Synthesis, structure, and reactivity of (tropon-2-ylimino)arsorane and in situ generation of its stiborane and bismuthorane analogues: Reactions with heterocumulenes and an activated acetylene giving heteroazulenes

Article abstract of DOI:10.1039/b103098c

(Tropon-2-ylimino)pnictoranes of the general structure RN=MPh₃ (R = tropon-2-yl; M = As, Sb, and Bi) 4-6 have been prepared for the first time by the reaction of 2-aminotropone with Ph₃MX₂ (M = As, Sb, and Bi) in the presence of a base. The arsorane derivative (M = As) 4 is isolated as a stable crystalline compound, while the stiborane (M = Sb) and the bismuthorane (M = Bi) derivatives 5 and 6 are not isolated and are prepared in situ due to their moisture sensitivity. The X-ray crystal analysis revealed that compound 4 exhibits two different conformations in the solid state, and that the As-O bond distances (2.33 A) lie below the sum of the van der Waals radii (3.37 A), and thus, there is appreciable bonding interaction between the arsine and the oxygen atoms. With a view to constructing a series of cyclohepta-annulated heterocycles and in order to gain a better understanding of a series of iminopnictoranes, compounds 4-6 were allowed to react with heterocumulenes such as carbon disulfide, phenyl isothiocyanate, phenyl isocyanate, and diphenylcarbodiimide, in an aza-Wittig/electrocyclization or a formal [8 + 2] type cycloaddition eliminating triphenylpnictorane oxide to give 2H-cycloheptaoxazol-2-one, its thione, and imine derivatives. On the other hand, the reaction of compounds 4 and 5 with dimethyl acetylenedicarboxylate (DMAD) gives postulated dimethyl cyclohepta[b]pyrrole-2,3-dicarboxylate, which subsequently reacts with DMAD to result in the formation of tetramethyl 2H-cyclohepta[gh]pyrrolizine-1,2,4,5-tetracarboxylate, while the reaction of 6 gives only intractable tarry materials. The reactivity of the compounds 4-6, which contain a formal N=M (M = As, Sb, and Bi) double bond, has been clarified to be in the order of 6 (M = Bi) > 5 (M = Sb) > 4 (M = As) > [the corresponding iminophosphorane derivative 3 (M = P)].

Full text of DOI:10.1039/b103098c

View Article Online / Journal Homepage / Table of Contents for this issue
Synthesis, structure, and reactivity of (tropon-2-ylimino)arsorane
and in situ generation of its stiborane and bismuthorane
analogues: reactions with heterocumulenes and an activated
acetylene giving heteroazulenes
1
Makoto Nitta,* Yuhki Mitsumoto and Hiroyuki Yamamoto
Department of Chemistry, School of Science and Engineering,
Materials Research Laboratory for Bioscience and Photonics,
Waseda University, Shinjuku-ku, Tokyo 169-8555, Japan
Received (in Cambridge, UK) 5th April 2001, Accepted 20th June 2001
First published as an Advance Article on the web 26th July 2001
(Tropon-2-ylimino)pnictoranes of the general structure RN᎐MPh (R = tropon-2-yl; M = As, Sb, and Bi) 4–6
᎐
3
have been prepared for the first time by the reaction of 2-aminotropone with Ph3MX2 (M = As, Sb, and Bi) in
the presence of a base. The arsorane derivative (M = As) 4 is isolated as a stable crystalline compound, while
the stiborane (M = Sb) and the bismuthorane (M = Bi) derivatives 5 and 6 are not isolated and are prepared
in situ due to their moisture sensitivity. The X-ray crystal analysis revealed that compound 4 exhibits two different
conformations in the solid state, and that the As–O bond distances (2.33 Å) lie below the sum of the van der Waals
radii (3.37 Å), and thus, there is appreciable bonding interaction between the arsine and the oxygen atoms. With
a view to constructing a series of cyclohepta-annulated heterocycles and in order to gain a better understanding
of a series of iminopnictoranes, compounds 4–6 were allowed to react with heterocumulenes such as carbon disulfide,
phenyl isothiocyanate, phenyl isocyanate, and diphenylcarbodiimide, in an aza-Wittig/electrocyclization or a formal
[8 ϩ 2] type cycloaddition eliminating triphenylpnictorane oxide to give 2H-cycloheptaoxazol-2-one, its thione,
and imine derivatives. On the other hand, the reaction of compounds 4 and 5 with dimethyl acetylenedicarboxylate
(DMAD) gives postulated dimethyl cyclohepta[b]pyrrole-2,3-dicarboxylate, which subsequently reacts with DMAD
to result in the formation of tetramethyl 2H-cyclohepta[gh]pyrrolizine-1,2,4,5-tetracarboxylate, while the reaction
of 6 gives only intractable tarry materials. The reactivity of the compounds 4–6, which contain a formal N᎐M
᎐
(M = As, Sb, and Bi) double bond, has been clarified to be in the order of 6 (M = Bi) > 5 (M = Sb) > 4
(M = As) > [the corresponding iminophosphorane derivative 3 (M = P)].
Introduction
Iminopnictoranes 1a–d are a class of compounds bearing a
formal double bond between the nitrogen and the pnictogen
elements (Fig. 1). They have been receiving considerable atten-
tion in view of their chemical analogy to pnictogen ylides as
well as their potential utility in organic synthesis.1–3 The prop-
erties of iminopnictoranes are highly dependent on the identity
of the pnictogen. The dipolar and nucleophilic character of
the iminopnictoranes appears to increase, and their stability
decreases, when the pnictogen stands lower in the Periodic
Table. The difference between iminophosphoranes and other
iminopnictoranes is commonly ascribed to the less efficient
pπ–dπ overlap between the N-p orbitals and the larger and
more diffuse 4d, 5d, and 6d orbitals of arsine, stibine, and
bismuth elements, and the decreased electrostatic interaction
across the imide bonds, but it is probable that these are not the
only factors involved.2 Iminoarsoranes (M = As) appear to be
more resistant to hydrolysis than the corresponding imino-
stiboranes (M = Sb) and iminobismuthoranes (M = Bi) for even
the simple example (R = H),2,4 and can be handled in air,
although they are less stable than their phosphorane analogues.
All known iminopnictoranes (M = Sb,5,6 Bi5–9) are stabilized by
highly electronegative organic sulfonyl5,8 and trifluoroacetyl10
groups on the nitrogen atom, but no iminopnictoranes (M = Sb,
Bi) bearing a functional group other than organic sulfonyl
and trifluoroacetyl10 groups have been reported to date. On
the other hand, the utility of (vinylimino)phosphoranes 2 as
Fig. 1
useful building blocks for the synthesis of azaheterocycles
hasbeendemonstratedconvincingly.11–15 (Vinylimino)phosphor-
anes undergo
a single-step annulation with compounds
containing two electrophilic centers such as α-bromo ketones,
α,β-unsaturated ketones and aldehydes, and related Michael
acceptors to give a variety of nitrogen heterocycles.13 In relation
to these studies, we have been interested recently in exploiting
DOI: 10.1039/b103098c
J. Chem. Soc., Perkin Trans. 1, 2001, 1901–1907
This journal is © The Royal Society of Chemistry 2001
1901

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the synthesis, structure, and reactivities afforded by the (tropon-
2-ylimino)phosphorane† 3.16 The X-ray crystallographic
analysis of 3 has revealed that the P---O distance is significantly
longer than a covalent bond, but the oxygen atom in 3 intra-
molecularly coordinates to the phosphorus atom. It is also
clarified that the reaction of 3 with heterocumulenes provides a
new methodology for constructing new cyclohepta-annulated
five-membered heterocycles (heteroazulenes). In order to gain
a better understanding of this class of iminopnictoranes, we
have embarked on the preparation of a series of iminopnic-
toranes 4–6, which could be stabilized by coordination of the
oxygen atom to the pnictogenes like the phosphorus analogue
3. We report herein the first synthesis, structure, and reactivity
of the (tropon-2-ylimino)arsorane 4 as well as in situ generation
of the (tropon-2-ylimino)stiborane 5 and bismuthorane 6 and
their reaction with heterocumulenes and dimethyl acetylene-
dicarboxylate (DMAD).
C11Ј) in apical positions, (N1, C21, and C31) and (N1Ј, C21Ј,
and C31Ј) in equatorial positions, respectively] and the center
of a tetrahedral configuration, with the bond angles shown in
Fig. 3. On the other hand, the intramolecular As1---O1 and
As1Ј---O1Ј distances (2.33 Å for I and II) are longer than a
covalent bond (1.74–1.90 Å) in spirobi(1,3,2λ5-dioxarsolane)
derivative,19 and are significantly shorter than the sum of the
van der Waals radii (3.37 Å).20 Thus, evidently, the oxygen atom
of compound 4 intramolecularly coordinates to the arsine
atom. The As1–N1 (1.81 Å for I) and As1Ј–N1Ј (1.82 Å for II)
bonds are slightly longer than a standard formal As᎐N
᎐
bond (1.71–1.78 Å).21 This is also in accord with the observed
relatively short N1–C2 (1.32 Å) and N1Ј–C2Ј (1.28 Å) bond
lengths for I and II, as compared with typical N–C(sp2)
bond length (1.38 Å).22 Thus, the As1᎐N1 and As1Ј᎐N1Ј
᎐
᎐
bonds possess little double-bond character, and the canonical
structures 4A and 4B best represent the actual bonding in 4.
The tropone moiety in compound 4 is nearly planar, and bond
length alternation is clearly seen (1.37–1.46 Å for I; 1.37–1.47 Å
for II); the result is also in agreement with the evidence
Results and discussion
In our previous paper, we reported a Kirsanov reaction,17
treating 2-aminotropone 7 with Ph3PCl2 in benzene to yield
(tropon-2-ylimino)phosphorane in good yield (Scheme 1).16
1
obtained from the H NMR spectra (Table 1). The carbonyl
absorption appearing at νmax 1590 cmϪ1 in the IR spectrum is
23
slightly lower than those found in tropone (νmax 1594 cmϪ1
)
and compound 3 (νmax 1596 cmϪ1),16 and the C᎐O bond lengths
᎐
(1.27 Å for I and 1.24 Å for II) do not differ appreciably
from those of tropone and compound 3 (1.26 Å).16,24 Com-
pound 4 is stable at room temperature for a month in dry nitro-
gen atmosphere, and it is not stable over silica gel. On treatment
of 4 with water or acid, it underwent hydrolysis to afford
2-aminotropone 7 and triphenylarsine oxide (Scheme 1).
25
On the other hand, the reaction of 7 with Ph3SbCl2 and
Ph3BiCl2 in the presence of ButOK in benzene proceeded in
26
5–10 min, but the usual work-up did not afford the stiborane 5
and bismuthorane 6, respectively, and only the starting material
7 was isolated. However, in situ generation of 5 and 6 in hexa-
deuteriobenzene (C6D6) was carried out, and the 1H NMR
spectra confirmed the formation of 5 and 6 (Scheme 1). The 1H
NMR spectral data of 5 and 6 as well as of isolated 4 and
1
in situ-generated 4 are summarized in Table 1. The H NMR
spectral data of 4–6 resemble each other and clearly suggest
the clean generation of 4, 5, and 6. Compounds 5 and 6 are
actually clarified by 1H NMR spectral studies as being moisture
sensitive. The addition of a trace amount of water caused
decomposition of 5 and 6 leading to 2-aminotropone 7 (Scheme
1). Furthermore, compounds 4 and 5 are stable under heating
in benzene (cf. Table 2), while compound 6 in benzene seems
to eliminate the tropon-2-ylnitrene moiety to give Ph3Bi in
84% yield after heating under reflux for 1 h (see Experimental
section).10 Thus, the moisture sensitivity of (tropon-2-ylimino)-
iminopnictoranes 4–6 seems to increase and the thermal
stability decreases when the pnictogen element stands lower
in the Periodic Table.
Scheme 1 Reagents and conditions: i, Ph3AsBr2, NEt3, PhH or C6D6,
rt; ii, H2O or H3Oϩ; iii, Ph3SbCl2, ButOK, PhH or C6D6, rt; iv Ph3BiCl2,
ButOK, PhH or C6D6, rt; v, H2O.
Previously, the iminophosphorane 3 was revealed to react
with heterocumulenes to afford cyclohepta-annulated hetero-
cycles (Table 2, Entries 1, 5, 15, and 20).16 In relation to that
study and to clarify the reactivities, the reactions of pnictoranes
4–6 with heterocumulenes 8a–d were investigated. The reaction
of compounds 4 and in situ-generated 5 and 6 with carbon
disulfide 8a was accomplished to give 2H-cycloheptaoxazole-
2-thione 11 (Scheme 2). Similarly, the reactions of compounds
4 and in situ-generated 4–6 with phenyl isothiocyanate 8b
were also carried out to give N-phenyl-2H-cycloheptaoxazole-
2-imine 12, which is a mixture of (Z )- and (E)-isomers in
the ratio 7 : 3.16 The reaction conditions and the yields of the
products are summarized in Table 2 (Entries 2–4 and 6–9). The
reaction of isolated 4 with 8b gave a good yield of 12, while that
of in situ-generated 4 with 8b gave a modest yield of 12 (Table 2,
Entries 6 and 7). The structures of compounds 11 and 12 were
confirmed on the basis of a comparison of their physical data
with those of the authentic specimens.16 The iminopnictoranes
This imination procedure is known to be useful also for
the preparation of (tropon-2-ylimino)pnictoranes 4, 5, and 6.
18
2-Aminotropone 7 reacted with Ph3AsBr2 in the presence of
NEt3 at room temperature to give (tropon-2-ylimino)arsorane
4 in good isolated yield. The structure of compound 4
was confirmed from an inspection of the spectroscopic data
including 1H NMR spectra (Table 1), IR, UV–visible, and mass
spectral data as well as elemental analysis, and finally X-ray
crystal structure analysis.
The X-ray crystal analysis revealed compound 4 exhibits two
different conformations in the solid state. Two ORTEP draw-
ings of the conformers I and II are shown in Fig. 2, where the
arsine atoms of conformers I and II lie between the center of a
trigonal bipyramidal configuration [(O1 and C11) and (O1Ј and
† The non-systematic term ‘tropon-2-yl’ will be used in both this section
and the Results and discussion; systematic nomenclature (7-oxo
cyclohepta-1,3,5-trienyl) will be used in the Experimental section.
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J. Chem. Soc., Perkin Trans. 1, 2001, 1901–1907

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Table 1 1H NMR spectral data (500 MHz) of pnictoranes 4–6
Compd
H3
H4
H5
H6
H7
Remaining signals
4a
4b
4c
5c
6c
δH
J
δH
J
δH
J
δH
J
δH
J
7.66
8.01
7.36
7.04
7.91
7.12
6.99
6.85
6.52
6.93
6.54
6.36
6.31
6.05
6.36
6.98
6.76
6.77
6.42
6.80
6.75
7.03
7.11
6.06
7.25
7.36–7.42 (9H, m, Ph),
7.62–7.66 (6H, m, Ph),
7.08–7.13 (9H, m, Ph)
7.72–7.90 (6H, m, Ph)
7.15–7.22 (9H, m, Ph),
7.72 (6H, d, J 6.6, Ph)
7.07–7.30 (15H, Ph)
10.5
11.0
11.6
10.4
11.9
9.3
9.4
9.0
9.5
9.4
9.5
9.4
10.7
10.8
10.3
11.0
10.2
10.0
9.1
7.18–7.21 (9H, m, Ph),
7.95 (6H, d, J 7.0, Ph)
9.0
a Isolated compound in CDCl3. b Isolated compound in C6D6. c Compound prepared in situ in C6D6.
Fig. 2 ORTEP drawing of conformations I and II for 4 with thermal ellipsoid plot (40% probability) (with crystallographic numbering). Selected
bond lengths (Å). For I: As1–O1 2.326, As1–C11 1.964(5), As1–C21 1.957(5), As1–C31 1.940(5), As1–N1 1.814(5), O1–C1 1.274(7), N1–C2 1.315(7),
C1–C2 1.462(8). C2–C3 1.409(8), C3–C4 1.369(9), C4–C5 1.435(10), C5–C6 1.378(11), C6–C7 1.395(9), C7–C1 1.370(8). For II: As1Ј–O1Ј 2.332,
As1Ј–C11Ј 1.976(5), As1Ј–C21Ј 1.948(5), As1Ј–C31Ј 1.961(5), As1Ј–N1Ј 1.820(5), O1Ј–C1Ј 1.237(7), N1Ј–C2Ј 1.284(7), C1Ј–C2Ј 1.471(8), C2Ј–C3Ј
1.405(8), C3Ј–C4Ј 1.420(10), C5Ј–C6Ј 1.370(11), C6Ј–C7Ј 1.419(9), C7Ј–C1Ј 1.391(8).
Scheme 2 Conditions: i, heat.
Fig. 3 Bond angles around nearly the trigonal bipyramidal structure
of conformations I and II for 4.
temperature, while reactions of 5 and 6 proceeded smoothly at
lower temperature (Table 2). Thus, it is clear that the reactivity
of 3–6 is in the order 3 < 4 < 5 < 6. The reactivity due to the
dipolar and nucleophilic character of the iminopnictoranes 3–6
appears to increase when the pnictogen stands lower in the
Periodic Table.
Since the reaction of the iminophosphorane 3 (Fig. 1) with
diphenylcarbodiimide 8c has not been investigated,16 the
iminopnictoranes 3–6 were allowed to react with diphenylcarbo-
4–6 undergo an aza-Wittig-type reaction to eliminate the sulfur
atom of 8a,b to lead to the intermediates 9 and 10, which then
undergo 10π-electron cyclization to give 11 and 12, respect-
ively.16 This is similar to the reaction of 3 with carbon disulfide
8a and phenyl isothiocyanate 8b, respectively (Table 2, Entries 1
and 5). Compounds 3 and 4 undergo the reaction at elevated
J. Chem. Soc., Perkin Trans. 1, 2001, 1901–1907
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Table 2 Results for the reactions of compounds 3, 4, 5 and 6 with heterocumulenes 8a–d and DMAD 17
Reaction conditions
Entry
Compd.
Cumulene or 17
Ratio of 8a–d or 17 : 3–6a
Solventb
Time t/h
Product (Yield/%)
d
1c
2
3
3
8a
8a
8a
8a
8b
8b
8b
8b
8b
8c
8c
8c
8c
8c
8d
8d
8d
8d
8d
17
17
17
excess
excess
CS2d
1 week
2 days
30
4
9
5
1
4.5
3
7
10
4.5
11 (82)
4e
5
CS2
11 (92)
excess
excess
2
10
10
10
10
5
5
5
5
5
PhH–CS2f
PhH–CS2
PhMe
PhH
11 (82)
11 (21)
4
6
5c
6
3
12 (72), 16 (7)
12 (81)
4e
4
7
8
9
PhH
12 (42)
5
PhH
12 (72)
6
PhHf
Xylenes
PhH
12 (26)
10
11
12
13
14
15c
16
17
18
19
20c
21
22
3
12 (63), 14 (11)
12 (20), 14 (57)
12 (3), 14 (42)
14 (63)
4e
4
PhH
5
PhH
1
6
PhHf
PhH
10 min
1
1
30 min
5 min
25
4.5
20
14 (54)
12 (26), 16 (74)
16 (42)
16 (53)
16 (34)
12 (15), 14 (34)
23 (43)
3
2
4
10
10
10
10
3
5
10
PhH
PhH
5
6
PhHf
Xylenes
PhBr
PhBr
PhBr
4e
3
4e
5
23 (60)
23 (10)
1
a In the case of in situ generation of 4–6, the amounts correspond to the amount of 2-aminotropone 7 used. b Unless otherwise specified, the reaction
was carried out under reflux. c Ref. 16. d Reaction was carried out in an autoclave at 100 ЊC. e Isolated compound. f Stirred at room temperature.
diimide 8c, which was prepared in situ by the reaction of phenyl
isocyanate 8d in the presence of a catalytic amount of Ph3-
AsO.27 The reaction conditions and the yields of the products
are summarized in Table 2 (Entries 10–14). The reactions of 3
and 4 with 8c proceeded at relatively high temperature to give
products 12 and 14 (Scheme 3; Table 2, Entries 10–12). On the
to proceed via an aza-Wittig reaction giving the intermediate
10 and via a formal [8 ϩ 2]-type electrocyclization to give the
intermediate 13, while those of 5 and 6 with 8c proceed via the
intermediate 13. The intermediates 10 and 13 then collapse to
result in the formation of 12 and 14, respectively. The formation
of 13 is suggestive of the M---O (M = P, As, Sb, Bi) coordin-
ating interaction in compounds 3–6, and the interaction may
appear to be larger when the pnictogen atom is lower in the
Periodic Table.
On the other hand, the reactions of 4–6 prepared in situ with
phenyl isocyanate 8d afforded 2H-cycloheptaoxazol-2-one 16,
which probably arises from an aza-Wittig-type reaction giving
the intermediate 15, in modest yields (Scheme 4, Table 2, Entries
Scheme 3 Conditions: i, heat.
other hand, the reactions of 5 and 6 with 8c proceeded select-
ively under mild conditions to give the single product 14
(Entries 13 and 14). The structure of new compound 14 was
assigned on the basis of its 1H and 13C NMR spectra, IR, UV–
visible spectra, mass spectral data, and analytical data, as well
as a comparison of its physical data with those of related
derivatives.28 Furthermore, it was found that compound 14 is
not a mixture of (E)- and (Z )-isomers. Although no evidence
for the stereochemical situation for 14 was obtained, we prefer
the (Z )-isomer for 14, because of the steric hindrance of the
phenyl groups. The reactions of 3 and 4 with 8c are considered
Scheme 4 Conditions: i, heat.
16–18). In these cases, the reactions of 5 and 6 seem to proceed
quickly or under mild conditions as compared with that of 4. In
the reaction of isolated 4 with 8d at elevated temperature of
refluxing xylenes, products 12 and 14, instead of 16, were
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J. Chem. Soc., Perkin Trans. 1, 2001, 1901–1907

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isolated (Table 2, Entry 19). This process is similar to the reac-
tion of 4 with 8c (Table 2, Entries 11 and 12). Ph3AsNPh is
generated in the reaction of 4 with 8d giving the intermediate
15, which probably reacts with excess of 8d to generate carbo-
diimide 8c and Ph3AsO. The latter compound further reacts
with 8d to generate Ph3AsNPh, and thus, 8c is generated in a
catalytic process.27 The independent reaction of 16 with
Ph3AsO in refluxing xylenes gives compound 4, which is
detected by its 1H NMR spectrum. Thus, compound 16, which
is generated by the reaction of isolated 4 with 8d at first,
collapses to give 4, which reacts with 8c to result in the
formation of 12 and 14 (Scheme 4).
aza-Wittig-type reaction to result in the formation of 20.
Reactions similar to the formation of 21 have been shown in the
reaction of simple iminophosphoranes,30 iminoarsoranes,2 and
iminostiboranes31 with DMAD. 1-Azaazulene has been shown
to react with DMAD to give an intermediate such as 22,32
in which hydrogen migration results in the formation of the
product 23.
In conclusion, we have demonstrated the synthesis of a series
of (tropon-2-ylimino)pnictoranes 4–6 and their reactions with
heterocumulenes and an activated acetylene to provide a variety
of cyclohepta-annulated five-membered heterocycles (hetero-
azulenes). The arsorane 4 was isolated as a stable crystalline
compound and clarified by X-ray structure analysis to be
stabilized by not only the electron-withdrawing tropone but
also by coordination of the carbonyl oxygen to the arsine
element. The stiborane and bismuthorane analogues 5 and 6
prepared in situ seemed also to be stabilized by a similar
coordination as in the case of 4, as demonstrated through their
reaction with diphenylcarbodiimide 8c. Through the reactions
of 4–6 and the phosphorane 3 in part with heterocumulenes, the
dipolar and nucleophilic character of a series of pnictoranes
3–6 appears to increase and their stability decreases when
the pnictogen stands lower in the Periodic Table. Further
studies concerning the synthesis of pnictoranes and their syn-
thetic applicability are underway.
Finally, as in the case of the reaction of the phosphorane 3,
the isolated 4 and in situ-prepared 5 reacted with DMAD 17
to give tetramethyl 2H-cyclohepta[gh]pyrrolizine-1,2,4,5-tetra-
carboxylate 23 (Scheme 5; Table 2, Entries 21 and 22). The reac-
Experimental
IR spectra were recorded on a Horiba FT-710 spectrometer.
UV–visible spectra were recorded on a Shimadzu UV-3101PC
spectrometer. Mass spectra and high-resolution mass spectra
(FAB) were run on JEOL JMS-AUTOMASS150 and JMS-
SX102A spectrometers. 1H NMR spectra and 13C NMR spectra
were recorded on a JEOL JNM-LA500 spectrometer using
CDCl3 and C6D6 as solvents, and the chemical shifts are
given relative to internal or external SiMe4 standard; J-values
are given in Hz. Compounds Ph3AsBr2,18 Ph3SbCl2,25 and
26
Ph3BiCl2 were prepared according to the procedure reported
in the literature. Mps were recorded on a Yamato MP-21
apparatus and are uncorrected. All the reactions except
hydrolysis were carried out under anhydrous conditions and
dry nitrogen atmosphere.
Preparation of (7-oxocyclohepta-1,3,5-trienylimino)triphenyl-
arsorane 4
To a stirred solution of Ph3As (919 mg, 3.0 mmol) in benzene
(5 cm3) was added a solution of bromine (479 mg, 3.0 mmol) in
benzene (2 cm3) dropwise at rt, and the mixture was stirred
for another 30 min. To this mixture was added a solution of
2-aminotropone 7 (363 mg, 3.0 mmol) and NEt3 (627 mg, 6.2
mmol) in benzene (2 cm3), and the mixture was stirred for 16 h
at rt. The reaction mixture was then filtered through Celite and
the filtrate was concentrated. The residue was washed with
diethyl ether under dry nitrogen atmosphere to give 4 (1.15 g,
90%) as yellow prisms; mp 154–158 ЊC (decomp. from AcOEt);
δC (CDCl3) 119.0 (C7), 121.7 (C5), 123.2 (C3), 128.7 (Ph), 130.2
(Ph), 131.7 (Ph), 136.3 (C4), 138.8 (Ph), 170.1 (C2), 173.6 (C1);
νmax (CHCl3)/cmϪ1 1590, 1498, 1424, 1400, 1354, 1086; λmax
(MeCN)/nm (log ε/dm3 molϪ1 cmϪ1) 252 (4.48), 364 (4.11),
397sh (3.64), 421sh (3.68), 444 (3.86) (Found: Mϩ ϩ 1,
426.0861; C, 70.4; H, 4.6; N, 3.2. C25H20AsNO requires M ϩ 1,
426.0840; C, 70.59; H, 4.74; N, 3.29%).
Scheme 5 Conditions: i, heat.
tion of 6 with DMAD 17 at rt, however, did not give compound
23, and only intractable tarry materials were obtained. In these
reactions, the reactivity of 4–6 seems to be also in the order
4 < 5 < 6. The structure of compound 23 was assigned on the
basis of a comparison of its physical data with those of the
authentic specimen.16 Michael-type addition of the nitrogen
atom of compound 4 and 5 to DMAD 17 gives the intermedi-
ates 18 and/or 19. Then the M–O (M = As and Sb)-bonded
intermediate 18 eliminates Ph3MO (M = As and Sb) to result
in the formation of 1-azaazulene derivative 20.16 An inter-
mediate similar to 20 has also been postulated in the reaction of
2-(triphenylphosphoranylidenemethyl)tropone with DMAD
giving an azulene derivative.29 An alternative pathway is a
ring-opening of 19 to give the intermediate 21 and the following
Hydrolysis of 4 in acidic and neutral conditions
A solution of 4 (51 mg, 0.12 mmol) in 0.5 M H2SO4 (water–
EtOH 10 : 1; 5 cm3) was stirred at rt for 30 min. This mixture
was neutralized with aq. NaHCO3, the mixture was extracted
with CH2Cl2, and the extract was dried over Na2SO4. After
evaporation of the mixture, the residue was separated by TLC
J. Chem. Soc., Perkin Trans. 1, 2001, 1901–1907
1905

View Article Online
on SiO2 (AcOEt) to give 7 (13 mg, 89%) and Ph3AsO (32 mg,
83%).
cmϪ1) 266 (4.64), 422 (4.39); m/z 297 (Mϩ, 72%), 77 (100)
(Found Mϩ ϩ 1, 298.1307; C, 80.8; H, 5.0; N, 14.1. C20H15N3
requires M ϩ 1, 298.1344; C, 80.78; H, 5.08; N, 14.13%).
A solution of 4 (85 mg, 0.2 mmol) in water–EtOH (1 : 1; 5
cm3) was stirred at rt for 4.5 h. Then the reaction mixture was
extracted with CH2Cl2, and the extract was dried over Na2SO4.
After evaporation of the mixture, the residue was separated by
TLC on SiO2 (AcOEt) to give 7 (20 mg, 83%) and Ph3AsO
(50 mg, 78%).
Reaction of 2H-cycloheptaoxazol-2-one 16 with Ph3AsO
to give 4
A solution of 16 (22 mg, 0.15 mmol) and Ph3AsO (49 mg, 0.15
mmol) in benzene (2 cm3) was heated under reflux for 15 h.
After evaporation of the mixture, the residue was monitored by
1H NMR to contain 4 and 7 in the ratio 7 : 4. The residue was
then separated by TLC on SiO2 (AcOEt) to give 7 (16 mg, 89%;
Rf = 0.5). The base line on the TLC plates was further
developed by CH2Cl2–EtOH 10 : 1 to give Ph3AsO (47 mg,
96%; Rf = 0.7).
1H NMR studies of (7-oxocyclohepta-1,3,5-trienylimino)triphen-
ylpnictoranes 4, 5, and 6
A suspension of 7 (29 mg, 0.24 mmol), NEt3 (61 mg, 0.6 mmol),
and Ph3AsBr2 (112 mg, 0.24 mmol) in C6D6 (5 cm3) was stirred
at room temperature for 10 min to give a suspension of 4. In a
similar manner, suspensions of 7 (29 mg, 0.24 mmol), ButOK
(67 mg, 0.6 mmol), and Ph3SbCl2 (102 mg, 0.24 mmol) or
Ph3BiCl2 (123 mg, 0.24 mmol) in C6D6 (5 cm3) were stirred for
5 min to make clean suspension of the product 5 or 6. The
suspensions were filtered through glass wool quickly, the filtrate
was introduced into an NMR tube under dry nitrogen atmos-
phere, and the 1H NMR spectra of the solutions of 4, 5, and 6
were recorded using Me4Si as external standard. The results are
summarized in Table 1.
In situ preparation of 4 and reactions with heterocumulenes 8b–d
To a stirred solution of Ph3As (153 mg, 0.5 mmol) in benzene
(5 cm3) was added bromine (80 mg, 0.5 mmol) and the mixture
was stirred for 5 min at room temperature. To this mixture were
added 7 (61 mg, 0.5 mmol) and NEt3 (111 mg, 1.1 mmol) and
the mixture was stirred for another 30 min. To this solution was
added a heterocumulene 8, and the mixture was heated for the
period indicated in Table 2. The reaction mixture was concen-
trated and the resulting residue was separated by TLC on SiO2
(AcOEt) to give the products, 12, 14, and 16 (Table 2, Entries 7,
12, and 16).
In the reaction with diphenylcarbodiimide 8c, a solution
of 8d (596 mg, 5.0 mmol) and Ph3AsO (32 mg, 0.1 mmol) in
benzene (3 cm3) was heated under reflux for 2 h. The generation
of 8c was confirmed by its IR spectrum. This solution was
subsequently used for the reaction with a solution of 4 prepared
above.
Thermal reaction of the bismuthorane 6
A solution of 7 (30 mg, 0.25 mmol), ButOK (50 mg, 0.5 mmol),
and Ph3BiCl2 (128 mg, 0.25 mmol) in benzene (2 cm3) was
stirred at rt for 5 min. The reaction mixture was heated under
reflux for 1 h. After evaporation of the mixture, the residue was
separated by column chromatography on SiO2 (hexane–AcOEt
5 : 1) to give Ph3Bi (92 mg, 84% base on 7).
Reaction of isolated 4 with carbon disulfide 8a
Reaction of the phosphorane 3 with the carbodiimide 8c
A solution of 4 (85 mg, 0.2 mmol) in carbon disulfide (8 cm3)
was heated at 100 ЊC in an autoclave for 2 days. After evapor-
ation of the mixture, the residue was crystallized from CH2Cl2
to give 11 (30 mg, 92%) (Table 2, Entry 2).
A solution of 8d (357 mg, 3 mmol) and Ph3AsO (10 mg, 0.03
mmol) in xylenes (5 cm3) was heated at 90 ЊC for 2 h. To this
reaction mixture was added the phosphorane 3 (114 mg, 0.3
mmol), and the mixture was heated under reflux for 7 h. After
evaporation of the mixture, the residue was separated by TLC
on SiO2 (AcOEt) to give the products, 12 and 14 (Table 2, Entry
10).
Reactions of isolated 4 with heterocumulenes 8b,c
A solution of 4 (64 mg, 0.15 mmol) and 8b,c in benzene (3 cm3)
was heated under reflux. After evaporation of the mixture,
the residue was purified by TLC on SiO2 (AcOEt) to give the
products, 12 and 14 (Table 2, Entries 6 and 11).
In the reaction with carbodiimide 8c, a solution of phenyl
isocyanate 8d (179 mg, 1.5 mmol) and Ph3AsO (10 mg, 0.03
mmol) in benzene (1 cm3) was heated under reflux for 2 h.
The generation of 8c was confirmed by its IR spectrum. This
solution was subsequently used for the reaction with 4 as
described above.
In situ preparation of 5 and reactions with heterocumulenes 8a–d
To a stirred solution of Ph3SbCl2 (212 mg, 0.5 mmol) and 7 (61
mg, 0.5 mmol) in benzene (3 cm3) was added ButOK (112 mg,
1.0 mmol), and the mixture was stirred for 30 min at rt. To this
solution was added a heterocumulene 8 and the mixture was
heated under reflux for the period indicated in Table 2. After
evaporation of the mixture, the resulting residue was separated
by TLC on SiO2 (AcOEt) to give the products, 11, 12, 14, and
16 (Table 2, Entries 3, 8, 13, and 17).
In the reaction with diphenylcarbodiimide 8c, a solution of
8d (596 mg, 5.0 mmol) and Ph3AsO (32 mg, 0.1 mmol) in
benzene (3 cm3) was heated under reflux for 2 h. The generation
of 8c was confirmed by its IR spectrum. This solution was
subsequently used for the reaction with a solution of 5 prepared
above.
Reaction of isolated 4 with 8d at high temperature
A solution of 4 (64 mg, 0.15 mmol) and 8d (179 mg, 1.5 mmol)
in xylenes (3 cm3) was heated under reflux for 25 h. After
evaporation of the mixture, the residue was separated by TLC
on SiO2 (AcOEt) to give the products, 12 and 14 (Table 2, Entry
19).
For N,1-diphenylcycloheptaimidazol-2(1H)-imine 14: dark
red prisms, mp 140–142 ЊC (from CH2Cl2–hexane); δH (CDCl3)
6.66 (1H, d, J 9.8, H8), 6.91 (1H, dd, J 10.8, 9.8, H6), 7.02 (1H,
m, Ph), 7.19 (1H, dd, 9.8, 10.0, H7), 7.31 (4H, m, Ph), 7.44 (1H,
dd, 9.8, 11.1, H5), 7.50 (2H, d, J 7.8, Ph), 7.52 (1H, t, J 7.5, Ph),
7.60 (1H, d, J 11.1, H4), 7.62 (2H, dd, J 7.5, 7.8, Ph); δC
(CDCl3) 110.2 (C8), 122.7 (Ph), 123.3 (Ph), 127.1 (C4), 127.9
(C6), 128.1 (Ph), 128.5 (Ph), 128.9 (Ph), 129.8 (Ph), 134.6
(quart), 136.2 (C7), 138.7 (C5), 149.1 (quart), 152.2 (quart),
159.3 (quart), 165.8 (quart); νmax/cmϪ1 (CHCl3) 1634, 1580,
1528, 1493, 1475, 1445, 1388; λmax (MeCN)/nm (log ε/dm3 molϪ1
In situ generation of 6 and reactions with heterocumulenes 8a–d
To a stirred solution of Ph3BiCl2 (256 mg, 0.5 mmol) and 7
(61 mg, 0.5 mmol) in benzene (3 cm3) was added ButOK (112
mg, 1.0 mmol), and the mixture was stirred for 5 min at rt. To
this solution was added a substrate 8, and the mixture was
stirred for the period indicated in Table 2. After the mixture was
filtered through Celite, the filtrate was concentrated and the
resulting residue was separated by TLC on SiO2 (AcOEt) to
give the products, 11, 12, 14, and 16 (Table 2, Entries 4, 9, 14,
and 18).
1906
J. Chem. Soc., Perkin Trans. 1, 2001, 1901–1907

View Article Online
3 N. C. Norman, Chemistry of Arsenic, Antimony and Bismuth,
In the reaction with the carbodiimide 8c, a solution of 8d
(596 mg, 5.0 mmol) and Ph3AsO (32 mg, 0.1 mmol) in benzene
(3 cm3) was heated under reflux for 2 h. The generation of 8c
was confirmed by its IR spectrum. This solution was sub-
sequently used for the reaction with a solution of 6 prepared
above.
Blackie Academic & Professional, London, Weinheim, New York,
Tokyo, Melbourne and Madras, 1998; H. Suzuki and Y. Matano,
Organobismuth Chemistry, Elsevier, Amsterdam, London, New
York, Oxford, Paris, Shannon and Tokyo, 2001.
4 R. Appel and D. Wagner, Angew. Chem., 1960, 72, 209.
5 G. Wittig and D. Hellwinkel, Chem. Ber., 1964, 97, 789.
6 H. Suzuki and T. Ikegami, J. Chem. Res. (S), 1996, 24.
7 H. Suzuki, C. Nakaya, Y. Matano and T. Ogawa, Chem. Lett., 1991,
105.
Reaction of 4 with DMAD 17
8 S. V. Pasenok, N. V. Kirij, Y. L. Yagupolskii, D. Naumann and
W. Tyrra, J. Fluorine Chem., 1993, 63, 179.
9 T. Ikegami and H. Suzuki, Organometallics, 1998, 17, 1013.
10 Y. Matano, H. Nomura, M. Shiro and H. Suzuki, Organometallics,
1999, 18, 2580.
11 Yu. G. Gololobov and L. F. Kasukhin, Tetrahedron, 1992, 48, 1353.
12 S. Eguchi, Y. Matsushita and K. Yamashita, Org. Prep. Proced. Int.,
1992, 24, 209.
A solution of 4 (64 mg, 0.15 mmol) and DMAD 17 (101 mg,
0.75 mmol) in bromobenzene (3 cm3) was heated under reflux
for 20 h. After evaporation of the mixture, the residue was
purified by TLC on SiO2 (AcOEt) to give 23 (35 mg, 60%),
which is identical with the authentic specimen (Table 2, Entry
21).
13 M. Nitta, Rev. Heteroatom. Chem., 1993, 9, 87 and references cited
therein.
In situ preparation of 5 and reaction with DMAD 17
14 P. Molina and M. J. Vilaplana, Synthesis, 1994, 1197.
15 H. Wamhoff, G. Richardt and M. Stölben, Adv. Heterocycl. Chem.,
1995, 64, 159.
16 H. Yamamoto, M. Ohnuma and M. Nitta, J. Chem. Res. (S), 1999,
173; (M), 1999, 901.
17 Yu. G. Gololobov, I. N. Zhmurova and L. F. Kasukhin, Tetrahedron,
1981, 37, 437.
18 A. D. Beveridge and G. S. Harris, J. Chem. Soc. (A), 1964, 6076.
19 R. O. Day, J. M. Holmes, A. C. Sau, J. R. Devillers, R. R. Holmes
and J. A. Deiters, J. Am. Chem. Soc., 1982, 104, 2127; R. H. Fish and
R. S. Tannous, Organometallics, 1982, 1, 1238; C. A. Poutasse, R. O
Day, J. M. Holmes and R. R. Holmes, Organometallics, 1985, 4, 708;
R. R. Holmes, R. O. Day and A. C. Sau, Organometallics, 1985, 4,
714.
To a stirred solution of Ph3SbCl2 (212 mg, 0.5 mmol) and 7
(61 mg, 0.5 mmol) in bromobenzene (3 cm3) was added ButOK
(112 mg, 1.0 mmol) and the mixture was stirred for 30 min at rt.
To this solution was added a solution of DMAD 17 (711 mg,
5 mmol) in bromobenzene (2 cm3) and the mixture was heated
under reflux for 1 h. The reaction mixture was then filtered
through Celite, the filtrated was concentrated, and the residue
was purified by TLC on SiO2 (hexane–AcOEt 1 : 2) to give 23
(Table 2, Entry 22).
Crystal structure determination of 4‡
Single crystal of [C H ON᎐AsPh ] 4 were recrystallised from
᎐
7
5
3
20 A. Bondi, J. Phys. Chem., 1964, 68, 441.
AcOEt.
21 H. W. Roesky, M. Witt, W. Clegg, W. Isenberg, M. Noltemeyer and
G. M. Sheldrick, Angew. Chem., Int. Ed. Engl., 1980, 19, 943;
M. Witt, H. W. Roesky, M. Noltemeyer, W. Clegg, M. Schmidt and
G. M. Sheldrick, Angew. Chem., Int. Ed. Engl., 1981, 20, 974;
R. Bohra, H. W. Roesky, J. Lucas, M. Noltemeyer and G. M.
Sheldrick, J. Chem. Soc., Dalton Trans., 1983, 1011; H. W. Roesky,
N. Bertel, F. Edelmann, M. Noltemeyer and G. M. Sheldrick,
Z. Naturforsch., Teil B, 1988, 43, 72; K. Bailey, I. Gosney, R. O.
Gould, D. Lloyd and P. Taylor, J. Chem. Res. (S), 1988, 386; (M),
1988, 2950.
Crystal data. C25H20AsNO, M = 425.37, orthorhombic,
a = 25.5308(0), b = 28.5381(0), c = 10.7821(0) Å, V = 7855.86(0)
Å3, T = 298 K, space group Pcnb (no. 60), Z = 16, µ(Cu-
Kα) = 2.4413 mmϪ1, 8598 reflections measured, 7190 unique
(Rint = 0.019). The final R(F 2) and wR(F 2) were 0.067 and
0.080 for 6515 observed reflections [F 2 > 2σ(F 2)] used in all
calculations.33
22 J. March, Advanced Organic Chemistry: Reactions, Mechanisms, and
Structure, Wiley, New York, Chichester, Brisbane, Toronto and
Singapore, 4th edn., 1992, p. 21, Table 1.5.
23 A. Krebs and B. Schrader, Justus Liebigs Ann. Chem., 1967, 709, 46.
24 M. J. Barrow, O. S. Mills and G. Filippini, J. Chem. Soc., Chem.
Commun., 1973, 66.
25 A. D. Beverridge, G. S. Harris and F. Inglis, J. Chem. Soc. (A), 1966,
520.
26 G. Wittig and K. Clauss, Justus Liebigs Ann. Chem., 1952, 578, 136.
27 J. J. Monagle, J. Org. Chem., 1962, 27, 3851; P. Frøyen, Acta Chem.
Scand., 1969, 23, 2935.
Acknowledgements
Financial support from Waseda University Grants for Special
Research Projects is gratefully acknowledged. We also thank
the Materials Characterization Central Laboratory, Waseda
University, for technical assistance with spectral data, elemental
analyses, and X-ray structure analysis.
28 I. Ueda, M. Matsuo, K. Taniguchi, S. Shigenaga and T. Ogawara,
Jpn. Kokai Tokkyo Koho, JP 64 03,172 [89 03,172] (Chem. Abstr.,
1989, 111, 57734g).
29 I. Kawamoto, Y. Sugimura, N. Soma and Y. Kishida, Chem. Lett.,
1972, 931.
‡ CCDC reference number 162394. See http://www.rsc.org/suppdata/
p1/b1/b103098c for crystallographic files in .cif or other electronic
format.
30 G. W. Brown, R. C. Cookson and I. D. R. Stevens, Tetrahedron Lett.,
1964, 1263; J. Barluenga, F. Lopez and F. Palacios, J. Chem. Soc.,
Perkin Trans. 1, 1989, 2273.
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31 P. Frøyen, Acta Chem. Scand., 1973, 27, 141.
2 D. Lloyd, I. Gosney and R. A. Ormiston, Chem. Soc. Rev., 1987,
16, 45; D. Lloyd and I. Gosney, in The Chemistry of Organic
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33 CRYSTAN, Crystal Structure Analysis Package, MAC Science Co.,
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J. Chem. Soc., Perkin Trans. 1, 2001, 1901–1907
1907