Synthesis of naphthalene derivatives through platinum(II)-catalyzed reaction of 2-alkynylbenzoates with vinyl ethers

Article abstract of DOI:10.1055/s-2007-983737

A concise method for the preparation of 1-acyl-4-alkoxy- or 1-acyl-4-alkylsulfanylnaphthalenes has been developed by the PtCl ₂-catalyzed reaction of o-ethynylbenzoates or benzothioates with vinyl ethers. Treatment of o-alkynylbenzoate derivatives with PtCl₂ generated the platinum(II)-containing carbonyl ylides as a key reactive intermediate and these species reacted with vinyl ethers to give substituted naphthalenes in good yields. The presence of the platinum-containing carbonyl ylide was confirmed by NMR analyses of the mixture of o-ethynylbenzoate and [PtCl₂(H₂C=CH₂)]₂. Furthermore, it was suggested that the naphthalene derivatives were produced by [3+2] cycloaddition of the ylide species with vinyl ethers, followed by 1,2-alkyl migration of the generated platinum-carbene intermediates. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2007-983737

2014
SPECIAL TOPIC
Synthesis of Naphthalene Derivatives through Platinum(II)-Catalyzed
Reaction of 2-Alkynylbenzoates with Vinyl Ethers
P
latinum(II)-Catal
i
yzed
S
y
r
nthesis
o
of
N
aphthale
y
ne
D
erivativ
u
es ki Kusama, Hideaki Funami, Nobuharu Iwasawa*
Department of Chemistry, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan
Fax +81(3)57342931; E-mail: niwasawa@chem.titech.ac.jp
Received 30 March 2007
R
R
O-n-Bu
Abstract: A concise method for the preparation of 1-acyl-4-
alkoxy- or 1-acyl-4-alkylsulfanylnaphthalenes has been developed
by the PtCl2-catalyzed reaction of o-ethynylbenzoates or benzothio-
ates with vinyl ethers. Treatment of o-alkynylbenzoate derivatives
with PtCl2 generated the platinum(II)-containing carbonyl ylides as
a key reactive intermediate and these species reacted with vinyl
ethers to give substituted naphthalenes in good yields. The presence
of the platinum-containing carbonyl ylide was confirmed by
NMR analyses of the mixture of o-ethynylbenzoate and
[PtCl2(H2C=CH2)]2. Furthermore, it was suggested that the naph-
thalene derivatives were produced by [3+2] cycloaddition of the
ylide species with vinyl ethers, followed by 1,2-alkyl migration of
the generated platinum-carbene intermediates.
R
cat.
+
+
W(CO)5(thf)
O
O
O
THF, r.t.
–
–
W(CO)5
W(CO)5
tungsten-containing carbonyl ylide
O
R
O
R
H
H
H
H
[3+2] cycloaddition
H
O
(OC)5W
O-n-Bu
n-Pr
H
Key words: platinum, naphthalene, carbonyl ylide, carbene, [3+2]-
Scheme 1
cycloaddition
As formation of such metal-containing ylides is rarely
known and their synthetic utility still remains relatively
unexplored, we have continued our efforts to examine the
generation and reaction of these carbonyl ylide species us-
ing other transition-metal complexes, expecting that char-
acteristic reactivity would be disclosed depending on the
nature of metals employed. In the preliminary communi-
cation,10 we reported that platinum-containing carbonyl
ylides could be generated by the reaction of o-alkynylben-
zoates or benzothioates with a catalytic amount of PtCl2,11
which reacted with vinyl ethers to give 1-acyl-4-alkoxy-
or 1-acyl-4-alkylsulfanylnaphthalenes in high yields
(Scheme 2). Here, we report the full account of the plati-
num-catalyzed synthesis of heteroatom-substituted naph-
thalenes including the studies on the reaction
mechanisms.
Naphthalene derivatives play an important role in the field
of organic and bioorganic chemistry.1 In particular, het-
eroatom-substituted naphthalene derivatives are found in
numerous biologically active natural products,2 and a
large number of synthetic methods for the preparation of
these compounds have been developed so far.1 For exam-
ple, Diels–Alder reactions of o-quinodimethanes3 or ben-
zynes,4 transition-metal-mediated cyclizations,5 and
rearrangement of strained rings6 have been utilized for the
construction of naphthalene core. Although some of these
methods showed wide generality and have been success-
fully applied for the syntheses of complex natural prod-
ucts, it is still desirable to explore an efficient
methodology which proceeds under mild conditions em-
ploying simple starting materials.
Recently, we reported a novel method for the generation
of tungsten-containing carbonyl ylides, a novel bifunc-
tional reactive intermediate, by the reaction of o-(1-alky-
nyl)phenyl ketones with pentacarbonyltungsten and their
[3+2] cycloaddition reaction with the electron-rich alk-
enes to give polycyclic compounds stereoselectively
(Scheme 1).7,8 The tungsten-containing carbonyl ylide in-
termediate reacts both as a carbonyl ylide9 and as a car-
bene complex and thus enables multiple bond formation
in one pot.
XR1
XR1
XR1
OR
cat.
PtCl2
+
O
O
R2
R2
PtCl2
–
O
R2
X = O, S
Scheme 2
First, we examined the reaction of various o-ethynylphe-
nyl carbonyl compounds with a vinyl ether employing
PtCl2, which is well known to activate alkynes electro-
philically by p-complex formation. Treatment of o-ethy-
nylbenzaldehyde or o-ethynylacetophenone with butyl
vinyl ether in the presence of a catalytic amount of PtCl2
in THF at room temperature resulted in a complex mix-
ture, and none of the addition product was obtained. On
SYNTHESIS 2007, No. 13, pp 2014–2024
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x.
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0
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Advanced online publication: 18.06.2007
DOI: 10.1055/s-2007-983737; Art ID: C02607SS
© Georg Thieme Verlag Stuttgart · New York

SPECIAL TOPIC
Platinum(II)-Catalyzed Synthesis of Naphthalene Derivatives
2015
the other hand, when a mixture of isopropyl o-ethynylben- Table 1 Screening of the Reaction Conditions for the Formation of
2a
zoate (1a) and butyl vinyl ether was treated with PtCl2 (10
mol%) in THF, the starting material was consumed within
O-i-Pr
O-i-Pr
several hours at room temperature,12 and purification of
the crude products revealed that 4-isopropoxynaphtha-
lene-1-carbaldehyde (2a) was obtained in moderate yield
instead of the polycyclic compound 3 (Scheme 3). As for-
mation of the naphthalene derivative 2a was rather unex-
pected, we decided to examine this platinum(II)-catalyzed
naphthalene synthesis in more detail.
10 mol%
catalyst
O
+
O-n-Bu
solvent, r.t.
O
2a
H
1a
Entry
Catalyst
PtCl2
PtCl2
PtCl2
PtCl2
PtCl2
Solvent
MeCN
CH2Cl2
Et2O
Time (h) Yield (%)a
1
48
16
9
47
71
84
86
91
81
47
10
O-i-Pr
O
O-n-Bu
10 mol%
PtCl2
O-i-Pr
O
i-Pr-O
2
H
THF, r.t.
3
H
O
n-Pr
4
toluene
toluene
6
H
O
H
1a
2a
55 %
3
–
5b
6c
7
10
6
[PtCl2(H2C=CH2)]2 toluene
Scheme 3
PtBr2
toluene
toluene
48
48
To improve the efficiency of this reaction, we first inves-
tigated the above reaction in various solvents (Table 1).
Although the use of acetonitrile did not improve the yield
of 2a (entry 1), the reactions in dichloromethane, diethyl
ether, and toluene smoothly proceeded to afford 2a in
71%, 84%, and 86% yield, respectively (entries 2–4). In
addition, when the reaction was carried out in toluene in
the presence of molecular sieves 4Å, the yield of 2a was
further improved to 91% (entry 5). [PtCl2(H2C=CH2)]2
also showed a comparable catalytic activity with PtCl2
(entry 6), while the use of PtBr2 or AuCl3 as a catalyst con-
siderably lowered the yield of the product (entries 7 and
8).
8
AuCl3
a Yield of the isolated product.
b 4 Å MS were added.
c The reaction was performed in the presence of 5 mol% of
[PtCl2(H2C=CH2)]2.
butanol which eliminated from intermediates of the final
step of the reaction (see Scheme 6).
To avoid this alkoxy exchange reaction, we further exam-
ined several vinyl ethers and found that formation of
butoxy-substituted naphthalenes could be suppressed by
using diphenylmethyl vinyl ether 5, a sterically demand-
ing substrate, and the desired naphthalenes were obtained
in good yields (Table 3). By this protocol, the easily re-
movable benzyl-protected naphthol 2e could be obtained
in good yield (entry 5). Substituent effect on the alkyne
carbon was also investigated; not only the terminal
alkynes, but also the internal alkynes 1i–l gave the corre-
sponding naphthyl ketone derivatives in good to high
yield (entries 9, 10 in Table 2 and entries 7, 8 in Table 3).
After determining the optimal reaction conditions, we
then investigated the generality of the reaction using var-
ious o-alkynylbenzoate derivatives, and the results are
summarized in Table 2. Concerning the ester functional-
ity, alkoxy, aryloxy, and alkylsulfanyl groups were appli-
cable and the corresponding heteroatom-substituted
naphthalenes were obtained in high yield in every case
(entries 1–6). In particular, formation of n-octylsulfanyl-
substituted naphthalene 2f is noteworthy because it is not
necessarily easy to introduce alkylsulfanyl group onto the
naphthalene nucleus. On the contrary, the reaction of an
amide derivative 1g did not proceed and most of the start-
ing material was recovered.13 As it was suspected that the
strong electron donation from the dimethylamino group
rendered the reaction with vinyl ether difficult, we expect-
ed that use of an amide derived from a weaker electron-
donating amine would effectively promote the desired
benzannulation. Indeed, by the use of a pyrrole derivative
1h as a substrate, the nitrogen-substituted naphthaldehyde
2h was obtained, albeit in moderate yield (entry 8). Ex-
cept for the reaction of the isopropyl ester 1a, the products
2b–f contained considerable amounts of butoxy-substitut-
ed naphthaldehyde 4. This compound was presumably
produced during the reaction by alkoxy exchange with
We also applied this naphthalene synthesis to the intramo-
lecular reactions using the enol ethers 6a and 6b. Both re-
actions proceeded smoothly with 10 mol% amounts of
PtCl2 to give the corresponding polycyclic compounds 7a
and 7b in 79% and 87% yield, respectively (Scheme 4 and
Scheme 5).
O
O
10 mol% PtCl2
OMe
toluene,
O
4 Å MS, r.t., 20 h
O
H
6a
7a
79%
Scheme 4
Synthesis 2007, No. 13, 2014–2024 © Thieme Stuttgart · New York

2016
H. Kusama et al.
SPECIAL TOPIC
Table 2 Reaction of Various o-Alkynylbenzoates, o-Alkynylbenzothioates, and o-Alkynylbenzamides
XR1
O-n-Bu
O-n-Bu
XR1
10 mol% PtCl2
O
+
toluene,
4 Å MS, r.t.
R2
O
R2
O
R2
1
2
4
Entry
XR1
R2
Time (h)
Yield (%)a
Ratio (2:4)
100:0
61:39
51:49
50:50
56:44
65:35
–
1
2
O-i-Pr
H
H
H
H
H
H
H
H
1a
10
12
10
11
8
91
84
90
86
77
84
–
OMe
1b
1c
1d
1e
1f
3
OPh
4
O(4-ClC6H4)
OCH2Ph
SC8H17
NMe2
5
6b
7
9
1g
1h
1i
48
14
72
120
8b
9
1-pyrrolyl
O-i-Pr
33
89
64
100:0
100:0
100:0
n-Pr
10b
O-i-Pr
Ph
1j
a Yield of the isolated product.
b The reaction was performed in the presence of 30 mol% of PtCl2.
Table 3 Reaction with Diphenylmethyl Vinyl Ether
O
3
O
OMe
XR1
XR1
10 mol% PtCl2
O
toluene,
4 Å MS, r.t., 22 h
Ph
10 mol% PtCl2
O
+
toluene,
Ph
O
O
H
4 Å MS, r.t.
6b
R2
R2
7b
87%
O
2
1
5
Scheme 5
Entry
XR1
R2
H
H
H
H
H
H
Time (h) Yield (%)a
1
O-i-Pr
OMe
OPh
1a
1b
1c
1d
1e
1f
8
8
86
83
87
60
83
60
83
79
ates a platinum(II)-containing carbonyl ylide 8, which
subsequently undergoes [3+2] cycloaddition with the vi-
nyl ether to give a platinum(II) carbene intermediate 9.
Finally, 1,2-alkyl-migration11f,14 onto the electrophilic
carbene carbon was promoted by electron-donation from
the alkoxy oxygen, giving the 4-alkoxy-1-naphthylcarbo-
nyl compounds with elimination of an alcohol and regen-
eration of the catalyst.
2
3
10
8
4
O(4-ClC6H4)
OCH2Ph
SC8H17
5
8
6b
7
10
48
48
To confirm the proposed mechanism, we then tried to de-
tect the key intermediate, the platinum-containing carbo-
nyl ylides. Since carbonyl ylides in general are highly
reactive and unstable species, we examined the mixture of
the substrate and the platinum complex by NMR spectros-
copy. When isopropyl o-ethynylbenzoate (1a) was treated
with 0.55 equivalent of [PtCl2(H2C=CH2)]2 (nearly
equimolar amount in regard to platinum) in CDCl3 at 273
K,15 the starting material 1a completely disappeared with-
in a few minutes and two kinds of new species A and B
were observed in a ratio of approximately 5:1 (Figure 1,
b).
OCH2Ph
SC8H17
n-Pr
n-Pr
1k
1l
8b
a Yield of the isolated product.
b The reaction was performed in the presence of 30 mol% of PtCl2.
A plausible mechanism is illustrated in Scheme 6. Initial-
ly, the alkyne moiety of o-alkynylbenzoates 1 is electro-
philically activated by platinum(II) through a p-complex
formation. The 6-endo mode of nucleophilic attack of the
carbonyl oxygen onto the activated alkyne moiety gener-
Synthesis 2007, No. 13, 2014–2024 © Thieme Stuttgart · New York

SPECIAL TOPIC
Platinum(II)-Catalyzed Synthesis of Naphthalene Derivatives
2017
OR1
OR1
8.28
80.8
cat.
PtCl2
H
O
H(a)
5.70
O
O
+
OR
7.73
127.0
H
C(1)
168.5
R2
O
R2
114.9
148.8
129.8
138.8
Cl2Pt
R1O
1
139.5
134.4
OR1
H
C(2)
H(b)
134.2
9.05
O
8.14
7.58
+
R2
[3+2] cycloaddition
O
H(c)
PtCl2
R2
H
H(d)
5.04
OR
Cl2Pt
–
PtCl2
92.0
: HMBC correlation
platinum carbene
platinum-containing
carbonyl ylide 8
H
H
intermediate 9
platinum-containing carbonyl ylide A
1
OR1
+
OR
1,2-alkyl
migration
Figure 2 Selected correlation in the HMBC spectrum. Note the
chemical shifts in 1H (italic) and 13C NMR spectra (plain).
– ROH
OR
R2
–
PtCl2
Cl2Pt
ylide A (Figure 4) based on the following experiment.18
When N2 gas was bubbled into the mixture of A and B in
CDCl3 at 273 K for 2 hours, the ratio of A and B changed
to ca. 1:1 from the initial ratio of 5:1 and the intensity of
the free ethylene signal increased (Figure 3, a). On the
contrary, when gaseous ethylene was bubbled into the
same reaction mixture, the peaks of B mostly disappeared
and only the carbonyl ylide A was observed (Figure 3, b).
These phenomena strongly suggest that the intermediate
B is the dimer complex of the platinum-containing carbo-
nyl ylide (Figure 4). Thus, we have succeeded in direct
observation of the key species, platinum-containing car-
bonyl ylides A and B, which are readily and quantitatively
generated by the reaction of 1a and [PtCl2(H2C=CH2)]2.
Compared to the tungsten-containing carbonyl ylide
which was generated in a small amount by the reaction of
o-ethynylphenyl ketone with excess amount of pentacar-
bonyl tungsten,7b the quantitative generation of the plati-
num-containing carbonyl ylide shows the highly
electrophilic nature of PtCl2.
O
2
R2
O
Scheme 6
The structure of the major intermediate A was unambigu-
ously assigned as the platinum-containing carbonyl ylide
by 13C NMR and 2D HMBC analyses at 273 K and the re-
sults are summarized in Figure 2. One of the key spectral
features was the HMBC correlation between C(1) (d =
168.5) derived from the carbonyl carbon and the singlet
proton H(b) (d = 7.58) derived from the alkynyl proton,
which strongly supports the formation of the six-mem-
bered ring intermediate. Ethylene proton (d = 5.04) had a
set of satellite signals due to the coupling with platinum-
195 (2JPt,H = 39.4 Hz, Figure 1, c),16,17 which means the
ethylene remains on the platinum as a ligand. This proton
H(d) also showed HMBC correlation with C(2) (d =
134.4), suggesting that this carbon C(2) is directly bound
with the platinum.
Concerning the structure of the minor species B, we be-
lieve that it is a dimer of the platinum containing carbonyl
Figure 1 1H NMR spectra of (a) benzoate 1a (500 MHz, CDCl3, 273 K), (b) a mixture of 1a and 0.55 equiv of [PtCl2(H2C=CH2)]2 (500 MHz,
CDCl3, 273 K), and (c) the expansion of the peak around d = 5.0 of the mixture of 1a and [PtCl2(H2C=CH2)]2 (300 MHz, CDCl3, 300 K).
Synthesis 2007, No. 13, 2014–2024 © Thieme Stuttgart · New York

2018
H. Kusama et al.
SPECIAL TOPIC
ture of the intermediate C was considered to be a plati-
num-containing carbonyl ylide having butyl vinyl ether as
a ligand as shown in Figure 5.19 After 14 hours at room
temperature, the ylides A–C were consumed and the
naphthalene 2a was produced in nearly 90% yield based
on an internal standard (1,1,2,2-tetrachloroethane: d =
5.96) (Figure 5, c).
Although the [3+2]-cycloaddition product, that is, the
platinum(II) carbene complex intermediate 9 was not ob-
served directly, we at present believe that the reaction pro-
ceeds through [3+2] cycloaddition of the platinum(II)-
containing carbonyl ylides 8 with vinyl ether, followed by
1,2-alkyl migration of the produced carbene intermediates
9 as shown in Scheme 6. To support this proposed mech-
anism, we conducted the following experiments. When
2,4-dimethoxyphenylmethyl vinyl ether is employed as an
electron-rich alkene,20 the C–H insertion product 10 of the
carbene intermediate 9 is obtained albeit in low yield
along with alkoxynaphthalene 2d and 2m in 29% and
55% yield, respectively (Scheme 7). Furthermore, the
platinum(II)-catalyzed reaction of o-(prop-1-ynyl)benzal-
dehyde (11) with 4-methoxyphenylmethyl vinyl ether
also gave the [3+2]-cycloaddition–carbene insertion prod-
uct 12 in reasonable yield (Scheme 8). These results clear-
ly show that [3+2]-cycloaddition reaction could actually
occur by the reaction of the platinum-containing ylides
with vinyl ethers.
Figure 3 Change in the 1H NMR spectra (400 MHz, CDCl3, 300 K)
of the mixture 1a and [PtCl2(H2C=CH2)]2: (a) after bubbling N2 at 273
K for 2 h; (b) after bubbling ethylene into (a) at 300 K for a few se-
conds.
O-i-Pr
+
O
O-i-Pr
+
O
–
N2 bubbling
Cl Pt Cl
–
Cl Pt Cl
–
PtCl2
+
O
O-i-Pr
platinum-containing carbonyl
platinum-containing carbonyl
ylide A
ylide B
Yamamoto, Asao and co-workers extensively studied the
gold(III) or copper(II)-catalyzed benzannulation reactions
of o-(1-alkynyl)phenylcarbonyl compounds and alkynes
or alkenes. They proposed that the reactions proceed
through the similar metal-containing zwitterionic inter-
mediates, which undergo [4+2] cycloaddition with
alkynes or alkenes followed by demetalation to give the
products.21 However, Straub’s recent report on DFT cal-
culation of the gold-catalyzed benzannulation suggested
Figure 4 Structure of platinum-containing carbonyl ylides A and B.
We next observed the reaction of these ylide intermediates
1
with vinyl ether by H NMR spectroscopy. When five
equivalents of n-butyl vinyl ether were added to a mixture
of A and B in CDCl3 at 300 K, a very small amount of the
naphthaldehyde 2a (P) was observed along with a set of
new signals (C) after five minutes (Figure 5, b). The struc-
Figure 5 Change in the 1H NMR spectra (400 MHz, CDCl3, 300 K) of the reaction of the platinum-containing carbonyl ylides with five equi-
valents of n-butyl vinyl ether: (a) mixture of A and B; (b) five minutes after the addition of vinyl ether; (c) after 14 h.
Synthesis 2007, No. 13, 2014–2024 © Thieme Stuttgart · New York

SPECIAL TOPIC
Platinum(II)-Catalyzed Synthesis of Naphthalene Derivatives
2019
as an internal standard. IR spectra were recorded on an IR-810 or a
FT/IR-460 plus spectrometer (JASCO Co., Ltd.). Silica Gel 60
(Kanto Chemical Co., Inc.) was used for flash column chromatog-
raphy. Merck Kieselgel 60 F254 plate (0.25 mm thickness, coated on
glass 20 × 20 cm2) was used for TLC, and Wakogel B-5F coated on
glass in a thickness of 0.7 mm was used for preparative TLC. All
solvents were distilled according to the usual procedures and stored
over molecular sieves. THF and CH2Cl2 were purchased from Kan-
to Chemical Co. Ltd., and used without further purification. High-
resolution mass spectra (FAB) were performed on a JEOL JMS-700
mass spectrometer using NBA as matrix. Elemental analyses were
performed on a PerkinElmer 2400 instrument. Compounds 1b,24
2b,25 2c26 are known and the spectral data were in good agreement
with literature values.
O-p-ClC6H4
30 mol% PtCl2
O
+
O
Ar
toluene,
4 Å MS, r.t.
[Ar = 2,4-(MeO)2C6H3]
1d
O
OR
p-ClC6H4-O
H
+
H
O
Ar
H
O
H
2
10
6%
29% (2d: R = 4-ClC6H4)
55% (2m: R = CH2Ar)
Isopropyl 2-Ethynylbenzoate (1a); Typical Procedure
Isopropyl 2-(2-Trimethylsilylethynyl)benzoate: To a mixture of 2-
(2-trimethylsilylethynyl)benzoic acid27 (175 mg, 0.8 mmol), pro-
pan-2-ol (0.24 mL, 3.2 mmol), and DMAP (98 mg, 0.8 mmol) in
CH2Cl2 (1.5 mL), was added a CH2Cl2 (0.5 mL) solution of DCC
(330 mg, 1.6 mmol) at 0 °C. After stirring for 8 h at r.t., the mixture
was filtered through Celite with EtOAc as eluent, and then the fil-
trate was concentrated under reduced pressure. The residue was pu-
rified by preparative TLC (hexane–EtOAc, 19: 1) to give isopropyl
2-(2-trimethylsilylethynyl)benzoate (194 mg) in 93% yield as a col-
orless oil.
Scheme 7
H
O
10 mol% PtCl2
toluene, r.t.
+
O
Ar
Me
(Ar = 4-MeOC6H4)
11
IR (neat): 2980, 2158, 1712, 1251, 844 cm–1.
O
O
H
H
H
Me
1H NMR (CDCl3, 400 MHz): d = 0.27 (9 H, s), 1.39 (6 H, d, J = 6.4
Hz), 5.28 (1 H, sept, J = 6.4 Hz), 7.33–7.37 (1 H, m), 7.39–7.43 (1
H, m), 7.56–7.58 (1 H, m), 7.84–7.87 (1 H, m).
13C NMR (CDCl3, 100 MHz): d = 0.02, 22.0, 69.0, 99.4, 103.4,
122.9, 128.0, 129.9, 131.0, 133.0, 134.7, 166.0.
Me
C–H insertion
H
Cl2Pt
O
O
Ar
H
Ar
12
43%
Anal. Calcd for C15H20O2Si: C, 69.19; H, 7.74. Found: C, 68.94; H,
7.79.
Scheme 8
Isopropyl 2-Ethynylbenzoate (1a): To a solution of isopropyl 2-(2-
trimethylsilylethynyl)benzoate (1.56 g, 6.0 mmol) in a mixture of
THF (30 mL) and MeOH (30 mL), was added a THF solution of
TBAF (1.0 M, 7.8 mL, 7.8 mmol) at 0 °C. After stirring for 30 min
at r.t., the reaction was quenched with pH 7 phosphate buffer and
the product was extracted with EtOAc (3 × 50 mL). The combined
extracts were dried (MgSO4) and concentrated under reduced pres-
sure. The residue was purified by silica gel column chromatography
(hexane–EtOAc, 19:1) to give the title compound 1a (1.11 g) in
98% yield as a colorless oil.
that successive [3+2]-cycloaddition–skeletal rearrange-
ment would be the reasonable mechanism rather than
[4+2]-cycloaddition pathway.22 Although we could not
have observed the platinum carbene complex intermedi-
ate of [3+2]-cycloaddition reaction by NMR experiments,
we believe the [3+2]-cycloaddition mechanism is reason-
able at least in our platinum(II)-catalyzed bezannulation
reaction.23
IR (neat): 2928, 2859, 1730, 1463, 1274, 1123, 742 cm–1.
1H NMR (CDCl3, 400 MHz): d = 1.38 (6 H, d, J = 6.4 Hz), 3.37 (1
H, s), 5.28 (1 H, sept, J = 6.4 Hz), 7.37–7.42 (1 H, m), 7.44–7.48 (1
H, m), 7.60–7.62 (1 H, m), 7.91–7.93 (1 H, m).
13C NMR (CDCl3, 100 MHz): d = 21.9, 69.0, 82.1, 82.2, 122.3,
128.3, 130.1, 131.3, 133.1, 134.8, 165.5.
In conclusion, we have developed a platinum(II)-cata-
lyzed preparation of 1-acyl-4-alkoxy- or 1-acyl-4-alkyl-
sulfanylnaphthalenes from o-alkynylbenzoates or
benzothioates and vinyl ethers through the novel plati-
num(II)-containing carbonyl ylides. The presence of the
platinum-containing carbonyl ylides is directly confirmed
by NMR measurement. We believe that the concept of the
metal-containing 1,3-dipoles will find abundant applica-
tion in organic chemistry and provide new opportunities
to develop useful synthetic methods of various organic
molecules.
Anal. Calcd for C12H12O2: C, 76.57; H, 6.43. Found: C, 76.27; H,
6.55.
Phenyl 2-(2-Trimethylsilylethynyl)benzoate
IR (neat): 2959, 2158, 1733, 1593, 1493, 1194, 843 cm–1.
1H NMR (CDCl3, 400 MHz): d = 0.18 (9 H, s), 7.24–7.29 (3 H, m),
7.41–7.46 (3 H, m), 7.52 (1 H, dt, J = 7.6, 1.6 Hz), 7.66 (1 H, dd,
J = 7.6, 1.2 Hz), 8.07 (1 H, dd, J = 8.0, 1.2 Hz).
13C NMR (CDCl3, 100 MHz): d = –0.11, 100.5, 102.9, 121.6, 123.7,
125.8, 128.2, 129.3, 130.7, 131.7, 132.0, 134.7, 150.8, 164.8.
All operations were performed under argon. 1H and 13C NMR spec-
tra were recorded on a Bruker DRX-500 (500 MHz for 1H and 125
MHz for 13C), JEOL Lambda-400 (400 MHz for 1H and 100 MHz
for 13C), or a JEOL Lambda-400 (400 MHz for 1H and 100 MHz for
Anal. Calcd for C18H18O2Si: C, 73.43; H, 6.16. Found: C, 73.61, H,
6.31.
1
13C) or a JEOL AL-400 (400 MHz for H and 100 MHz for 13C)
spectrometer using CHCl3 (1H, d = 7.26) and CDCl3 (13C, d = 77.0)
Synthesis 2007, No. 13, 2014–2024 © Thieme Stuttgart · New York

2020
H. Kusama et al.
SPECIAL TOPIC
Phenyl 2-Ethynylbenzoate (1c)
Anal. Calcd for C20H30OSSi: C, 69.31; H, 8.72; S, 8.10. Found: C,
69.26; H, 8.93; S, 8.15.
IR (neat): 3262, 1737, 1478, 1249, 1194, 1054, 764 cm–1.
1H NMR (CDCl3, 400 MHz): d = 3.42 (1 H, s), 7.24–7.30 (3 H, m),
7.41–7.51 (3 H, m), 7.54–7.58 (1 H, m), 7.70 (1 H, dd, J = 8.0, 1.2
Hz), 8.16 (1 H, dd, J = 8.0, 1.2 Hz).
13C NMR (CDCl3, 100 MHz): d = 81.7, 83.0, 121.6, 123.2, 125.9,
128.6, 129.4, 130.8, 131.6, 132.3, 135.0, 150.7, 164.3.
S-Octyl 2-(Pent-1-ynyl)benzothioate (1f)
IR (neat): 2927, 1678, 1199, 907 cm–1.
1H NMR (CDCl3, 400 MHz): d = 0.86–0.90 (3 H, m), 1.05 (3 H, t,
J = 7.6 Hz), 1.24–1.37 (8 H, m), 1.42–1.46 (2 H, m), 1.61–1.71 (4
H, m), 2.42 (2 H, t, J = 6.8 Hz), 3.05 (2 H, t, J = 7.6 Hz), 7.27–7.32
(1 H, m), 7.37–7.41 (1 H, m), 7.47–7.50 (1 H, m), 7.69–7.71 (1 H,
m).
Anal. Calcd for C15H10O2: C, 81.07; H, 4.54. Found: C, 81.11; H,
4.36.
13C NMR (CDCl3, 100 MHz): d = 13.6, 14.2, 21.8, 22.1, 22.7, 29.0,
29.2, 29.5, 29.8, 31.9, 78.7, 95.8, 121.6, 127.1, 127.7, 130.9, 133.8,
140.1, 192.6.
4-Chlorophenyl 2-(2-Trimethylsilylethynyl)benzoate
IR (neat): 2960, 2158, 1752, 1487, 1199, 843 cm–1.
1H NMR (CDCl3, 400 MHz): d = 0.19 (9 H, s), 7.20 (2 H, d, J = 8.8
Hz), 7.39–7.45 (3 H, m), 7.53 (1 H, t, J = 7.2 Hz), 7.66 (1 H, d,
J = 7.2 Hz), 8.05 (1 H, d, J = 8.0 Hz).
Anal. Calcd for C20H28OS: C, 75.90; H, 8.92; S, 10.13. Found: C,
75.62; H, 9.06; S, 10.28.
13C NMR (CDCl3, 100 MHz): d = –0.09, 100.7, 102.9, 123.0, 123.8,
128.3, 129.4, 130.8, 131.2, 132.2, 134.8, 149.2, 164.5.
N,N-Dimethyl 2-(Trimethylsilylethynyl)benzamide
IR (neat): 2958, 2159, 1644, 1395, 1250, 865 cm–1.
1H NMR (CDCl3, 400 MHz): d = 0.21 (9 H, s), 2.88 (3 H, s), 3.11
(3 H, s), 7.27–7.38 (3 H, m), 7.43–7.47 (1 H, m).
Anal. Calcd for C18H17ClO2Si: C, 65.74; H, 5.21. Found: C, 65.57;
H, 5.29.
13C NMR (CDCl3, 100 MHz): d = –0.14, 34.7, 38.2, 97.7, 102.1,
120.0, 126.5, 128.5, 128.9, 132.0, 140.1, 170.0.
4-Chlorophenyl 2-Ethynylbenzoate (1d)
IR (neat): 3291, 1747, 1488, 1245, 1200, 1037, 756 cm–1.
Anal. Calcd for C14H19NOSi: C, 68.52; H, 7.80; N, 5.71. Found: C,
68.45; H, 8.04; N, 5.64.
1H NMR (CDCl3, 400 MHz): d = 3.43 (1 H, s), 7.19–7.23 (2 H, m),
7.37–7.41 (2 H, m), 7.49 (1 H, dt, J = 8.0, 1.2 Hz), 7.57 (1 H, dt,
J = 8.0, 1.2 Hz), 7.69–7.71 (1 H, m), 8.12–8.14 (1 H, m).
13C NMR (CDCl3, 100 MHz): d = 81.6, 83.1, 123.0, 123.3, 128.6,
129.4, 130.8, 131.17, 131.24, 132.4, 135.1, 149.1, 164.0.
N,N-Dimethyl 2-Ethynylbenzamide (1g)
IR (KBr): 3221, 2940, 2102, 1611, 1394, 1070, 779 cm–1.
1H NMR (CDCl3, 400 MHz): d = 2.88 (3 H, s), 3.13 (3 H, s), 3.16
(1 H, s), 7.29 (1 H, dd, J = 7.6, 1.6 Hz), 7.33 (1 H, dt, J = 7.6, 1.6
Hz), 7.39 (1 H, dt, J = 7.6, 1.6 Hz), 7.49–7.53 (1 H, m).
Anal. Calcd for C15H9ClO2: C, 70.19; H, 3.53. Found: C, 70.40; H,
3.79.
13C NMR (CDCl3, 100 MHz): d = 34.8, 38.3, 80.4, 80.8, 118.9,
126.3, 128.6, 129.1, 132.7, 140.2, 169.7.
Benzyl 2-(2-Trimethylsilylethynyl)benzoate
IR (neat): 2958, 2158, 1731, 1249, 843, 758 cm–1.
Anal. Calcd for C11H11NO: C, 76.28; H, 6.40; N, 8.09. Found: C,
76.45; H, 6.64; N, 8.06.
1H NMR (CDCl3, 400 MHz): d = 0.22 (9 H, s), 5.39 (2 H, s), 7.31–
7.40 (4 H, m), 7.42–7.47 (3 H, m), 7.58–7.60 (1 H, m), 7.91–7.93 (1
H, m).
13C NMR (CDCl3, 100 MHz): d = –0.08, 66.8, 100.0, 103.3, 123.3,
128.0, 128.1, 128.5, 130.3, 131.5, 132.2, 134.7, 135.9, 166.0.
1-[2-(Trimethylsilylethynyl)benzoyl]-1H-pyrrole
IR (KBr): 3149, 2960, 2163, 1706, 1469, 1337 cm–1.
1H NMR (CDCl3, 400 MHz): d = 0.06 (9 H, s), 6.30 (2 H, t, J = 2.0
Hz), 7.14 (2 H, br s), 7.41–7.53 (3 H, m), 7.53–7.57 (1 H, m).
13C NMR (CDCl3, 100 MHz): d = –0.36, 100.4, 100.7, 113.3, 120.6,
121.6, 127.9, 128.4, 130.4, 132.3, 137.3, 166.9.
Anal. Calcd for C19H20O2Si: C, 73.98; H, 6.54. Found: C, 74.03; H,
6.58.
Benzyl 2-Ethynylbenzoate (1e)
IR (KBr): 3245, 1710, 1484, 1274, 1076, 757 cm–1.
Anal. Calcd for C16H17NOSi: C, 71.87; H, 6.41; N, 5.24. Found: C,
72.13; H, 6.71; N, 5.25.
1H NMR (CDCl3, 400 MHz): d = 3.37 (1 H, s), 5.39 (2 H, s), 7.33–
7.41 (4 H, m), 7.46–7.50 (3 H, m), 7.62–7.64 (1 H, m), 7.97–7.99 (1
H, m).
13C NMR (CDCl3, 100 MHz): d = 67.0, 82.0, 82.5, 122.6, 128.2,
128.3, 128.4, 130.27, 130.31, 131.7, 132.2, 134.9, 135.6, 165.6.
1-(2-Ethynylbenzoyl)-1H-pyrrole (1h)
IR (neat): 3282, 3146, 2111, 1712, 1469, 1335 cm–1.
1H NMR (CDCl3, 400 MHz): d = 3.14 (1 H, s), 6.32 (2 H, t, J = 2.0
Hz), 7.15 (2 H, br s), 7.44–7.53 (3 H, m), 7.63 (1 H, d, J = 6.8 Hz).
13C NMR (CDCl3, 100 MHz): d = 79.8, 82.2, 113.4, 120.6, 120.7,
127.8, 128.5, 130.5, 133.3, 137.0, 166.4.
Anal. Calcd for C16H12O2: C, 81.34; H, 5.12. Found: C, 81.05; H,
5.07.
S-Octyl 2-(2-Trimethylsilylethynyl)benzothioate
Anal. Calcd for C13H9NO: C, 79.98; H, 4.65; N, 7.17. Found: C,
79.81; H, 4.91; N, 7.13.
IR (neat): 2926, 2161, 1677, 1199, 859 cm–1.
1H NMR (CDCl3, 400 MHz): d = 0.26 (9 H, s), 0.87–0.90 (3 H, m),
1.28–1.34 (8 H, m), 1.40–1.47 (2 H, m), 1.68 (2 H, quint, J = 7.6
Hz), 3.06 (2 H, t, J = 7.6 Hz), 7.35 (1 H, dt, J = 7.6, 1.2 Hz), 7.40 (1
H, dt, J = 7.6, 1.2 Hz), 7.55 (1 H, dd, J = 7.6, 1.2 Hz), 7.70 (1 H, dd,
J = 7.6, 1.2 Hz).
13C NMR (CDCl3, 100 MHz): d = –0.15, 14.2, 22.7, 29.0, 29.20,
29.22, 29.5, 29.9, 31.9, 100.0, 102.6, 120.5, 127.6, 128.1, 130.8,
134.1, 140.7, 192.2.
Isopropyl 2-(Pent-1-ynyl)benzoate (1i)
IR (neat): 2966, 1726, 1290, 1109, 758 cm–1.
1H NMR (CDCl3, 400 MHz): d = 1.06 (3 H, t, J = 7.2 Hz), 1.37 (6
H, d, J = 6.4 Hz), 1.66 (2 H, sext, J = 7.2 Hz), 2.44 (2 H, t, J = 7.2
Hz), 5.27 (1 H, sept, J = 6.4 Hz), 7.28–7.32 (1 H, m), 7.37–7.42 (1
H, m), 7.49–7.51 (1 H, m), 7.83–7.85 (1 H, m).
13C NMR (CDCl3, 100 MHz): d = 13.7, 21.8, 22.0, 22.2, 68.5, 79.4,
95.5, 124.1, 127.0, 129.8, 131.1, 132.6, 134.1, 166.1.
Synthesis 2007, No. 13, 2014–2024 © Thieme Stuttgart · New York

SPECIAL TOPIC
Platinum(II)-Catalyzed Synthesis of Naphthalene Derivatives
2021
Anal. Calcd for C15H18O2: C, 78.23; H, 7.88. Found: C, 77.93; H,
8.15.
13C NMR (CDCl3, 100 MHz): d = 20.4, 24.3, 28.5, 29.6, 55.9, 59.5,
64.7, 65.0, 82.10, 82.11, 82.2, 82.3, 101.5, 105.1, 122.51, 122.53,
128.39, 128.44, 130.25, 130.31, 131.5, 131.6, 132.7, 132.8, 134.9,
135.0, 146.9, 147.8, 166.0 (overlapped).
Isopropyl 2-(2-Phenylethynyl)benzoate (1j)
IR (neat): 2980, 1721, 1290, 1107, 756 cm–1.
Anal. Calcd for C15H16O3: C, 73.75; H, 6.60. Found: C, 73.77; H,
6.85.
1H NMR (CDCl3, 400 MHz): d = 1.38 (6 H, d, J = 6.4 Hz), 5.30 (1
H, sept, J = 6.4 Hz), 7.34–7.40 (4 H, m), 7.48 (1 H, dt, J = 7.6, 1.6
Hz), 7.54–7.60 (2 H, m), 7.63–7.65 (1 H, m), 7.94–7.96 (1 H, m).
13C NMR (CDCl3, 100 MHz): d = 22.0, 68.8, 88.3, 94.0, 123.28,
123.31, 127.8, 128.2, 128.3, 130.2, 131.3, 131.5, 132.5, 134.0,
165.8.
Platinum-Catalyzed Reaction of 1 with n-Butyl Vinyl Ether;
General Procedure (Tables 1 and 2)
To a mixture of a benzoate derivative 1 (0.10 mmol), n-butyl vinyl
ether (1.0 mmol, Table 1) or diphenylmethyl vinyl ether (0.50
mmol, Table 2), and 4 Å MS (100 mg) in toluene (1.0 mL) was add-
ed PtCl2 (0.01 mmol) at r.t. After the disappearance of the starting
material was confirmed by TLC, the mixture was filtered through
Celite with EtOAc as eluent, and then the filtrate was concentrated
under reduced pressure. The residue was purified by preparative
TLC (hexane–EtOAc, 9:1–19:1) to afford the desired naphthalene
derivatives.
Anal. Calcd for C18H16O2: C, 81.79; H, 6.10. Found: C, 81.50; H,
6.40.
Benzyl 2-(Pent-1-ynyl)benzoate (1k)
IR (neat): 2962, 2234, 1730, 1286, 1245, 1127, 757 cm–1.
1H NMR (CDCl3, 400 MHz): d = 1.02 (3 H, t, J = 7.2 Hz), 1.58 (2
H, sext, J = 7.2 Hz), 2.34 (2 H, t, J = 7.2 Hz), 5.37 (2 H, s), 7.28–
7.53 (8 H, m), 7.91–7.93 (1 H, m).
13C NMR (CDCl3, 100 MHz): d = 13.7, 21.8, 22.1, 66.9, 79.4, 96.0,
124.5, 127.1, 128.1, 128.2, 128.4, 130.2, 131.5, 131.7, 134.2, 135.9,
166.3.
4-Isopropoxynaphthalene-1-carbaldehyde (2a)
IR (neat): 2976, 2732, 1681, 1106, 769 cm–1.
1H NMR (CDCl3, 400 MHz): d = 1.51 (6 H, d, J = 6.0 Hz), 4.90 (1
H, sept, J = 6.0 Hz), 6.91 (1 H, d, J = 8.0 Hz), 7.54–7.58 (1 H, m),
7.67–7.71 (1 H, m), 7.91 (1 H, d, J = 8.0 Hz), 8.35–8.37 (1 H, m),
9.29–9.31 (1 H, m), 10.19 (1 H, s).
13C NMR (CDCl3, 100 MHz): d = 22.0, 70.9, 104.3, 122.6, 124.3,
124.7, 126.0, 126.1, 129.4, 132.1, 139.7, 159.2, 192.0.
Anal. Calcd for C19H18O2: C, 81.99; H, 6.52. Found: C, 81.70; H,
6.68.
S-Octyl 2-(Pent-1-ynyl)benzothioate (1l)
IR (neat): 2927, 1678, 1199, 907 cm–1.
Anal. Calcd for C14H14O2: C, 78.48; H, 6.59. Found: C, 78.47; H,
6.85.
1H NMR (CDCl3, 400 MHz): d = 0.86–0.90 (3 H, m), 1.05 (3 H, t,
J = 7.6 Hz), 1.24–1.37 (8 H, m), 1.42–1.46 (2 H, m), 1.61–1.71 (4
H, m), 2.42 (2 H, t, J = 6.8 Hz), 3.05 (2 H, t, J = 7.6 Hz), 7.27–7.32
(1 H, m), 7.37–7.41 (1 H, m), 7.47–7.50 (1 H, m), 7.69–7.71 (1 H,
m).
13C NMR (CDCl3, 100 MHz): d = 13.6, 14.2, 21.8, 22.1, 22.7, 29.0,
29.2, 29.5, 29.8, 31.9, 78.7, 95.8, 121.6, 127.1, 127.7, 130.9, 133.8,
140.1, 192.6.
4-(4-Chlorophenoxy)naphthalene-1-carbaldehyde (2d)
IR (neat): 1685, 1571, 1485, 1242, 1052, 764 cm–1.
1H NMR (CDCl3, 400 MHz): d = 6.81 (1 H, d, J = 8.4 Hz), 7.10–
7.14 (2 H, m), 7.40–7.44 (2 H, m), 7.63–7.67 (1 H, m), 7.75–7.79 (1
H, m), 7.86 (1 H, d, J = 8.0 Hz), 8.43 (1 H, d, J = 8.4 Hz), 9.34 (1
H, d, J = 8.8 Hz), 10.25 (1 H, s).
13C NMR (CDCl3, 100 MHz): d = 108.8, 121.9, 122.2, 124.9, 125.8,
126.5, 127.0, 129.9, 130.2, 130.3, 132.2, 138.2, 153.7, 159.3, 192.1.
Anal. Calcd for C20H28OS: C, 75.90; H, 8.92; S, 10.13. Found: C,
75.62; H, 9.06; S, 10.28.
Anal. Calcd for C17H11ClO2: C, 72.22; H, 3.92. Found: C, 71.92; H,
4.18.
2-(2-Methoxyethenyl)phenyl 2-Ethynylbenzoate (6a)
Compound 6a was obtained as an inseparable mixture of (Z)-6a and
(E)-6a in a ratio of 95:5.
IR (neat): 3269, 2948, 2105, 1745, 1651, 1482 cm–1.
1H NMR (CDCl3, 400 MHz): d (major isomer) = 3.40 (1 H, s), 3.75
(3 H, s), 5.36 (1 H, d, J = 7.2 Hz), 6.16 (1 H, d, J = 7.2 Hz), 7.13–
7.26 (3 H, m), 7.49 (1 H, dt, J = 7.6 1.6 Hz), 7.56 (1 H, dt, J = 7.6,
1.6 Hz), 7.70 (1 H, dd, J = 7.6, 1.6 Hz).
13C NMR (CDCl3, 100 MHz): d (major isomer) = 60.7, 81.8, 83.2,
98.1, 122.0, 123.3, 125.9, 126.5, 128.3, 128.5, 129.9, 130.8, 131.6,
132.2, 135.1, 146.9, 149.1, 164.1.
4-Benzyloxynaphthalene-1-carbaldehyde (2e)
1H NMR (CDCl3, 400 MHz): d = 5.35 (2 H, s), 7.00 (1 H, d, J = 8.0
Hz), 7.37–7.47 (3 H, m), 7.52–7.60 (3 H, m), 7.69–7.74 (1 H, m),
7.91 (1 H, d, J = 8.0 Hz), 8.42 (1 H, d, J = 8.8 Hz), 9.32 (1 H, d,
J = 8.8 Hz), 10.21 (1 H, s).
13C NMR (CDCl3, 100 MHz): d = 70.5, 104.1, 122.5, 124.8, 125.0,
125.5, 126.4, 127.4, 128.3, 128.7, 129.5, 131.9, 135.8, 139.5, 159.7,
192.2.
Anal. Calcd for C18H14O2: C, 82.42; H, 5.38. Found: C, 82.15; H,
5.62.
Anal. Calcd for C18H14O3: C, 77.68; H, 5.07. Found: C, 77.45; H,
5.15.
4-Octylsulfanylnaphthalene-1-carbaldehyde (2f)
IR (neat): 2926, 1676, 1558, 955, 818 cm–1.
5-Methoxypent-4-enyl 2-Ethynylbenzoate (6b)
Compound 6b was obtained as an inseparable mixture of (E)-6b and
(Z)-6b in a ratio of 81:19.
IR (neat): 3283, 2936, 2106, 1726, 1656 cm–1.
1H NMR (CDCl3, 400 MHz): d = 1.82 (2 H, quint, J = 7.3 Hz), 2.11
(1.62 H, q, J = 7.3 Hz), 2.20–2.28 (0.38 H, m), 3.38 (0.81 H, s), 3.39
(0.19 H, s), 3.50 (2.43 H, s), 3.56 (0.57 H, s), 4.32–4.39 (2.19 H, m),
4.73 (0.81 H, dt, J = 12.7, 7.3 Hz), 5.91 (0.19 H, d, J = 6.4 Hz), 6.33
(0.81 H, d, J = 12.7 Hz), 7.37–7.43 (1 H, m), 7.43–7.50 (1 H, m)
7.59–7.64 (1 H, m), 7.92–7.98 (1 H, m).
1H NMR (CDCl3, 400 MHz): d = 0.87–0.90 (3 H, m), 1.25–1.41 (8
H, m), 1.49–1.54 (2 H, m), 1.78–1.85 (2 H, quint, J = 7.6 Hz), 3.14
(2 H, t, J = 7.6 Hz), 7.45 (1 H, d, J = 7.6 Hz), 7.59–7.63 (1 H, m),
7.69–7.73 (1 H, m), 7.87 (1 H, d, J = 7.6 Hz), 8.34 (1 H, d, J = 8.4
Hz), 9.31 (1 H, d, J = 8.4 Hz), 10.30 (1 H, s).
13C NMR (CDCl3, 100 MHz): d = 14.2, 22.7, 28.4, 29.1, 29.2, 31.8,
32.1, 120.5, 124.1, 125.4, 126.8, 128.1, 129.2, 130.4, 131.1, 136.3,
145.9, 192.6.
Synthesis 2007, No. 13, 2014–2024 © Thieme Stuttgart · New York

2022
H. Kusama et al.
SPECIAL TOPIC
Anal. Calcd for C19H24OS: C, 75.95; H, 8.05; S, 10.67. Found: C,
76.13, H, 8.30; S, 10.59.
Anal. Calcd for C22H30OS: C, 77.14; H, 8.83; S, 9.36. Found: C,
77.20; H, 9.06; S, 9.31.
4-(1H-Pyrrol-1-yl)naphthalene-1-carbaldehyde (2h)
Platinum-Catalyzed Intramolecular Cycloaddition Reaction of
6; General Procedure
IR (KBr): 3129, 2750, 1686, 1576, 1513 cm–1.
To a mixture of a benzoate derivative 6 (0.10 mmol) and 4 Å MS
(100 mg) in toluene (1.0 mL), was added PtCl2 (0.01 mmol) at r.t.
After the disappearance of the starting material was confirmed by
TLC, the mixture was filtered through Celite with EtOAc as eluent,
and then the filtrate was concentrated under reduced pressure. The
residue was purified by preparative TLC (hexane–EtOAc, 9:1–
19:1) to afford the desired naphthalene derivatives 7.
1H NMR (CDCl3, 400 MHz): d = 6.46 (2 H, t, J = 2.0 Hz), 7.05 (2
H, t, J = 2.0 Hz), 7.55–7.67 (2 H, m), 7.75 (1 H, ddd, J = 8.5, 7.1,
1.2 Hz), 7.97 (1 H, d, J = 8.5 Hz), 8.04 (1 H, d, J = 7.6 Hz), 9.37 (1
H, d, J = 8.8 Hz), 10.42 (1 H, s).
13C NMR (CDCl3, 100 MHz): d = 110.1, 121.8, 123.0, 124.0, 125.0,
127.7, 129.45, 129.51, 130.3, 131.8, 136.2, 143.7, 192.4.
Anal. Calcd for C15H11NO: C, 81.43; H, 5.01; N, 6.33. Found: C,
81.23; H, 5.25; N, 6.16.
Naphtho[1,2-b]benzofuranyl-6-carbaldehyde (7a)
IR (KBr): 3063, 2924, 1692, 1205, 743 cm–1.
1H NMR (CDCl3, 400 MHz): d = 7.45–7.51 (1 H, m), 7.53–7.58 (1
H, m), 7.72–7.81 (3 H, m), 8.04–8.08 (1 H, m), 8.50–8.55 (1 H, m),
8.55 (1 H, s), 9.40–9.46 (1 H, m), 10.48 (1 H, s).
13C NMR (CDCl3, 100 MHz): d = 112.1, 118.5, 120.4, 121.3, 121.4,
123.9, 124.2, 125.8, 127.2, 127.5, 127.7, 129.0, 130.6, 130.8, 155.7,
156.4, 192.6.
1-(4-Isopropoxynaphthalen-1-yl)butan-1-one (2i)
IR (neat): 2963, 1668, 1575, 1509, 1220, 1112, 767 cm–1.
1H NMR (CDCl3, 400 MHz): d = 1.03 (3 H, t, J = 7.2 Hz), 1.49 (6
H, d, J = 6.0 Hz), 1.82 (2 H, sext, J = 7.2 Hz), 3.01 (2 H, t, J = 7.2
Hz), 4.84 (1 H, sept, J = 6.0 Hz), 6.78 (1 H, d, J = 8.0 Hz), 7.48–
7.52 (1 H, m), 7.58–7.62 (1 H, m), 7.95 (1 H, d, J = 8.0 Hz), 8.35 (1
H, d, J = 8.4 Hz), 8.88 (1 H, d, J = 8.4 Hz).
13C NMR (CDCl3, 100 MHz): d = 14.0, 18.7, 22.0, 43.2, 70.5,
103.6, 122.3, 125.4, 125.9, 126.4, 127.2, 128.31, 128.33, 130.4,
132.2, 157.0, 202.8.
Anal. Calcd for C17H10O2: C, 82.91; H, 4.09. Found: C, 82.67; H,
4.27.
Benzo[h]chromanyl-6-carbaldehyde (7b)
IR (KBr): 2935, 1669, 1568, 1509, 1412, 1243 cm–1.
Anal. Calcd for C17H20O2: C, 79.65; H, 7.86. Found: C, 79.46; H,
8.12.
1H NMR (CDCl3, 400 MHz): d = 2.11–2.20 (2 H, m), 2.94 (2 H, t,
J = 6.3 Hz), 4.46 (2 H, t, J = 5.2 Hz), 7.53 (1 H, t, J = 8.5 Hz), 7.59–
7.66 (2 H, m), 8.22 (1 H, d, J = 8.5 Hz), 9.23 (1 H, d, J = 8.5 Hz),
10.16 (1 H, s).
4-Isopropoxynaphthalen-1-yl Phenyl Ketone (2j)
IR (neat): 2978, 1650, 1577, 1509, 1251, 1112, 767 cm–1.
1H NMR (CDCl3, 400 MHz): d = 1.50 (6 H, d, J = 6.0 Hz), 4.85 (1
H, sept, J = 6.0 Hz), 6.79 (1 H, d, J = 8.0 Hz), 7.44–7.61 (6 H, m),
7.83–7.85 (2 H, m), 8.38–8.41 (2 H, m).
13C NMR (CDCl3, 100 MHz): d = 22.0, 70.5, 103.6, 122.5, 125.5,
125.6, 126.4, 127.3, 127.9, 128.1, 130.2, 131.6, 132.3, 132.8, 139.4,
156.6, 197.2.
13C NMR (CDCl3, 100 MHz): d = 21.9, 24.5, 67.4, 115.0, 121.8,
124.1, 124.7, 125.2, 126.2, 128.7, 130.8, 140.8, 155.8, 192.1.
Anal. Calcd for C14H12O2: C, 79.22; H, 5.70. Found: C, 79.49; H,
5.67.
Reaction of 4-Chlorophenyl 2-Ethynylbenzoate (1d) with 2,4-
Dimethoxybenzyl Vinyl Ether
Anal. Calcd for C18H18O2: C, 82.73; H, 6.25. Found: C, 82.48; H,
6.55.
To a mixture of a 4-chlorophenyl 2-ethynylbenzoate (1d; 25.7 mg,
0.10 mmol), 2,4-dimethoxybenzyl vinyl ether (38.8 mg, 0.20 mmol)
and 4 Å MS (100 mg) in toluene (0.5 mL), was added PtCl2 (8.0 mg,
0.03 mmol) at r.t. After 11 h, the mixture was filtered through Celite
with EtOAc as eluent, and then the filtrate was concentrated under
reduced pressure. The residue was purified by preparative TLC
(hexane–EtOAc, 4:1) to give naphthalene derivatives 2d (8.2 mg,
29%), 2m (16.7 mg, 55%), and polycyclic ketal 10 (2.5 mg, 6%).
1-(4-Benzyloxynaphthalen-1-yl)butan-1-one (2k)
IR (neat): 2961, 1669, 1576, 1510, 1220, 1076, 768 cm–1.
1H NMR (CDCl3, 400 MHz): d = 1.03 (3 H, t, J = 7.2 Hz), 1.82 (2
H, sext, J = 7.2 Hz), 3.01 (2 H, t, J = 7.2 Hz), 5.32 (2 H, s), 6.86 (1
H, d, J = 8.0 Hz), 7.36–7.46 (3 H, m), 7.51–7.55 (3 H, m), 7.60–
7.64 (1 H, m), 7.93 (1 H, d, J = 8.0 Hz), 8.40–8.42 (1 H, m), 8.85–
8.87 (1 H, m).
13C NMR (CDCl3, 100 MHz): d = 14.0, 18.7, 43.3, 70.3, 103.3,
122.2, 125.7, 125.9, 126.0, 127.3, 128.1, 128.2, 128.4, 128.6, 130.1,
132.0, 136.2, 157.6, 203.0.
4-(2,4-Dimethoxybenzyloxy)naphthalene-1-carbaldehyde (2m)
IR (neat): 3009, 2719, 1686, 1574, 1512, 1208, 763 cm–1.
1H NMR (CDCl3, 400 MHz): d = 3.84 (3 H, s), 3.86 (3 H, s), 5.32
(2 H, s), 6.52–6.54 (2 H, m), 7.05 (1 H, d, J = 8.0 Hz), 7.40–7.42 (1
H, m), 7.53–7.57 (1 H, m), 7.67–7.71 (1 H, m), 7.92 (1 H, d, J = 8.0
Hz), 7.39 (1 H, d, J = 8.4 Hz), 9.31 (1 H, d, J = 8.4 Hz), 10.2 (1 H,
s).
Anal. Calcd for C21H20O2: C, 82.86; H, 6.62. Found: C, 83.16; H,
6.79.
1-(4-Octylsulfanylnaphthalen-1-yl)butan-1-one (2l)
13C NMR (CDCl3, 100 MHz): d = 55.4, 55.5, 65.7, 98.5, 104.2,
104.3, 116.6, 122.6, 124.7, 125.7, 126.2, 129.4, 130.0, 131.9, 139.7,
158.2, 160.2, 161.0, 192.2.
IR (neat): 2926, 2360, 1674, 1561, 1507, 762 cm–1.
1H NMR (CDCl3, 400 MHz): d = 0.87–0.90 (3 H, m), 1.03 (3 H, t,
J = 7.6 Hz), 1.25–1.35 (8 H, m), 1.45–1.51 (2 H, m), 1.72–1.86 (4
H, m), 2.99–3.08 (4 H, m), 7.39 (1 H, d, J = 7.6 Hz), 7.54–7.62 (2
H, m), 7.79 (1 H, d, J = 7.6 Hz), 8.34–8.36 (1 H, m), 8.64–8.67 (1
H, m).
13C NMR (CDCl3, 100 MHz): d = 14.0, 14.2, 18.4, 22.7, 28.7, 29.1,
29.2, 31.8, 32.8, 43.9, 121.9, 124.5, 126.35, 126.41, 127.2, 128.0,
130.3, 132.0, 133.2, 141.0, 204.1.
Anal. Calcd for C20H18O4: C, 74.52; H, 5.63. Found: C, 74.39; H,
5.77.
5-(4-Chlorophenyloxy)-1-(2,4-dimethoxyphenyl)-3,5-methano-
1,3,3a,9b-tetrahydrofuro[3,4-c]isochromene (10)
IR (neat): 2936, 1734, 1613, 1488, 1224, 1082, 829 cm–1.
Synthesis 2007, No. 13, 2014–2024 © Thieme Stuttgart · New York

SPECIAL TOPIC
Platinum(II)-Catalyzed Synthesis of Naphthalene Derivatives
2023
1H NMR (CDCl3, 400 MHz): d = 2.43 (1 H, d, J = 12.8 Hz), 2.50 (1
H, dd, J = 12.8, 7.6 Hz), 3.76 (3 H, s), 3.88–3.94 (4 H, m), 4.80 (1
H, t, J = 6.8 Hz), 5.29 (1 H, d, J = 3.6 Hz), 5.54 (1 H, t, J = 6.8 Hz),
6.15 (1 H, d, J = 7.6 Hz), 6.19 (1 H, dd, J = 7.6, 2.4 Hz), 6.45–6.48
(2 H, m), 6.80 (1 H, dt, J = 7.6, 0.8 Hz), 6.95–7.00 (3 H, m), 7.10–
7.14 (2 H, m), 7.22–7.24 (1 H, m).
13C NMR (CDCl3, 100 MHz): d = 44.6, 47.5, 55.3, 55.4, 76.5, 78.5,
81.6, 97.6, 103.6, 106.2, 118.8, 121.4, 122.4, 125.7, 126.6, 127.5,
128.0, 128.9, 130.3, 131.7, 140.5, 153.0, 156.6, 160.1.
Moll, H.; Heubl, G.; Mudogo, V. J. Org. Chem. 2006, 71,
9348. (h) Mejorado, L. H.; Pettus, T. R. R. J. Am. Chem. Soc.
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HRMS: m/z calcd for C26H23ClO5 [MH+]: 451.1307; found:
451.1339.
Reaction of 2-(Propyn-1-yl)benzaldehyde (11) with 4-Methoxy-
benzyl Vinyl Ether
To a mixture of a 2-(propyn-1-yl)benzaldehyde (11; 14.4 mg, 0.10
mmol), 4-methoxybenzyl vinyl ether (164.2 mg, 1.0 mmol), and tol-
uene (1.0 mL), was added PtCl2 (2.7 mg, 0.01 mmol) at r.t. After 12
h, the mixture was filtered through Celite with EtOAc as eluent, and
the filtrate was concentrated under reduced pressure. The residue
was purified by preparative TLC (hexane–EtOAc, 9:1) to give the
polycyclic compound 12 (13.2 mg, 43%).
3,5-Methano-1-(4-methoxyphenyl)-3a-methyl-1,3,9b-trihydro-
furo[3,4-c]isochromene (12)
IR (neat): 2939, 1614, 1514, 1250, 1059, 758 cm–1.
1H NMR (CDCl3, 400 MHz): d = 1.82 (1 H, s), 2.18 (1 H, dd,
J = 13.2 Hz), 2.46–2.53 (1 H, m), 3.29 (1 H, d, J = 4.4 Hz), 3.77 (3
H, s), 4.36 (1 H, d, J = 7.2 Hz), 5.01 (1 H, d, J = 7.2 Hz), 5.31 (1 H,
d, J = 4.4 Hz), 6.00 (1 H, d, J = 7.6 Hz), 6.68–6.80 (5 H, m), 7.03–
7.06 (2 H, m).
13C NMR (CDCl3, 100 MHz): d = 22.7, 44.4, 54.4, 55.2, 78.0,
83.19, 83.22, 85.5, 89.4, 112.8, 123.7, 125.6, 125.9, 127.9, 129.8,
130.2, 130.8, 141.8, 158.8.
(7) (a) Iwasawa, N.; Shido, M.; Kusama, H. J. Am. Chem. Soc.
2001, 123, 5814. (b) Kusama, H.; Funami, H.; Shido, M.;
Hara, Y.; Takaya, J.; Iwasawa, N. J. Am. Chem. Soc. 2005,
127, 2709. (c) Kusama, H.; Iwasawa, N. Chem. Lett. 2006,
35, 1082. For generation of tungsten-containing azomethine
ylides, see: (d) Kusama, H.; Takaya, J.; Iwasawa, N. J. Am.
Chem. Soc. 2002, 124, 11592. (e) Takaya, J.; Kusama, H.;
Iwasawa, N. Chem. Lett. 2004, 33, 16. (f) Kusama, H.;
Suzuki, Y.; Takaya, J.; Iwasawa, N. Org. Lett. 2006, 8, 895.
(8) Ohe et al. extensively studied the synthesis of furylcarbene
complexes through 5-exo-dig cyclization of carbonyl-ene-
yne compounds. For reviews, see: (a) Ohe, K.; Miki, K.;
Uemura, S. J. Synth. Org. Chem. Jpn. 2004, 62, 978.
(b) Miki, K.; Uemura, S.; Ohe, K. Chem. Lett. 2005, 34,
1068.
(9) For reviews on the carbonyl ylides, see: (a) Padwa, A.;
Weingarten, M. D. Chem. Rev. 1996, 96, 223. (b) Dörwald,
F. Z. Metal Carbenes in Organic Synthesis; Wiley-VCH:
Weinheim, 1999, 206. (c) Mehta, G.; Muthusamy, S.
Tetrahedron 2002, 58, 9477. (d) Padwa, A.; Pearson, W. H.
Synthetic Applications of 1,3-Dipolar Cycloaddition
Chemistry Toward Heterocycles and Natural Products;
Wiley-Interscience: Hoboken, 2003, 253. (e) Padwa, A.
Helv. Chim. Acta 2005, 88, 1357. For some recent
examples, see: (f) Mejía-Oneto, J. M.; Padwa, A. Org. Lett.
2006, 8, 3275. (g) Geng, Z.; Chen, B.; Chiu, P. Angew.
Chem. Int. Ed. 2006, 45, 6197. (h) Nakamura, S.; Sugano,
Y.; Kikuchi, F.; Hashimoto, S. Angew. Chem. Int. Ed. 2006,
45, 6532. (i) Hirata, Y.; Nakamura, S.; Watanabe, N.;
Kataoka, O.; Kurosaki, T.; Anada, M.; Kitagaki, S.; Shiro,
M.; Hashimoto, S. Chem. Eur. J. 2006, 12, 8898.
Anal. Calcd for C20H20O3: C, 77.90; H, 6.54. Found: C, 77.82; H,
6.81.
Acknowledgment
This research was partly supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports, Science,
and Technology of Japan. H.F. was granted a Research Fellowship
of the Japan Society for the Promotion of Science for Young Scien-
tists.
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Synthesis 2007, No. 13, 2014–2024 © Thieme Stuttgart · New York

2024
H. Kusama et al.
SPECIAL TOPIC
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Synthesis 2007, No. 13, 2014–2024 © Thieme Stuttgart · New York