Synthesis and structure of 1-methyl-2,6-bis(electron-withdrawing group)-substituted selenabenzenes

Article abstract of DOI:10.1039/b008562f

The synthesis and structure of 1-methyl-2,6-bis(electron-withdrawing group)-substituted selenabenzenes from dihalides was presented. The monocyclic selenabenzene derivatives stabilized by two electron withdrawing groups at the 2- and 6-positions were isolated. The x-ray structural analysis of the dibenzoyl derivatives showed that the six-membered ring containing a selenium atom is planar and the structure of selenium atom is tetrahedral with four sp³ hybridized orbitals.

Full text of DOI:10.1039/b008562f

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Synthesis and structure of 1-methyl-2,6-bis(electron-withdrawing
group)-substituted selenabenzenes
Eiji Honda,a Tatsunori Iwamura,a Shin-ichi Watanabe,a Tadashi Kataoka,*a Osamu Muraokab
and Genzoh Tanabeb
1
a Gifu Pharmaceutical University, 6-1 Mitahora-higashi 5-chome, Gifu 502-8585, Japan
b Kinki University, Faculty of Pharmaceutical Sciences, 3-4-1, Kowakae, Higashi-osaka,
Osaka 577-0818, Japan
Received (in Cambridge, UK) 24th October 2000, Accepted 11th January 2001
First published as an Advance Article on the web 6th February 2001
Selenabenzenes 12a–c with two electron-withdrawing groups (EWGs) at the 2- and 6-positions were synthesized
from dihalides 1a, 1b and 1cЈ via seven steps and isolated as stable compounds at room temperature. According to
X-ray structural analysis of the dibenzoyl derivative 12c, the six-membered ring containing a selenium atom is
almost planar and the structure of the selenium atom is tetrahedral with four sp3 hybridized orbitals.
The chemistry of heterobenzenes is one of the interesting
research fields in heterocyclic chemistry and has recently been
the focus of attention. Heterobenzenes containing a group 15
element have been widely studied and well documented,1 and
very recently, silabenzenes containing a group 14 element were
prepared by Tokitoh et al.2 Thiabenzenes have been studied for
a long time and many papers reporting these studies have been
published.3 In contrast, selenabenzenes were generated by
proton-abstraction of the selenonium salts in the 1970s.4 After
more than fifteen years cyano-stabilized selenanaphthalenes
were synthesized5 and their reactions were studied. Successful
synthesis of monocyclic selenabenzenes was required before
their intrinsic properties would be studied. Monocyclic selena-
benzene derivatives with one electron-withdrawing group
(EWG) could not be isolated as stable compounds at room
temperature but their generation was confirmed at Ϫ30 ЊC by
NMR spectroscopy,6 whereas the corresponding thiabenzenes
have been isolated as stable crystals.7 We recently succeeded in
the isolation of monocyclic selenabenzene derivatives stabilized
by two EWGs at the 2- and 6-positions.8 This paper describes
the details of the synthesis and structure of monocyclic selena-
benzenes having two EWGs such as ester or benzoyl groups.
which are key starting materials for the synthesis of selena-
benzenes, were synthesized by ring closure reaction of dihalides
1a–c and 1cЈ with metal selenides (Scheme 1, Table 1).
The reaction of dibromides 1a,b with sodium selenide9 at
room temperature gave the desired cyclic compounds 2a,b. The
reaction of dibromide 1b with sodium selenide under gentle
reflux in ethanol gave only dehalogenated compound 3b (78%),
which would be formed by single electron reduction with
sodium selenide or by the nucleophilic attack of sodium
selenide on a halogen atom10 (entry 3). In the case of the
benzoyl derivatives the reduction product 3c was formed even
from the reactions of both the bromide 1c and the chloride 1cЈ
at 0 ЊC (entries 4 and 5). Therefore, lithium selenide,11 having a
higher oxidation–reduction potential than sodium selenide, was
used. Although the reaction of the bromide 1c with lithium
selenide at room temperature formed 3c in 54% yield, the reac-
tion of the chloride 1cЈ at 0 ЊC afforded selenane 2c in moderate
yield and by-products 3c and 4 in low yields (entries 6 and 7).
Selenanes 2a–c consisted of two isomers, cis-2a–c and trans-
2a–c, and the isomers could be separated by PTLC on silica
gel. The stereostructure of 2a was determined by 1H-NMR
spectroscopy (Fig. 1). Two coupling constants, 2 and 12 Hz, due
to H(2,6) of cis-2a are typical axial–equatorial and axial–axial
coupling constants, respectively. Therefore, the two EWGs at
the 2- and 6-positions are located in equatorial positions and
the cis isomer takes the chair form shown in Fig. 1. On the other
hand, if trans-2a takes a chair form or a boat form, the two
protons at the 2- and 6-positions are not equivalent and should
Results and discussion
Synthesis of selenabenzenes 12a–c
Selenanes 2a–c having two EWGs at the 2- and 6-positions,
Scheme 1 Reagents and conditions: (i), Na2Se or Li2Se (1 equiv.), EtOH, 0.5 h; (ii), MCPBA (1.1 equiv.), CH2Cl2, 3 h; (iii), PPSE, ClCH2CH2Cl,
reflux, 20 h.
DOI: 10.1039/b008562f
J. Chem. Soc., Perkin Trans. 1, 2001, 529–536
This journal is © The Royal Society of Chemistry 2001
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Table 1 Cyclization of halides 1a–c with metal selenides (see Scheme 1)
Entry
Dihalide
M2Se
Temp.
Products (% yield)
1
2
3
4
5
6
7
1a
1b
1b
1c
1cЈ
1c
1cЈ
Na2Se
Na2Se
Na2Se
Na2Se
Na2Se
Li2Se
rt
rt
reflux
0 ЊC
0 ЊC
rt
trans-2a (31), cis-2a (23)
trans-2b (35), cis-2b (36)
3b (78)
3c (58), 4 (10)
3c (29), 4 (2)
3c (54), 4 (40)
trans-2c (24), cis-2c (25), 3c (14), 4 (19)
Li2Se
0 ЊC
Table 2 Reactions of selenanes 2a–c with MCPBA (see Scheme 1)
Entry
2
Temp. Products (% yield)
1
2
3
4
5
6
7
8
9
trans-2a
0 ЊC
reflux 5a (70), 6a (16)
0 ЊC 5a (35), 6a (16)
reflux 5a (70), 6a (25)
reflux 5a (64), 6a (23)
reflux 5b (46), 6b (29)
5a (14), 6a (7)
trans-2a
cis-2a
cis-2a
trans-2a ϩ cis-2a
trans-2b ϩ cis-2b
cis-2c
trans-2c
trans-2c
0 ЊC
0 ЊC
trans-5c (18), cis-5c (24), 6c (39)
trans-5c (13), cis-5c (23), 6c (5)
reflux trans-5c (7), cis-5c (12), 6c (41)
Scheme 2 Mechanism of the reactions of selenanes 2 with MCPBA.
Fig. 1 Conformation of 2a.
signal intensities of H(6) at δ 4.06 (trans-5a) and H(6) at δ 3.77
and one of CH2CH3 at δ 3.74 (cis-5a) (overlapped), and H(6)
at δ 4.07–4.09 (trans-5b) and OMe at δ 3.38 (cis-5b) in the
1H NMR spectra. This cis-predominant selectivity can be
explained by attack of m-chlorobenzoate anion on the carbon
atom at the 6-position of C from the opposite side of the EWG
at the 2-position, avoiding its steric hindrance. In the case of the
benzoyl derivative, dihydroselenine 6c was produced in prefer-
ence to benzoate 5c. This is attributed to an assumption that
steric hindrance of the benzoyl group at the 6-position of C
prevented the m-chlorobenzoate anion from attacking the
carbon atom at the 6-position and deprotonation of 5-H was
predominantly brought about.
Benzoates 5a–c have two isomers, trans-5a–c and cis-5a–c, as
shown in Fig. 2. These conformations are explained by a discus-
sion similar to that for selenanes 2a–c. Two coupling constants,
3 and 12 Hz, due to H(6) of one isomer of 5a are typical axial–
equatorial and axial–axial coupling constants, respectively.
Therefore, this isomer takes a chair form and the EWG at the
6-position occupies an equatorial position. The chemical shift
of H(6) appeared at δ 4.06, lower than that of the other isomer
at δ 3.77. This lower-field shift is attributed to the anisotropic
effect of the axial carbonyl (ethyl ester) group β to the H(6).
From these 1H NMR data the isomer was identified as trans-5a
bearing a 6-equatorial ethyl ester group, a 2-equatorial chloro-
benzoyloxy group and a 2-axial ethyl ester group. On the other
hand, the other isomer, cis-5a, showed an H(6) signal at δ 3.77
as a triplet (J 5 Hz). This indicates that the methylene protons
at the 5-position affect H(6) equivalently and the selenane ring
adopts a twist conformation. In this conformation H(6) is apart
from the ethyl ester group at the 2-position and therefore the
down-field shift of H(6) was not observed.
1
show complex signals. They were equivalent in a 400 MHz H
NMR spectrum with coupling constants of 4 and 7 Hz. This
indicates that the twist conformation is adopted by trans-2a.
In order to construct a C᎐C bond between the 2- and
᎐
3-positions of the selenane ring, we used the method developed
by our group,6 i.e. the peracid oxidation of selenanes 2a–c and
successive Pummerer reaction of the resulting selenoxides
as shown in Scheme 1. Reactions of selenanes 2a–c with
m-chloroperbenzoic acid (MCPBA) gave benzoates 5a–c and
the desired products, dihydro-2H-selenines 6a–c (Table 2).
Reactions of ethyl ester 2a under reflux in dichloromethane
gave 5a and 6a in better yields than those at 0 ЊC (entries 1, 2, 3
and 4). Both cis and trans isomers reacted similarly with
MCPBA under reflux in dichloromethane (entries 2 and 4).
Reaction of the trans-benzoyl derivative trans-2c under reflux in
dichloromethane gave dihydroselenine 6c in better yield than
that at 0 ЊC (entries 8 and 9), whereas the reaction of cis-2c
proceeded even at 0 ЊC to give 5c and 6c in good yields
(combined yield of 5c and 6c: 81%) (entry 7).
Benzoates 5 and dihydroselenines 6 are formed via the path-
ways shown in Scheme 2. First, MCPBA oxidises the selenium
atom to give selenoxide A and m-chlorobenzoic acid. The
benzoic acid protonates the oxygen atom of selenoxide A to
give selenonium ion B. The concurrent m-chlorobenzoate anion
abstracts the α-proton of B to form intermediate C with
dehydration. m-Chlorobenzoate anion nucleophilically attacks
at the 6-position of C to give benzoates 5a–c (path a) or
deprotonates a hydrogen at the 5-position to give dihydro-
selenines 6a–c (path b). Since benzoate 5a did not react with
MCPBA, m-chlorobenzoic acid, or m-chlorobenzoate anion,
conversion of benzoates 5a–c to dihydroselenines 6a–c during
the reactions was ruled out.
In order to convert undesired benzoates 5a–c to the desired
dihydroselenines 6a–c, we treated 5a–c with polyphosphoric
acid trimethylsilyl ester (PPSE)12 which is usually used as a
good reagent for dehydration under neutral conditions and is
The benzoates 5a–c are mixtures of two isomers, cis-5a–c and
trans-5a–c, and the cis:trans isomer ratios of ca. 3 for 5a, 5b
and 1.3–1.8 for 5c were determined by comparison with the
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Table
3
Reactions of dihydroselenines 6a–c with MCPBA (see
8c in moderate yields. The reaction of 6c under reflux in
Scheme 3)
dichloromethane for 15 min (entry 6) gave a better result than
those at 0 ЊC and under reflux for 3 h in entries 4 and 5.
Since the reactions with PPSE in dichloroethane did not
proceed and starting materials 7a,b were recovered, 7a,b were
treated with PPSE in refluxing toluene to give 4H-selenines 8a,b
and the double bond regio-isomers 9a,b. The reaction of 7c
with PPSE in dichloroethane at 0 ЊC gave a complex mixture.
Methylation of mixtures of 8a,b and 9a,b with MeI–AgBF4
and successive deprotonation with triethylamine afforded
selenabenzenes 12a,b.8 The 4H-selenine 8c was too unstable to
be isolated and a mixture of 7c and 8c obtained from the reac-
tions in Table 3 was used for the preparation of selenabenzene
12c. The selenabenzenes 12a–c thus prepared were stable in the
atmosphere at room temperature and could be purified by
silica-gel PTLC (Scheme 3).
Entry
6
Temp.
Time
Products (% yield)a
1
2
3
4
5
6
6a
6a
6b
6c
6c
6c
0 ЊC
reflux
0 ЊC
0 ЊC
reflux
reflux
3 h
3 h
3 h
3 h
3 h
7a (52), 8a (trace)
7a (50), 8a (trace)
7b (71), 8b (9)
7c (31), 8c (trace)
7c (39), 8c (31)
15 min
7c (32),b 8c (54)b
a Isolated yield. b Based on the signal intensities of H(5) of 7c and
H(3,5) of 8c in a 1H NMR spectrum.
The structures of selenonium salts13 10a, 11a and selena-
benzenes8 12a–c based on the 1H and 13C NMR and IR spectral
data have been described in previous papers. The molecular
structure of 12c was unequivocally established by crystal
structure analysis and is discussed on the basis of the X-ray
analytical data in this paper.
X-Ray analysis
The ORTEP drawing of 12c and characteristic crystal data are
shown in Fig. 3 and in Table 4, respectively. Two torsion angles
(C1–C2–C3–C4 and C2–C3–C4–C5) show that the carbon
chain composed of C1, C2, C3, C4 and C5 is planar. The
dihedral angle between the plane and another plane involving
C1, Sel, and C5 was found to be ca. 5Њ, the selenium atom
deviating slightly from the planar structure. The bond lengths of
the four C–C bonds of the C1–C5 chain are in the range 1.357–
1.390 Å, which corresponds well to the C–C bond length of
benzene (1.397 Å). On the other hand, the lengths of the two
Se–C bonds in the selenabenzene (1.915 and 1.918 Å) and
that of the Sel–C20 bond (1.970 Å) are in good agreement
with those of C(sp2)–Se (1.91 Å)14,15 and C(sp3)–Se (1.98 Å)14,15
bonds, respectively, suggesting that these three bonds are
Fig. 2 Conformation of 5a–c.
prepared from hexamethyldisiloxane and phosphorus penta-
oxide in a variety of organic solvents (Scheme 1).
The benzoates 5a–c were not converted into 6a–c by refluxing
with PPSE in dichloromethane, but were converted by refluxing
in dichloroethane in high yield (85–99%).
Treatment of 6a–c with MCPBA one more time gave the
benzoates 7a–c and 4H-selenines 8a–c (Scheme 3, Table 3).
single bonds (cf. 1.67 Å for C᎐Se).15 Furthermore, two kinds
᎐
of coupling constant, 33 Hz for C2– or C6–Sel and 39 Hz for
C20–Sel in the 13C NMR spectrum, also indicates that the
bonds of the selenium atom are sp3 hybridized.16 Further-
more, this was supported by calculation of the simplified
molecule, 2,6-diformyl-1-methylselenabenzene by MOPAC-
PM3. The bond orders of the three C–Se bonds are 0.964
(Se1–C1), 0.963 (Se1–C5), and 0.841 (Se1–C20) indicating
that these bonds are single bonds.
The ORTEP drawing in Fig. 3 shows that the two carbonyl
groups face the selenium and the phenyl groups are directed to
C2–H and C4–H in the solid state. The distances between
Se1 ؒ ؒ ؒ O2 and Se1 ؒ ؒ ؒ O1 are 2.723 and 2.873 Å, respectively
and are significantly less than the sum of their van der Waals
radii (ca. 3.40 Å). An NOE enhancement between H(3, 5) and
1
protons of the phenyl group (11%) was observed in the H
NMR spectrum. This observation indicates that the phenyl
groups are located in the direction of C2–H and C4–H in a
CDCl3 solution as well. The arrangement of the benzoyl groups
is attributed to the electrostatic interaction between the benzoyl
oxygen and the positively charged selenium atoms.
The intermolecular distances between one of the Se-methyl
hydrogen atoms and the six carbons of the benzene ring of the
benzoyl group are 2.89 (H16–C14), 3.02 (H16–C15), 3.09
(H16–C18) and 2.93 (H16–C19) Å. These values are very close
to the sum of the van der Waals radii of H and C (ca. 2.90 Å),
and show the presence of a CH–π interaction17 between them.
However, π–π interactions between two intermolecular benzene
rings of the benzoyl groups do not occur because the angle
between them is unfavorable according to the packing diagram
(Fig. 4).
Scheme 3 Reagents and conditions: (i), MCPBA (1.1 equiv.), CH2Cl2;
(ii), PPSE, toluene, reflux, 20 h; (iii), MeI (6 equiv.), AgBF4 (1.5 equiv.),
CH2Cl2, 0 ЊC, 2 h; (iv), Et3N (3 equiv.), EtOH, 0 ЊC, 5 h.
Ester derivatives 6a,b produced benzoates 7a,b in good yields
accompanied by a small amount of 4H-selenines 8a,b (entries 2,
3), and benzoyl derivative 6c gave benzoate 7c and 4H-selenine
J. Chem. Soc., Perkin Trans. 1, 2001, 529–536
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Table 4 Selected data of 12c
Torsion angle/Њ
Bond length/Å
Angle/Њ
C1–C2–C3–C4
C2–C3–C4–C5
Se1–C1–C2–C3
Se1–C5–C4–C3
C1–Se1–C5–C4
C2–C1–Se1–C5
Se1–C1–C13–O2
Se1–C5–C6–O1
1(1)
0(1)
C1–C2
C2–C3
C3–C4
C4–C5
Se1–C1
C5–Se1
C20–Se1
1.370(7)
C1–Se1–C5
C1–Se1–C20
C5–Se1–C20
97.0(2)
99.4(3)
99.9(3)
1.375(8)
1.390(7)
1.357(7)
1.915(5)
1.918(5)
1.970(7)
Ϫ6.2(9)
2.1(9)
Ϫ4.9(5)
6.7(5)
Ϫ1.3(7)
6.0(7)
silane, CDCl3 or CD3CN as solvent, and external dimethyl
selenide, respectively. The J values are given in Hz. Mass spectra
were recorded on a JEOL JMS-SX 102A spectrometer with a
direct-insertion probe at 70 eV. Elemental analyses of new
compounds were performed on a Yanaco CHN Corder MT-5.
All chromatographic isolations were accomplished with either
Kieselgel 60 (Merck) or BW-127ZH (Fuji Silysia) for column
chromatography or Kieselgel 60 PF254 containing gypsum
(Merck) for PTLC. The recycling preparative HPLC was per-
formed by LC-918 liquid chromatography (Japan Analytical
Industry Co. Ltd.) equipped with JAIGEL-1H and -2H
columns (polystyrene gels).
Synthesis of diethyl 2,6-dibromoheptanedioate 1a
Title compound 1a (52 g, 90%) was synthesised from heptane-
dioic acid (25 g, 156 mmol) according to the procedure used
previously for the synthesis of diethyl 2,5-dibromohexenedioate
from hexanedioic acid.18 Brown oil, νmax(film)/cmϪ1 1730 (ester
C᎐O); δ (270 MHz; CDCl ) 1.30 (6 H, t, J 7, CH CH ), 1.48–
᎐
H
3
2
3
1.70 (2 H, m, 4-H), 2.00–2.34 (4 H, m, 3- and 5-H), 4.20–4.27
(6 H, m, 2-, 6-H and CH2CH3); m/z (EI) 372 (Mϩ, 79Br, 3%), 247
(100).
Fig. 3 ORTEP drawing for 12c.
Dimethyl 2,6-dibromoheptanedioate 1b
Title compound 1b (45 g, 81%) was similarly prepared from
heptanedioic acid (26 g, 160 mmol). Yellow oil; νmax(film)/cmϪ1
1740 (ester C᎐O); δ (400 MHz; CDCl3) 1.40–1.77 (2 H, m,
᎐
H
4-H), 1.97–2.17 (4 H, m, 3- and 5-H), 3.79 (6 H, s, OMe × 2),
4.24 (2 H, t, J 6, 2- and 6-H); m/z (EI) 344 (Mϩ, 1%), 233 (100).
1
The H NMR signals of this compound were identical with
those of an authentic sample in the literature.19
Synthesis of 1,5-dibenzoylpentane 3c
Title compound 3c (218 g, 86%) was synthesised from heptane-
dioic acid (144 g, 0.9 mol) according to the procedure used
previously for the synthesis of 1,4-dibenzoylbutane starting
from hexanedioic acid.20 White needles, mp 64–65 ЊC (from
benzene); νmax(KBr)/cmϪ1 1670 (C᎐O); δ (400 MHz; CDCl3)
Fig. 4 Packing diagram for 12c.
Conclusion
᎐
H
1.49 (2 H, quintet, J 8, 3-H), 1.81 (4 H, quintet, J 8, 2- and 4-H),
3.00 (4 H, t, J 8, 1- and 5-H), 7.46 (4 H, t, J 8, aromatic), 7.55
(2 H, t, J 8, aromatic), 7.96 (4 H, d, J 8, aromatic); δC (100 MHz;
CDCl3) 24.0 (t × 2), 28.9 (t), 38.3 (t × 2), 128.0 (d × 4), 128.5
(d × 4), 132.9 (d × 2), 137.0 (s × 2), 200.3 (s × 2).
We have succeeded in synthesising monocyclic selenabenzenes
having two EWGs, ethyl ester, methyl ester, and benzoyl groups,
at the 2- and 6-positions. They were stable at room temperature
and against moisture. According to X-ray analysis of selena-
benzene 12c, its bond lengths and angles show a tetragonal
structure arising from sp3 hybridization of the selenium atom.
Synthesis of 1,5-dibenzoyl-1,5-dibromopentane 1c
Title compound 1c (194 g, 89%) was synthesised from heptane-
dioic acid (140 g, 0.5 mol) according to the procedure used
previously for the synthesis of α-bromoacetophenone starting
Experimental
General
Melting points were obtained with a Yanagimoto micro melting
point apparatus and are uncorrected. IR spectra of solids
(KBr) and liquids (NaCl) were recorded on a JASCO FT/IR-
230 spectrophotometer. The 1H, 13C, and 77Se NMR spectra
were measured at 400, 100, and 76 MHz, respectively, with a
from acetophenone.21 Yellow oil; νmax(film)/cmϪ1 1685 (C᎐O);
᎐
δH (400 MHz; CDCl3) 1.69 (2 H, quintet, J 8, 3-H), 2.22–2.27
(4 H, m, 2- and 4-H), 5.15 (2 H, t, J 7, 1- and 5-H), 7.47 (4 H, t,
J 8, aromatic), 7.59 (2 H, t, J 8, aromatic), 8.00 (4 H, d, J 8,
aromatic); δC (100 MHz; CDCl3) 25.5 (t), 32.7 (t × 2), 46.4
(d × 2), 128.76 (d × 4), 128.81 (d × 4), 133.7 (d × 2), 134.2
JEOL EX-400 spectrometer. The H, 13C and 77Se chemical
1
1
shifts are given in ppm relative to those of internal tetramethyl-
(s × 2), 192.9 (s × 2). The H NMR signals of this compound
532
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were identical with those of an authentic sample in the
literature.22
28.6 (t × 2), 33.7 (d × 2), 52.3 (q × 2), 173.3 (s × 2); δSe (76
MHz; CDCl3) 346; m/z (EI) 266 (Mϩ, 34%), 234 (100).
Dimethyl cis-selenane-2,6-dicarboxylate cis-2b. Pale yellow
plates, mp 41–43 ЊC (from hexane–ethyl acetate) (Found: C,
40.5; H, 5.3; C9H14O4Se requires C, 40.8; H, 5.3%); νmax(film)/
cmϪ1 1731 (ester C᎐O); δ (400 MHz; CDCl3) 1.25–1.42 (1 H,
m, 3-, 4- or 5-H), 1.82–1.94 (2 H, m, 3-, 4- or 5-H), 2.05–2.15
(1 H, m, 3-, 4- or 5-H), 2.25–2.40 (2 H, m, 3-, 4- or 5-H), 3.73
(6 H, s, OMe × 2), 3.87 (2 H, dd, J 3 and 11, 2- and 6-H);
δC (100 MHz; CDCl3) 25.5 (t), 29.5 (t × 2), 37.1 (d × 2), 52.4
(q × 2), 172.0 (s × 2); δSe (76 MHz; CDCl3) 348; m/z (EI) 266
(Mϩ, 50%), 147 (100).
Synthesis of 1,5-dibenzoyl-1,5-dichloropentane 1cЈ
A solution of sulfuryl chloride (297 mg, 2.2 mmol) in tetra-
chloromethane (3 cm3) was added to a solution of 1,5-
dibenzoylpentane (280 mg, 1 mmol) in tetrachloromethane
(5 cm3) with stirring at 0 ЊC. The mixture was stirred for 1 day at
room temperature, and then a saturated sodium hydrogen
carbonate solution was added to it. The organic layer was
separated and the aqueous layer was extracted with dichloro-
methane. The organic layer and the extracts were combined,
washed with water, dried (MgSO4), and concentrated to dry-
ness. The residue was purified by PTLC on silica gel using
hexane–ethyl acetate (3:1) to give title compound 1cЈ (321
mg, 92%). Yellow oil, νmax(film)/cmϪ1 1690 (C᎐O); δ (400
MHz; CDCl3) 1.59–1.89 (2 H, m, 3-H), 2.02–2.25 (4 H, m,
2- and 4-H), 5.12 (2 H, dd, J 6 and 7, 1- and 5-H), 7.44–7.51
(4 H, m, aromatic), 7.56–7.61 (2 H, m, aromatic), 7.95–8.00
(4 H, m, aromatic); δC (100 MHz; CDCl3) 23.1 (t), 32.8 (t), 32.9
(t), 57.0 (d × 2), 128.8 (d × 4), 128.9 (d × 4), 133.9 (d × 2),
134.3 (s × 2), 193.2 (s × 2); m/z (EI) 351 (Mϩ Ϫ 35Cl, 2%), 105
(100).
᎐
H
Synthesis of selenane 2c
A solution of 1,5-dibenzoyl-1,5-dichloropentane 1cЈ (349 mg,
1 mmol) in THF (2.5 cm3) was added to a solution of lithium
selenide in THF (2.5 cm3) prepared from selenium powder (79
mg, 1 mmol), Super-Hydride in a THF solution (1.0 M) (2.1
cm3, 2.1 mmol) and tert-butyl alcohol (0.15 cm3) at 0 ЊC under
an argon atmosphere. The reaction mixture was stirred at 0 ЊC
for 0.5 h under an argon atmosphere. The reaction mixture was
similarly worked up and purified to give 1,5-dibenzoylpentane
3c (38 mg, 14%), trans-2,6-dibenzoylselenane, trans-2c (85 mg,
24%), cis-2,6-dibenzoylselenane, cis-2c (89 mg, 25%), and
1-benzoyl-2-hydroxy-2-phenylcyclohexane 4 (48 mg, 19%).
᎐
H
Synthesis of selenane 2a
NaBH4 (250 mg, 6.5 mmol) was gradually added to a suspen-
sion of selenium powder (158 mg, 2 mmol) in ethanol (4 cm3).
After the reaction mixture turned colorless, it was cooled to rt.
A solution of diethyl 2,6-dibromoheptanedioate 1a (748 mg,
2 mmol) in ethanol (4 cm3) degassed by an aspirator was added
dropwise to the solution of sodium selenide and the mixture
was stirred for 0.5 h at rt. Air was bubbled into the mixture and
then water was added to it. The whole was extracted with
dichloromethane. The extracts were dried (MgSO4) and concen-
trated under reduced pressure. The residue was fractionated by
PTLC on silica gel using hexane–ethyl acetate (4:1) to give
diethyl trans-selenane-2,6-dicarboxylate, trans-2a (182 mg,
31%) and cis-isomer cis-2a (135 mg, 23%).
trans-2,6-Dibenzoylselenane trans-2c. Pale yellow oil (Found:
C, 63.7; H, 5.15; C19H18O2Se requires C, 63.9; H, 5.1%);
νmax(film)/cmϪ1 1680 (C᎐O); δ (400 MHz; CDCl3) 2.20–2.26
(6 H, m, 3-, 4- and 5-H), 4.81–4.83 (2 H, m, 2- and 6-H), 7.44
(4 H, t, J 7, aromatic), 7.54 (2 H, t, J 7, aromatic), 7.94 (4 H, dd,
J 1 and 7, aromatic); δC (100 MHz; CDCl3) 22.7 (t), 28.5 (t × 2),
37.7 (d × 2), 128.5 (d × 4), 128.6 (d × 4), 133.1 (d × 2), 135.2
(s × 2), 198.3 (s × 2); δSe (76 MHz; CDCl3) 355; m/z (EI) 358
(Mϩ, 8%), 105 (100).
᎐
H
cis-2,6-Dibenzoylselenane cis-2c. White needles, mp 97 ЊC
(from ethyl acetate–hexane) (Found: C, 63.7; H, 5.1; C19H18-
O2Se requires C, 63.9; H, 5.1%); νmax(KBr)/cmϪ1 1660 (C᎐O); δ
᎐
H
Diethyl trans-selenane-2,6-dicarboxylate trans-2a. Yellow oil
(Found: C, 44.9; H, 6.2; C11H18O4Se requires C, 45.1; H, 6.2%);
νmax(film)/cmϪ1 1720 (ester C᎐O); δ (400 MHz; CDCl3) 1.28
(400 MHz; CDCl3) 1.67 (1 H, tt, J 3 and 14, 3-, 4- or 5-H), 2.15
(2 H, dq, J 3 and 13, 3-, 4- or 5-H), 2.25–2.32 (1 H, m, 3-, 4- or
5-H), 2.35–2.41 (2 H, m, 3-, 4- or 5-H), 4.97 (2 H, dd, J 2 and
11, 2- and 6-H), 7.47 (4 H, t, J 7, aromatic), 7.57 (2 H, t, J 7,
aromatic), 8.03 (4 H, d, J 7, aromatic); δC (100 MHz; CDCl3)
26.6 (t), 29.8 (t × 2), 42.8 (d × 2), 128.66 (d × 4), 128.72 (d × 4),
133.4 (d × 2), 135.1 (s × 2), 197.6 (s × 2); δSe (76 MHz; CDCl3)
389; m/z (EI) 358 (Mϩ, 23%), 105 (100).
᎐
H
(6 H, t, J 7, CH2CH3), 1.92–2.17 (6 H, m, 3-, 4- and 5-H), 3.87
(2 H, dd, J 4 and 7, 2- and 6-H), 4.18 (4 H, q, J 7, CH2CH3);
δC (100 MHz; CDCl3) 14.0 (q × 2), 22.0 (t), 28.7 (t × 2), 34.0
(d × 2), 61.1 (t × 2), 172.8 (s × 2); δSe (76 MHz; CDCl3) 353;
m/z (EI) 294 (Mϩ, 25%), 248 (100).
Diethyl cis-selenane-2,6-dicarboxylate cis-2a. Yellow oil;
νmax(film)/cmϪ1 1720 (ester C᎐O); δ (400 MHz; CDCl3) 1.27
1-Benzoyl-2-hydroxy-2-phenylcyclohexane 4. Colourless
needles, mp 128 ЊC (from acetone–hexane) (Found: C, 81.5; H,
7.3; C19H20O2 requires C, 81.4; H, 7.2%); νmax(KBr)/cmϪ1 1650
᎐
H
(6 H, t, J 7, CH2CH3), 1.30–2.39 (6 H, m, 3-, 4- and 5-H), 3.87
(2 H, dd, J 2 and 12, 2- and 6-H), 4.18 (4 H, q, J 7, CH2CH3);
δC (100 MHz; CDCl3) 14.1 (q × 2), 26.0 (t), 29.7 (t × 2), 37.6
(d × 2), 61.5 (t × 2), 171.6 (s × 2); δSe (76 MHz; CDCl3) 357; m/z
(EI) 294.0355 (C11H18O4Se requires 294.0370), 294 (Mϩ, 50%),
147 (100).
(C᎐O), 3425 (OH); δ (400 MHz; CDCl ) 1.50–1.56 (1 H, m, 3-,
᎐
H
3
4-, 5- or 6-H), 1.65-1.72 (2 H, m, 3-, 4-, 5- or 6-H), 1.86–2.09
(5 H, m, 3-, 4-, 5- or 6-H), 3.99 (1 H, dd, J 3 and 12, 1-H), 5.14
(1 H, d, J 2, OH), 7.09 (1 H, t, J 7, aromatic), 7.21 (2 H, t, J 7,
aromatic), 7.39 (2 H, t, J 7, aromatic), 7.47 (2 H, d, J 7, aro-
matic), 7.51 (1 H, t, J 7, aromatic), 7.81 (2 H, d, J 8, aromatic);
δC (100 MHz; CDCl3) 21.6 (t), 25.5 (t), 27.1 (t), 40.5 (t), 50.7 (d),
74.4 (s), 124.4 (d × 2), 126.4 (d), 128.1 (d × 4), 128.6 (d × 2),
133.5 (d), 136.1 (s), 148.4 (s), 206.4 (s); m/z (EI) 280 (Mϩ, 5%),
105 (100).
Synthesis of selenane 2b
Similar preparation of dimethyl 2,6-dibromoheptanedioate 1b
(692 mg, 2 mmol) gave dimethyl trans-selenane-2,6-dicarb-
oxylate, trans-2b (186 mg, 35%) and cis-isomer cis-2b (191 mg,
36%).
Oxidation of diethyl selenane-2,6-dicarboxylate 2a with
MCPBA
Dimethyl trans-selenane-2,6-dicarboxylate trans-2b. Pale yel-
low oil (Found: C, 41.1; H, 5.3; C9H14O4Se requires C, 40.8; H,
MCPBA (75%) (253 mg, 1.1 mmol) was added to a solution of
2a (293 mg, 1 mmol) in dichloromethane (10 cm3) at 0 ЊC with
stirring. The reaction mixture was stirred for 3 h under reflux,
and then a saturated sodium hydrogen carbonate solution was
5.3%); νmax(film)/cmϪ1 1731 (ester C᎐O); δ (400 MHz; CDCl )
᎐
H
3
1.94–2.11 (6 H, m, 3-, 4- and 5-H), 3.73 (6 H, s, OMe × 2), 3.89
(2 H, dd, J 4 and 7, 2- and 6-H); δC (100 MHz; CDCl3) 22.0 (t),
J. Chem. Soc., Perkin Trans. 1, 2001, 529–536
533

View Article Online
added to the cooled reaction mixture. The whole was extracted
with dichloromethane. The extracts were dried (MgSO4) and
concentrated under reduced pressure. The residue was purified
by PTLC on silica gel using hexane–ethyl acetate (5:1) to give a
mixture of the diethyl selenane-2,6-dicarboxylate 5a (313 mg,
70%) and diethyl 3,4-dihydro-2H-selenine-2,6-dicarboxylate 6a
(47 mg, 16%). Diethyl cis-2-(m-chlorobenzoyloxy)selenane-2,6-
dicarboxylate, cis-5a was isolated from a mixture of trans-5a
and cis-5a by recrystallisation (hexane–ethyl acetate).
(3 H, s, OMe), 4.07–4.09 (1 H, m, 6-H); δC (100 MHz; CDCl3)
22.3 (t), 29.3 (t), 35.4 (d), 37.2 (t), 52.5 (q), 53.3 (q), 80.5 (s),
127.8 (d), 129.6 (d), 130.7 (d), 130.8 (s), 133.6 (d), 134.6 (s),
163.0 (s), 169.7 (s), 171.6 (s); δSe (76 MHz; CDCl3) 464. These
signals were picked up from the mixture of trans-5b and cis-5b
and other signals were overlapped with the signals of cis-5b.
Dimethyl 3,4-dihydro-2H-selenine-2,6-dicarboxylate 6b. Red
oil (Found: C, 41.3; H, 4.6; C9H12O4Se requires C, 41.1; H,
4.6%); νmax(film)/cmϪ1 1720 (ester C᎐O); δ (400 MHz; CDCl )
᎐
H
3
Diethyl cis-2-(m-chlorobenzoyloxy)selenane-2,6-dicarboxylate
cis-5a. Colourless prisms, mp 75 ЊC (from hexane–ethyl acetate)
(Found: C, 48.2; H, 4.8; C18H21ClO6Se requires C, 48.3; H,
4.7%); νmax(KBr)/cmϪ1 1720 (ethyl ester); δH (400 MHz; CDCl3)
1.05 (3 H, t, J 7, CH2CH3), 1.27 (3 H, t, J 7, CH2CH3), 1.84–
1.94 (1 H, m, 3-H), 2.04–2.12 (1 H, m, 5-H), 2.28–2.54 (4 H, m,
3-, 4- and 5-H), 3.74 (1 H, dq, J 11 and 7, CH2CH3), 3.77 (1 H,
t, J 5, 6-H), 3.93 (1 H, dq, J 11 and 7, CH2CH3), 4.26 (2 H, q,
J 7, CH2CH3), 7.41 (1 H, t, J 8, aromatic), 7.56 (1 H, d, J 9,
aromatic), 7.94 (1 H, d, J 8, aromatic), 8.03 (1 H, s, aromatic);
δC (100 MHz; CDCl3) 13.8 (q), 13.9 (q), 19.0 (t), 27.1 (t), 34.6
(d), 35.5 (t), 61.1 (t), 62.5 (t), 79.6 (s), 128.1 (d), 129.7 (d), 130.0
(d), 131.0 (s), 133.5 (d), 134.6 (s), 163.4 (s), 169.7 (s), 172.7 (s);
δSe (76 MHz; CDCl3) 466; m/z (EI) 448 (Mϩ, 5%), 139 (100).
2.05–2.19 (2 H, m, 3- or 4-H), 2.35 (1 H, ddt, J 20, 8 and 5, 3- or
4-H), 2.67 (1 H, ddt, J 20, 7 and 5, 3- or 4-H), 3.75 (3 H, s,
OMe), 3.79 (3 H, s, OMe), 4.00 (1 H, dd, J 4 and 7, 2-H), 7.34
(1 H, t, J 5, 5-H); δC (100 MHz; CDCl3) 23.4 (t), 25.0 (t), 33.7
(d), 52.4 (q × 2), 120.9 (s), 136.7 (d), 164.9 (s), 172.4 (s); δSe (76
MHz; CDCl3) 303; m/z (EI) 264 (Mϩ, 33%), 145 (100).
Oxidation of 2,6-dibenzoylselenane 2c with MCPBA
The MCPBA oxidation of 2,6-dibenzoylselenane 2c (357 mg,
1 mmol) and purification by recycling preparative HPLC, elut-
ing with chloroform, gave trans-2,6-dibenzoyl-2-(m-chloro-
benzoyloxy)selenane, trans-5c (90 mg, 18%), cis-isomer cis-5c
(123 mg, 24%) and 2,6-dibenzoyl-3,4-dihydro-2H-selenine 6c
(137 mg, 39%).
Diethyl trans-2-(m-chlorobenzoyloxy)selenane-2,6-dicarboxyl-
ate trans-5a. δH (400 MHz; CDCl3) 4.06 (1 H, dd, J 3 and 12,
6-H); δC (100 MHz; CDCl3) 13.9 (q), 14.0 (q), 22.4 (t), 29.4 (t),
35.5 (t), 37.5 (d), 61.6 (t), 62.6 (t), 80.9 (s), 127.9 (d), 129.7 (d),
129.8 (d), 131.1 (s), 133.5 (d), 134.6 (s), 163.1 (s), 169.3 (s), 171.2
(s); δSe (76 MHz; CDCl3) 461. These signals were picked up
from the mixture of trans-5a and cis-5a and other signals were
overlapped with the signals of cis-5a.
cis-2,6-Dibenzoyl-2-(m-chlorobenzoyloxy)selenane
cis-5c.
White prisms, mp 135 ЊC (from ether) (Found: C, 61.1; H, 4.2;
C26H21O4ClSe requires C, 61.0; H, 4.1%); νmax(film)/cmϪ1 1680
(C᎐O), 1730 (ester C᎐O); δ (400 MHz; CDCl ) 2.05–2.11 (1 H,
᎐
᎐
H
3
m, 3-, 4- or 5-H), 2.23–2.27 (1 H, m, 3-, 4- or 5-H), 2.51–2.55
(1 H, m, 3-, 4- or 5-H), 2.66–2.78 (3 H, m, 3-, 4- or 5-H), 4.79
(1 H, t, J 5, 6-H), 7.29 (2 H, t, J 7, aromatic), 7.35 (2 H, t, J 8,
aromatic), 7.39 (1 H, t, J 8, aromatic), 7.42 (1 H, t, J 7, aro-
matic), 7.49 (1 H, t, J 7, aromatic), 7.57 (1 H, d, J 8, aromatic),
7.70 (2 H, d, J 8, aromatic), 7.82 (1 H, d, J 7, aromatic), 7.91
(1 H, s, aromatic), 8.02 (2 H, d, J 8, aromatic); δC (100 MHz;
CDCl3) 19.8 (t), 26.7 (t), 34.5 (t), 38.5 (d), 87.6 (s), 128.1 (d),
128.3 (d × 2), 128.48 (d × 2), 128.52 (d × 2), 128.8 (d × 2), 129.8
(d), 130.0 (d), 130.5 (s), 133.0 (d × 2), 133.2 (s), 133.7 (d), 134.6
(s), 135.2 (s), 163.5 (s), 194.4 (s), 197.9 (s); δSe (76 MHz; CDCl3)
476; m/z (EI) 512 (Mϩ, >1%), 105 (100).
Diethyl 3,4-dihydro-2H-selenine-2,6-dicarboxylate 6a. Red
oil; νmax(film)/cmϪ1 1720 (ester C᎐O); δ (400 MHz; CDCl3)
᎐
H
1.28 (3 H, t, J 7, CH2CH3), 1.31 (3 H, t, J 7, CH2CH3), 2.06–2.16
(2 H, m, 3- or 4-H), 2.34 (1 H, ddt, J 19, 8 and 4, 3- or 4-H), 2.66
(1 H, ddt, J 19, 7 and 5, 4-H), 3.98 (1 H, dd, J 3 and 8, 2-H),
4.20 (2 H, dq, J 3 and 7, CH2CH3), 4.24 (2 H, q, J 7, CH2CH3),
7.33 (1 H, t, J 5, 5-H); δC (100 MHz; CDCl3) 14.0 (q), 14.1 (q),
23.5 (t), 25.2 (t), 34.1 (d), 61.4 (t), 61.5 (t), 121.4 (s), 136.3 (d),
164.5 (s), 172.0 (s); δSe (76 MHz; CDCl3) 301; m/z (EI) 292.0220
(C11H16O4Se requires 292.0213), 292 (Mϩ, 56%), 246 (100).
trans-2,6-Dibenzoyl-2-(m-chlorobenzoyloxy)selenane trans-5c.
White needles, mp 148–149 ЊC (from ether) (Found: C, 61.1; H,
4.2; C26H21ClO4Se requires C, 61.0; H, 4.1%); νmax(KBr)/cmϪ1
Oxidation of dimethyl selenane-2,6-dicarboxylate 2b with
MCPBA
1680 (C᎐O), 1730 (ester C᎐O); δ (400 MHz; CDCl ) 2.13–2.33
᎐
᎐
H
3
(3 H, m, 3-, 4- or 5-H), 2.48 (1 H, dq, J 14 and 3, 3-, 4- or 5-H),
2.59 (1 H, ddd, J 3, 13 and 15, 3-, 4- or 5-H), 2.98 (1 H, dt, J 15
and 3, 3-, 4- or 5-H), 5.24 (1 H, dd, J 2 and 11, 6-H), 7.36 (2 H,
t, J 8, aromatic), 7.42 (2 H, t, J 8, aromatic), 7.46 (2 H, t, J 8,
aromatic), 7.56 (1 H, t, J 7, aromatic), 7.61 (1 H, ddd, J 1, 2 and
8, aromatic), 7.92 (2 H, dd, J 1 and 7, aromatic), 7.98 (1 H, dt,
J 7 and 1, aromatic), 8.06 (1 H, t, J 2, aromatic), 8.13 (2 H, dd,
J 1 and 7, aromatic); δC (100 MHz; CDCl3) 22.8 (t), 29.5 (t),
34.8 (t), 42.9 (d), 88.9 (s), 127.8 (d), 128.5 (d × 2), 128.6 (d × 2),
128.7 (d × 2), 128.9 (d × 2), 129.7 (d), 130.2 (d), 130.8 (s), 133.2
(d), 133.3 (s), 133.6 (d), 133.9 (d), 134.9 (s), 135.0 (s), 163.4 (s),
194.1 (s), 197.5 (s); δSe (76 MHz; CDCl3) 512; m/z (EI) 512 (Mϩ,
>1%), 105 (100).
The MCPBA oxidation of dimethyl selenane-2,6-dicarboxylate
2b (265 mg, 1 mmol) gave a mixture of dimethyl trans-2-(m-
chlorobenzoyloxy)selenane-2,6-dicarboxylate, trans-5b and
cis-isomer cis-5b (194 mg, 46%), and dimethyl 3,4-dihydro-2H-
selenine-2,6-dicarboxylate 6b (76 mg, 29%).
Dimethyl cis-2-(m-chlorobenzoyloxy)selenane-2,6-dicarboxyl-
ate cis-5b. Colourless prisms, mp 98 ЊC (from hexane–ethyl
acetate) (Found: C, 45.75; H, 4.15; C16H17ClO6Se requires C,
45.8; H, 4.1%); νmax(KBr)/cmϪ1 1740 (ester); δH (400 MHz;
CDCl3) 1.85–1.94 (1 H, m, 3-, 4- or 5-H), 2.03–2.12 (1 H, m, 3-,
4- or 5-H), 2.27–2.57 (4 H, m, 3-, 4- or 5-H), 3.38 (3 H, s, OMe),
3.78 (1 H, t, J 4, 6-H), 3.80 (3 H, s, OMe), 7.42 (1 H, t, J 8,
aromatic), 7.57 (1 H, d, J 8, aromatic), 7.94 (1 H, d, J 8,
aromatic), 8.02 (1 H, s, aromatic); δC (100 MHz; CDCl3) 18.8
(t), 27.1 (t), 34.3 (d), 35.5 (t), 52.2 (q), 53.3 (q), 79.4 (s), 128.1
(d), 129.7 (d), 130.0 (d), 130.8 (s), 133.6 (d), 134.6 (s), 163.3 (s),
170.2 (s), 173.0 (s); δSe (76 MHz; CDCl3) 468; m/z (EI) 420 (Mϩ,
6%), 139 (100).
2,6-Dibenzoyl-3,4-dihydro-2H-selenine 6c. Brown oil (Found:
C, 64.3; H, 4.7; C19H16O2Se requires C, 64.2; H, 4.5%);
νmax(film)/cmϪ1 1640, 1680 (C᎐O); δ (400 MHz; CDCl ) 2.22–
᎐
H
3
2.26 (1 H, m, 3- or 4-H), 2.32–2.41 (1 H, m, 3- or 4-H), 2.51
(1 H, ddt, J 20, 8 and 4, 3- or 4-H), 2.92 (1 H, ddt, J 20, 7 and 5,
3- or 4-H), 4.96 (1 H, dd, J 4 and 7, 2-H), 7.08 (1 H, t, J 5, 5-H),
7.43 (2 H, t, J 8, aromatic), 7.48 (2 H, t, J 8, aromatic), 7.52
(1 H, t, J 8, aromatic), 7.58 (1 H, t, J 7, aromatic), 7.62 (2 H, d,
J 7, aromatic), 7.99 (2 H, d, J 7, aromatic); δC (100 MHz;
Dimethyl trans-2-(m-chlorobenzoyloxy)selenane-2,6-dicarb-
oxylate trans-5b. δH (400 MHz; CDCl3) 3.70 (3 H, s, OMe), 3.80
534
J. Chem. Soc., Perkin Trans. 1, 2001, 529–536

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CDCl3) 23.1 (t), 26.1 (t), 36.6 (d), 128.2 (d × 2), 128.4 (d × 2),
128.7 (d × 2), 129.0 (d × 2), 131.8 (d), 132.4 (s), 133.4 (d), 135.4
(s), 136.9 (s), 142.4 (d), 194.3 (s), 196.8 (s); δSe (76 MHz; CDCl3)
310; m/z (EI) 356 (Mϩ, 25%), 105 (100).
(s), 122.3 (s), 127.8 (d), 129.6 (d), 129.8 (d), 130.5 (s), 133.6
(d), 134.5 (s), 135.2 (d), 163.8 (s), 164.3 (s), 169.6 (s); δSe (76
MHz; CDCl3) 460; m/z (EI) 417.9715 (C16H15ClO6Se requires
417.9722), 418 (Mϩ, 4%), 139 (100).
Reaction of 2-(m-chlorobenzoyloxy)selenane derivatives 5a–c
with PPSE
Dimethyl 4H-selenine-2,6-dicarboxylate 8b. Colourless
needles, mp 81 ЊC (from hexane–ether) (Found: C, 41.3; H, 3.8;
C9H10O4Se requires C, 41.4; H, 3.9%); νmax(KBr)/cmϪ1 1700,
Hexamethyldisiloxane (1.7 cm3, 10 mmol) was added to a sus-
pension of phosphorus pentaoxide (850 mg, 10 mmol) in dry
1,2-dichloroethane (3.3 cm3) under an argon atmosphere and
the mixture was refluxed for 1 h. A solution of 5a (365 mg, 0.8
mmol) in dry 1,2-dichloroethane (5 cm3) was added to the PPSE
solution under an argon atmosphere and the mixture was
refluxed for 20 h. Water was added to the cooled reaction mix-
ture, and the whole was extracted with dichloromethane. The
extracts were washed with a saturated hydrogen carbonate solu-
tion, dried (MgSO4) and concentrated under reduced pressure.
The residue was purified by silica gel column chromatography
using hexane–ethyl acetate (5:1) to give diethyl 3,4-dihydro-2H-
selenine-2,6-dicarboxylate 6a (198 mg, 85%).
1730 (ester C᎐O); δ (400 MHz; CDCl ) 3.18 (2 H, t, J 5, 4-H),
᎐
H
3
3.808 (3 H, s, OMe), 3.812 (3 H, s, OMe), 7.00 (2 H, t, J 5,
3- and 5-H); δC (100 MHz; CDCl3) 31.0 (t), 52.6 (q × 2), 124.9
(s × 2), 131.9 (d × 2), 164.2 (s × 2); δSe (76 MHz; CDCl3) 298;
m/z (EI) 262 (Mϩ, 25%), 203 (100).
Oxidation of 2,6-dibenzoyl-3,4-dihydro-2H-selenine 6c with
MCPBA
The MCPBA oxidation of 6c (263 mg, 1 mmol) and purifi-
cation by recycling preparative HPLC, eluting with chloroform,
gave 2,6-dibenzoyl-2-(m-chlorobenzoyloxy)-3,4-dihydro-2H-
selenine 7c (199 mg, 39%) and 2,6-dibenzoyl-4H-selenine 8c
(110 mg, 31%).
Selenane 5b (21.43 g, 51 mmol) gave dihydroselenine 6b
(13.32 g, 99%).
Selenane 5c (480 mg, 0.9 mmol) gave dihydroselenine 6c (290
mg, 96%).
2,6-Dibenzoyl-2-(m-chlorobenzoyloxy)-3,4-dihydro-2H-
selenine 7c. White needles, mp 60 ЊC (from ethyl acetate–
hexane) (Found: C, 61.1; H, 3.8; C26H19ClO4Se requires C,
61.25; H, 3.8%); νmax(KBr)/cmϪ1 1640, 1680 (C᎐O), 1720 (ester
Oxidation of diethyl 3,4-dihydro-2H-selenine-2,6-dicarboxylate
6a with MCPBA
᎐
C᎐O); δ (400 MHz; CDCl3) 2.51–2.61 (1 H, m, 3- or 4-H),
᎐
H
2.67–2.81 (2 H, m, 3- or 4-H), 2.93–3.01 (1 H, m, 3- or 4-H),
7.19 (1 H, dd, J 3 and 6, 5-H), 7.37 (2 H, t, J 8, aromatic), 7.39
(2 H, t, J 8, aromatic), 7.47 (2 H, t, J 8, aromatic), 7.50 (1 H, t,
J 8, aromatic), 7.55 (1 H, d, J 8, aromatic), 7.68 (2 H, d, J 8,
aromatic), 7.88 (1 H, d, J 8, aromatic), 7.96 (1 H, s, aromatic),
8.20 (2 H, d, J 8, aromatic); δC (100 MHz; CDCl3) 23.7 (t), 28.8
(t), 87.5 (s), 128.0 (d), 128.4 (d × 2), 128.7 (d × 2), 128.8 (d × 2),
129.2 (d × 2), 129.8 (d), 130.0 (d), 130.5 (s × 2), 132.2 (d), 133.4
(d), 133.6 (s), 133.9 (d), 134.8 (s), 136.7 (s), 141.3 (d), 164.0 (s),
192.9 (s), 193.9 (s); δSe (76 MHz; CDCl3) 468; m/z (EI): 510 (Mϩ,
3%), 105 (100).
Oxidation of 6a (291 mg, 1 mmol) with MCPBA gave diethyl 2-
(m-chlorobenzoyloxy)-3,4-dihydro-2H-selenine-2,6-dicarboxyl-
ate 7a (232 mg, 52%) and diethyl 4H-selenine-2,6-dicarboxylate
8a (trace).
Diethyl 2-(m-chlorobenzoyloxy)-3,4-dihydro-2H-selenine-2,6-
dicarboxylate 7a. Red oil; νmax(film)/cmϪ1 1720 (ester); δH (400
MHz; CDCl3) 1.28 (3 H, t, J 7, CH2CH3), 1.30 (3 H, t, J 7,
CH2CH3), 2.24–2.32 (1 H, m, 3- or 4-H), 2.55–2.71 (3 H, m,
3- and 4-H), 4.25 (2 H, q, J 7, CH2CH3), 4.29 (2 H, q, J 7,
CH2CH3), 7.38–7.42 (2 H, m, 5-H and aromatic), 7.57 (1 H,
dt, J 8 and 1, aromatic), 7.91 (1 H, d, J 8, aromatic), 7.98 (1 H,
s, aromatic); δC (100 MHz; CDCl3) 13.9 (q), 14.0 (q), 23.1 (t),
30.2 (t), 61.7 (t), 62.7 (t), 81.0 (s), 122.8 (s), 127.9 (d), 129.7
(d), 129.8 (d), 130.7 (s), 133.6 (d), 134.6 (s), 134.8 (d), 163.9
(s), 164.1 (s), 169.2 (s); δSe (76 MHz; CDCl3) 459; m/z (EI)
446.0031 (C18H19ClO6Se requires 446.0035), 446 (Mϩ, 2%),
139 (100).
2,6-Dibenzoyl-4H-selenine 8c. Green powder, mp 70–72 ЊC
(dec.) (from CHCl3–ether) (Found: C, 64.7; H, 4.0; C19H14O2Se
requires C, 64.6; H, 4.0%); νmax(KBr)/cmϪ1 1600, 1620
(C᎐O); δ (400 MHz; CDCl3) 3.24 (2 H, t, J 5, 4-H), 6.76
᎐
H
(2 H, t, J 5, 3- and 5-H), 7.46 (4 H, t, J 7, aromatic), 7.56
(2 H, t, J 7, aromatic), 7.70 (4 H, dd, J 1 and 7, aromatic);
δC (100 MHz; CDCl3) 32.3 (t), 128.4 (d × 4), 129.2 (d × 4),
132.3 (d × 2), 135.5 (d × 2), 136.4 (s × 2), 137.4 (s × 2), 192.8
(s × 2); δSe (76 MHz; CDCl3) 317; m/z (EI) 353 (Mϩ, 15%), 105
(100).
Diethyl 4H-selenine-2,6-dicarboxylate 8a. Red oil, νmax(film)/
cmϪ1 1720 (ester C᎐O); δ (400 MHz; CDCl ) 1.32 (6 H, t, J 7,
᎐
H
3
CH2CH3), 3.18 (2 H, t, J 5, 4-H), 4.27 (4 H, q, J 7, CH2CH3),
6.99 (2 H, t, J 5, 3- and 5-H); δC (100 MHz; CDCl3) 14.1 (q × 2),
31.0 (t), 61.8 (t × 2), 125.2 (s × 2), 131.6 (d × 2), 163.8 (s × 2);
δSe (76 MHz; CDCl3) 294; m/z (EI) 290.0049 (C11H14O4Se
requires 290.0057), 290 (Mϩ, 58%), 217 (100).
Reaction of 2-(m-chlorobenzoyloxy)-3,4-dihydro-2H-selenine
derivatives 7a,b with PPSE
The reaction of dihydroselenine 7a (446 mg, 1 mmol) with
PPSE in toluene gave a mixture of diethyl 4H-selenine-2,6-
dicarboxylate 8a and diethyl 2H-selenine-2,6-dicarboxylate 9a
(192 mg, 66%).
Oxidation of dimethyl 3,4-dihydro-2H-selenine-2,6-dicarboxyl-
ate 6b with MCPBA
The MCPBA oxidation of 6b (263 mg, 1 mmol) gave dimethyl
2-(m-chlorobenzoyloxy)-3,4-dihydro-2H-selenine-2,6-dicarb-
oxylate 7b (297 mg, 71%) and dimethyl 4H-selenine-2,6-dicarb-
oxylate 8b (24 mg, 9%).
Diethyl 2H-selenine-2,6-dicarboxylate 9a. δH (400 MHz;
CDCl3) 5.77 (1 H, dd, J 6 and 10, 3-H), 6.26 (1 H, ddd,
J 1, 7 and 10, 4-H), 7.31 (1 H, d, J 7, 5-H); δSe (76 MHz; CDCl3)
248.
1
Dimethyl 2-(m-chlorobenzoyloxy)-3,4-dihydro-2H-selenine-
These signals were picked up from the H and 13C NMR
2,6-dicarboxylate 7b. Red oil; νmax(film)/cmϪ1 1730 (ester C᎐O);
spectra of the mixture of diethyl 4H-selenine-2,6-dicarboxylate
8a and diethyl 2H-selenine-2,6-dicarboxylate 9a.
The reaction of dihydroselenine 7b (418 mg, 1 mmol) simi-
larly gave a mixture of dimethyl 4H-selenine-2,6-dicarboxylate
8b and dimethyl 2H-selenine-2,6-dicarboxylate 9b (260 mg,
44%).
᎐
δH (400 MHz; CDCl3) 2.27–2.31 (1 H, m, 3- or 4-H), 2.61–2.65
(3 H, m, 3- and 4-H), 3.79 (3 H, s, OMe), 3.83 (3 H, s, OMe),
7.39–7.43 (2 H, m, 5-H and aromatic), 7.56 (1 H, d, J 8,
aromatic), 7.91 (1 H, d, J 8, aromatic), 7.97 (1 H, s, aromatic);
δC (100 MHz; CDCl3) 23.0 (t), 30.2 (t), 52.4 (q), 53.4 (q), 80.7
J. Chem. Soc., Perkin Trans. 1, 2001, 529–536
535

View Article Online
Dimethyl 2H-selenine-2,6-dicarboxylate 9b. δH (400 MHz;
CDCl3) 3.75 (3 H, s, OMe), 3.81 (3 H, s, OMe),† 4.35 (1 H, dd,
J 1 and 6, 2-H), 5.78 (1 H, dd, J 6 and 10, 3-H), 6.28 (1 H, ddd,
J 1, 6 and 10, 4-H), 7.33 (1 H, d, J 6, 5-H); δC (100 MHz;
CDCl3) 33.1 (d), 52.5 (q), 53.0 (q), 120.1 (d), 123.7 (s), 128.6 (d),
130.6 (d), 164.1‡ (s), 165.2 (s); δSe (76 MHz; CDCl3) 251.
This compound was also purified by column chromato-
graphy on silica gel using hexane–ethyl acetate (5:1).
Crystal structure analysis of 12c.§ Crystal data for C20H16-
O2Se: M = 367.3, triclinic, a = 8.658(2), b = 13.031(3), c =
7.875(2) Å, α = 103.77(2), β = 98.21(2), γ = 105.39(2)Њ, V =
1
3
These signals were picked up from the H and 13C NMR
811.6(4) Å , T = 293 K. Space group P1 (No. 2), Z = 2,
¯
spectra of the mixture of dimethyl 4H-selenine-2,6-dicarboxyl-
ate 8b and dimethyl 2H-selenine-2,6-dicarboxylate 9b.
µ(Mo-Kα) = 2.32 mmϪ1, 3976 reflections measured, 3727
unique (Rint = 0.038) which were used in all calculations. The
final R-factor was 0.042 and the wR-factor was 0.048 (all data).
Synthesis of diethyl 1-methyl-1ꢀ4-selenabenzene-2,6-dicarboxyl-
ate 12a
§ CCDC reference number 152309. See http://www.rsc.org/suppdata/
p1/b0/b008562f/ for crystallographic files in .cif format.
The synthetic procedure and data of dimethyl 1-methyl-1λ4-
selenabenzene-2,6-dicarboxylate 12b were described in a previ-
ous report.8 A mixture of selenines 8a and 9a (8a:9a = 5:1; 291
mg, 1 mmol) gave title compound 12a (292 mg, 96%) [purifi-
cation by PTLC on silica gel using hexane–ethyl acetate (5:1)],
red powder, mp 35 ЊC (from ethyl acetate–hexane) (Found: C,
47.3; H, 5.3; C12H16O4Se requires C, 47.5; H, 5.3%); νmax(KBr)/
cmϪ1 1640 (ethyl ester); δH (400 MHz; CDCl3) 1.32 (6 H, t,
J 7, CH2CH3 × 2), 2.13 (3 H, s, SeMe), 4.26 (2 H, q, J 7,
CH2CH3), 4.27 (2 H, q, J 7, CH2CH3), 5.21 (1 H, t, J 9, 4-H),
7.40 (2 H, t, J 9, 3- and 5-H); δC (100 MHz; CDCl3) 14.5
(q × 2), 26.6 (q), 60.8 (t × 2), 83.9 (s × 2), 100.7 (d), 139.1
(d × 2), 165.4 (s × 2); δSe (76 MHz; CDCl3) 311; m/z (EI) 304
(Mϩ, 65%), 231 (100).
References
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and Tellurium Compounds, ed. S. Patai and Z. Rappoport, Wiley,
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15 C. Paulmier, Selenium Reagents and Intermediates in Organic
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1993, 49, 6045.
Synthesis of 2,6-dibenzoyl-1-methyl-1ꢀ4-selenabenzene 12c
MCPBA (75%) (759 mg, 3.3 mmol) was added to a solution of
dihydroselenine 6c (1.065 g, 3 mmol) in dichloromethane (30
cm3) at 0 ЊC with stirring. The reaction mixture was stirred for
15 min under reflux, followed by addition of a saturated sodium
hydrogen carbonate solution. The whole was extracted with
dichloromethane. The extracts were dried (MgSO4) and concen-
trated under reduced pressure. The residue and iodomethane
(1.2 cm3, 9 mmol) were dissolved in dry dichloromethane (30
cm3). Silver tetrafluoroborate (975 mg, 4.5 mmol) was added to
this solution at 0 ЊC. The reaction mixture was stirred for 10
min, and then the precipitate was filtered off and washed with a
small amount of dry dichloromethane. The filtrate and the
washings were combined. Triethylamine (1.7 cm3, 12 mmol) was
added to this solution at 0 ЊC with stirring. The reaction mix-
ture was stirred for 15 min at 0 ЊC and then water was added to
it. The whole was extracted with dichloromethane. The extracts
were dried (MgSO4) and concentrated under reduced pressure.
The residue was purified by recycling preparative HPLC, elut-
ing with chloroform, to give title compound 12c (212 mg,
19%), dark green plates, mp 165 ЊC (from benzene) (Found:
C, 65.7; H, 4.5; C20H16O2Se requires C, 65.4; H, 4.4%);
νmax(KBr)/cmϪ1 1540 (C᎐O); δ (400 MHz; CDCl3) 2.55 (3 H,
᎐
H
s, SeMe), 5.18 (1 H, t, J 9, 4-H), 7.20 (2 H, d, J 9, 3- and 5-
H), 7.44–7.51 (6 H, m, aromatic), 7.63 (4 H, d, J 7, aro-
matic); δC (100 MHz; CDCl3) 26.8 (q), 102.3 (s × 2), 103.1
(d), 128.3 (d × 4), 128.7 (d × 4), 131.1 (d × 2), 137.5 (s × 2),
141.8 (d × 2), 189.3 (s × 2); δSe (76 MHz; CDCl3) 289; m/z
(EI) 353 (Mϩ, 85%), 105 (100).
20 R. C. Fuson and J. T. Walker, Org. Synth., 1943, Coll. Vol. 2, 169.
21 R. M. Comper and L. H. Davidson, Org. Synth., 1943, Coll. Vol. 2,
480.
† This signal was overlapped with the OMe signal of 8b.
22 T. Imamoto, T. Hatajima, N. Takiyama, T. Takeyama, Y. Kamiya
and T. Yoshizawa, J. Chem. Soc., Perkin Trans. 1, 1991, 3127.
‡ This signal was overlapped with the C᎐O signal of 8b.
᎐
536
J. Chem. Soc., Perkin Trans. 1, 2001, 529–536