Ruthenium-catalyzed cyclization of epoxide with a tethered alkyne: Formation of ketene intermediates via oxygen transfer from epoxides to terminal alkynes

Article abstract of DOI:10.1021/ja049943c

Treatment of (o-ethynyl)phenyl epoxides with TpRuPPh₃(CH ₃CN)₂PF₆ (10 mol %) in hot toluene (100 °C, 3-6 h) gave 2-naphthols or 1-alkylidene-2-indanones very selectively with isolated yields exceeding 72%, depen

Full text of DOI:10.1021/ja049943c

Published on Web 05/14/2004
Ruthenium-Catalyzed Cyclization of Epoxide with a Tethered
Alkyne: Formation of Ketene Intermediates via Oxygen
Transfer from Epoxides to Terminal Alkynes
Reniguntala J. Madhushaw, Ming-Yuan Lin, Shariar Md. Abu Sohel, and
Rai-Shung Liu*
Contribution from the Department of Chemistry, National Tsing-Hua UniVersity,
Hsinchu, Taiwan, Republic of China
Received January 5, 2004; E-mail: rsliu@mx.nthu.edu.tw
Abstract: Treatment of (o-ethynyl)phenyl epoxides with TpRuPPh3(CH3CN)2PF6 (10 mol %) in hot toluene
(100 °C, 3-6 h) gave 2-naphthols or 1-alkylidene-2-indanones very selectively with isolated yields exceeding
72%, depending on the nature of the epoxide substituents. Surprisingly, the reaction intermediate proved
to be a ruthenium-π-ketene species that can be trapped efficiently by alcohol to give an ester compound.
This phenomenon indicates a novel oxygen transfer from epoxide to its terminal alkyne catalyzed by a
ruthenium complex. A plausible mechanism is proposed on the basis of reaction products and the deuterium-
labeling experiment. The 2-naphthol products are thought to derive from 6-endo-dig cyclization of (o-alkenyl)-
phenyl ketene intermediates, whereas 1-alkylidene-2-indanones are given from the 5-endo-dig cyclization
pathway.
W(CO)6-catalyzed cyclization of R-ethynyl epoxides.4 The first
Introduction
intermolecular alkyne-epoxide coupling was recently reported
One current trend in catalytic reactions is the formation of
carbon-carbon bonds among two or three π-typed molecules
such as alkyne, alkene, 1,3-diene, methylenecyclopropane, car-
bon monoxide, imines, allene, ketone, and aldehyde.1,2 Few
studies are focused on the metal-mediated coupling reaction on
σ-typed epoxide molecules.3,4 Although several metal salts effect
the coupling of epoxide with alkyne via a one-electron radical
process3a-c or acid-induced opening of epoxides,4c the reaction
generally requires an excess amount of metal reagents (>1.0
equiv). Gansauer reported that a catalytic amount of titanium-
(III) complexes sufficed to implement radical epoxide-alkyne3c
cyclization in the presence of excess manganese powder.
McDonald and co-workers achieved the synthesis of furans via
by Jamison5 with the use of Ni(0)-PBu3 catalyst. To our best
knowledge, there is no precedent for a catalytic epoxide-alkyne
coupling leading to a complete transfer of an oxygen atom from
epoxide6 to alkyne to generate a ketene intermediate (Scheme
1, eq 1), ultimately giving useful cyclized products.
Recently, we reported the aromatization of (o-alkenyl)-
ethynylbenzene with a 1,2-shift of halo and aryl substituents,7c
and the mechanism involves ruthenium-vinylidenium inter-
mediates.8 We now extend the ruthenium-catalyzed electrocy-
clization to R-ethynylphenyl epoxides to assess the feasibility
of the electrocyclization of epoxide-olefin-vinylidenium func-
tionalities. Such an electrocyclization is still unknown and very
interesting in mechanistic aspects. The reaction pathway possibly
leads to cleavage of the carbon-carbon or carbon-oxygen bond
of an epoxide.3-5,9 We are delighted to discover that the
cyclization generates a ruthenium-ketene intermediate via an
oxygen transfer process (Scheme 1, eq 2); here, we report details
of this remarkable phenomenon.
(1) Selected reviews: (a) Lautens, M.; Klute, W.; Tam, W. Chem. ReV. 1996,
96, 49. (b) Aubert, C.; Buisine, O.; Malacria, M. Chem. ReV. 2002, 102,
813. (c) Trost, B. M.; Toste, F. D.; Pinkerton, A. B. Chem. ReV. 2001,
101, 2067. (d) Schore, N. E. In ComprehensiVe Organometallic Chemistry;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Hegedus, L. S., Eds.; Pergamon
Press: Oxford, 1995; Vol. 12, p 703. (e) Geis, O.; Schaltz, H. Angew.
Chem., Int. Ed. 1998, 37, 911. (f) Fruhauf, H. W. Chem. ReV. 1997, 97,
523.
(2) For selected examples, see: (a) Brummond, K. M.; Lu, J. J. Am. Chem.
Soc. 1999, 121, 5087. (b) Tobisu, M.; Chatani, N.; Asaumi, T.; Amako,
K.; Ie, Y.; Fukumoto, Y.; Murai, S. J. Am. Chem. Soc. 2000, 122, 12633.
(c) Kablaoui, N. M.; Hicks, F. A.; Buchwald, S. L. J. Am. Chem. Soc.
1996, 118, 5818. (d) Chatani, N.; Morimoto, T.; Fukumoto, Y.; Murai, S.
J. Am. Chem. Soc. 1996, 118, 5335. (e) Chatani, N.; Tobisu, M.; Asaumi,
T.; Murai, S. Synthesis 2000, 925. (f) Shibata, T.; Toshida, N.; Takagi, K.
Org. Lett. 2002, 4, 1619. (g) Seo, J.; Chui, H. M. P.; Heeg, M. J.;
Montgomery, J. J. Am. Chem. Soc. 1999, 121, 476. (h) Takimoto, M.; Mori,
M. J. Am. Chem. Soc. 2002, 124, 10008. (i) Yamamoto, Y.; Takagishi, H.;
Itoh, K. J. Am. Chem. Soc. 2002, 124, 6844.
(5) Molinaro, C.; Jamison, T. F. J. Am. Chem. Soc. 2003, 125, 8076.
(6) For reviews of the metal-catalyzed oxygen transfer reaction, see: Organic
Syntheses by Oxidation with Metal Compounds; Mijs, W. J., de Joughe, C.
R. H. I., Eds.; Plenum: New York, 1986.
(7) For catalytic reactions that use this ruthenium catalyst, see: (a) Yeh, K.-
L.; Liu, B.; Lo, C.-Y.; Liu, R.-S. J. Am. Chem. Soc. 2002, 124, 6510. (b)
Datta, S.; Chang, C.-L.; Yeh, K.-L.; Liu, R.-S. J. Am. Chem. Soc. 2003,
125, 9294. (c) Shen, H.-C.; Pal, S.; Lian, J.-J.; Liu, R.-S. J. Am. Chem.
Soc. 2003, 125, 15762. (d) Lo, C.-Y.; Guo, H.-Y.; Lian, J.-J.; Liu, R.-S. J.
Org. Chem. 2002, 67, 3930.
(8) (a) Trost, B. M. Acc. Chem. Res. 2002, 35, 695. (b) Bruneau, C.; Dixneuf,
P. Acc. Chem. Res. 1999, 32, 311.
(9) For coupling of epoxide with alkyne and alkene via cleavage of the C-C
bond of epoxide, see selective examples: (a) Chou, W.-N.; White, J. B.
Tetrahedron Lett. 1991, 32, 7637. (b) Gaebert, C.; Mattaay, J. Tetrahedron
1997, 53, 14297. (c) Palomino, E.; Schaap, A. P.; Heeg, M. J. Tetrahedron
Lett. 1989, 30, 6801.
(3) (a) RajanBabu, T. V.; Nugent, W. A. J. Am. Chem. Soc. 1994, 116, 986.
(b) Gansauer, A.; Pierobon, M.; Bluhm, H. Angew. Chem., Int. Ed. 1998,
37, 101. (c) Gansauer, A.; Bluhm, H.; Pierobon, M. J. Am. Chem. Soc.
1998, 120, 12849. (d) Odedra, A.; Wu, C.-J.; Madhushaw, R. J.; Wang, S.
L.; Liu, R.-S. J. Am. Chem. Soc. 2003, 125, 9610.
(4) McDonald, F. E.; Schultz, C. C. J. Am. Chem. Soc. 1994, 116, 9363.
9
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J. AM. CHEM. SOC. 2004, 126, 6895-6899
6895

A R T I C L E S
Madhushaw et al.
Scheme 1
yields of 72-95%. The reaction proceeds well with naphthyl
epoxide 7 to deliver 3-phenanthrol 19 in 83% yield. The alkyne-
epoxide coupling is very effective for compounds 8,9 bearing
a 5-fluoro substituent (entries 5,6) and extended well to the
substrates 10-13 bearing a π-donor group (X ) F, Cl, Br, OMe)
at the phenyl C(4) carbon (entries 7-10). The corresponding
products 20-25 were obtained in as high as 87-93% yields
without the formation of byproducts. Electron-rich benzene
species 14,15 gave 85-88% yields of cyclized products 26,27.
The structures of compounds 21 and 22 were unambiguously
Scheme 2
1
confirmed by H NOE spectra (see the Supporting Informa-
tion).15
As shown in Table 2, we prepared various 1′,2′,2′-epoxide
substrates 28-35 to examine the possible formation of naphthol
products bearing a tertiary carbon. Notably, 1′,2′,2′-trisubstituted
epoxide 28 gave 1-alkylidene-2-indenone 36 in 89% yield under
similar conditions (entry 1). This transformation involves a
complicated reorganization of the molecular skeleton. Assign-
ment of the structure of indanone 36 was made on the basis of
13C-1H HMBC spectra.15 The proposed structure was recon-
1
firmed by the match of the H NMR spectra with those of an
authentic sample which we prepared according to the literature
method16 as depicted in Scheme 3. This framework is envisaged
to derive from the bond connection between the epoxide C1′
and terminal acetylene carbons, whereas the oxygen atom
migrates to the same acetylene carbon. Additional examples are
provided in entries 2-10 to illustrate the generality. Entries 2,3
show efficient cyclization of epoxides 29 and 30 which bear
different 2′,2′-epoxide alkyl substituents, to give 2-indanones
37 and 38 in 83-86% yields. NMR signals of Z- and E-isomers
Results and Discussion
TpRuPPh3(CH3CN)2PF610 [Tp ) tris(1-pyrazolyl)borate] was
chosen as a catalyst because it readily reacted with terminal
alkyne7 to produce a cationic and highly electrophilic ruthenium-
vinylidenium species.7,8 This characteristic is responsible for
catalytic reactions including transfer hydrogenation,7a cleavage
of a carbon-carbon triple bond,7b and cyclization of (o-alkenyl)-
ethynylbenzene with a skeletal rearrangement.7c This catalyst
was prepared from heating TpRu(PPh3)2Cl with LiPF6 in
CH3CN.10 We first examined the structural effect of epoxides
on catalytic reactions. As shown in Scheme 2, treatment of
(o-ethynyl)phenyl epoxides 1a and 1b (E/Z ) 1.6) with this
ruthenium catalyst (10 mol %) in hot toluene (100 °C, 24 h)
failed to give any noticeable product. However, the epoxide 1c
bearing a long n-propyl group gave naphthol 2c in 91% yield
(toluene, 100 °C, 3 h). Under similar conditions, ketone 3 failed
to give the same product, but gave an enyne (Z/E ) 2.1) via
dimerization of its terminal alkyne.11 This information suggests
that the epoxy-ketone isomerization12 is not operable under
catalytic conditions. The yields of naphthol 2c are highly
dependent on reaction solvents, shown in the results as fol-
lows: dichloroethane (58%, 90 °C, 36 h), dimethoxyethane
(53%, 85 °C, 35 h), acetonitrile (25%, 90 °C, 48 h), 3-pentanone
(27%, 100 °C, 5.5 h), and DMF (12%, 100 °C, 6 h). No ac-
tivity was observed for related ruthenium catalysts including
C5H5RuPPh3(CH3CN)2PF613 and TpRuPPh3(CH3CN)Cl.10 This
information suggests that the basic tris(1-pyzarolyl)borate ligand
and two vacant sites in TpRuPPh3(CH3CN)2PF6 are crucial for
the catalytic activity.
1
of indanone 37 were assigned on the basis of H NMR NOE
spectra.15 Naphthyl epoxide 31 gave the analogous product 39
in 72% yield. The cyclization also works well with the substrates
32-35 bearing a 5-fluoro-, 4-fluoro-, 4-methoxy, and 4,5-
methylenedioxy substituent, respectively, giving 72-91% yields
of the cyclized products 40-43.
Scheme 4 shows crucial experiments to better understand
the reaction mechanism. We were delighted to discover that a
key reaction intermediate can be trapped using isobutyl alco-
hol as a solvent. Heating epoxide 1a in hot isobutyl alcohol
in the presence of 10 mol % ruthenium catalyst gave ester 44a
in low yield (21%) over a long period (100 °C, 48 h). In con-
trast, heating epoxides 5, 9, and 28 in hot isobutyl alcohol
(100 °C) for 6 h gave esters 44b, 44c, and 45 in respective
yields of 71%, 79%, and 90%. Only the trans-isomer of
compound 44b and 44c was obtained despite the different
E/Z ratios of the starting epoxides 5 and 9 (E/Z ) 4.2 and
0.53).
We prepared deuterated samples d-1c and d-28 for the
isotope-labeling experiment, and the results are given in Scheme
(10) Chan, W.-C.; Lau, C.-P.; Chen, Y.-Z.; Fang, Y.-Q.; Ng, S.-M.; Jia, G.
Organometallics 1997, 16, 34.
We prepared various (o-ethynyl)phenyl epoxides 4-15 to
examine the generality of this cyclization. As shown in Table
1, these epoxides contained a mixture of E- and Z-isomers (E/Z
) 0.71-2.9)14 except for styryl oxide derivative 6 (entry 3)
that was obtained as E-isomer. All substrates bear a long or
bulky 2′-alkyl substituent to ensure the catalytic activity. 1′,2′-
Disubstituted epoxides 4-6 bearing a n-pentyl, isopropyl, and
phenyl group were compatible with this cyclization (10 mol %
catalyst, toluene, 100 °C, 3 h), giving the products 16-18 in
(11) See the related reaction: Slugovc, C.; Mereiter, K.; Zobetz, E.; Schmid,
R.; Kirchner, K. Organometallics 1996, 15, 5275.
(12) Okuda, K.; Katsura, T.; Tanino, H.; Kakoi, H.; Inoue, S. Chem. Lett. 1994,
197.
(13) This complex was prepared by treatment of CpRu(CH3CN)3PF6 with PPh3
in equal molar proportion.
(14) The E/Z ratios of epoxides 4-15 were described in the Supporting
Information.
(15) The 1H NOE spectra of compounds 21-22, 37 and 13C-1H HMBC NMR
spectra of compound 36 were provided in the Supporting Information.
(16) Ensley, H. E.; Balakrishnan, P.; Hogan, C. Tetrahedron Lett. 1989, 30,
1625.
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6896 J. AM. CHEM. SOC. VOL. 126, NO. 22, 2004

Ruthenium-Catalyzed Cyclization of Epoxide
A R T I C L E S
Table 1. Ruthenium-Catalyzed Cyclization of (o-Ethynyl)phenyl Epoxides
a 10 mol % catalyst, [substrate] ) 1.2 M, 100 °C, 3 h. b Yields were reported after separation from column chromatograph. c The E/Z ratios of the
epoxides are provided in the Supporting Information.
Table 2. Ruthenium-Catalyzed Synthesis of 1-Alkylidene-2-indanone
a 10 mol % catalyst, [substrate] ) 1.2 M, 100 °C, 3 h. b Yields were reported after separation from column chromatograph.
Scheme 3
information indicates the involvement of ruthenium-vinylide-
nium intermediates in the reaction mechanism.17
The formation of esters 44b,c and 45 strongly indicates that
a ruthenium-π-ketene intermediate D is the key reaction
intermediate (Scheme 6).18 We propose that the ruthenium
catalyst first forms vinylidene-ruthenium species A,7,8 which is
also supported by deuterium-labeling experiments given in
Scheme 5. Intramolecular electrocyclization via attack of the
epoxide of species A at its central allene carbon produces seven-
membered ether ring B, which is stabilized by extensive cationic
5. The alkynyl deuterium of species d-1c was transferred
exclusively to the naphthyl C1 carbon of naphthol 2c, whereas
the corresponding proton of epoxide d-28 was located at one
of the methylene protons of indanone d-36. Both cases show a
1,2-shift for the alkynyl deuterium of epoxides d-1c and d-28
as compared to their respective products d-2c and d-36. This
delocalization. This species undergoes subsequent cleavage of
the ether ring to give ruthenium-π-ketene species C that is in
(17) (a) Merlic, C. A.; Pauly, M. E. J. Am. Chem. Soc. 1996, 118, 11319. (b)
Maeyama, K.; Iwasa, N. J. Org. Chem. 1999, 64, 1344. (c) Miura, T.;
Iwasawa, N. J. Am. Chem. Soc. 2002, 124, 518.
(18) Tidwell, T. T. Ketene; John Wiley: New York, 1995.
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J. AM. CHEM. SOC. VOL. 126, NO. 22, 2004 6897

A R T I C L E S
Madhushaw et al.
Scheme 4
is shown to be inefficient possibly due to the difficulty of the
nucleophilic attack.
The esters 44,45 are unlikely generated from the reaction of
TpRu-acyl intermediates with isobutyl alcohol. According to
our previous studies,7b TpRu-vinylacyl species readily underwent
decarbonylation to liberate carbon monoxide and alkene even
in the presence of carbon monoxide (10 atm).20,21 The decar-
bonylation was so rapid that TpRu-acyl intermediates could not
be trapped by aliphatic alcohols to form esters.7b,20,21
Conclusion
In summary, we have reported a cascade alkyne-epoxide
cyclization of (o-ethynyl)phenyl epoxides catalyzed by ruthe-
nium complexes. The reaction products are highly dependent
on the epoxide substituents. 1′,2′-Disubstituted epoxides gave
2-naphthol derivatives efficiently, whereas 1′,2′,2′-trisubstituted
produced 1-alkylidene-2-indanones in good yields. We propose
a plausible mechanism involving ketene-alkene intermediates,
generated from an oxygen migration from epoxide to terminal
alkyne. The 2-naphthol products are thought to derive from
6-endo-dig cyclization of ketene-alkene intermediates, whereas
1-alkylidene-2-indanones are given from the 5-endo-dig cy-
clization pathway. This proposed mechanism is supported by
trapping experiments using isobutyl alcohol as well as the
deuterium-labeling experiment. Examination of this reaction on
molecules bearing various alkyne-epoxide functionalities is
under investigation.
Scheme 5
Experimental Section
equilibrium with isomeric species D. In the case of 1′,2′-
disubstituted olefin (R2 ) H), species D undergoes 6-endo-dig
electrocyclization (path a)19 to form six-membered ketone
species E, and ultimately gives naphthol 2c, 16-18 via loss of
a proton and subsequent reprotonation. For 1′,2′,2′-trisubstituted
olefin (R2 ) alkyl), species D undergoes 5-endo-dig cyclization
(path b) to give species F, and finally gives 1-alkylidene-2-
indanones 36-38. According to this mechanism, the E/Z ratios
of resulting styrene 44,45 are expected to follow their thermal
equilibrium values, in favor of E-styrene derivatives.
(1) General. Unless otherwise noted, all reactions were carried out
under a nitrogen atmosphere in oven-dried glassware using standard
syringe, cannula, and septa apparatus. Benzene, diethyl ether, tetrahy-
drofuran, and hexane were dried with sodium benzophenone and
distilled before use. TpRuPPh3(CH3CN)2PF6 catalyst was prepared by
heating TpRu(PPh3)2Cl with LiPF6 in CH3CN.10 2-Bromobenzaldehyde
was obtained commercially and used without purification. o-(2′-
Trimethylsilylethynyl)benzaldehyde was obtained by the Sonogashira
coupling reaction of 2-bromobenzaldehyde with trimethylsilylacety-
lene.22
(2) Typical Procedure for the Synthesis of (o-Ethynyl)phenyl
Epoxide (1c). To a THF solution (20 mL) of n-butyltriphenylphos-
phonium bromide (2.96 g, 7.42 mmol) at 0 °C was added n-BuLi (2.5
mL, 6.43 mmol), and the mixture was stirred at 0 °C for 0.5 h. To this
solution was added o-(2′-trimethylsilylethynyl)benzaldehyde (1.0 g, 4.95
mmol), and the mixture was stirred at room temperature for 4 h. The
solution was quenched with water and concentrated in vacuo. The
organic layer was extracted with diethyl ether, dried over MgSO4, and
chromatographed (hexane, Rf ) 0.71) over a silica column to give the
olefination product as a colorless oil (1.01 g, 4.17 mmol, 85%). This
silyl compound was then dissolved in THF (10 mL) and added to
Bu4NF (1 M) (4.6 mL, 4.58 mmol), and the mixture was stirred at 26
°C for 8 h before addition of water (10 mL). The solution was
concentrated, extracted with diethyl ether, and chromatographed on a
silica column (hexane, Rf ) 0.86) to give an enyne (0.67 g, 3.94 mmol,
The 6-endo-dig (path a) cyclization in the proposed mech-
anism was strongly supported by literature reports.18,19 1,3-
Dienyl-4-ketenes readily formed similar 2-naphthols via 6-endo-
dig cyclization at ambient conditions.19 Although 5-endo-dig
cyclization (path b) is little known in ketene chemistry, we
observed similar behavior in the aromatization of (o-styryl)-
ethynylbenzene7c in which the styryl C′1-carbon attacks at the
central ruthenium-vinylidenium carbon in a 5-endo-dig fashion.
The dimethyl substituents of epoxide species D enhance the
5-endo-dig cyclization via formation of a stable tertiary car-
bocation F.
The success of this catalytic reaction relies on the cleavage
of the ether ring of the Fischer-typed ruthenium-oxacarbenium
B. We believe that a long alkyl or bulky R1 substituent is
required to weaken this carbon-oxygen bond because of
increasing steric hindrance. This hypothesis accounts well for
the catalytic inactivity of epoxides 1a and 1b (Scheme 2) bearing
a small hydrogen and methyl group, respectively. Generation
of ester 44a from epoxide 1a is presumably generated from
nucleophilic attack of isobutyl alcohol at the carbenium CR-
carbon of intermediate B, to generate species G that ultimately
gives the observed product (Scheme 7). This catalytic pathway
(19) (a) Danheiser, R. L.; Brisbois, R. G.; Kowalczyk, J. J.; Miller, R. T. J.
Am. Chem. Soc. 1990, 112, 3093. (b) Merlic, C. A.; Xu, D. J. Am. Chem.
Soc. 1991, 113, 7418. (c) Masamune, S.; Fukumoto, K. Tetrahedron Lett.
1965, 4647. (d) Mayr, H.; Huisgen, R. J. Chem. Soc., Chem. Commun.
1976, 57.
(20) We previously reported the ruthenium-catalyzed transformation of ethynyl
alcohol into alkene and carbon monoxide.7b This catalytic reaction
proceeded via formation of TpRu-vinylacyl intermediates that cannot be
trapped by isobutyl alcohol. The reaction was not inhibited by carbon
monoxide (10 atm) because of its facile decarbonylation.
(21) Datta, S.; Chang, C.-L.; Yeh, K.-L.; Liu, R.-S., unpublished results.
(22) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 4467.
9
6898 J. AM. CHEM. SOC. VOL. 126, NO. 22, 2004

Ruthenium-Catalyzed Cyclization of Epoxide
A R T I C L E S
Scheme 6
Scheme 7
NMR (400 MHz, CDCl3) (E/Z ) 1.8), E-isomer, δ 7.46 (d, J ) 7.3
Hz, 1H), 7.31-7.19 (m, 2H), 7.17 (d, J ) 8.0 Hz, 1H), 4.06 (d, J )
2.4 Hz, 1H), 3.30 (s, 1H), 2.83 (dt, J ) 5.5, 2.4 Hz, 1H), 1.72-1.50
(m, 2H), 1.43-1.18 (m, 2H), 0.98 (t, J ) 7.4 Hz, 3H), minor Z-isomer
(selected peaks), δ 7.46 (d, J ) 7.3 Hz, 1H), 7.31-7.19 (m, 2H), 7.17
(d, J ) 8.0 Hz, 1H), 4.29 (d, J ) 4.4 Hz, 1H), 3.30-3.29 (m, 2H),
0.82 (t, J ) 7.4 Hz, 3H), the rest peaks are overlapped with those of
the major E-isomer; 13C NMR (100 MHz, CDCl3) major E-isomer δ
140.4, 138.4, 132.4, 129.1, 127.2, 123.7, 81.8, 81.0, 63.0, 56.7, 34.3,
19.1, 13.9; HRMS calcd for C13H14O, 186.1045; found, 186.1041.
(5) 3-Propylnaphthalen-2-ol (2c). IR (Nujol, cm-1) 3610(s), 3100-
(s), 3067(s), 2258(m), 2119(s), 1624(w); 1H NMR (400 MHz, CDCl3)
δ 7.60 (d, J ) 7.6 Hz, 1H), 7.58 (d, J ) 7.6 Hz, 1H), 7.55 (s, 1H),
7.32 (t, J ) 7.6 Hz, 1H), 7.26 (t, J ) 7.6 Hz, 1H), 7.10 (s, 1H), 2.73
95%) as colorless oil. To a CH2Cl2 solution (15 mL) of this enyne (0.5
g, 2.94 mmol) was added m-chloroperbenzoic acid (0.65 g, 3.82 mmol),
and the mixtures were stirred for 3 h at 28 °C. The resulting solution
was quenched with an aqueous NaHCO3 solution, extracted with diethyl
ether, and dried over anhydrous MgSO4. The resulting solution was
filtered through a small basic Al2O3 bed, concentrated, and eluted
through a Et3N-pretreated silica column (diethyl ether-hexane, 1:1)
to afford (o-ethynyl)phenyl epoxide (1c) as a colorless oil (0.41 g, 2.20
mmol, 75%).
(t, J ) 8.0 Hz, 2H), 1.77-1.67 (m, 2H), 0.99 (t, J ) 7.2 Hz, 3H); 13
C
NMR (150 MHz, CDCl3) δ 153.4, 131.6, 129.1, 128.9, 127.5, 126.1,
126.0, 125.8, 123.6, 109.6, 33.0, 23.2, 14.4; HRMS calcd for C13H14O,
186.1045; found, 186.1047.
Acknowledgment. We wish to thank the National Science
(3) Experimental Procedure for Cyclization of (o-Ethynyl)phenyl
Epoxide (1c) to Naphthanol. A long tube containing TpRu(PPh3)-
(CH3CN)2PF6 (41.0 mg, 0.054 mmol) was dried in vacuo for 2 h before
it was charged with epoxide 1 (100 mg, 0.54 mmol) and toluene (0.45
mL). The mixture was heated at 100 °C for 4 h before cooling to room
temperature. The solution was concentrated and eluted through a silica
column (hexane/diether ) 5/1) to afford naphthol 2c (91 mg, 0.49
mmol, 91%) as a yellow oil.
Council, Taiwan for supporting this work.
Supporting Information Available: Synthetic schemes and
spectral data of compounds 1a,1b and 3-45 in repetitive
experiments and 1H-13C NMBC spectra of compound 36. This
material is available free of charge via the Internet at
http://pubs.acs.org.
(4) 2-(2-Ethynylphenyl)-3-propyloxirane (1c). IR (Nujol, cm-1
)
1
3330(s), 3100(s), 3065(s), 2258(m), 2119(s), 1625(w), 1250(m); H
JA049943C
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J. AM. CHEM. SOC. VOL. 126, NO. 22, 2004 6899