Platinum-catalyzed chemoselectively hydrative dimerization of 2-alkynyl-1-acetylbenzenes for one-pot facile synthesis of chrysene derivatives

Article abstract of DOI:10.1021/jo701580r

(Chemical Equation Presented) We report one-pot syntheses of chrysene compounds via PtCl₂-catalyzed hydrative dimerization of readily available 2-alkynyl-1-acetylbenzenes. This new tandem catalysis comprises an initial selective hydration of th

Full text of DOI:10.1021/jo701580r

Platinum-Catalyzed Chemoselectively Hydrative Dimerization of
2-Alkynyl-1-acetylbenzenes for One-Pot Facile Synthesis of Chrysene
Derivatives
Arindam Das, Hsuan-Hung Liao, and Rai-Shung Liu*
Department of Chemistry, National Tsing-Hua UniVersity, Hsinchu, Taiwan, ROC
rsliu@mx.nthu.edu.tw
ReceiVed July 20, 2007
We report one-pot syntheses of chrysene compounds via PtCl2-catalyzed hydrative dimerization of readily
available 2-alkynyl-1-acetylbenzenes. This new tandem catalysis comprises an initial selective hydration
of the alkyne, followed by chemoselective dimerization of diketone intermediates. The mechanism of
this cyclization has been elucidated by 13C labeling experiments as well as isolation of reaction
intermediates.
Introduction
aromatic hydrocarbons of one important class, which exhibit
good hole5 and electron transport capabilities.6 Such compounds
can also serve as blue emitters in organic electroluminescent
devices because of their high fluorescence quantum efficiency.7
Published procedures for the synthesis of chrysene derivatives8
are based exclusively on naphthalenes bearing special functional
groups,9 which generally require a tedious synthetic procedure.
Kuznetsov et al. reported10 that treatment of benzopyrylium salt
I with HCl gave a mixture of the chrysene products II (22%)
and III (30%) as depicted in eq 1.
One advance in contemporary catalytic science is to achieve
one-pot syntheses of complex molecules through metal-catalyzed
multicomponent coupling reactions.1,2 Such reactions are typi-
cally accompanied by tandem cyclizations to form two or three
rings sequentially. This synthetic approach has found widespread
applications in synthetic organic chemistry,3,4 but less impact
on material chemistry. Chrysene derivatives represent polycyclic
(1) For general reviews, see: (a) Ho, T.-L. Tactics of Organic Synthesis;
Wiley-Interscience: New York, 1994; p 79. (b) Tietze, L. F. Chem. ReV.
1996, 96, 115. (c) Winkler, J. D. Chem. ReV. 1996, 96, 167. (d) Denmark,
S. E.; Thorarensen, A. Chem. ReV. 1996, 96, 137.
(2) For selected examples, see: (a) de Meijere, A.; von Zezschwitz, P.;
Brase, S. Acc. Chem. Res. 2005, 38, 413. (b) Kamijo, S.; Jin, T.; Huo, Z.;
Yamamoto, Y. J. Am. Chem. Soc. 2003, 125, 7786. (c) Patel, S. J.; Jamison,
T. F. Angew. Chem., Int. Ed. 2003, 42, 1364. (d) Yoshida, H.; Fukushima,
H.; Ohshita, J.; Kunai, A. Angew. Chem., Int. Ed. 2004, 43, 3935. (e)
Tamaru, Y.; Yasui, K.; Takanabe, H.; Tanaka, S.; Fugami, K. Angew. Chem.,
Int. Ed. 1992, 31, 645. (f) Yoshida, M.; Fujita, M.; Ishii, T.; Ihara, M. J.
Am. Chem. Soc. 2003, 125, 4874. (g) Varela, J. A.; Rubin, S. G.; Gonzalez-
Rodriguez, C.; Castedo, L.; Saa, C. J. Am. Chem. Soc. 2006, 128, 9262.
(3) For selected reviews, see: (a) Overman, L. E.; Abelman, M. M.;
Kucera, D. J.; Tran, V. D.; Ricca, D. J. Pure Appl. Chem. 1992, 64, 1813.
(b) Grigg, R. J. Heterocycl. Chem. 1994, 31, 631. (c) de Meijere, A.; Meyer,
P. E. Angew. Chem., Int. Ed. Engl. 1994, 33, 2379. (d) Nie, Y.; Niah, W.;
Jaenicke, S.; Chuah, G. K. J. Catal. 2007, 248, 1. (e) Ray, D.; Ray, J. K.
Org. Lett. 2007, 9, 191. (f) Quinn, K. J.; Isaacs, A. K.; Arvary, R. A. Org.
Lett. 2004, 6, 4143.
Unfortunately, the chrysene syntheses were only reported for
the related species of 6,7-dimethoxybenzopyrylium I. The
difficult preparation11 of general benzopyrylium salts and the
lack of chemoselectivity limit the extensive application of this
method for chrysene synthesis. In this investigation, we report
one-pot syntheses of chrysene compounds via Pt(II)-catalyzed
10.1021/jo701580r CCC: $37.00 © 2007 American Chemical Society
Published on Web 10/25/2007
9214
J. Org. Chem. 2007, 72, 9214-9218

One-Pot Synthesis of Chrysene DeriVatiVes
SCHEME 1 a
a Conditions: 10 mol% of PtCl2, 1,4-dioxane, H2O (6 equiv), [substrate] ) 0.80-1.0 M. bYields of products are given after separation using a silica
c
d
column. The reaction was run in dry 1,4-dioxane as solvent. This reaction was run in wet 1,2-dioxane in the presence of 2,6-lutidine (20 mol %).
hydrative dimerization of readily available 2-alkynyl-1-acetyl-
benzenes. This reaction sequence comprises an initial alkyne
hydration, followed by a chemoselective dimerization of the
resulting diketone intermediates.
1-yl)benzene 1a; the intermediate was proposed to derive from
diketone species 2a through selective alkyne hydration13 as
depicted in Scheme 1 (entry 1). When this cyclization was
extended to two alkyl ketone analogues 1b and 1c (R ) Me,
Et), herein, we found that the corresponding cyclization of
species 1c proceeded distinctly from that of species 1a and 1b,
giving chrysene 4 in 78% yield; the molecular structure of
compound 4 is unambiguously determined by an X-ray diffrac-
tion study.14 Entries 4 and 5 affirm the intermediacy of diketone
species 2c because it was isolable from the reaction at a short
reaction time and was subsequently convertible to chrysene 4
efficiently by PtCl2/CO15 in wet 1,4-dioxane. Water is crucial
for the efficient transformation of diketone species 2c into
product 4 (entry 5); the corresponding yield decreased to 38%
in dry 1,4-dioxane. In the presence of 2,6-lutidine (20 mol %),
treatment of species 1a with PtCl2 gave only diketone 2c in
65% yield (entry 6). The value of this chrysene synthesis is
manifested by readily available starting material 1a, prepared
from commercially available 2-bromoacetophenone via a single
coupling reaction (Supporting Information).
Results and Discussions
We reported12 the synthesis of 2-naphthanols 3a via PtCl2/
CO-catalyzed hydrative cyclization of 1-carbonyl-2-(prop-1-yn-
(4) For selected examples, see: (a) Trost, B. M.; Shi, Y. J. Am. Chem.
Soc. 1991, 113, 701. (b) Overman, L. E.; Ricca, D. J.; Tran, V. D. J. Am.
Chem. Soc. 1993, 115, 2042. (c) Trost, B. M.; Shen, H. Angew. Chem., Int.
Ed. 2001, 40, 2313. (d) Trost, B. M.; Calkins, T. L.; Bochet, C. G. Angew.
Chem., Int. Ed. Engl. 1997, 36, 2632. (e) Vorogushin, A. V.; Wulff, W.
D.; Hansen, H.-J. J. Am. Chem. Soc. 2002, 124, 6512.
(5) Masakazu, F. Eur. Patent Application EP 1 561 794 A1.
(6) (a) Eckert, J.-F.; Nicoud, J.-F.; Nierengarten, J.-F.; Liu, S.-G.;
Echegoyen, L.; Armaroli, N.; Barigelletti, F.; Ouali, L.; Krasnikov, V.;
Hadziioannou, G. J. Am. Chem. Soc. 2000, 122, 7467. (b) Cravino, A.;
Sariciftci, N. S. J. Mater. Chem. 2002, 12, 1931. (c) El-Ghayoury, A.;
Schenning, A. P. H. J.; van Hal, P. A.; van Duren, J. K. J.; Janssen, R. A.
J.; Meijer, E. W. Angew. Chem., Int. Ed. 2001, 40, 3660. (d) Pourtois, G.;
Beljonne, D.; Cornil, J.; Ratner, M. A.; Bredas, J. L. J. Am. Chem. Soc.
2002, 124, 4436.
Table 1 shows the activity screening of common π-acids for
hydrative dimerization of 2-prop-1-yn-1-yl-1-acetylbenzene 1c.
In the absence of CO, PtCl2 alone gave a diminished yield (58%,
entry 2) of chrysene 4 because of the decreased catalyst
electrophilicity compared to PtCl2/CO catalyst, whereas AgOTf,
HOTf, HCl, and Zn(OTf)2 were less efficient for the production
of chrysene 4 with 15-42% yields (entries 3-6). Gold catalysts,
(7) (a) Dimitrakopoulos, C. D.; Malenfant, P. R. L. AdV. Mater. 2002,
14, 99. (b) Horowitz, G. AdV. Mater. 1998, 4, 365. (c) Cai, X.; Hara, M.;
Kawai, K.; Tojo, S.; Majima, T. Chem. Phys. Lett. 2003, 368, 365.
(8) For chrysene synthesis, see refs 9 and: (a) Clar, E. Polycyclic
Hydrocarbons; Academic Press: New York, 1964. (b) Wood, C. S.; Mallory,
F. B. J. Org. Chem. 1964, 29, 3373. (c) Lee-Ruff, E.; Hopkinson, A. C.;
Dao, L. H. Can. J. Chem. 1981, 59, 1675. (d) Gore, P. H.; Kamonah, F. S.
Synthesis 1978, 773. (e) Davies, W; Wilmshurst, J. R. J. Chem. Soc. 1961,
4079. (f) Corbett, T. G.; Porter, Q. N. Aust. J. Chem. 1965, 18, 1781. (g)
Levy, L. A.; Sashikumar, V. P. J. Org. Chem. 1985, 50, 1760.
(9) For chrysene synthesis using functionalized naphthalenes, see: (a)
Fonken, G. F. Chem. Ind. (London) 1962, 1327. (b) LeHoullier, C. S.;
Gribble, G. W. J. Org. Chem. 1983, 48, 1682. (c) Blackburn, E. V.; Loader,
C. E.; Timmons, C. J. J. Chem. Soc. 1970, 163. (d) Leznof, C. C.; Hayward,
R. J. Can. J. Chem. 1972, 50, 528. (e) Leznof, C. C.; Hayward, R. J. Can.
J. Chem. 1970, 48, 1842. (f) Carruthers, W.; Evans, N.; Pooranamoorthy,
R. J. Chem. Soc. 1973, 144. (g) Casagrande, M.; Gennari, G.; Cauzzo, G.
Gazz. Chim. Ital. 1974, 104, 1251. (h) Masetti, F.; Bartocci, G.; Galiazzo,
G. Gazz. Chim. Ital. 1975, 105, 419. (i) Nagel, D. L.; Kupper, R.; Antonson,
K.; Wallcave, L. J. Org. Chem. 1977, 42, 3626. (j) Harvey, R. G.
Tetrahedron Lett. 1988, 29, 3885. (k) Lyle, T. A.; Daub, G. H. J. Org.
Chem. 1979, 44, 4933.
(12) Chang, H.-K.; Datta, S.; Das, A.; Odedra, A.; Liu, R.-S. Angew.
Chem., Int. Ed. 2007, 46, 4744.
(13) In our preceding paper,12 the selective hydration of 1-carbonyl-2-
(prop-1-yn-1-yl)benzenes 1a-1c to diketone species 2a-2c proceeded via
formation of intermediate D.
(10) Discussion of the formation mechanism of acylchrysene III will be
provided in Supporting Information; for related Kuznetsov’s papers, see:
(a) Korobka, Kuznetsov, E. V. Khim. Geterotsikl. Soedin. 1982, 1184. (b)
Korobka, I. V.; Voloshina, A. I.; Kuznetsov, E. V. Khim. Geterotsikl. Soedin.
1984, 1472. (c) Korobka, I. V.; Revinskii, Yu. V.; Kuznetsov, E. V. Khim.
Geterotsikl. Soedin. 1985, 910.
(11) For synthesis of benzopyrylium salt, see the review paper: Kuz-
netsov, E. V.; Shcherbakova, I. V.; Balaban, A. T. AdV. Heterocycl. Chem.
1990, 50, 157-254.
(14) The crystallographic data for compounds 4 and 11 were provided
in Supporting Information.
(15) In the presence of CO, PtCl2 was thought to form PtCl2(CO)n which
showed better electrophilicity for alkyne; see: (a) Fu¨rstner, A.; Davies, P.
W.; Gress, T. J. Am. Chem. Soc. 2005, 127, 8244. (b) Fu¨rstner, A.; Davies,
P. W. J. Am. Chem. Soc. 2005, 127, 15024. (c) Fu¨rstner, A.; Aissa, C. J.
Am. Chem. Soc. 2006, 128, 6306. (d) Taduri, B. P.; Ran, Y.-F.; Huang,
C.-W.; Liu, R.-S. Org. Lett. 2006, 8, 883. (e) Lo, C.-Y.; Lin, C.-C.; Cheng,
H.-M.; Liu, R.-S. Org. Lett. 2006, 8, 3153.
J. Org. Chem, Vol. 72, No. 24, 2007 9215

Das et al.
TABLE 1. Catalytic Dimerization of
1-Carbonyl-2-(prop-1-yn-1-yl)benzene over Various Acid Catalysts
TABLE 2. Catalytic Synthesis of Chrysenes from
2-Alkynyl-1-acetylbenzenes
time
(h)
products
entry substratea
catalyst
(yields)b,c
1
2
3
4
5
6
7
1c
1c
1c
1c
1c
1c
1c
10 mol % of PtCl2/CO
10 mol % of PtCl2
10 mol % of Ag(OTf)
10 mol % of HOTf
10 mol % of HCl
10 mol % of Zn(OTf)2
5 mol % of PPh3AuCl
5 mol % of AgOTf
5 mol % of AuCl
5 mol % of AuCl3
5 mol % of AuCl
5 mol % of AuCl3
10 mol % of Zn(OTf)2
10 mol % of HOTf
12
12
15
8
12
15
13
4 (78%)
4 (58%)
4 (42%)
4 (32%), 5 (49%)
4 (15%), 5 (65%)
4 (26%)
4 (3%), 5 (46%)
8
9
10
11
12
13
1c
1c
2c
2c
2c
2c
13
13
14
14
12
14
4 (8%), 5 (51%)
4 (2%), 5 (62%)
4 (39%)
4 (34%)
4 (36%)
4 (43%)
a At 100 °C, 1,4-dioxane, H2O (6 equiv), [substrate] ) 0.80-1.0 M.
b Yields of products are given after separation using a silica column.
c Starting substrates were completely consumed for entries 1-11.
including AuCl, AuCl3, and PPh3AuOTf, gave preferably the
undesired 2,3-dimethylindenone 5, via aldol condensation of
another diketone intermediate 2d (entries 7-9). We screened
also the catalyst activity on the hydrative dimerization of the
diketone species 2c in wet 1,4-dioxane because it is the crucial
step for this chrysene synthesis. The results in entries 10-13
reveal nevertheless that AuCl, AuCl3, AgOTf, and HOTf were
inefficient for this chrysene synthesis with the yields of desired
chrysene 4 less than 43%.
Because of its synthetic and mechanistic interest, we further
examined the generality of this catalytic reaction over various
2-alkynyl-1-acetylbenzenes 6a-6m, which were easily prepared
by Stille or Sonogashira coupling16 of the corresponding
2-acetyl-1-bromobenzenes (Table 2). This chrysene synthesis
provides desired products 7a-7m with various functionalities
on their R1 and R2 substituents. Entries 1-5 show the suitability
of this cyclization to alternation of the aryl R2 and the alkynyl
R3 substituents with an alkyl group; the resulting chrysenes 7a-
7e were obtained in 66-79% yields. In this catalysis, species
6f-6g bearing R1 ) OMe are more efficient than its analogue
6h with R2 ) OMe, as shown by the yields of products 7f-7g
(81-83%) and 7h (56%). This cyclization works well for
substrates 6i-6k bearing a fluoro at the R1 or R2 substituent,
and the corresponding fluorochrysenes 7i-7k were obtained
with yields exceeding 59%. In the case of species 6l, we
obtained chrysene 7l in low yield (27%) with HOAc solvent;
herein, the use of wet 1,4-dioxane preferably gave 2,3-
dimethylindenone 7n (56% yield) in addition to chrysene 7l in
minor proportion (12% yield). This catalytic dimerization
became less efficient for 6m bearing a methylenedioxy group;
the yield of chrysene products 7m was only 29%.
a 10 mol % PtCl2, CO (1 atm), 100 °C, [substrate] ) 0.80-1.0 M.
b Yields of products are given after separation using a silica column. c This
reaction was run in HOAc solvent, and in the case of wet 1,4-dioxane, we
obtained chrysene 7l and 2,3-dimethylindenone 7n in 12 and 56 yields,
respectively.
SCHEME 2
The value of this cyclization is reflected by its applicability
to the syntheses of novel and large polyaromatic compounds
9a and 9b in respective yields of 28 and 31% from PtCl2-
catalyzed dimerization of benzothiophene analogues 8a and 8b
in HOAc solvent (entries 1 and 2, Scheme 2); the thiophene
group in these substrates is known to tolerate Pd(II) and Pt(II)
catalysts.17 In the cyclization of species 8b, we isolated species
9c, and its subsequent conversion to chrysene 9b by PtCl2/CO
(16) (a) Stille, J. K. Angew. Chem., Int. Ed. 1986, 25, 508. (b) Milstein,
D.; Stille, J. K. J. Am. Chem. Soc. 1978, 100, 3636. (c) Sonogashira, K. In
Handbook of Organopalladium Chemistry for Organic Synthesis; Negishi,
E.-i., Ed.; Wiley-Interscience: New York, 2002, pp 493-529. (d) Negishi,
E.-i.; Anastasia, L. Chem. ReV. 2003, 103, 1979. (e) Tykwinski, R. R.
Angew. Chem., Int. Ed. 2003, 42, 1566.
9216 J. Org. Chem., Vol. 72, No. 24, 2007

One-Pot Synthesis of Chrysene DeriVatiVes
SCHEME 3
intermediacy of species C, which loses an acetyl group before
its formation. In the presence of PtCl2, we envisage that diketone
2c forms a dehydrated cyclized ether 2c′, which also generates
benzopyrylium species 2c′′ in this acidic medium. A subsequent
[4 + 2]-cycloaddition of this benzopyrylium species with cyclic
ether 2c′ generates oxonium species A,20 which is prone to loss
of an acetyl group upon hydrolysis according to recent reports
by Yamamoto.21,22 The final aromatization reaction of resulting
species B enables the formation of desired intermediate C with
its 13C labeling consistent with observation. This mechanism
not only rationalizes the chemoselectivity of chrysene 4 but also
explains the deacetylation reaction for intermediate C.
In summary, we report a novel PtCl2-catalyzed dimerization
of hydrative dimerization of 2-alkynyl-1-acetylbenzenes to give
chrysenes, whereas, before this work, chrysenes were commonly
prepared from tedious procedures.8-10 The new tandem catalysis
comprises an initial selective hydration of the alkyne, followed
by chemoselective dimerization of diketone intermediates. The
value of this cyclization is reflected by its extension to the
synthesis of novel polyaromatic compounds including 9a, 9b,
and 11. Studies toward the synthesis of functionalized polycyclic
molecules via PtCl2-catalyzed condensation of multi-aldehyde
and ketone groups are under current studies.
SCHEME 4
SCHEME 5
Experimental Section
(a) Typical Procedure for the Synthesis of 1-[2-(Prop-1-ynyl)-
phenyl]ethanone (1c).
suggested that it is likely to be the reaction intermediate (entries
3 and 4). Scheme 3 shows an additional application for the
synthesis of polyaromatic species 11 via dimerization of
naphthyl derivative 10; the corresponding yield was 26%. The
molecular structure of compound 11 was confirmed by an X-ray
diffraction study.12
To a toluene solution of 2-bromoacetophenone (1.0 g, 5.02 mmol)
was added Pd(PPh3)4 (290 mg, 0.251 mmol) at 25 °C, and the
mixture was stirred for 10 min before addition of tributyltinpropyne
(1.98 g, 6.03 mmol). The resulting mixture was refluxed at 110 °C
for 3 h before it was cooled to 25 °C. To this solution was added
KF solution, and the solution was extracted with ethyl acetate (50
mL), dried over MgSO4, and concentrated under reduced pressure.
A
13C-labeling experiment was performed to elucidate the
mechanism because the chrysene synthesis involved complex
structural organization. As depicted in Scheme 4, we prepared
compound 1c bearing 10% 13C at the carbonyl carbon; the
reaction using isotopically labeled 1c and produced the desired
chrysene 4 with 13C enrichment at the tertiary C(5) and C(6a)
carbons, identified by HMBC and HMQC NMR spectra.18 This
information indicates that the acetic acid byproduct arose from
a hydrative cleavage of the propynyl triple bond. In this manner,
the newly generated naphthalene core is constructed from two
acetyl and one propynyl group, in addition to one cleaved
carbide carbon. The organization verifies the hypothesis that
ketone 9c was the intermediate for chrysene 4.
(19) We envisage that the aldol reaction proceeds via an initial addition
of the more enolizable ArCH2COMe to the less enolizable ArCOMe, giving
the aldol product E. In the manner, this reaction route is expected to give
naphthalene species G ultimately as the major projects.
Scheme 5 shows a plausible mechanism to rationalize the
formation of chrysene 4 via the dimerization of diketone species
2c. In this four-ketone coupling process, the traditional aldol
condensation alone fails to rationalize the observed chemose-
lectivity.19 The preceding results in Scheme 2 support the
(20) (a) Asao, N.; Takahashi, K.; Lee, S.; Kasahara, T.; Yamamoto, Y.
J. Am. Chem. Soc. 2002, 124, 12650. (b) Iwasawa, N.; Shido, M.; Kusama,
H. J. Am. Chem. Soc. 2001, 123, 5814.
(21) (a) Asao, N.; Nogami, T.; Lee, S.; Yamamoto, Y. J. Am. Chem.
Soc. 2003, 125, 10921. (b) Asao, N.; Aikawa, H. J. Org. Chem. 2006, 71,
5249.
(17) Selected examples: (a) Zhao, C.; Zhang, Y.; Ng, M.-T. J. Org.
Chem. 2007, 72, 8384. (b) Silva, N. O.; Abreu, A. S.; Ferreira, P. M. T.;
Monteiro, L. S.; Queiroz, M.-J. R. P. Eur. J. Org. Chem. 2002, 2524. (c)
Wang, Z.; Elokdah, H.; McFarlane, G.; Pan, S.; Antane, M. Tetrahedron
Lett. 2006, 47, 3365.
(18) HMBC, HMQC spectra of compound 4 are provided in Supporting
Information.
(22) Acetic acid given from the production of chrysene 4 was identified
by GC analysis using DB-WAX column (30 m × 0.32 mm i.d.).
J. Org. Chem, Vol. 72, No. 24, 2007 9217

Das et al.
The residue was eluted through a silica column to afford compound
1c (589 mg, 3.71 mmol, 74%) as yellow liquid.
(b) Catalytic Operations.
(d, J ) 8.0 Hz, 1H), 7.40-7.36 (m, 1H), 7.33-7.28 (m, 1H), 2.69
(s, 3H), 2.08 (s, 3H); 13C NMR (100 MHz, CDCl3) δ 200.0, 140.5,
133.4, 130.6, 127.8, 127.0, 121.9, 91.7, 78.4, 29.3, 4.0; HRMS calcd
for C11H10O, 158.0732; found, 158.0735.
Spectral Data for 5,12-Dimethylchrysene (4): White solid, mp
108.5-109.7 °C; IR (neat, cm-1) 3035(s), 2025(w), 1610(s), 885-
(w); 1H NMR (600 MHz, CDCl3) δ 8.96 (d, J ) 8.0 Hz, 1H), 8.71
(d, J ) 8.2 Hz, 1H), 8.57 (s, 1H), 8.16 (d, J ) 7.6 Hz, 1H), 7.87
(d, J ) 7.6 Hz, 1H), 7.78 (s, 1H), 7.66-7.58 (m, 4H), 3.19 (s,
3H), 2.87 (s, 3H); 13C NMR (150 MHz, CDCl3) δ 132.9, 132.8,
132.7, 131.8, 131.7, 129.8, 129.5, 129.2, 128.5, 127.9, 127.3, 126.3,
125.7, 125.6, 124.8, 124.4, 123.1, 122.2, 27.6, 20.4; HRMS calcd
for C20H16, 256.1252; found, 256.1248.
A long-neck tube containing PtCl2 (17 mg, 0.063 mmol) was dried
in vacuo for 1 h, and vacuum was released with CO gas using a
CO balloon before it was charged with 1-(2-(prop-1-ynyl)phenyl)-
ethanone 1c (100 mg, 0.63 mmol), water (0.068 mL, 3.78 mmol),
and 1,4-dioxane (2.0 mL, 0.20 M). The mixture was stirred at
25 °C for 30 min and heated at 100 °C for 1 h. The solution was
concentrated and eluted through a silica column (hexane/ethyl
acetate) to afford compound 2c (53.0 mg, 0.3 mmol, 48%),
compound 4 (11 mg, 0.04 mmol, 13%, yellow oil), and starting
compound 1c (23 mg, 0.15 mmol, 23%).
Acknowledgment. The authors wish to thank the National
Science Council, Taiwan, for supporting this work.
Supporting Information Available: Experimental procedures,
spectral data, and NMR spectra of key compounds. This material
is available free of charge via the Internet at http://pubs.acs.org.
Spectral Data for 1-[2-(Prop-1-ynyl)phenyl]ethanone (1c):
Yellow oil, IR (neat, cm-1) 3125(s), 2125(w), 1730(s), 770(s); 1H
NMR (400 MHz, CDCl3) δ 7.64 (dd, J ) 7.6, 1.2 Hz, 1H), 7.46
JO701580R
9218 J. Org. Chem., Vol. 72, No. 24, 2007