuri, K. PCT Int. Appl. WO
1996030370 A2, 1996. (b) Kundu, D.; Chatterjee, T.; Ranu, B. C. Adv.
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ACKNOWLEDGMENTS
■
We are pleased to acknowledge the financial support from
DST, New Delhi, with an award of JCB Fellowship to BCR
(Grant No. SR/S2/JCB-11/2008). D.K. and S.A. thank CSIR
for their fellows.
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