On the reaction of prop-2-enylidenetriphenylphosphorane derivatives. Novel synthesis of the azulene ring system

Article abstract of DOI:10.1039/a605581h

Reaction of prop-2-enylidenetriphenylphosphorane derivatives with several tropones has been studied in an attempt to provide a short new route to the azulene ring system. (2-Ethoxyprop-2-enylidene)triphenylphosphorane 4 reacts with 2-chloro-, 2-methoxy- and 2,3,5,7-tetrachlorotropones 7a-c to give azulene derivatives 8 and 9 in moderate yields. On the other hand, reaction of [2-ethoxy-3-(ethoxycarbonyl)prop-2-enylidene]triphenylphosphorane 6 with tropones 7a,c results in the formation of azulene esters 10 and 11 in low yields, whilst that with tropone 7b gives no azulene and substrate 7b is recovered. In order to gain insight into the mechanistic pathways, reaction of phosphoranes 4 and 6 with deuteriated tropones 14a,b which are the corresponding trideuteriated derivatives of compounds 7a,b, have also been studied. Furthermore, compound 4 reacts also with 5-(dimethylaminomethylene)cyclopenta-1,3-dienecarbaldehyde 33 to give 6-ethoxyazulene 37 in moderate yield.

Full text of DOI:10.1039/a605581h

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On the reaction of prop-2-enylidenetriphenylphosphorane derivatives.
Novel synthesis of the azulene ring system
Tohru Takayasu and Makoto Nitta*
Department of Chemistry, School of Science and Engineering, Waseda University, Sinjuku-ku,
Tokyo 169, Japan
Reaction of prop-2-enylidenetriphenylphosphorane derivatives with several tropones has been
studied in an attempt to provide a short new route to the azulene ring system. (2-Ethoxyprop-2-
enylidene)triphenylphosphorane 4 reacts with 2-chloro-, 2-methoxy- and 2,3,5,7-tetrachlorotropones
7a–c to give azulene derivatives 8 and 9 in moderate yields. On the other hand, reaction of [2-ethoxy-3-
(ethoxycarbonyl)prop-2-enylidene]triphenylphosphorane 6 with tropones 7a,c results in the formation of
azulene esters 10 and 11 in low yields, whilst that with tropone 7b gives no azulene and substrate 7b is
recovered. In order to gain insight into the mechanistic pathways, reaction of phosphoranes 4 and 6 with
deuteriated tropones 14a,b which are the corresponding trideuteriated derivatives of compounds 7a,b, have
also been studied. F urthermore, compound 4 reacts also with 5-(dimethylaminomethylene)cyclopenta-1,3-
dienecarbaldehyde 33 to give 6-ethoxyazulene 37 in moderate yield.
R1
R2
N
PR3
R1
R2
CH PR3
Introduction
Previously, we have demonstrated a simple preparation of
(vinylimino)phosphoranes 1, which have two nucleophilic
centres at the α- and β-positions.1 (Vinylimino)phosphoranes
are found to react with compounds bearing two electrophilic
centres or Michael acceptors [e.g. α-bromo ketones,2 α,β-un-
saturated ketones or aldehydes,3 tropone derivatives,4 methano-
[11]annulenones5 and 5-(dimethylaminomethylene)cyclopenta-
1,3-dienecarbaldehyde6,7] in an enamine alkylation process
followed by an aza-Wittig reaction. This provides efficient routes
to pyrroles, pyridines, 1-azaazulenes, methanocycloundeca[b-
]pyrrole and 5-azaazulenes. On the other hand, it was shown
that prop-2-enylidenephosphoranes 2 also have two nucle-
ophilic centres, at the α- and γ-positions. Although there are
several reports demonstrating substitution at both the α- and γ-
position,8 aldehydes and ketones usually react at the α-position
in a normal Wittig reaction.9 Acylation occurs predominantly
at the γ-position,10 whilst the regioselectivity of the alkylation is
uncertain because of a paucity of examples.11 It was shown that
prop-2-enylidenephosphoranes react with compounds contain-
ing two electrophilic centres, (e.g. α,β-unsaturated aldehydes,
ketones12,13 and α-halogeno ketones14) to give cyclohexadienes
and cyclopentadienes, respectively, bearing a variety of sub-
stituents. However, the synthetic utility of the prop-2-enyl-
idenephosphoranes in various annulation reactions is still
unexplored. In this context, we planned to take advantage of
the above methodology for the preparation of the azulene ring
system by using the reaction of (2-ethoxyprop-2-enylidene)-
triphenylphosphorane 4,15 which is prepared in situ by base
treatment of phosphonium salt 3,16 and the isolated analogue
[2-ethoxy-3-(ethoxycarbonyl)prop-2-enylidene]triphenylphos-
phorane 614 (see Scheme 1) with 2-chloro-, 2-methoxy- and
2,3,5,7-tetrachloro-tropones 7a–c and 5-(dimethylamino-
methylene)cyclopenta-1,3-dienecarbaldehyde 33. In order to
gain insight into the reaction pathways, 2-chloro-3,5,7-tri-
deuteriotropone 14a 17 and 3,5,7-trideuterio-2-methoxytropone
14b18 were also studied. We describe here our results in detail.
1
2
OEt
OEt
+
PPh3
PPh3
Br –
3
4
OEt
OEt
+
PPh3
PPh3
CO2Et
CO2Et
Br –
5
6
Scheme 1
summarized in Table 1. The reaction is considered to proceed
via a Michael addition from the γ-position of phosphoranes 4
and 6 onto the tropone nucleus as in the case of the reaction of
compounds 1 with tropones.4 The reaction of phosphorane 4
with tropones 7a and 7b proceeded under mild conditions to
give 2-ethoxyazulene 819 in moderate yield (entries 1–3). The
reaction of phosphorane 4 with tetrachlorotropone 7c, which
has four electron-withdrawing chlorine atoms, did not proceed
at room temperature, but was successful at 70 ЊC to give
4,5,7-trichloro-2-ethoxyazulene 9 in modest yield (entry 4). On
the other hand, reaction of ester phosphorane 6, which has an
additional electron-withdrawing CO2Et group on the parent
structure 4, did not react with the tropone 7a at room temp-
erature, and tropone 7a was recovered. However, compound 6
reacted with the tropone 7a to give 2-ethoxy-1-ethoxycarbonyl-
azulene 1020 under forcing conditions (entry 5). Similarly, the
reaction of compound 6 with the tropone 7c afforded azulene
derivative 13 in low yield (entry 7). Compound 6 did not react
with tropone 7b, and the starting material 7b was recovered
(entry 6). It is clear that the phosphorane 4, which has an
electron-donating substituent, reacts smoothly under mild con-
ditions to result in moderate yields of the products. The phos-
Results and discussion
Reaction of prop-2-enylidenephosphoranes 4 and 6 with tro-
pones 7a–c was carried out to give azulene derivatives (Scheme
2). The reaction conditions and the yields of the products are
J. Chem. Soc., Perkin Trans. 1, 1997
681

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Table 1 Reaction of phosphoranes 4 and/or 6 with tropones 7a–c, 14a,b and carbaldehyde 33
Reaction conditions
Entry
Phosphorane
Tropone
Solvent
T/ЊC
t/h
Product
Yield (%)
1
2
3
4
5
6
7
8
9
4a
4a
4b
4b
6
7a
7b
7b
7c
7a
7b
7c
14a
14b
14a
33
DMSO
DMSO
DMF
DMF
DMSO
DMF
r.t.c
r.t.
r.t.
70
140
145
90
r.t.
r.t.
120
95
12
12
10
1
12
12
12
2
8
8
8
9
60
55
55
21
27
10
none
11
6
6
DMF
4
50
54
27
66
4b
4b
6
DMSO
DMSO
DMSO
DMF
24
2
12
12
24/28d
29/30e
37
10
11
4b
a
ButOK was used to generate phosphorane 4. b KN(SiMe3)2 was used to generate phosphorane 4. c Room temp. d A mixture of products 24 and 28 in
the ratio 1:3. e A mixture of products 29 and 30 in the ratio 1:6.
O
to take place at C-7 (abnormal substitution), while that onto 2-
methoxytropone7boccursat C-2(normalsubstitution)to give2-
substituted tropones.21 It was shown that methylenetriphenyl-
phosphorane 12 does not undergo Wittig reaction with tropone
7a but it does react with this tropone to give oxaphosphole
derivative 13, the structure of which was assigned by X-ray crys-
tallographic analysis.22 Since mechanistic aspects of the reac-
tion are unclear,18 the pathways for the formation of compound
13 are confirmed here by labelling the troponoid ring with deu-
terium (Scheme 3). Thus, the attempted reaction of phos-
phorane 12 with compound 14a afforded compound 17. The
structural assignment of 17 was based on high-resolution mass
spectral data as well as on a comparison of the 1H NMR spec-
tral data with those of the parent compound 13. Thus it is clear
that compound 12 attacks at C-7 of tropone 14a to give inter-
mediate 15, which undergoes proton migration, regenerating a
phosphorane compound, 16. The elimination of DCl, followed
by cyclization, gives bicycle 17. On the other hand, methylene-
phosphorane 12 attacks at C-2 in the reaction with 2-methoxy-
tropone 14b to give the intermediate 18, which undergoes pro-
ton transfer to regenerate a phosphorane, compound 19. The
elimination of HOMe in compound 19 occurs readily, and the
subsequent cyclization gives the oxaphosphole 20. The struc-
ture 20 was assigned unequivocally on the basis of high-
resolution mass and 1H NMR data. The formation of
oxaphospholes 17 and 20 suggests that reaction of phos-
phorane 12 with tropones 14a and 14b proceeds in a different
way to give the products, and the results are in good accord with
the reactivity observed in usual nucleophilic substitutions of
tropones 7a,b.21
X
4
OEt
7a; X = Cl
b; X = OMe
8
Cl
O
Cl
Cl
Cl
Cl
4
OEt
Cl
Cl
7c
7a
9
6
OEt
CO2Et
10
Cl
Cl
Cl
6
OEt
CO2Et
7c
11
On the other hand, the reaction of the phosphorane 4 with
tropone 14a gave compound 24 (Scheme 4, Table 1). The H
Scheme 2
1
phorane 6, which has an additional CO2Et group, is considered
to be less reactive. 2-Chlorotropone 7a seems to be more effec-
tive than 2-methoxytropone 7b for the preparation of the
azulene ring system (cf. entries 5 and 6).
NMR spectrum unequivocally showed, besides an ethyl group,
three signals. These signals are assigned to the C-1/3, C-4/8 and
C-6 protons, respectively. This fact suggests that initial γ-
alkylation of compound 4 onto tropone 14a (7a) occurred at
C-7 to give the intermediate 21, which regenerates a phos-
phorane 22 as suggested also in Scheme 3. The subsequent
Wittig reaction leading to the azulene derivative 23 followed by
elimination of DCl results in the formation of final product 24
(8). The regioselectivity observed in 14a (7a) is similar to that
observed for methylenephosphorane 12 in Scheme 3. In the
reaction of the phosphorane 4 with methoxytropone 14b, the
dideuterioazulene 24 and trideuterioazulene 28 were obtained
in the ratio 1:3 (Scheme 5, Table 1). The compound 24 is clearly
derived from γ-alkylation of compound 4 at C-7 of tropone 14b
(cf. Scheme 4). An alternative pathway is observed here. The
phosphorane 4 attacks at C-2 of tropone 14b to give the inter-
mediate 25, which regenerates a phosphorane, 26. The inter-
mediate 26 undergoes an intramolecular Wittig reaction to give
the dihydroazulene 27, which eliminates HOMe readily to give
the azulene 28. Unexpectedly, alkylation by compound 4 occurs
The structures of known compounds 8 and 10 were
unequivocally assigned on the basis of a comparison of their
1
physical data with those reported in the literature.19,20 The H
and 13C NMR spectra clearly suggest that compound 9 does
not have a symmetrical structure; the proton signal at δ 8.03 is
typical for azulene and is assigned to 8-H. The structure of
compound 9 was deduced from this. The spectral data of
compounds 10 and 11 can be considered consistent with their
structures. The proton signals of 8-H of compounds 10 and 11
appear at δ 9.37 and 9.50, respectively, suggesting that each 8-H
proton of compounds 10 and 11 is located very close to the
CO2Et group: thus the structure 11 was deduced. The results
suggest that the Michael addition of phosphoranes 4 and 6
onto the tropone 7c takes place mainly at C-7 of tropone 7c
(vide infra).
Nucleophilic substitution onto 2-chlorotropone 7a is known
682
J. Chem. Soc., Perkin Trans. 1, 1997

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Cl
O
7a
D
O–
CH2 PPh3
PPh3
4
+
PPh3
14a
C-7 attack
12
13
D
OEt
D
21
Cl
O
D
O–
D
Cl
12
C-7 attack
C
PPh3
D
Cl
H
Cl
H2
H
D
D
D
D
D
O
D
D
PPh3
OEt
OEt
14a
15
D
D
23
22
Cl
H
D
D
O
O
PPh3
C
H
PPh3
D
D
D
D
D
OEt
17
16
24
D
O
O–
Scheme 4
D
OMe
D
12
C-2 attack
4
D
C
PPh3
H2
OMe
14b
24
C-7 attack
D
D
14b
18
C-2 attack
D
D
D
D
H
H
O–
O
O
O
+
PPh3
D
PPh3
PPh3
OEt
D
D
C
PPh3
D
H
OMe
OMe
D
OEt
OMe
D
D
D
25
26
20
19
Scheme 3
D
D
D
H
on tropone 14b (7b) at both C-7 and C-2, with preference for
C-2 attack. In the reaction of phosphorane 6 with tropone 14a,
the dideuterioazulene 29 and the trideuterioazulene 30 were
obtained in the ratio 1:6 (Scheme 6, Table 1). It is clear that
alkylation of compound 6 occurs at C-7 as well as C-2, with
preference for C-2, as in the case of the reaction of phosphorane
4 with tropone 14b.
D
OEt
D
OEt
OMe
D
27
28
Scheme 5
In the reaction of phosphoranes 4 and 6 with tropone 7c,
alkylation on 7c ocurs at C-7, leading to intermediate 31, and
finally to formation of the products 9 and 11. No C-2 attack is
observed here, and this is probably due to the large steric hin-
drance preventing formation of intermediate 32: the presence of
the adjacent chlorine substituents at C-2 and C-3 probably
prevents C-2 attack of phosphoranes 4 and 6 onto the tropone
nucleus 7c. As observed above the regioselectivity of the nucleo-
philic γ-attack of compounds 4 and 6 onto tropone 14a (7a)
and 14b (7b) does not follow the pathway observed in the reac-
tions of compound 12 with 14a (7a) and 14b or that of nucleo-
philes with compounds 7a,b.21 Furthermore, α-attack (carbon
atom bearing the PPh3 group) of phosphoranes 4 and 6 leading
to the intermediates, such as that in the reactions of phospho-
rane 12 with tropones 14a,b, may occur in the present reactions.
However, we could not isolate any product expected from
α-attack of substrates 4 and 6. One may consider that such an
attack on the tropone nucleus would reduce the yield of the
products. This point is unclear at this stage.
and electrophilic reagents, indicating a participation of the
polar structure 33B.23 Previously, we have prepared 5-aza-
azulene derivatives by the reaction of (vinylimino)phos-
phoranes 1 with aldehyde 33.7 The results prompted us to
investigate the reaction of phosphoranes 4 with aldehyde 33.
As expected, compound 4 reacted with aldehyde 33 to give
6-ethoxyazulene 3724 (Scheme 7). The physical data of com-
pound 37 are consistent with its assigned structure.24 Similar to
the reaction of aldehyde 33 with (vinylimino)phosphoranes 1,
we propose the reaction pathways outlined in Scheme 7.
Michael addition of substrate 4 occurs at the C-6 position of
aldehyde 33 to give the intermediate 34. The following proton
transfer and ketonization of intermediate 34 regenerates a
phosphorane 35, which then undergoes an intramolecular
Wittig reaction to give bicycle 36, which eliminates HNMe2 to
afford the azulene 37 in moderate yield (Table 1, entry 11).
In conclusion, the utility of substituted prop-2-enylidene-
phosphoranes 4 and 6 for the preparation of the azulene ring
system having substituents on either the five-membered ring or
Regarding carbaldehyde 33, it reacts with both nucleophilic
J. Chem. Soc., Perkin Trans. 1, 1997
683

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Me2N+
Me2N
D
D
6
14a
OEt
CO2Et
CHO
CHO
C-7 attack
–
29
33A
4
33B
C-2 attack
D
6
D
OEt
CO2Et
OEt
OEt
+
PPh3
Me2N
Me2N
D
PPh3
30
CH
CHO
Cl
O–
Cl
O–
+
PPh3
4 or 6
34
35
7c
C-7 attack
Cl
OEt
R
Cl
Me2N
C-2 attack
31
4 and 6
OEt
OEt
Cl
Cl
O–
36
37
9 and 11
+
PPh3
Scheme 7
Cl
OEt
R
Cl
46%) as crystals, mp 161–162 ЊC (decomp.) (from MeCN–
AcOEt) [lit.,16 173 ЊC (decomp.)]; δH (90 MHz) 0.71 (3 H, t, J
7.0), 2.61 (3 H, s), 4.05 (2 H, q, J 7.0), 5.75 (1 H, br d, J 19.9)
and 7.52–7.88 (15 H, m).
32
Scheme 6
the seven-membered ring has been demonstrated. Phosphorane
4 is more efficient than its analogue 6, but the parent prop-2-
enylidenetriphenylphosphorane does not react with carbonyl
compounds 7a or 33 to give any product except for tarry
materials (see Experimental section). Detailed reasons for this
are not given here. Further applications of prop-2-enylidene-
phosphoranes and related compounds toward the preparation
of theoretically interesting compounds are now in progress in
our laboratory.
Preparation of phosphorane 6
To stirred aq. (2-ethoxy-3-ethoxycarbonylprop-2-enyl)tri-
phenylphosphonium bromide 5 (8.99 g, 18 mmol in 200 ml) was
added dropwise aq. NaOH (790 mg, 20 mmol in 50 mol) over
a period of 1 h at 0 ЊC. Then the resulting precipitate was
collected by filtration, washed with water and dried in vacuo at
60 ЊC to give compound 6 (7.17 g, 95%) as a yellow powder, mp
162–164 ЊC (from MeCN–AcOEt) (lit.,14 164–167 ЊC); δH (90
MHz) 0.58 (3 H, t, J 7.0), 1.31 (3 H, t, J 7.0), 3.69 (2 H, q, J 7.0),
4.12 (2 H, q, J 7.0), 4.41 (1 H, d, J 5.7), 4.86 (1 H, br d, J 15.4)
and 7.27–7.77 (15 H, m).
Experimental
IR Spectra were recorded on a Shimadzu IR-400 spectrometer.
Mass spectra and high-resolution mass spectra were run on a
JEOL Automass 150 and a DX-300 spectrometer. Unless
General procedure for the reaction of phosphorane 4 with
tropones 7a–c
To a stirred solution of KN(SiMe3)2 (2 ml of a 0.5  solution
in toluene, 1 mmol) or ButOK (112 mg, 1 mmol) was added
a solution of phosphonium bromide 3 (427 mg, 1 mmol) in
anhydrous dimethylformamide (DMF) (1 ml) or in dimethyl
sulfoxide (DMSO) (1 ml), and the mixture was stirred at room
temperature for 30 min. To this was added solution of a
tropone 7a–c (0.5 mmol) in DMF (1 ml) or DMSO (1 ml) at
room temperature, and the mixture was stirred at room tem-
perature or with heating for periods indicated in Table 1. After
the reaction was complete, the solvent was removed in vacuo,
and the residue was separated by TLC on alumina [hexane–
AcOEt (10:1)] to give azulenes 8 and 9. The reaction conditions
and the yields of the products are summarized in Table 1.
For compound 8: violet prisms, mp 76–77 ЊC (from EtOH)
(lit.,19 76–77 ЊC); δH (90 MHz) 1.41 (3 H, t, J 7.0), 4.20 (2 H, q, J
7.0), 6.73 (2 H, s), 7.21–7.45 (3 H, m) and 7.97 (2 H, d, J 9.9).
For 4,5,7-trichloro-2-ethoxyazulene 9: light violet needles,
mp 133–135 ЊC (from EtOH); δH (90 MHz) 1.52 (3 H, t, J 7.35,
CH3), 4.33 (2 H, q, J 7.3, CH2), 6.69 (1 H, d, J 2.0, 1- or 3-H),
7.16 (1 H, d, J 2.0, 3- or 1-H), 7.91 (1 H, d, J 2.0, 6-H) and 8.03
(1 H, d, J 2.0, 8-H); δC(100.6 MHz) 14.7, 66.8, 102.5, 107.6,
128.1, 128.2, 129.9, 130.2, 133.9, 134.1, 137.9 and 170.9;
1
otherwise specified, H NMR spectra at 90, 270 and 400 MHz
were recorded on a Hitachi R-90, a JEOL EX-270 and a JNM-
GSX-400 spectrometer, and 13C NMR spectra at 100.6 MHz
were recorded on a JNM-GSX-400 spectrometer. All spectra
were recorded in CDCl3, and the chemical shifts are given
relative to internal SiMe4 standard. J Values are given in Hz.
Mps were recorded on a Yamato MP-21 apparatus and are
uncorrected. All reactions were carried out under anhydrous
conditions and dry nitrogen. Samples were dried over P2O5 in
vacuo.
Preparation of phosphonium bromide 3
To stirred aq. acetonyltriphenylphosphonium chloride (8.85 g,
25 mmol in 30 ml) was added aq. Na2CO3 (2.00 g, 19 mmol in
20 ml) over a period of 20 min at 0 ЊC. The resulting precipitates
were collected by filtration, washed with water and dried in
vacuo at 60 ЊC to give acetonylidenetriphenylphosphorane (6.64
g, 89%). The dried crystals were then dissolved in EtBr (100 ml)
at room temperature, and the mixture was stirred at room tem-
perature for 24 h. The precipitate was collected by filtration
and dried in vacuo at 60 ЊC to give title compound 3 (3.98 g,
684
J. Chem. Soc., Perkin Trans. 1, 1997

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νmax(CHCl3)/cmϪ1 2976, 2915, 1515, 1439, 1389, 1364, 1317,
1288, 1171, 1129, 1111, 1021, 935, 925, 873 and 847; m/z (rel.
int.) 278, 276 and 274 (M+, 13, 49 and 50%) and 246 (100)
(Found: M+, 273.9709; C, 52.4; H, 2.9. C12H9Cl3O requires M,
273.9719; C, 52.31; H, 3.29%).
[hexane–AcOEt (5:1)] to give dideuterioazulene 24 or a mix-
ture of 24 and trideuterioazulene 28 in the ratio ~1:3, which
1
was deduced from the following H NMR spectral data. The
results are also summarized in Table 1.
For compound 24: δH (270 MHz) 1.51 (3 H, t, J 7.2, CH3),
4.31 (2 H, q, J 7.2, CH2), 6.82 (2 H, s, 1- and 3-H), 7.39 (1 H, s,
6-H) and 8.08 (2 H, s, 4- and 8-H); m/z (rel. int.) 174 (M+, 33%)
and 146 (100).
General procedure for the reaction of phosphorane 6 with
tropones 7a–c
To a stirred solution of K2CO3 (83 mg, 0.6 mmol) and phos-
phorane 6 (418 mg, 1 mmol) in anhydrous solvent (1 ml) was
added a solution of tropone 7a–c (0.5 mmol) at room tem-
perature, and the mixture was heated for periods indicated in
Table 1. After the reaction was complete, the solvent was
removed in vacuo and the residue was chromatographed on
alumina [hexane–AcOEt (5:1)]. The fractions were collected
and concentrated, and the residue was further purified by TLC
on alumina [hexane–AcOEt (5:1)] to give azulenes 10 and 11.
The reaction conditions and the yields of the products are
summarized in Table 1.
For compound 10: pink needles, mp 80–81 ЊC (from EtOH)
(lit.,20 84–85 ЊC); δH (90 MHz) 1.44 (3 H, t, J 7.0, Me), 1.55 (3 H,
t, J 7.0, Me), 4.33 (2 H, q, J 7.0, CH2), 4.36 (2 H, q, J 7.0, CH2),
6.73 (1 H, s, 3-H), 7.30–7.61 (3 H, m, 5-, 6- and 7-H), 8.13 (1 H,
d, J 7.0, 4-H) and 9.37 (1 H, d, J 11.2, 8-H).
For a mixture of 24 and 28: δH (270 MHz) 1.44 (3 H, t, J 7.2,
CH3), 4.23 (2 H, q, J 7.2, CH2), 6.82 (2 H, s, 1- and 3-H), 7.25–
7.40 (1.8 H, m, 5-, 6- and 7-H) and 8.08 (0.5 H, br s, 4- and
8-H); m/z (rel. int.) 175 (M+, 38%), 174 (M+, 41) and 117 (100).
Reaction of phosphorane 6 with deuteriotropone 14a
A solution of phosphorane 6 (418 mg, 1 mmol) and tropone
14a (73 mg, 0.5 mmol) in DMSO (1 ml) was heated at 120 ЊC
for 12 h. The reaction mixture was then poured into water,
extracted with diethyl ether, and the extract was dried over
MgSO4. After the solvent had been removed in vacuo, the resi-
due was separated by TLC on alumina [hexane–AcOEt (5:1)]
to give a mixture of dideuterioazulene 29 and trideuterio-
azulene 30 in the ratio ~1:6, which was determined by the fol-
1
lowing H NMR spectral data. The results are summarized in
Table 1.
For a mixture of 29 and 30: δH (270 MHz) 1.44 (3 H, t, J 7.0,
CH3), 1.55 (3 H, t, J 7.0, CH3), 4.33 (2 H, q, J 7.0, CH2), 4.36 (2
H, q, J 7.0, CH2), 6.73 (1 H, s, 3-H), 7.38 (0.86 H, br s, 5- or 7-
H), 7.50 (0.86 H, br s, 7- or 5-H), 7.55 (0.14 H, br s, 6-H), 8.13
(0.14 H, br s, 4-H) and 9.37 (0.22 H, br s, 8-H); m/z (rel. int.) 247
(M+, 100%) and 246 (M+, 26).
For compound 11: mp 134–136 ЊC (decomp.) (from EtOH);
δH (90 MHz) 1.26–1.59 (6 H, m, CH3 × 2), 4.19–4.56 (4 H, m,
CH2 × 2), 7.13 (1 H, s, 3-H), 8.05 (1 H, d, J 1.5, 6-H) and 9.50 (1
H, d, J 1.5, 8-H); δC(100.6 MHz) 14.2, 14.4, 59.7, 65.7, 93.4,
95.2, 109.2, 120.9, 126.5, 131.6, 132.3, 132.4, 164.9 and 172.1;
νmax(CHCl3)/cmϪ1 1724 and 1686; m/z (rel. int.) 348 and 346
(M+, 29 and 33%) and 139 (100) (Found: M+, 345.9907.
C15H13Cl3O3 requires M, 345.9932).
Reaction of phosphorane 4 with compound 33
To a stirred solution of KN(SiMe3)2 (2 ml of a 0.5 M solution in
toluene, 1 mmol) was added a solution of phosphonium salt 3
(427 mg, 1 mmol) in DMF (1 ml). To this mixture was added a
solution of aldehyde 33 (75 mg, 0.5 mmol) in DMF (2 ml), and
the mixture was heated at 95 ЊC for 12 h. After the reaction was
complete the solvent was removed in vacuo, and the residue was
purified by TLC on alumina [hexane–AcOEt (5:1)] to give
6-ethoxyazulene 37, as purple needles, mp 79–81 ЊC (from
EtOH) (lit.,24 80–81 ЊC); δH (90 MHz) 1.44 (3 H, t, J 7.0), 4.10 (2
H, q, J 7.0), 6.75 (2 H, d, J 11.0, 5- and 7-H), 7.26 (2 H, d, J 3.7,
1- and 3-H), 7.60 (1 H, t, J 3.7, 2-H) and 8.16 (2 H, d, J 11.0,
4- and 8-H); m/z (rel. int.) 172 (M+, 50%) and 144 (100) (Found:
C, 83.9; H, 7.3. Calc. for C12H12O: C, 83.69; H, 7.20%).
General procedure for the reaction of methylenephosphorane 12
with tropone 7a and deuteriotropones 14a,b
To a stirred solution of phosphorane 12, which was prepared by
the reaction of CH3PPh3Br (357 mg, 1 mmol) and KN(SiMe3)2
(2 ml of a 0.5 M solution in toluene, 1 mmol) in DMSO (1 ml),
was added a tropone 7a (0.5 mmol) or 14a,b (0.5 mmol), and
the mixture was stirred at room temperature for 1 h. After
evaporation of the mixture in vacuo, the resulting residue was
chromatographed on alumina. The fractions eluted with
hexane–AcOEt (5:1) were collected and concentrated, and the
residual solids were crystallized from benzene–hexane (1:1) to
give products 13,18 17 and 20, respectively, in quantitative yields.
For compound 13: mp 87–88 ЊC [from PhH–hexane (1:1)];
δH (90 MHz) 4.29 (1 H, br d, J 37.8, 3-H), 6.17 (2 H, m, 4- and
6-H), 6.70 (2 H, m, 5- and 7-H), 7.06 (1 H, d, J 9.9, 8-H) and
7.36–7.70 (15 H, m, Ph); m/z (rel. int.) 380 (M+, 77%), 277
(19), 262 (100) and 183 (93).
For compound 17: δH (270 MHz) 4.30 (1 H, br d, J 36.0, 3-H),
6.15 (2 H, br s, 4- and 6-H), 7.04 (1 H, br s, 8-H) and 7.36–
7.59 (15 H, m, Ph); m/z (rel. int.) 382 (M+, 5%), 277 (28), 262
(83) and 183 (100) (Found: M+, 382.1497. C26H19D2OP requires
M, 382.1457).
For compound 20: δH (90 MHz) 4.28 (1 H, br d, J 37.8, 3-H),
6.70 (2 H, br s, 5- and 7-H) and 7.36–7.70 (15 H, m, Ph); m/z
(rel. int.) 383 (M+, 61%), 277 (100), 262 (67), 184 (61) and 181
(29) (Found: M+, 383.1508. C26H18D3OP requires M, 383.1519).
Reaction of prop-2-enylidenetriphenylphosphorane with carbonyl
compounds 7a and 33
To a stirred solution of KN(SiMe3)2 (2 ml of a 0.5 M solution in
toluene, 1 mmol) was added dropwise a solution of prop-2-
enyltriphenylphosphonium bromide(383mg, 1mmol)in DMSO
(1 ml) at 0 ЊC, and the solution was stirred for 30 min until the
solution turned a red–orange colour. To this solution was added
a solution of carbonyl compound 7a or 33 (0.5 mmol) in
DMSO (2 ml), and the mixture was stirred at room temperature
for another 30 min until the reagent 7a or 33 had been con-
sumed. The reaction mixture was extracted with diethyl ether,
and the extract was washed with brine and dried over MgSO4.
After evaporation of the mixture, the residue was purified by
TLC on silica gel [hexane–AcOEt (3:1)] to give no identified
products except triphenylphosphine oxide and tarry materials.
Reaction of phosphorane 4 with deuteriotropones 14a,b
A solution of phosphonium bromide 3 (427mg, 1 mmol) and
KN(SiMe3)2 (2 ml of a 0.5 M solution in toluene, 1 mmol) in
DMSO (1 ml) was stirred at room temperature for 10 min. To
this solution was added a tropone 14a (73 mg, 0.5 mmol) or 14b
(70 mg, 0.5 mmol) and the mixture was stirred at room tem-
perature for 2 h. The reaction mixture was then poured into
water, extracted with diethyl ether and the extract was dried
over MgSO4. After the diethyl ether had been evaporated off
in vacuo, the resulting residue was purified by TLC on alumina
Acknowledgements
This work was financially supported by a Waseda University
Grant for Special Research Project.
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Paper 6/05581H
Received 9th August 1996
Accepted 15th November 1996
686
J. Chem. Soc., Perkin Trans. 1, 1997