Platinum-catalyzed tandem cyclization-Nazarov cylization reactions: An easy access to complex carbocyclic molecules from 2-alkenyl-(1′-hydroxyl-4-en- 2-ynyl)benzenes

Article abstract of DOI:10.1055/s-2008-1042809

In the presence of PtCl₂/CO catalyst, 2-alkenyl-(1′- hydroxyl-4-en-2-ynyl)benzenes undergo a tandem electrophilic 6-exo-dig cyclization-Nazarov cyclization sequence to give 1H-cyclopenta[a]naphthalenes efficiently and regioselectively. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1042809

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745
Platinum-Catalyzed Tandem Cyclization–Nazarov Cylization Reactions:
An Easy Access to Complex Carbocyclic Molecules from 2-Alkenyl-(1¢-hydro-
xyl-4-en-2-ynyl)benzenes
E
asyAccess to
h
C
omplex
C
a
arbocyclic
r
Molecul
i
Department of Chemistry, National Tsing-Hua University, Hsinchu 300, Taiwan
E-mail: rsliu@mx.nthu.edu.tw
Received 20 November 2007
we recently reported a novel oxidative cyclization8 of
Abstract: In the presence of PtCl2/CO catalyst, 2-alkenyl-(1¢-hy-
droxyl-4-en-2-ynyl)benzenes undergo a tandem electrophilic 6-
exo-dig cyclization–Nazarov cyclization sequence to give 1H-cy-
clopenta[a]naphthalenes efficiently and regioselectively.
dien-yn-ol 1 to 2-naphthyl aldehydes and ketones 2 via a
tandem 6-exo-dig cyclization–oxidation sequence.
Scheme 1 shows a proposed mechanism involving forma-
tion of 2-naphthylidene species D, which is subject to ox-
idation with H2O2 and H2O to give desired product 2,
accompanied by regeneration of the catalysts.
Key words: alcohols, alkynes, carbenoids, catalysis, tandem reac-
tions
To pursue additional value of this investigation, we envis-
age that such substrates bearing a vinylalkynol moiety
would undergo unprecedented 6-exo-dig–Nazarov9 tan-
dem cyclizations, according to a protocol depicted in
Scheme 2. A metal-catalyzed carbophilic activation of the
carbon–carbon triple bond would trigger a 6-exo-dig cy-
clization, leading to formation of 2-naththylidene inter-
mediate D¢, thereby setting a protocol for Nazarov
cyclization. In this paper we report an expedient cycliza-
tion of 2-alkenyl-(1¢-hydroxyl-4-en-2-ynyl)benzenes to
give 1H-cyclopenta[a]naphthalenes efficiently.
Tandem reactions have been the subject of intensive in-
vestigations in organic synthesis.1 Their high efficiency
and brief operation procedures are the beneficial features
of these reactions. With a single workup, one can deliver
a complicated molecule that would otherwise have to be
prepared over the course of several individual steps. Tran-
sition-metal-catalyzed cyclizations of enynes2–6 have
emerged as powerful tools for the synthesis of carbocyclic
compounds, and Pt(II) and Au(I) catalysts are commonly
used to activate organic alkynes towards nucleophilic at-
tack,7 leading to new carbocyclizations. In this direction,
R1
R1
R1
M
oxidant
R2
R2
M
R2
M
O
1
D
2
OH
H2O
M
M = PtCl2/CO or PEt3AuCl
R1
R1
+
R1
H+
R2
R2
H+
R2
OH M–
OH
M
OH
A
B
C
M
Scheme 1
R1
R1
R1
6-exo-dig
Nazarov
R2
M
R2
OH
D'
R2
Scheme 2
SYNLETT 2008, No. 5, pp 0745–0750
x
x.
x
x.
2
0
0
8
Advanced online publication: 26.02.2008
DOI: 10.1055/s-2008-1042809; Art ID: Y01507ST
© Georg Thieme Verlag Stuttgart · New York

746
S. Md. Abu Sohel et al.
CLUSTER
(entries 3 and 4). Both PPh3AuSbF6 and AuCl also cata-
lyzed this tandem sequence, albeit with only modest
yields (59–64%, entries 5 and 6) whereas AuCl3 gave only
a 24% yield (entry 7). Entries 8 and 9 showed our efforts
to obtain 2-naphthyl vinyl ketone (R1 = Me,
R2 = H2C=CMe) through oxidation of 2-naphthyl car-
benes D¢ with H2O2 and H2O8 according to the protocol in
Scheme 1. These two oxidants either led to unreacted 317
exclusively (entries 8), or gave the same 1H-cyclopen-
ta[a]naphthalene 418 over a long period (72 h, entry 9).
Notably, we obtained no regioisomer 4¢ from the screen-
ing of catalysts; this information implies that the Nazarov
cyclization of the 2-naphthyl carbene intermediate D¢, as
depicted in Scheme 2, proceeds in a completely regiose-
lective manner. The exclusive formation of compound 4
stems from the greater electron density at the C(1) carbon
than at C(2) carbon.12
SnBu3 (1.05 equiv),
O
CuCl (1.5 equiv)
O
Pd(PPh3)4 (5 mol%), LiBr (1.5 equiv)
sealed tube (8 h), 60 °C, 81%
Br
Li (1.1 equiv)
–78 °C to r.t., 1.5 h, 88%
OH
3
Scheme 3 Preparation of 2-alkenyl(1¢-hydroxyl-4-en-2-ynyl)ben-
zene 3
To test the feasibility of this concept, we examined the
PtCl2-catalyzed cyclization of substrate 3, which was
readily prepared from commercially available 2-bro-
mobenzaldehyde through Stille coupling10 followed by an
alkynylation reaction, as depicted in Scheme 3. Substrate
3 was subsequently treated with various gold and plati-
num catalysts in suitable solvents, each at 5% loading, to
optimize the yields of desired 1H-cyclopenta[a]naphtha-
lenes 4, as shown in entries 1–7. Treatment of species 3
with PtCl2 in THF (25 °C, 22 h) under N2 gave compound
4 in 72% yield (Table 1, entry1); the yield increased to
89% under CO (1 atm,11 entry 2). This PtCl2/CO system
became less efficient in CH2Cl2 and 1,2-dichloroethane
than in THF upon comparison of their respective yields
With optimized conditions, we prepared various alcohol
substrates 5–13 to examine the scope and generality of
this catalytic reaction sequence; the resulting 1H-cyclo-
penta[a]naphthalene derivatives 14–22 were obtained in
satisfactory yields except for entry 9. As shown in
Table 2, alcohol substrate 5 bearing a 1-phenylethenyl
group was transformed into tricyclic compound 14 with a
yield up to 87% (entry 1). This tandem cyclization is also
suitable for substrates 6–9 bearing various phenyl X and
Y substituents (X = OMe; Y = OMe or F, entries 2–5); the
resulting cyclized products 15–18 were obtained with
yields ranging from 53% to 96%. A high catalytic effi-
Table 1 Catalyst Screening for Alcohol 3 under Various Conditions
catalyst
additive
OH
3
4
4' (not observed)
Entrya
Catalyst
Additive
Solvent
THF
Temp (time, h)
r.t. (22)
Yield (%)b
1
PtCl2
–
72
89
72
74
64
59
24
n.r.e
69
2
PtCl2/CO
PtCl2/CO
PtCl2/CO
AuCl(PPh3)/AgSbF6
AuCl
–
THF
r.t. (20)
3
–
CH2Cl2
DCE
r.t. (20)
4
–
r.t. (21)
5
–
CH2Cl2
CH2Cl2
CH2Cl2
DCE
0 °C to r.t. (8)
r.t. (10)
6
–
7
AuCl3
–
r.t. (20)
8c,d
9f,g
AuClPEt3
PtCl2/CO
H2O2
H2O
r.t. (50)
THF
r.t. (72)
a [Substrate] = 0.23 M and 5 mol% metal catalyst.
b Yield of isolated product after silica gel column chromatography.
c With 4 equiv of H2O2.
d Starting material (89%) was recovered.
e No reaction.
f Starting material (24%) was recovered.
g With 20 equiv of H2O.
Synlett 2008, No. 5, 745–750 © Thieme Stuttgart · New York

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Easy Access to Complex Carbocyclic Molecules
747
ciency was maintained for alcohol 10 bearing a benzothie- presence of proton scavenger MgO;13 the expected 1H-cy-
nyl group, which afforded the cyclized product 19 in 74% clopenta[a]naphthalene 22 was obtained in a 12% yield in
yield. The cyclization efficiency is sensitive to the types this case.
of vinylalkynyl substituents; the examples are manifested
Scheme 4 shows additional examples to assess the effect
in entries 7–9. Substrates 11 and 12, bearing 1,2-disubsti-
of vinylalkynyl substituents of substrates 25, 27, 30, 33,
tuted and 1,1-disubstituted alkenes, respectively, are ap-
and 34 bearing a cycloalkyl substituent at the alkyne
plicable to this cyclization and give the corresponding
group; herein, we observed substrate-dependent chemose-
desired products 20 and 21 in 68% and 84% yields, re-
lectivities. Similar to species 13, indene product 26 was
spectively. For substrate 13 bearing a trisubstituted alk-
obtained in 77% yield. The same tandem catalysis on al-
cohol substrate 27 gave tetracyclic ketone 28 in 62% yield
ene, the reaction was plagued by undesired indene product
24, produced by a single Nazarov cyclization even in the
together with indene product 29 (32%). This ketone syn-
Table 2 Tandem 6-exo-dig–Nazarov Cyclization of Alcohol Substrates
Entry
Substratea
Time (h)
Product (yield,b %)
R
R
X
X
Y
Y
OH
1
2
3
4
5
5: X = Y = H, R = Ph
7
20
6
14 (87)
15 (53)
16 (96)
17 (87)
18 (90)
6: X = OMe, Y = H, R = Me
7: X = H, Y = OMe, R = Me
8: X = Y = OMe, R = Me
9: X = H, Y = F, R = Me
6
10
HO
6
7
19
16
S
S
10
19 (74)
OH
11
12
20 (68)
8
19
OH
Et
Et
21 (84)
23 (14)
24 (78)
9
22
Et
OH
Et
13
22 (12)
a Isolated yield after the purification by silica gel column chromatography.
b Conditions: 25 °C, CO (1 atm), [substrate] = 0.23 M, 5 mol% PtCl2.
Synlett 2008, No. 5, 745–750 © Thieme Stuttgart · New York

748
S. Md. Abu Sohel et al.
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PtCl2 (5 mol%), CO
24 h, MgO
OH
26 (77%)
25
PtCl2 (5 mol%), CO
40 h
O
+
OH
29 (32%)
28 (62%)
27
Ph
Ph
Ph
PtCl2 (5 mol%), CO
40 h
O
+
OH
30
31 (62%)
32 (6%)
+
PtCl2 (5 mol%), CO
X
F
F
40 h
OH
O
36 (52%)
35 (40%)
X = F
33 X = F
34 X = OMe
X = OMe
messy mixture
Scheme 4
thesis lacks the generality in chemoselectivities; for in- and the mechanism of their formation is depicted in
stance, its 1-phenylethenyl and 5-fluorobenzene Scheme 5. We envisage that one molecule of water to be
analogues 30 and 33 gave tetracyclic olefins 31 (62%), 35 produced as starting alcohol substrates 3 and 5–13 be-
(40%), and cyclohexanone 36 (52%). Formation of ketone come transformed by PtCl2 into carbenium intermediate
derivative 36 apparently proceeded through a distinct 6- D¢, which possesses a cationic pentadienyl resonance to
endo-dig cyclization pathway.14
initiate Nazarov cyclization to form species E, ultimately
giving desired products through hydrodemetalation. For
species 13 and 25 bearing a trisubstituted alkenylalkynol,
their corresponding cyclizations preferably gave indene
derivatives 24 and 26. Scheme 6 shows the rationalization
Finally, we obtained a messy mixture of products for the
5-methoxyphenyl analogue 34. In this tandem catalysis,
1H-cyclopenta[a]naphthalenes 4, 14–22 are produced ex-
clusively from most substrates that we tested in Table 2;
R1
R1
R1
[Pt]–
R2
6-exo-dig
[Pt]
+
– H2O
D"
R3
D'
R2
R2
OH
3, 5–13
R3
R3
R1
R1
R1
H+
+
[Pt]–
[Pt]–
H+
[Pt]
H
R3
4, 14–22
R3
R2
F
E
R2
R3
R2
Scheme 5
Synlett 2008, No. 5, 745–750 © Thieme Stuttgart · New York

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Easy Access to Complex Carbocyclic Molecules
749
+
.
.
PtCl2
OH
OH(PtCl2)–
13
+
G,
G
OH(PtCl2)–
+ H+
+
– H+
H2O + PtCl2
Et
24
H
Scheme 6
Me
R
R
H2O
H+ + H2O
H+
[Pt] –
O
27, 30
[Pt]
R = Me
28
R = Ph
F'
H
H
[Pt]
I
31
Scheme 7
of this substituent effect on cyclization chemoselectivity. prepared
2-alkenyl(1¢-hydroxyl-4-en-2-ynyl)ben-
We propose that initial treatment of alcohol 13 with PtCl2 zenes.15,16 This catalytic sequence comprises tandem 6-
forms propargyl cation G, which subsequently gave cy- exo-dig cyclization–Nazarov cyclizations. Current studies
clopentenyl cation H through Nazarov cyclization, and ul- focus on the asymmetric version of this tandem sequence.
timately produced compound 24 with release of one
proton. Regeneration of the catalyst was achieved by re-
Acknowledgment
action of PtCl2(OH)– with proton. For species 13 and 25,
We thank the National Science Council, Taiwan for their generous
support.
the 1-methyl and cyclohexyl substituents stabilize reso-
nance form G¢, which will enhance this chemoselectivity.
Although tetracyclic ketone 28 was produced exclusively
only from substrate 27, its mechanism of formation de-
serves attention (see Scheme 7). Herein, we only obtained
a 32% yield of indene species 29 because its correspond-
ing resonance structure G¢ is less stabilized by its nonpla-
nar cyclopentyl framework. One molecule of water and
proton are expected to be released in the transformation of
species 27 into intermediate F¢, of which the highly
strained bicyclo[3.3.0]octene core becomes subsequently
protonated to give carbene species I, finally rendering de-
sired ketone 26 through H2O oxidation. For its phenyl an-
alogue 30, we envisage that the corresponding carbene
species I preferably undergoes 1,2-hydride shift to give
tetracyclic alkene 31. This hydrogen shift also inhibits the
ketone synthesis in addition to the competitive indene for-
mation (see Scheme 5). At the present stage, we do not
know the exact reason for the formation of tetracyclic ke-
tone 28 from species 27.
References and Notes
(1) (a) Ho, T. L. In Tandem Organic Reactions; New York:
Wiley, 1992. (b) Nicolaou, K. C.; Yue, E. W.; Oshima, T. In
The New Chemistry; Hall, N., Ed.; Cambridge University
Press: Cambridge, 2001, 168. (c) Tietze, L. F.; Hautner, F.
In Stimulating Concepts in Chemistry; Vögtle, F.; Stoddart,
J. F.; Shibasaki, M., Eds.; Wiley-VCH: Weinheim, 2000,
38. (d) Tietze, L. F.; Beifuss, U. Angew. Chem., Int. Ed.
Engl. 1993, 32, 131; Angew. Chem. 1993, 105, 103.
(e) Tietze, L. F. Chem. Rev. 1996, 96, 115.
(2) (a) Corkey, B. K.; Toste, F. D. J. Am. Chem. Soc. 2007, 129,
2764. (b) Trost, B. M.; Krische, M. J. Synlett 1998, 1.
(c) Aubert, C.; Buisine, O.; Malacria, M. Chem. Rev. 2002,
102, 813. (d) Lloyd-Jones, G. C. Org. Biomol. Chem. 2003,
1, 215.
(3) For recent reviews for gold and platinum catalysis, see:
(a) Fürstner, A.; Davies, P. W. Angew. Chem. Int. Ed. 2007,
46, 3410. (b) Gorin, D. J.; Toste, F. D. Nature (London)
2007, 446, 395. (c) Jimenez-Nunez, E.; Echavarren, A. M.
Chem. Commun. 2007, 333. (d) Zhang, L.; Sun, J.; Kozmin,
S. A. Adv. Synth. Catal. 2006, 348, 2271. (e) Hashmi, A. S.
H. Angew. Chem. Int. Ed. 2005, 44, 6990.
In summary, we have developed a convenient preparation
of 1H-cyclopenta[a]naphthalene derivatives from readily
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750
S. Md. Abu Sohel et al.
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(4) For gold-catalyzed cycloisomerizations of enynes, see
selected examples: (a) Nieto-Oberhuber, C.; Munoz, P. M.;
Bunuel, E.; Nevado, C.; Cardenas, D. J.; Echavarren, A. M.
Angew. Chem. Int. Ed. 2004, 43, 2402. (b) Luzung, M. R.;
Markham, J. P.; Toste, F. D. J. Am. Chem. Soc. 2004, 126,
10858. (c) Horino, Y.; Luzung, M. R.; Toste, F. D. J. Am.
Chem. Soc. 2006, 128, 11364. (d) Zhang, L.; Kozmin, S. A.
J. Am. Chem. Soc. 2004, 126, 11806. (e) Zhang, L. J. Am.
Chem. Soc. 2005, 127, 16804. (f) Sun, J.; Conley, M. P.;
Zhang, L.; Kozmin, S. A. J. Am. Chem. Soc. 2006, 128,
9705. (g) Buzas, A.; Gagosz, F. J. Am. Chem. Soc. 2006,
128, 12614. (h) Kirsch, S. F.; Binder, J. T.; Crone, B.;
Duschek, A.; Haug, T. T.; Liébert, C.; Menz, H. Angew.
Chem. Int. Ed. 2007, 46, 2310.
Pergamon: Oxford, 1995. (e) Espinet, P.; Echavarren, A. M.
Angew. Chem. Int. Ed. 2004, 43, 4704. (f) Jung, M. E.; Ho,
D.; Chu, H. V. Org. Lett. 2005, 7, 1649.
(11) For the PtCl2/CO catalysis, see ref. 7a and: (a) Fürstner, A.;
Aïssa, C. J. Am. Chem. Soc. 2006, 128, 6306. (b) Fürstner,
A.; Davies, P. W. J. Am. Chem. Soc. 2005, 127, 15024.
(12) Norman, R. O. C.; Coxon, J. M. In Principles of Organic
Synthesis, 3rd ed.; Blackie Academic and Professional:
Glasgow, 1993, 68.
(13) Magnesium oxide was added to remove Brønsted acid given
from PtCl2 and water in this system. We envisage that
Brønsted may enhance the transformation of alcohol
substrate 13 into indene derivative 24 through a simple
Nazarov cyclization as depicted in Scheme 6.
(5) For PtCl2-catalyzed cycloisomerization of enynes, see
selected examples: (a) Chatani, N.; Furukawa, N.; Sakurai,
H.; Murai, S. Organometallics 1996, 15, 901. (b) Trost, B.
M.; Doherty, G. A. J. Am. Chem. Soc. 2000, 122, 3801.
(c) Fürstner, A.; Szillat, H.; Stelzer, F. J. Am. Chem. Soc.
2000, 122, 6785. (d) Méndez, M.; Munoz, M. P.; Nevado,
C.; Cardenas, D. J.; Echavarren, A. M. J. Am. Chem. Soc.
2001, 123, 10511. (e) Mamane, V.; Gress, T.; Krause, H.;
Fürstner, A. J. Am. Chem. Soc. 2004, 126, 8654. (f) Harrak,
Y.; Blaszykowski, C.; Bernard, M.; Cariou, K.; Mainetti, E.;
Mouriès, V.; Dhimane, A.-L.; Fensterbank, L.; Malacria, M.
J. Am. Chem. Soc. 2004, 126, 8656. (g) Blaszykowski, C.;
Harrak, Y.; Goncalves, M.-H.; Cloarec, J.-M.; Dhimane, A.-
L.; Fensterbank, L.; Malacria, M. Org. Lett. 2004, 6, 3771.
(h) Soriano, E.; Marco-Contelles, J. J. Org. Chem. 2005, 70,
9345. (i) Harrison, T. J.; Patrick, B. O.; Dake, G. R. Org.
Lett. 2007, 9, 367.
(6) For cycloisomerization of enynes by other metals, see
selected examples: (a) Trost, B. M.; Hashmi, A. S. K.
Angew. Chem., Int. Ed. Engl. 1993, 32, 1085. (b) Goeke,
A.; Sawamura, M.; Kuwano, R.; Ito, Y. Angew. Chem., Int.
Ed. Engl. 1996, 35, 662. (c) Wender, P. A.; Sperandio, D. J.
Org. Chem. 1998, 63, 4164. (d) Chatani, N.; Kataoka, K.;
Murai, S.; Furukawa, N.; Seki, Y. J. Am. Chem. Soc. 1998,
120, 9104. (e) Trost, B. M.; Toste, F. D. J. Am. Chem. Soc.
2000, 122, 714. (f) Sémeril, D.; Cléran, M.; Bruneau, C.;
Dixneuf, P. H. Adv. Synth. Catal. 2001, 343, 184.
(14) See ref. 7d for the formation mechanism of the ketone
product 36.
(15) Typical Procedure for the Synthesis of 4-Methyl-1-[2-
(prop-1-en-2-yl)phenyl]pent-4-en-2-yn-1-ol (3)
To a THF (15 mL) solution of 2-bromobenzaldehyde (1.00 g,
5.40 mmol) was added tributyl(prop-1-en-2-yl)stannane
(1.87 g, 1.05 mmol), Pd(PPh3)4 (311 mg, 0.27 mmol), CuCl
(0.80 g, 8.10 mmol) and LiBr (0.7 g, 8.10 mmol); the
mixture was heated in a sealed tube at 60 °C for 8 h. The
resulting solution was concentrated under reduced pressure,
and the residues were eluted through a silica column
(hexane–EtOAc, 98:2) to afford 2-(prop-1-en-2-yl)benz-
aldehyde (639 mg, 4.37 mmol, 81%) as colorless oil. To a
THF (8 mL) solution of 2-methylbut-1-en-3-yne (0.29 g,
4.45 mmol) was slowly added n-BuLi (1.6 mL, 2.5 M in
hexane) at –78 °C; the solution was stirred for 30 min at –78
°C before addition of a THF solution (2 mL) of 2-(prop-1-
en-2-yl)benzaldehyde (0.50 g, 3.42 mmol). After 30 min, to
this solution was added H2O (3 mL); the solution was
extracted with EtOAc, and concentrated to afford crude
alcohol. The crude product was eluted through a silica
column (hexane–EtOAc, 5:1) to afford substrate 3 (640 mg,
3.01 mmol, 88%) as a light yellow oil.
(16) Typical Procedure for the 6-exo-dig–Nazarov tandem
cyclization of 4-Methyl-1-(2-prop-1-en-2-yl)phenylpent-
4-en-2-yn-1-ol(1) to 1,5-Dimethyl-1H-
cyclopenta[a]naphthalene (4)
(g) Chatani, N.; Inoue, H.; Kotsuma, T.; Murai, S. J. Am.
Chem. Soc. 2002, 124, 10294.
A long tube containing PtCl2 (6.3 mg, 0.023 mmol) was
evacuated and backfilled with CO. After repeating this
procedure twice, the tube was charged with alcohol substrate
3 (100 mg, 0.472 mmol) and dry THF (2 mL). The resulting
mixture was stirred at 23 °C for 20 h. The solution was
concentrated and eluted through a silica column (hexane) to
give compound 4 (81 mg, 0.417 mmol, 89%) as viscous oil.
(17) 4-Methyl-1-[2-(prop-1-en-2-yl)phenyl])pent-4-en-2-yn-
1-ol (3)
(7) (a) Fürstner, A.; Davies, P. W.; Gress, T. J. Am. Chem. Soc.
2005, 127, 8244. (b) Fürstner, A.; Stelzer, F. J. Am. Chem.
Soc. 2001, 123, 11863. (c) Lin, M.-Y.; Das, A. J. Am. Chem.
Soc. 2006, 128, 9340. (d) Tang, J.-M.; Bhunia, S.; Sohel, S.
M. A.; Lin, M.-Y.; Liao, H.-Y.; Datta, S.; Das, A.; Liu, R.-
S. J. Am. Chem. Soc. 2007, 129, 15677.
(8) Taduri, B. P.; Sohel, S. M. A.; Cheng, H.-M.; Lin, G.-Y.;
Liu, R.-S. Chem. Commun. 2007, 2530.
IR (neat): 3654 (m), 1624 (m), 1610 (m) cm–1. 1H NMR (400
MHz, CDCl3): d = 7.76 (d, J = 7.0 Hz, 1 H), 7.33–7.29 (m, 2
H), 7.17 (d, J = 7.0 Hz, 1 H), 5.79 (s, 1 H), 5.32 (s, 1 H), 5.25
(s, 1 H), 5.24 (s, 1 H), 4.99 (s, 1 H), 2.12 (s, 3 H), 1.89 (s, 3
H). 13C NMR (100 MHz, CDCl3): d = 144.0, 142.4, 137.5,
128.0, 127.8, 127.4, 127.1, 126.1, 122.1, 116.0, 88.7, 87.1,
61.8, 25.3, 23.1. HRMS: m/z calcd for C15H16O: 212.1201;
found: 212.1204.
(9) Selected examples: (a) Nazarov, I. N.; Torgov, I. B.;
Terekhova, L. N. Izv. Akad. Nauk. SSSR Otd. Khim. Nauk
1942, 200. (b) Janka, M.; He, W.; Haedicke, I. E.; Fronczek,
F. R.; Frontier, A. J.; Eisenberg, R. J. Am. Chem. Soc. 2006,
128, 5312. (c) Malona, J. A.; Colbourne, J. M.; Frontier, A.
J. Org. Lett. 2006, 8, 5661. (d) Lee, J. H.; Toste, F. D.
Angew. Chem. Int. Ed. 2007, 46, 912. (e) Zhang, L.; Wang,
S. J. Am. Chem. Soc. 2006, 128, 1442. (f) He, W.; Sun, X.;
Frontier, A. J. J. Am. Chem. Soc. 2003, 125, 14278.
(g) Bee, C.; Leclerc, E.; Tius, M. Org. Lett. 2003, 5, 4927.
(10) (a) Milstein, D.; Stille, J. K. J. Am. Chem. Soc. 1979, 101,
4992. (b) Scott, W. J.; Crisp, G. T.; Stille, J. K. J. Am. Chem.
Soc. 1984, 106, 4630. (c) Stille, J. K. Angew. Chem., Int. Ed.
Engl. 1986, 25, 508; Angew. Chem. 1986, 98, 504.
(18) 1,5-Dimethyl-1H-cyclopenta[a]naphthalene (4)
IR (neat): 1598 (m) cm–1. 1H NMR (400 MHz, CDCl3): d =
7.96 (d, J = 8.0 Hz, 1 H), 7.68 (d, J = 8.0 Hz, 1 H), 7.44 (t,
J = 8.0 Hz, 1 H), 7.36 (t, J = 8.0 Hz, 1 H), 7.31 (s, 1 H), 6.53
(s, 1 H), 3.58 (s, 2 H), 2.69 (s, 3 H), 2.22 (s, 3 H). 13C NMR
(100 MHz, CDCl3): d = 145.6, 142.9, 137.2, 133.0, 129.9,
129.8, 127.6, 125.6, 125.1, 123.7, 123.6, 120.8, 41.5, 19.7,
16.8. HRMS: m/z calcd for C15H14: 194.1096; found:
194.1092.
(d) Farina, V. In Comprehensive Organometallic Chemistry
II, Vol. 12; Abel, E. W.; Stone, F. G. A.; Wilkinson, G., Eds.;
Synlett 2008, No. 5, 745–750 © Thieme Stuttgart · New York

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