Synthesis of novel 2,5-diarylselenophenes from selenation of 1,4-diarylbutane-1,4-diones or methanol/arylacetylenes

Article abstract of DOI:10.1039/b924986a

Reaction of 2,4-bis(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide [PhP(Se)(μ-Se)]₂ (Woollins' reagent, WR) with one equivalent of 1,4-diarylbutane-1,4-diones 1a-g in refluxing toluene affords the corresponding 2,5-diarylselenophenes 2a-g in

Full text of DOI:10.1039/b924986a

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www.rsc.org/obc | Organic & Biomolecular Chemistry
Synthesis of novel 2,5-diarylselenophenes from selenation of
1,4-diarylbutane-1,4-diones or methanol/arylacetylenes†
Guoxiong Hua,a John B. Henry,b Yang Li,a Andrew R. Mount,b Alexandra M. Z. Slawina and
J. Derek Woollins*a
Received 27th November 2009, Accepted 18th January 2010
First published as an Advance Article on the web 5th February 2010
DOI: 10.1039/b924986a
Reaction of 2,4-bis(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide [PhP(Se)(m-Se)]2 (Woollins’
reagent, WR) with one equivalent of 1,4-diarylbutane-1,4-diones 1a–g in refluxing toluene affords the
corresponding 2,5-diarylselenophenes 2a–g in excellent yields (up to 99%). Alternatively, the
2,5-diarylselenophenes (2a and 2b) can be obtained in 70–80% yields from the reaction of arylacetylene
with an equivalent of O-methyl Se-hydrogen phenylphosphonodiselenoate; the latter was derived from
WR and methanol. The first X-ray structure of 2,5-diarylselenophenes is presented along with
characterisation of their redox properties.
as a selenation agent for the synthesis of a wide range of
Introduction
selenoamides and selenoaldehydes by simple oxygen/selenium
exchange or reaction with ArCN followed by hydrolysis as well
as for the synthesis of a variety of P–Se heterocycles.13–16 We
have recently applied WR to the syntheses of symmetrical and
unsymmetrical (E)-olefins from the corresponding ketones or
aldehydes.17 Furthermore, deoxygenation of sulfoxides with WR
gives the corresponding sulfides under mild conditions.18 As part
of our interest in exploring the reactivity of WR towards different
organic substrates, herein we report two efficient routes for the
synthesis of new 2,5-diarylselenophenes by reaction of WR with
1,4-diarylbutane-1,4-diones or WR/methanol with arylacetylene
under mild conditions. The first representative sample of the
X-ray crystallographic structure of 2,5-diarylselenophenes and
electrochemical properties were also investigated.
Selenophenes play an important role in the chemistry
of organochalcogen compounds.1–3 The first synthesis of
selenophene was reported in 1885 by Paal, who obtained 2,5-
dimethylselenophene by heating hexane-2,5-dione with phospho-
rus pentaselenide.4 Since then, several selenium analogues of fu-
rans and thiophenes have been prepared by replacing the oxygen or
the sulfur atom, respectively, in order to improve the bioactivity of
these compounds. Some examples of the synthesis of selenophene
and its 2,5-substituted derivatives include (1) the nucleophilic
addition of hydrogen selenide or sodium selenide to diacetylenes5–7
to give 2,5-diphenylselenophenes in low yield in the presence of
Ag+ or Cu+; (2) the reaction of complicated reduced systems such
as elemental selenium/N2H4·H2O/KOH/H2O/DMSO, elemen-
tal selenium/NaBH4/EtOH/DMF, elemental selenium/NaBH4/
KOH/H2O/DMF or elemental selenium/SnCl2/KOH/H2O/
DMSO with diphenyldiacetylene;8 (3) the electrophilic cycliza-
tion of selenoenynes or the palladium-catalyzed Suzuki cross-
coupling of 2-haloselenophenes,9,10 and (4) the synthesis of 2,5-
diarylselenophenes by thermolysis of 4-arylselenadiazoles with
arylacetylenes. However, the latter method requires a large excess
of arylacetylene (up to 10 equiv.) and has low selectivity (a mixture
of three different symmetrical and unsymmetric selenophenes) and
low yield.11
Results and discussion
Synthesis of 2,5-diarylselenophenes 2a–g
Preparation of 1,4-diarylbutane-1,4-diones 1b–g was straightfor-
ward via one-pot Friedel–Crafts acylation from succinyl chloride
with two equivalents of alkyl-substituted aromatics in the presence
of anhydrous aluminium chloride at 0 ◦C to room temperature in
high yields (Scheme 1). However, we were unable to synthesize ana-
logues of 1,4-diarylbutane-1,4-diones with electron-withdrawing
groups such as NO2, +N(CH3)3, COOH, C(O)R and CF3, as
2,4-Bis(phenyl)-1,3-diselenadiphosphetane-2,4-diselenide
[PhP(Se)(m-Se)]2, known as Woollins’ reagent, WR, is a sele-
nium counterpart of the well-known Lawesson’s reagent, [p-
MeOC6H4P(S)(m-S)]2. Compared with other selenium reagents,
WR has less unpleasant chemical properties, and is readily
prepared and safely handled in air.12 WR has been applied
aEaSTCHEM, School of Chemistry, University of St Andrews, Fife, UK
KY16 9ST. E-mail: jdw3@st-and.ac.uk; Tel: (+44)-1334-463384
bEaSTCHEM, School of Chemistry, University of Edinburgh, The King’
Buildings, West Mains Road, Edinburgh, UK EH9 3JJ
† Electronic supplementary information (ESI) available: CCDC reference
number 657441. For crystallographic data in CIF or other electronic
format see DOI: 10.1039/b924986a
Scheme 1 The preparation of 1,4-diarylbutane-1,4-diones 1b–g by
Friedel–Crafts acylation.
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Friedel–Crafts acylation does not occur when these groups are
on the aromatic ring.
Preparation of 2,5-diarylselenophenes 2a–g were carried out
by a typical procedure: an equimolar mixture of WR and 1,4-
diarylbutane-1,4-dione was refluxed in toluene for 20 h. During
this period, the red suspension gradually disappeared and the pale
yellow solution was formed with precipitation of small amounts
of grey elemental selenium. Upon cooling to room temperature
the solution was passed through a silica gel column (toluene
as eluent). The fractions containing the product were combined
and concentrated in vacuum to give the air and moisture stable
pale yellow solids of 2a–g in excellent isolated yields (83–99%)
(Scheme 2).
Scheme 3 Preparation of 2,5-diarylselenophenes 2a and 2b from pheny-
lacetylene or 4-ethynyltoluene.
It is well known that WR is an efficient oxygen/selenium
exchange reagent.12–15 Mechanistically, we propose that the 1,4-
dioxo groups are initially converted to 1,4-diselenones, a known
replacement of carbonyl by selenone. The latter subsequently
undergoes in situ cyclisation and elimination of H2Se to give a more
stable five-membered ring selenophene (Scheme 2). Formation of
by-product (PhPO2)3 trimer was confirmed in the crude mixture
by 31P NMR.18
In an alternative approach, a methanolic suspension of WR
was stirred at room temperature for 2 h, then at 50 ◦C for 1 h. The
red suspension became a yellow solution accompanied by trace
amount of grey precipitate of elemental selenium. After removal
of the trace amount of selenium by filtration, the filtrate was
evaporated in vacuum and the residue was dissolved in toluene.
Equimolar amounts of phenylacetylene or 4-ethynyltoluene were
added and the mixture was refluxed for 10 h. The mixture was
cooled to room temperature and purified by silica gel chromatog-
raphy (toluene as eluent) to give 2a and 2b in good yields (70
and 72% isolated yields, respectively) after recrystallization from
dichloromethane–n-hexane. The use of excess of phenylacetylene
or 4-ethynyltoluene (two or three equivalents) did not improve the
yields of 2a and 2b. However, longer refluxing (up to 48 h) did
enhance the yields of 2a and 2b to 75 and 80%.
822 Hz) ppm and dSe = 221.3 (J(P–Se) = 460 Hz) and 95.5 (J(P
=
=
Se)
822 Hz) ppm].
Although 2a and 2b are known compounds,9–11 we have found
no published 77Se NMR and X-ray crystal structure data on
2,5-diarylselenophenes, and thus describe the first example here
(Fig. 1). All compounds were ascertained by accurate mass mea-
surement, IR, MS and solution multi-nuclear NMR spectroscopy.
2a–g showed the anticipated [M]+ peak in their mass spectra. Their
accurate mass measurements were satisfactory. The 77Se NMR
spectra show single peaks in the range of 569.0–576.9 ppm for
2a–g. These values are considerably lower than that of nonsub-
stituted selenophene (605 ppm),19 but much higher than that of
double fused ring selenophene (549 ppm).20 Recrystallisation from
chloromethane–n-hexane gave a colourless crystal of 2b. The X-
ray structure of 2b shows the expected five membered (C–C–Se–C–
C) ring skeleton. The bond lengths and angles in 2b are as expected
compared with other substituted selenophenes with the presence
˚
of relatively long Se–C bonds (ca. 1.92–1.94 A expected for a
single C–Se bond),20–22 indicating that the extent of delocalisation
is limited.
Electrochemical studies
The reaction pathway (Scheme 3) involves the generation
of O-methyl Se-hydrogen phenylphosphonodiselenoate 3, which
reacts with phenylacetylene or 4-ethynyltoluene to afford the
corresponding 2,5-diarylselenophenes 2a and 2b and byproduct 4.
The presence of byproduct 4 in the crude mixture was confirmed
CV’s of 2a and the nitrogen substituted analogue 2,5-diphenyl–3,4-
diazaselenophene (dpas)23 are shown in Fig. 2 and 3, respectively.
2a shows two successive one-electron oxidation processes with
peak oxidation potentials of +0.82 and +0.98 V vs. Fc/Fc+
whilst the CV of dpas does not show a distinct oxidation peak,
by 31P and 77Se NMR spectra [dP = 81.2 (J(P–Se) = 460 Hz, J(P
=
=
Se)
Scheme 2 Preparation of 2,5-diarylselenophenes 2a–g from the selenation of the corresponding 1,4-diarylbutane-1,4-diones 1a–g.
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1–10 mM concentration range. Comparison of the fluorescence of
this film, when dissolved in ethanol, showed no change compared
with 2a, with both exhibiting maximum peak excitation and
emissions wavelengths of 326 and 370 nm respectively and a
(0,0) transition at 348 nm. This suggests that the electrooxidation
of 2a yields an insoluble product which retains the fluorescence
properties of 2a. In contrast, upon electrooxidation, dpas formed
a non-conducting layer of material (shown by the loss of electrode
activity on successive CV cycling) on the electrode surface; both
dpas and the formed film showed dramatically weaker fluorescence
emission, with dpas peak excitation and emission wavelengths in
ethanol at 279 and 345 nm, respectively, and a (0,0) transition
around 315 nm.
˚
Fig. 1 X-Ray crystal structure of 2b, selected bond lengths (A)
and angles (◦) Se(1)–C(1) 1.877(3), C(3)–C(4) 1.365(5), Se(1)–C(4)
1.879(3), C(1)–C(5) 1.473(5), C(1)–C(2) 1.372(5), C(4)–C(11) 1.478(5),
C(2)-C(3) 1.410(5), C(1)–Se(1)–C(4) 87.7(8), C(4)–C(3)–C(2) 116.1(3),
C(2)–C(1)–Se(1) 110.2(2), C(3)–C(4)–Se(1) 110.2(3), C(3)–C(2)–C(1)
115.7(3).
The calculated peak oxidation potentials for the first one
electron oxidations were +0.80 0.03 V and +1.54 0.03 V
vs. Fc/Fc+ for 2a and dpas, respectively. These are in good
agreement with that measured for 2a and the centre of the broad
oxidation peak observed for dpas. Fig. 4 shows the electron spin
density maps for the resulting radical cations of both species; as
expected, the regions of highest electron spin density (blue) show
the largest change in electron density on oxidation and therefore
are also the regions of most positive cationic charge density in the
radical cation. It can be seen that for both diphenylselenophenes
that the majority of the electron spin density is at the 2 and
5 positions of the central selenophene ring and not delocalised
across the peripheral benzene rings. Given that the coupling
of such heteroaromatic radical cations is thought to occur at
peripheral sites of high electron spin density,24 this predominantly
central location of the electron spin density at sites inaccessible to
coupling could explain the absence of extensive polymerisation on
electrooxidation observed with other heteroaromatics.25
Fig. 2 CV of 2,5-diphenylselenophene (2a) (1 mM) in acetonitrile and
background electrolyte. Sweep rate = 100 mV s-1.
Fig. 4 Spin density distribution mapped onto a 99% electron density
isosurface for the planar radical cations of (a) 2a and (b) dpas. The
colouring is schematic as follows: blue indicates a positive electron spin
density (0.004) whilst red is negative (-0.001).
Conclusions
In summary, the synthesis of 2,5-diarylselenophenes 2a–g has been
carried out by direct selenation of 1,4-diarylbutane-1,4-diones by
WR. The same diarylselenophenes can also be obtained from the
reaction of arylacetylene and the methanolised intermediate of
WR. Due to the limited availability of arylacetylene analogues, we
only synthesised two examples; 2a and 2b. Representative 2a shows
significant redox, fluorescence and thin conducting film formation
properties, which indicate that 2,5-diarylselenophene systems may
be of interest for materials applications.
Fig. 3 CV of 2,5-diphenyl–3,4-diazaselenophene (dpas) (1.1 mM) in
acetonitrile and background electrolyte. Sweep rate = 100 mV s-1.
but shows a broad one electron oxidation feature between +1.4
and +1.6 V vs. Fc/Fc+. The first oxidation of each species is
chemically irreversible. This behavior is often seen for 5-membered
heterocyclic systems such as pyrroles, thiophenes and furans; in
these cases this is attributed to monomer radical cation coupling
following oxidation to give (typically conducting) polymeric
products.24 Although CV cycling to potentials past the first
oxidation peak gave a thin conducting layer from 2a, successive
cycling showed no evidence for progressive film growth in the
Experimental
1,4-Diphenylbutane-1,4-dione (1a) was purchased from
Sigma-Aldrich. Other reagents or solvents, purchased from
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Sigma-Aldrich or Alfa Aesar were used without further
purification. Unless otherwise stated, all reactions were carried
out under an oxygen-free nitrogen atmosphere using pre-
dried solvents and standard Schlenk techniques; subsequent
chromatographic and work up procedures were performed under
diethyl ether–toluene and diethyl ether extracts were washed with
water (30 cm3 ¥ 3) and brine (30 cm3). The combined extracts were
dried over K2CO3 (2.0 g) overnight and filtered. The filtrate was
evaporated in vacuo. The residue was dissolved in dichloromethane
and purified by column chromatography (silica gel, 1 : 9 ethyl
acetate–dichloromethane as eluent) to give the expected products
1b–g.
1
aerobic conditions. H (270 Hz), 13C (67.9 Hz), 31P (109 Hz) and
77Se (51.4 Hz referenced to external Me2Se) NMR spectra were
recorded at 25 ◦C (unless stated otherwise) on a JEOL GSX 270.
IR spectra were recorded as KBr pellets in the range of 4000–
250 cm-1 on a Perkin-Elmer 2000 FTIR/Raman spectrometer.
Microanalysis was performed by the University of St Andrews
microanalysis service. Mass spectrometry was performed by the
EPSRC National Mass Spectrometry Service Centre, Swansea
(U.K.) and the University of St Andrews Mass Spectrometry
Service.
1,4-Di-p-tolylbutane-1,4-dione (1b). 4.53 g as a white solid in
92% yield. Selected IR (KBr, cm-1): 2963(m), 2929(w), 1680(s),
1602(s), 1565(m), 1399(m), 1358(m), 1230(s), 1170(m), 832(s),
557(s). 1H NMR (CDCl3, d), 7.92 (d, J(H,H) = 8.4 Hz, 4H, ArH),
7.25 (d, J(H,H) = 8.4 Hz, 4H, ArH), 3.41 (s, 4H, CH2), 2.29 (s,
6H, CH3) ppm. 13C NMR (CDCl3, d), 198.5 (C O), 144.0, 134.4,
=
129.4, 128.2, 32.6, 21.7 ppm. MS (ES+, m/z): 289 [M + Na]+. Anal.
calcd. for C18H18O2: C, 81.17; H, 6.81. Found: C, 81.49; H, 7.00.
Electrochemistry
1,4-Bis(4-ethylphenyl)butane-1,4-dione (1c). 5.05 g as a white
solid in 93% yield. Selected IR (KBr, cm-1): 2965(m), 2931(w),
1680(s), 1604(s), 1565(m), 1397(m), 1358(m), 1228(s), 1170(m),
993(s), 832(s), 558(s), 497(m). 1H NMR (CD2Cl2, d), 7.97 (d,
J(H,H) = 7.7 Hz, 4H, ArH), 7.32 (d, J(H,H) = 7.7 Hz, 4H, ArH),
3.40 (s, 4H, CH2), 2.72 (q, J(H,H) = 7.4 Hz, 4H, CH2), 1.28 (t,
Electrochemical studies were carried out using a modular po-
tentiostat/galvanostat with combined waveform generator and
voltage sources (PGSTAT12, Autolab), with PC control, data
collection and analysis carried out using the General Purpose
Electrochemical System (GPES, Autolab) software. The working
electrode was a platinum rotating disc electrode, RDE, (Oxford
Electrodes Ltd.), disc area 0.387 cm2. A 2 cm2 platinum gauze was
used as the counter electrode. The reference electrode (Bioanalyt-
ical Systems Inc.) consisted of a silver wire dipped in a 0.01 M
solution of AgClO4 in background electrolyte in a glass body with
a VYCOR frit.
Electrochemical calculations: structures were calculated using
the Gaussian 03 program26using uB3LYP/6-311+G(d,p), with
acetonitrile solvation modeled with the SCRF method. It has
previously been shown that accurate calculation of absolute values
of experimental indole oxidation potentials is possible to within
a few tens of millivolts, making this suitable as a reference redox
reaction.25c Calculation of the free energy of the reaction 4+∑ +
In → 4 + In+∑ gives the standard reduction potential of 4+∑/4
relative to the indole (In) redox couple In+∑/In. This can then be
converted to a calculated peak oxidation potential on any reference
scale by using the experimentally measured value of the indole
peak oxidation potential, if reactants and products have similar
diffusion coefficients in solution, which is usually a reasonable
assumption for extended aromatics.26c The error limits quoted are
those determined from comparison of the calculated and observed
redox potentials of a range of redox-active aromatics.25c
J(H,H) = 7.4 Hz, 6H, CH3) ppm. 13C NMR (CD2Cl2, d), 198.2
+
=
(C O), 150.2, 134.8, 129.3, 128.1, 32.5, 29.0, 15.2 ppm. MS (ES ,
m/z): 317 [M + Na]+. Anal. calcd. for C20H22O2: C, 81.60; H, 7.53.
Found: C, 81.30; H, 7.85.
1,4-Bis(4-propylphenyl)butane-1,4-dione (1d). 5.20 g as a white
solid in 88% yield. Selected IR (KBr, cm-1): 2955(m), 2868(w),
1675(s), 1604(s), 1315(m), 1174(s), 1002(s), 785(s). 1H NMR
(CD2Cl2, d), 7.95 (d, J(H,H) = 8.3 Hz, 4H, ArH), 7.30 (d,
J(H,H) = 8.3 Hz, 4H, ArH), 3.40 (s, 4H, CH2), 2.66 (t, J(H,H) =
7.5 Hz, 4H, CH2), 1.75-1.61 (m, 4H, CH2), 0.96 (t, J(H,H) =
13
=
7.5 Hz, 6H, CH3) ppm. C NMR (CD2Cl2, d), 198.2 (C O),
148.6, 134.8, 128.7, 128.2, 38.0, 32.5, 24.4, 13.7 ppm. MS (ES+,
m/z): 345 [M + Na]+. Anal. calcd. for C22H26O2: C, 81.95; H, 8.12.
Found: C, 82.20; H, 8.32.
1,4-Bis(4-butylphenyl)butane-1,4-dione (1e). 5.61 g as a white
solid in 87% yield. Selected IR (KBr, cm-1): 2956(m), 2859(w),
1673(s), 1605(s), 1324(m), 1178(s), 1006(s), 787(m). 1H NMR
(CD2Cl2, d), 7.95 (d, J(H,H) = 8.0 Hz, 4H, ArH), 7.31 (d,
J(H,H) = 8.0 Hz, 4H, ArH), 3.40 (s, 4H, CH2), 2.66 (t, J(H,H) =
7.4 Hz, 4H, CH2), 1.66-1.58 (m, 4H, CH2), 1.42-1.33 (m, 4H, CH2),
0.95 (t, J(H,H) = 7.4 Hz, 6H, CH3) ppm. 13C NMR (CD2Cl2, d),
=
198.2 (C O), 148.9, 134.7, 128.7, 128.2, 35.7, 33.4, 32.5, 22.4,
13.8 ppm. MS (ES+, m/z): 373 [M + Na]+. Anal. calcd. for
The general procedure for the preparation of
1,4-diarylbutane-1,4-dione (1b–g)
C24H30O2: C, 82.24; H, 8.63. Found: C, 82.66; H, 8.52.
Alkyl-substituted benzene (15 cm3) and anhydrous aluminium
chloride (5.0 g, 37 mmol) were placed in a three-necked flask fitted
with a thermometer, a dropping funnel and a water condenser,
while stirring under N2 with a magnetic stirrer. The mixture was
cooled to 0 ◦C and succinyl chloride (2.7 g, 18.5 mmol) was added
dropwise within 30 min. The ice bath was removed and the mixture
was allowed to stir at room temperature for one hour. Then, the
mixture was poured slowly onto a stirring solution of concentrated
hydrochloric acid (10%, 20 cm3). The contents were transferred to
a separation funnel with the help of diethyl ether (30 cm3). The
1,4-Bis(4-sec-butylphenyl)butane-1,4-dione (1f). 5.50 g as a
white solid in 85% yield. Selected IR (KBr, cm-1): 2963(m),
2920(w), 1675(s), 1604(s), 1362(m), 1228(s), 1181(m), 992(s),
1
835(s), 570(s). H NMR (CD2Cl2, d), 7.96 (d, J(H,H) = 8.3 Hz,
4H, ArH), 7.30 (d, J(H,H) = 8.3 Hz, 4H, ArH), 3.40 (s, 4H, CH2),
2.75-2.62 (m, 2H, CH), 1.68-1.60 (m, 4H, CH2), 1.25 (d, J(H,H) =
6.9 Hz, 6H, CH3), 0.82 (t, J(H,H) = 6.9 Hz, 6H, CH3) ppm. 13
C
=
NMR (CD2Cl2, d), 198.3 (C O), 153.6, 134.9, 128.2, 127.8, 41.9,
32.5, 31.0, 21.4, 12.0 ppm. MS (ES+, m/z): 373 [M + Na]+. Anal.
calcd. for C24H30O2: C, 82.24; H, 8.63; Found: C, 82.14; H, 9.15.
1658 | Org. Biomol. Chem., 2010, 8, 1655–1660
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1,4-Bis(4-pentylphenyl)butane-1,4-dione (1g). 5.20 g as a white
solid in 75% yield. Selected IR (KBr, cm-1): 2922(m), 2857(w),
1671(s), 1604(s), 1411(s), 1324(s), 1177(s), 1006(s), 786(s), 561(m),
573.3 ppm. MS (EI+, m/z): 312 [M]+. Accurate mass measurement
(EIMS): 312.0417, calculated mass for C18H16Se: 312.0421.
2,5-Bis(4-ethylphenyl)selenophene (2c). Pale yellow solid
(330 mg, 97% yield). IR (KBr, cm-1), 1503(m), 1460(m), 1121(m),
1022(m), 830(s), 790(s). 1H NMR (CD2Cl2, d), 7.67 (d, J(H,H) =
1
524(m). H NMR (CD2Cl2, d), 7.95 (d, J(H,H) = 8.3 Hz, 4H,
ArH), 7.30 (d, J(H,H) = 8.3 Hz, 4H, ArH), 3.40 (s, 4H, CH2),
2.68 (t, J(H,H) = 8.0 Hz, 4H, CH2), 1.71-1.62 (m, 4H, CH2), 1.37-
=
8.0 Hz, 2H, CH CH), 7.41 (d, J(H,H) = 8.3 Hz, 4H, ArH), 7.23
1.34 (m, 8H, CH2), 0.92 (t, J(H,H) = 8.0 Hz, 6H, CH3) ppm. 13
C
(d, J(H,H) = 8.3 Hz, 4H, ArH), 2.66 (q, J(H,H) = 7.4 Hz, 4H,
CH2), 1.25 (t, J(H,H) = 7.4 Hz, 6H, CH3) ppm. 13C NMR (CD2Cl2,
d), 153.3, 149.3, 142.1, 128.5, 125.9, 123.6, 28.7, 15.5 ppm.
77Se NMR (CD2Cl2, d), 569.4 ppm. MS (EI+, m/z): 340 [M]+.
Accurate mass measurement (EIMS): 336.0752, calculated mass
for C20H2076Se: 336.0774.
=
NMR (CD2Cl2, d), 198.2 (C O), 148.9, 134.7, 128.7, 128.2, 36.0,
32.5, 31.6, 30.9, 22.6, 13.9 ppm. MS (ES+, m/z): 401 [M + Na]+.
Anal. calcd. for C26H34O2: C, 82.49; H, 9.05. Found: C, 82.59; H,
9.43.
The general procedure for the synthesis of 2,5-diarylselenophenes
(2a–g) from the selenation of 1,4-diarylbutane-1,4-dione
2,5-Bis(4-propylphenyl)selenophene (2d). Pale yellow paste
(332 mg, 90% yield). IR (KBr, cm-1), 1503(m), 1462(m), 1022(m),
1,4-Diarylbutane-1,4-dione (1.0 mmol) and WR (1.0 mmol) in
dry toluene (10 cm3) was refluxed for 20 h. The red suspension
gradually disappeared and a pale yellow solution formed along
with small amount of elemental selenium precipitate. Upon
cooling to room temperature the mixture was purified by silica
gel column chromatography (toluene as eluent). The fractions
containing the product were combined and the solvent was
removed in vacuo to give the target product 2a–g.
1
790(s). H NMR (CD2Cl2, d), 7.67 (d, J(H,H) = 8.0 Hz, 2H,
=
CH CH), 7.49 (d, J(H,H) = 8.3 Hz, 4H, ArH), 7.23 (m, J(H,H) =
8.3 Hz, 4H, ArH), 2.60 (t, J(H,H) = 8.0 Hz, 4H, CH2), 1.71-1.63
(m, 4H, CH2), 0.97 (t, J(H,H) = 8.0 Hz, 6H, CH3) ppm. 13C NMR
(CD2Cl2, d), 153.3, 142.2, 133.8, 128.9, 125.7, 123.6, 37.7, 24.7,
13.7 ppm. 77Se NMR (CD2Cl2, d), 569.1 ppm. MS (EI+, m/z): 368
[M]+, 304 [M - C4H16]+, 275 [M - C4H16 - C2H5]+. Accurate mass
measurement (EIMS): 364.0902, calculated mass for C22H2476Se:
364.1062.
The synthesis of 2,5-diarylselenophenes 2a and 2b from the
reaction of WR/methanol with arylacetylene
2,5-Bis(4-butylphenyl)selenophene (2e). Pale yellow paste
(350 mg, 83% yield). IR (KBr, cm-1), 1503(m), 1462(m), 1022(m),
831(m), 780(s). 1H NMR (CD2Cl2, d), 7.68 (d, J(H,H) = 8.0 Hz,
A red suspension of WR (1.0 mmol) in methanol (20 cm3) was
stirred at room temperature for 2 h, then at 50 ◦C for 1 h. During
this period the red suspension gradually disappeared and a yellow
solution formed along with trace amount of elemental selenium
precipitate. The mixture was filtered to remove the trace amount
of elemental selenium and the filtrate was evaporated in vacuum
to give O-methyl Se-hydrogen phenylphosphonodiselenoate (3) as
a white solid in 99% yield. To the solution of 3 in dry toluene
(10 cm3), phenylacetylene or 4-ethynyltoluene (2.0 mmol) was
added and the mixture was refluxed for 20 h. The mixture was
cooled to room temperature and purified by column chromatog-
raphy (silica gel, toluene as eluent) to afford 2a and 2b.
=
2H, CH CH), 7.50 (d, J(H,H) = 8.3 Hz, 4H, ArH), 7.23 (m,
J(H,H) = 8.3 Hz, 4H, ArH), 2.65 (t, J(H,H) = 8.0 Hz, 4H,
CH2), 1.71-1.62 (m, 4H, CH2), 1.47-1.34 (m, 4H, CH2), 0.97 (t,
J(H,H) = 8.0 Hz, 6H, CH3) ppm. 13C NMR (CD2Cl2, d), 153.3,
142.7, 133.8, 129.0, 125.8, 123.6, 35.5, 33.7, 22.5, 13.9 ppm. 77Se
NMR (CD2Cl2, d), 569.1 ppm. MS (EI+, m/z): 396 [M]+, 332 [M -
C4H16]+, 289 [M - C4H16 - C3H7]+. Accurate mass measurement
(EIMS): 392.1377, calculated mass for C24H2876Se: 392.1375.
2,5-Bis(4-sec-butylphenyl)selenophene (2f). Pale yellow paste
(390 mg, 98% yield). IR (KBr, cm-1), 1503(m), 1462(m), 1022(m),
1
790(s). H NMR (CD2Cl2, d), 7.67 (d, J(H,H) = 8.0 Hz, 2H,
2,5-Diphenylselenophene (2a). Pale yellow solid, 280 mg (99%
yield) fromtheselenation of1,4-diphenylbutane-1,4-dione; 199mg
(70% yield) from the reaction of WR/methanol with pheny-
lacetylene. IR (KBr, cm-1), 1480 (m), 1460(m), 1447(m), 1262(m),
1024(m), 796(m), 756(s), 690(s), 672(m). 1H NMR (CDCl3, d), 7.76
=
CH CH), 7.49 (d, J(H,H) = 8.3 Hz, 4H, ArH), 7.23 (m, J(H,H) =
8.3 Hz, 4H, ArH), 2.64 (d, J(H,H) = 7.2 Hz, 6H, CH3), 1.64-1.52
(m, 2H, CH), 1.26-1.23 (m, 4H, CH2), 0.97 (t, J(H,H) = 7.2 Hz,
6H, CH3) ppm. 13C NMR (CD2Cl2, d), 153.3, 147.5, 134.0, 127.7,
125.8, 123.6, 41.5, 31.1, 21.6, 12.1 ppm. 77Se NMR (CD2Cl2, d),
569.1 ppm. 77Se NMR (CD2Cl2, d), 569.2 ppm. MS (EI+, m/z): 396
[M]+. Accurate mass measurement (EIMS): 396.1356, calculated
mass for C24H28Se: 396.1357.
=
(d, J(H,H) = 7.4 Hz, 2H, CH CH), 7.58 (d, J(H,H) = 7.2 Hz, 4H,
ArH), 7.40 (m, J(H,H) = 7.2 Hz, 4H, ArH), 7.29 (m, J(H,H) =
7.2 Hz, 2H, ArH) ppm. 13C NMR (CDCl3, d), 150.0, 136.5, 129.0,
127.7, 127.4, 126.2, 126.1 ppm. 77Se NMR (CDCl3, d), 576.9 ppm.
MS (EI+, m/z): 284 [M]+. Accurate mass measurement (EIMS):
284.0104, calculated mass for C16H12Se: 284.0109.
2,5-Bis(4-pentylphenyl)selenophene (2g). Pale yellow paste
(360 mg, 85% yield). IR (KBr, cm-1), 1503(m), 1462(m), 1122(m),
1025(m), 832(m), 793(s). 1H NMR (CD2Cl2, d), 7.66 (d, J(H,H) =
2,5-Di-p-toluoylselenophene (2b). Greenish yellow solid,
307 mg (99% yield) from the selenation of 1,4-di-p-toluoylbutane-
1,4-dione; 225 mg (72% yield) from the reaction of WR/methanol
with 4-ethynyltoluene. IR (KBr, cm-1), 1503 (m), 1461 (w), 1122
=
8.3 Hz, 2H, CH CH), 7.49 (d, J(H,H) = 8.3 Hz, 4H, ArH), 7.24
(m, J(H,H) = 8.3 Hz, 4H, ArH), 2.63 (t, J(H,H) = 7.5 Hz, 4H,
CH2), 1.66-1.61 (m, 4H, CH2), 1.37-1.33 (m, 8H, CH2), 0.92 (t,
J(H,H) = 7.5 Hz, 6H, CH3) ppm. 13C NMR (CD2Cl2, d), 153.3,
149.3, 142.5, 128.8, 125.8, 123.6, 35.7, 31.6, 31.2, 22.6, 13.9 ppm.
77Se NMR (CD2Cl2, d), 569.0 ppm. MS (EI+, m/z): 424 [M]+.
Accurate mass measurement (EIMS): 420.1691, calculated mass
for C26H3276Se: 420.1714.
1
(w), 1021 (w), 821 (m), 797 (vs), 541 (w), 498 (m), 449 (m). H
=
NMR (CDCl3, d), 7.63 (d, J(H,H) = 7.9 Hz, 2H, CH CH), 7.44
(d, J(H,H) = 7.9 Hz, 4H, ArH), 7.17 (d, J(H,H) = 7.9 Hz, 4H,
ArH), 2.28 (s, 6H, CH3) ppm. 13C NMR (CDCl3, d), 149.7, 136.5,
133.8, 129.4, 126.0, 125.7, 123.7, 21.3 ppm. 77Se NMR (CDCl3, d),
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O-Methyl Se-hydrogen phenylphosphonodiselenoate (3). 1H
NMR (CD2Cl2, d), 7.92 (m, 2H, ArH), 7.49 (m, 1H, ArH), 7.33 (m,
2H, ArH), 3.78 (d, 3J(P,C) = 16.1 Hz, 3H, OCH3) ppm. 13C NMR
12 J. C. Fitzmaurice, D. J. Williams, P. T. Wood and J. D. Woollins, J. Chem.
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5251.
1
3
(CD2Cl2, d), 131.4 (d, J(P,C) = 98.6 Hz), 130.3 (d, J(P,C) =
11.4 Hz), 128.5 (d, 2J(P,C) = 31.1 Hz), 128.4, 53.5 (d, (d, 2J(P,C) =
54.0 Hz) ppm. 31P NMR (CD2Cl2, d), 84.31 (s, J(P–Se) = 441 Hz,
J(P Se) = 831 Hz) ppm. 77Se NMR (CD2Cl2, d), 241.41 (d, J(P–
=
Se) = 441 Hz), -111.52 (d, J(P–Se) = 831 Hz) ppm. MS (ESI+,
m/z): 321 [M + Na].
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Crystallographic data for 2b. C18H16Se, M = 311.27, or-
thorhombic, space group Pbca, a = 14.556(2), b = 5.8313(9), c =
3
-3
˚
˚
33.051(5) A, U = 2805.4(8) A , Z = 8, Dc = 1.474 Mg m , m =
2.660 mm-1, 16 322 reflections, 3107 unique (Rint = 0.0688); R1 =
0.0560, wR2 = 0.1337. X-Ray crystal data were collected at 93 K
by using a Rigaku MM007 high brilliance RA generator/confocal
optics and Mercury CCD system. Intensities were corrected
for Lorentz-polarisation and for absorption. The structure was
solved by direct methods. Hydrogen atoms bound to carbon were
idealised. Structural refinements were obtained with full-matrix
least-squares based on F2 by using the program SHELXTL.27
CCDC 657441 contains the supplementary crystallographic data
for this paper. These data are available in the ESI.†
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Acknowledgements
The authors are thankful to the Engineering and Physical Science
Research Council (EPSRC, U.K.) for financial support. This
work has made use of the resources provided by the EaStCHEM
Research Computing Facility (http://www.eastchem.ac.uk/rcf).
This facility is partially supported by the eDIKT initiative
(http://www.edikt.org). All authors are part of the EaStCHEM
joint Chemistry Research School; we acknowledge the financial
support of the Scottish Funding Council.
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1660 | Org. Biomol. Chem., 2010, 8, 1655–1660
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