Gold-catalyzed synthesis of bicyclo[4.3.0]nonadiene derivatives via tandem 6-endo-dig/Nazarov cyclization of 1,6-allenynes

Article abstract of DOI:10.1021/jo0707939

(Chemical Equation Presented) Catalytic cyclization of 1,6-allenynes was achieved by AuPPh₃SbF₆ (5 mol %) in cold CH ₂Cl₂ (0°C, 0.5-4 h) to form bicyclo[4.3.0]nonadiene products; this cyclization proceeded more

Full text of DOI:10.1021/jo0707939

Gold-Catalyzed Synthesis of Bicyclo[4.3.0]nonadiene Derivatives via
Tandem 6-endo-dig/Nazarov Cyclization of 1,6-Allenynes
Guan-You Lin, Chun-Yao Yang, and Rai-Shung Liu*
Department of Chemistry, National Tsing-Hua UniVersity, Hsinchu, Taiwan, 30043, Republic of China
rsliu@mx.nthu.edu.tw
ReceiVed April 16, 2007
Catalytic cyclization of 1,6-allenynes was achieved by AuPPh3SbF6 (5 mol %) in cold CH2Cl2 (0 °C,
0.5-4 h) to form bicyclo[4.3.0]nonadiene products; this cyclization proceeded more efficiently for a
substrate bearing R ) alkyl (yields >70%). We propose a reaction mechanism involving a 6-endo-dig
cyclization of Au(I)-π-alkyne, followed by Nazarov cyclization.
Introduction
of allenynes via metallacyclopentene intermediates to give
cyclohexenyl compounds (eq 1). Only a limited number of
reports are related to the synthesis of bicyclic carbocyclic
products.4,5 Cycloisomerization of allenynes is also catalyzed
by platinum and gold complexes, via nucleophilic attack of the
central allene carbon at the π-alkyne functionality.6 1,7-Allenyne
substrates containing geminal dialkyl groups were cyclized with
PtCl2 or AuCl3 catalysts to form bicyclo[4.3.0]nonadienes (eq
2); this interesting cyclization is restricted to terminal alkynes.5a,b
Murakami reported5c that 1,6-allenynes underwent PtCl2-
catalyzed intramolecular [2+2]-cycloaddition to form bicyclo-
[3.2.0]heptadienes; the initial intermediate involves a six-
membered platinum carbene as depicted in eq 3. Herein, we
report a new gold-catalyzed cyclization of 1,6-allenynes bearing
internal alkynes, which provides new bicyclic carbocyclic
compounds at 0 °C in a one-pot operation.
Metal-catalyzed transformation of acyclic molecules into
bicyclic carbocyclic species is synthetically useful because
bioactive compounds typically comprise polycyclic structural
frameworks.1 Transition metal-catalyzed cycloisomerization of
allenynes provides rapid and efficient access to carbocyclic
compounds. Although considerable interest has been growing
rapidly in this area,2-5 literature reports focused exclusively on
formation of products bearing one carbocyclic ring.2-3 Malacria2
and Brummond3 reported metal-catalyzed Alder-ene reaction
(1) For selected examples, see: (a) Kusama, H.; Hara, R.; Kawahara,
S.; Nishimori, T.; Kashima, H.; Nakamura, N.; Morihira, K.; Kuwajima, I.
J. Am. Chem. Soc. 2000, 122, 3811. (b) Va´zquez, A.; Williams, R. M. J.
Org. Chem. 2000, 65, 7865. (c) Fuwa, H.; Ebine, M.; Bourdelais, A. J.;
Baden, D. G.; Sasaki, M. J. Am. Chem. Soc. 2006, 128, 16989. (d) Artman,
G. D.; Grubbs, A. W.; Williams, R. M. J. Am. Chem. Soc. 2007, 129, 6336.
(2) (a) Petit, M.; Aubert, C.; Malacria, M. Tetrahedron 2006, 62, 10582.
(b) Petit, M.; Aubert, C.; Malacria, M. Org. Lett. 2004, 6, 3937. (c) Llerena,
D.; Buisine, O.; Aubert, C.; Malacria, M. Tetrahedron 1998, 54, 9373. (d)
Llerena, D.; Aubert, C.; Malacria, M. Tetrahedron Lett. 1996, 37, 7027.
(e) Aubert, C.; Llerena, D.; Malacria, M. Tetrahedron Lett. 1994, 35, 2341.
(3) (a) Brummond, K. M.; Painter, T. O.; Probst, D. A.; Mitasev, B.
Org. Lett. 2007, 9, 347. (b) Bayden, A. S.; Brummond, K. M.; Jordan, K.
D. Organometallics 2006, 25, 5204. (c) Brummond, K. M.; Curran, D. P.;
Mitasev, B.; Fischer, S. J. Org. Chem. 2005, 70, 1745. (d) Brummond, K.
M.; Mitasev, B. Org. Lett. 2004, 6, 2245. (e) Brummond, K. M.; Chen, H.;
Mitasev, B.; Casarez, A. D. Org. Lett. 2004, 6, 2161.
Results and Discussion
Before this investigation, Au(I)- and Pt(II)-catalyzed synthesis
of bicyclo[4.3.0]nonadienes was restricted to 6-exo-dig-cycliza-
(5) (a) Cadran, N.; Cariou, K.; Herve´, G.; Aubert, C.; Fensterbank, L.;
Malacria, M.; Marco-Contelles, J. J. Am. Chem. Soc. 2004, 126, 3408. (b)
Lemie´re, G.; Gandon, V.; Agenet, N.; Goddard, J.; de Kozak, A.; Aubert,
C.; Fensterbank, L.; Malacria, M. Angew. Chem., Int. Ed. 2006, 45, 7596.
(c) Matsuda, T.; Kadowaki, S.; Goya, T.; Murakami, M. Synlett 2006, 575.
(6) Hashmi, A. S. K. Angew. Chem., Int. Ed. 2000, 112, 3737.
(4) Lee, S. I.; Sim, S. H.; Kim, S. M.; Kim, K.; Chung, Y. K. J. Org.
Chem. 2006, 71, 7120.
10.1021/jo0707939 CCC: $37.00 © 2007 American Chemical Society
Published on Web 08/03/2007
J. Org. Chem. 2007, 72, 6753-6757
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Lin et al.
SCHEME 1
tion of 1,7-allenynes bearing a terminal alkyne (eq 2).4,5 We
sought to achieve catalytic cyclization of 1,n-allenynes (n ) 5,
6, 7) via a distinct n-endo-dig cyclization of π-alkyne intermedi-
ates. We prepared three different 1,n-allenynes 1, 2a, and 3 to
examine the chemoselectivity of this Au(I)-catalyzed cyclization
reaction;7 these substrates contain a phenylacetylene group
because we envisage that the π-alkyne intermediate forms a
hypothetical vinyl cation to direct the desired n-endo-dig
cyclization,8,9 as depicted in Table 1. Treatment of 1,7-allenyne
1 (0.2 M, entry 1) with AuPPh3OTf (5%) in wet dioxane at
100 °C gave cyclized ketone product 4 (trans/cis ) 5.1) in 73%
yield; we observed no reaction with 5% AuPPh3SbF6 catalyst
in dry or wet CH2Cl2 (23 °C). In the case of 1,6-allenyne 2a
(entry 2), its AuPPh3SbF6-catalyzed cyclization in CH2Cl2 at 0
°C gave bicyclic product 5a in 43% yield. The structure of
compound 5a was elucidated by 1H NOE spectroscopy.10
Treatment of 1,5-allenyne 3 (entry 3) with 5% AuPPh3OTf in
wet CH2Cl2 at 23 °C gave cyclopentenol product 6 in 52%
without formation of the desired bicyclo[3.3.0]octadiene. For-
mation of oxygen-containing compounds 4 and 6 requires water
TABLE 1. Chemoselectivity for Gold-Catalyzed Cyclization of
1,n-Allenynes
(7) For selected examples to use PPh3AuSbF6 as catalysts see: (a) Genin,
E.; Toullec, P. Y.; Antoniotti, S.; Brancour, C.; Geneˆt, J.-P.; Michelet, V.
J. Am. Chem. Soc. 2006, 128, 3112. (b) Wang, S.; Zhang, L. J. Am. Chem.
Soc. 2006, 128, 14274. (c) Me´zailles, N.; Ricard, L.; Gagosz, F. Org. Lett.
2005, 7, 4133. (d) Nieto-Oberhuber, C.; Mun˜oz, M. P.; Bun˜uel, E.; Nevado,
C.; Ca´rdenas, D. J.; Echavarren, A. M. Angew. Chem., Int. Ed. 2004, 43,
2402. (e) Luzung, M. R.; Markham, J. P.; Toste, F. D. J. Am. Chem. Soc.
2004, 126, 10858. (f) Sherry, B. D.; Toste, F. D. J. Am. Chem. Soc. 2004,
126, 15978. (g) Lin, C.-C.; Deng, T.-M.; Odedra, A.; Liu, R.-S. J. Am.
Chem. Soc. 2007, 129, 3798.
(8) For 5- or 6-endo-dig catalytic cyclization triggered by a π-phenyl-
acetylene intermediate, see selected examples: (a) Harrison, T. J.; Patrick,
B. O.; Dake, G. R. Org. Lett. 2007, 9, 367. (b) Zhao, J.; Hughes, C. O.;
Toste, D. F. J. Am. Chem. Soc. 2006, 128, 7436. (c) Zhang, J.; Schmalz,
H.-G. Angew. Chem., Int. Ed. 2006, 45, 6704. (d) Zhang, L.; Kozmin, S. J.
Am. Chem. Soc. 2005, 127, 6962. (e) Asao, N.; Nogami, T.; Lee, S.;
Yamamoto, Y. J. Am. Chem. Soc. 2003, 125, 10921. (f) Lian, J.-J.; Chen,
P.-C.; Lin, Y.-P.; Ting, H.-C.; Liu, R.-S. J. Am. Chem. Soc. 2006, 128,
11372.
a Yields are reported after separation from a silica column. b Trans/cis
ratio ) 5.1
in an equimolar proportion, which is incompatible with the
AuPPh3SbF6 catalyst because of its great sensitivity toward
water.7,11
To optimize the condition given in entry 2 (Table 1), we tested
the reactivity of 1,6-allenyne 2a in the presence of various
catalysts as depicted in Table 2. No reaction occurred in the
presence of AuCl, AuCl3, AuClPPh3, and AgSbF6 (5 mol %
each) in CH2Cl2 at 23 °C (entries 1-4). The best results were
observed by using AuClPPh3/AgSbF6 (5 mol %) with a dilute
substrate concentration (0.02 M) at 0 °C to minimize the
allenyne polymerization; the yield of desired compound 5a was
increased to 61% (entry 5). The use of AuClPPh3/AgOTf (5
mol %) and PtCl2 (10 mol %) in dioxane or toluene at 23 °C
showed no trace of the desired reaction, but produced a mixture
(9) Recent review for gold catalysis: (a) Fu¨rstner, A.; Davies, P. W.
Angew. Chem., Int. Ed. 2007, 46, 3410. (b) Hashmi, A. S. K. Angew. Chem.,
Int. Ed. 2005, 44, 6990. (c) Hashmi, A. S. K.; Hutchings, G. J. Angew.
Chem., Int. Ed. 2006, 45, 7896. (d) Jime´nez-Nu´n˜ez, E.; Echavarren, A. M.
Chem. Commun. 2007, 333. (e) Zhang, L.; Sun, J.; Kozmin, S. A. AdV.
Synth. Catal. 2006, 348, 2271.
(10) 1H NOE map of key compounds and X-ray data of compound 5j
are provided in the Supporting Information.
(11) (a) Dube´, P.; Toste, F. D. J. Am. Chem. Soc. 2006, 128, 12062. (b)
Lin, M.-Y.; Das, A.; Liu, R.-S. J. Am. Chem. Soc. 2006, 128, 9340.
6754 J. Org. Chem., Vol. 72, No. 18, 2007

Synthesis of Bicyclo[4.3.0]nonadiene DeriVatiVes
TABLE 2. Catalytic Activity over Various Gold and Platinum
Catalysts
TABLE 3. Au(I)-Catalyzed Cyclization of 1,6-allenynes
a 5 mol % catalyst. b 5 mol % Au and 5 mol % Ag catalysts. c 10 mol
% PtCl2. d [allenyne] ) 0.02 M. e N.R. ) no reaction.
of [4+2]-cycloadduct 7 and its dehydrogenation derivative 8
in hot dioxane or toluene (entries 6 and 7). Structural elucidation
of [4+2]-cycloadduct 8 relies on 1H NOE spectroscopy.10 The
reaction with PtCl2/CO in hot toluene (10 mol %, 100 °C) gave
[4+2]-cycloadducts 7 (24%) and its dehydrogenated form 8
(12%) in addition to desired product 5a (24%).
a 5.0% AuClPPh3, 5.0% AgSbF6, CH2Cl2 (0.02 M, 0 °C), 4 h for entries
1-7 and 0.5 h for entries 8-12. b Isolated yields are given after column
chromatography.
With optimal conditions (5% PPh3AuSbF6, 0.02 M substrate,
CH2Cl2, 0 °C), the scope of this reaction was studied thoroughly.
Table 3 shows the results with various 1,6-allenynes (2b-m)
via alteration of the alkynyl phenyl R2, and the allenyl R1, R3,
and R4 substituents. Entries 1-5 show 1,6-allenynes 2b-f with
their alkynyl and allenyl groups bearing phenyl, 4-methylphenyl,
4-fluorophenyl, and naphthyl substituents; the resulting bicyclo-
[4.3.0]nonadienes 5a-f were obtained in reasonable yields (52-
65%). However, when the alkyne contained an electron-rich
4-methoxyphenyl or when both the terminal allene and alkyne
groups contained a 4-fluorophenyl group as in compounds 2g
and 2h, respectively, the corresponding cyclized products 5g
and 5h were obtained in low yields (26-42%). The allenyl C(3)-
substituent R3 plays an important role for the reaction; a methyl
or butyl group not only maintained the good yields (70-81%),
but also reduced the duration of reaction (0.5 h, entries 8-12).
When a 3-methoxyphenyl group was introduced at the C(1)-
allene carbon of compound 2m (entry 12), an 81% yield was
obtained. An X-ray diffraction study of product 5j has been
performed to confirm the bicyclo[4.3.0]nonadiene framework
(see the Supporting Information).
The synthetic utility of this new cyclization is also manifested
by its applicability to 1,6-allenynes 2n-o bearing an alkenyl
group at the allenyl C(1)-carbon. The gold-catalyzed cyclization
of these two allenynes at 0 °C proceeded smoothly to give
bicyclo[4.3.0]nonatrienes 5n and 5o in 65% and 61% yields,
respectively.
We performed deuterium-labeling experiments to elucidate
the reaction mechanism (Scheme 3). Cyclization of d5-2a
bearing a C6D5 group with AuPPh3SbF6 (5 mol %) produced
the desired d4-5a with its vinyl deuterium content X ) 0.61 D;
SCHEME 2
SCHEME 3
t
in the presence of BuOH, this deuterium content is decreased
to 0.35 D. This information indicates that a protodeauration is
likely to occur at this vinyl carbon.
Scheme 4 shows a proposed mechanism to account for the
chemoselectivity in the formation of bicyclo[4.3.0]nonadiene
5a and cyclopentol 6. We envisage that these two products arise
from π-alkyne intermediates A, in which a partial positive
character resides at the tCPh carbon to induce a 6-endo-dig
attack of the allene group to form allyl cation B. An extensive
delocalization of species B is highly suitable for Nazarov
J. Org. Chem, Vol. 72, No. 18, 2007 6755

Lin et al.
SCHEME 4
SCHEME 5
cyclization,12,13 and leads ultimately to observed bicyclo[4.3.0]-
nonadiene 5a. This hypothetical mechanism is supported not
only by our deuterium-labeling experiments, but also by the
formation of cyclopentenol 6, which follows a similar pathway
to form allyl cation B′. Nazarov cyclization of species B′
encounters difficulty because the expected bicyclo[3.3.0]-
octadiene framework is too strained to form.14,15
Experimental Section
(I) Experimental procedures for synthesis of the substrates.
(1) Synthesis of 1,8-Diphenyl-1,2-octadien-7-yne. (a) Synthesis
of 6-Phenylhex-5-yn-1-ol (s-1). To a triethylamine solution (30
mL) of iodobenzene (2.49 g, 12.2 mmol) was added Pd(PPh3)2Cl2
(71.7 mg, 0.10 mmol) and CuI (38.0 mg, 0.2 mmol) at 28 °C, and
the mixture was stirred for 5 min before addition of hex-5-yn-1-ol
(1.00 g, 10.2 mmol). The resulting mixture was stirred for 12 h,
and the solvent was removed in vacuo and treated with a saturated
NaHCO3 solution. The solution was extracted with ethyl acetate,
washed with a saturated NaCl solution, and dried over anhydrous
MgSO4. The residues were chromatographed through a silica gel
column (hexane: ethyl acetate/4:1) to afford compound s-1 (1.37
g, 7.9 mmol, 77%) as a yellow oil.
In summary, we have reported a new efficient PPh3AuSbF6-
catalyzed cyclization of 1,6-allenynes to generate bicyclo[4.3.0]-
nonadienes chemoselectively under 0 °C. The mechanism of
this new cyclization has been investigated,16 and is proposed
to proceed through a tendem 6-endo-dig/Nazarov cyclization
of Au(I)-π-alkyne intermediates. The utility of this reaction is
manifested by its applicability to various 1,6-allenynes, and the
utilization of this synthetic method toward bioactive molecules
is under current investigation.
(15) For catalytic cyclization via a π-allene intermediate, see: (a) Lee,
J. H.; Toste, F. D. Angew. Chem., Int. Ed. 2007, 46, 912. (b) Funami, H.;
Kusama, H.; Iwasawa, N. Angew. Chem., Int. Ed. 2007, 46, 909. (c) Nishina,
N.; Yamamoto, Y. Angew. Chem., Int. Ed. 2006, 45, 3314. (d) Gockel, B.;
Krause, N. Org. Lett. 2006, 8, 4485. (e) Wang, S.; Zhang, L. Org. Lett.
2006, 8, 4585. (f) Hashmi, A. S. K.; Schwartz, L.; Choi, J.-H.; Frost, T. M.
Angew. Chem., Int. Ed. 2000, 39, 2285. (g) Hashmi, A. S. K.; Blanco, M.
C.; Fischer, D.; Bats, J. W. Eur. J. Org. Chem. 2006, 1387.
(12) Nazarov, I. N.; Torgov, I. B.; Terekhova, L. N. IzV. Akad. Nauk.
SSSR Otd. Khim. Nauk 1942, 200.
(13) (a) Janka, M.; He, W.; Haedicke, I. E.; Fronczek, F. R.; Frontier,
A. J.; Eisenberg, R. J. Am. Chem. Soc. 2006, 128, 5312-5313. (b) Malona,
J. A.; Colbourne, J. M.; Frontier, A. J. Org. Lett. 2006, 8, 5661-5664.
(14) Formation of cyclopentyl phenyl ketone 4 is thought to arise from
Au(I)-π-allene intermediate, which initiates a 5-exo-trig cyclization to form
vinyl cation E, and ultimately producing desired ketone 4 upon water attack.
The uncommon feature of this cyclization is the nature of the Au(I)-π-
allene intermediate, which is characterized also by resonance structure D′
such that an intramolecular attack occurs at the terminal allene carbon
(16) According to recent Au(I)-π-allene chemistry,15 one alternative
mechanism involves initial Nazarov cyclization, followed by 6-endo-dig
cyclization of π-alkyne H as depicted below; the initial intermediate is Au-
(I)-π-allene intermediate F′, which activates indene formation to give species
G. After protodeauration, a subsequent 6-endo-dig cyclization of alkyne
intermediate H provides the desired bicyclo[4.3.0]nonadiene 5a. This
pathway, however, is opposed by formation of cyclopentol 6, which indicates
initial formation of a cyclopentene ring rather than the indene ring.
.
6756 J. Org. Chem., Vol. 72, No. 18, 2007

Synthesis of Bicyclo[4.3.0]nonadiene DeriVatiVes
(b) Synthesis of 6-Phenylhex-5-ynal (s-2). To a dichloromethane
solution of oxalyl chloride (1.50 g, 11.8 mmol) was carefully added
DMSO (1.84 g, 23.6 mmol) at -78 °C. After 30 min, a dichlo-
romethane solution of compound s-1 (1.71 g, 9.8 mmol) was
injected, and the reaction mixture was stirred for 1 h before addition
of triethylamine (5.00 g, 49 mmol). The reaction mixture was
warmed to room temperature, and the solution was extracted with
dichloromethane, washed with water, dried over MgSO4, and
concentrated under reduced pressure. The residues were purified
by passing through a short silica pad to afford compound s-2 (1.57
g, 9.1 mmol, 93%) as a yellow oil.
(2 × CH), 123.9, 95.0, 94.2, 89.6, 81.0, 28.0, 27.8, 18.9; HRMS
calcd for C20H18 258.1409, found 258.1410.
(II) A Procedure for Catalytic Cyclization of 1,7-Dipheny-
hepta-1,2-dien-6-yne. (a) Synthesis of 1-Phenyl-4,4a-dihydro-
3H-fluorene (5a). A solution of PPh3AuSbF6 (5 mol %) was
(c) 1-(1-Ethynyl)-6-phenyl-5-hexynyl Methanesulfonate (s-3).
To a mixture of trimethylsilyl acetylene (1.14 g, 11.6 mmol) and
THF (20 mL) was added n-BuLi (2.5 M in hexanes, 3.0 mL, 7.5
mmol) dropwise at -78 °C, and the mixture was stirred for 30
min before addition of compound s-2 (1.00 g, 5.8 mmol). After 3
h at room temperature, this solution was treated with MsCl (2.00
g, 17.4 mmol), and the mixture was stirred for 1 h before addition
of a methanol solution of KF (461 mg, 7.95 mmol). The resulting
mixture was stirred for 1.0 h, quenched by addition of water, and
extracted with ethyl acetate. The extract was washed with a saturated
NaCl solution, dried over anhydrous MgSO4, and concentrated
under reduced pressure. The residues were chromatographed
through a silica gel column (hexane:ethyl acetate/10:1) to afford
compound s-3 (1.86 g, 4.77 mmol, 82%) as colorless oil.
(d) Synthesis of 1,8-Diphenylocta-1,2-dien-7-yne (1). To a THF
solution of phenylmagnesium bromide (181 mg, 1.0 mmol) was
added ZnCl2 (1.0 M in THF, 1.0 mL, 1.0 mmol) dropwise at 0 °C,
and the resulting mixture was stirred for 1.0 h before adding Pd-
(PPh3)4 (4.6 mg, 0.004 mmol) and compound s-3 (312 mg, 0.8
mmol). The resulting mixture was then stirred for 1.0 h before being
warmed to room temperature, and the solvent was removed in vacuo
and treated with a saturated NaHCO3 solution. The solution was
extracted with diethyl ether, washed with a saturated NaCl solution,
and dried over anhydrous MgSO4. The residues were chromato-
graphed through a silica gel column (hexane) to afford compound
1 (155 mg, 0.6 mmol, 75%) as a colorless oil. IR (neat, cm-1) 3082
(m), 2210 (w), 1963 (s), 1598 (m), 1495 (s); 1H NMR (400 MHz,
CDCl3) δ 7.39-7.35 (m, 2H), 7.29 (t, J ) 8.0 Hz, 4H), 7.27-7.24
(m, 3H), 7.18 (t, J ) 8.0 Hz, 1H), 6.17-6.15 (m, 1H), 5.60 (q, J
) 6.4 Hz, 1H), 2.48 (t, J ) 7.2 Hz, 2H), 2.34-2.28 (m, 2H), 1.83-
1.76 (m, 2H); 13C NMR (100 MHz, CDCl3) δ 205.3, 134.9, 131.5
(2 × CH), 128.6 (2 × CH), 128.2 (2 × CH), 127.5, 126.7, 126.6
prepared by mixing PPh3AuCl (9.9 mg, 0.02 mmol) and AgSbF6
(6.9 mg, 0.02 mmol) in dichloromethane (2.0 mL). The mixture
was stirred for 10 min before addition of excess dichloromethane
(18 mL). To the resulting mixture was added compound 2a (100
mg, 0.41 mmol) dropwise at 0 °C and the solution was stirred for
4.0 h before warming to room temperature. The resulting solution
was filtered through a celite bed and eluted through a silica gel
column (hexane) to give compound 5a (56 mg, 0.23 mmol, 61%)
as a colorless oil. IR (neat, cm-1) 2875 (s), 1648 (w), 1522 (s); 1H
NMR (400 MHz, CDCl3) δ 7.48-7.43 (m, 3H), 7.38 (t, J ) 6.8
Hz, 2H), 7.34-7.28 (m, 2H), 7.26-7.22 (m, 1H), 7.17 (t, J ) 7.2
Hz, 1H), 6.55 (s, 1H), 6.00-5.98 (m, 1H), 3.49 (dd, J ) 13.8 Hz,
4.0 Hz, 1H), 2.63-2.54 (m, 3H), 1.45-1.35 (m, 1H); 13C NMR
(100 MHz, CDCl3) δ 148.5, 146.5, 145.0, 140.2, 136.8, 128.8, 128.3
(2 × CH), 127.9 (2 × CH), 127.3, 126.8, 124.4, 124.2, 122.6, 121.0,
48.6, 27.7, 27.5; HRMS calcd for C19H16 244.1252, found 244.1253.
Acknowledgment. The authors wish to thank the National
Science Council, Taiwan for supporting this work.
Supporting Information Available: Experimental procedures
including synthesis of allenyne 3, spectra data for compounds 1-8,
2a-o, and 5a-o, and X-ray data for compound 5j; copies of
1H and 13C NMR spectra for compounds 1-8, 2a-o, and 5a-o.
This material is available free of charge via the Internet at
http://pubs.acs.org.
JO0707939
J. Org. Chem, Vol. 72, No. 18, 2007 6757