New Method for Preparation of Coumarins and Quinolinones via Pd-Catalyzed Intramolecular Hydroarylation of C-C Triple Bonds

Article abstract of DOI:10.1021/jo000861q

A new and general method has been developed for preparation of coumarins and quinolinones by intramolecular hydroarylation of alkynes. Various aryl alkynoates and alkynanilides undergo fast intramolecular reaction at room temperature in the presence of a

Full text of DOI:10.1021/jo000861q

7516
J . Org. Chem. 2000, 65, 7516-7522
New Meth od for P r ep a r a tion of Cou m a r in s a n d Qu in olin on es via
P d -Ca ta lyzed In tr a m olecu la r Hyd r oa r yla tion of C-C Tr ip le Bon d s
Chengguo J ia, Dongguo Piao, Tsugio Kitamura, and Yuzo Fujiwara*
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu University,
Hakozaki, Fukuoka, 812-8581, J apan
yfujitcf@mbox.nc.kyushu-u.ac.jp
Received J une 5, 2000
A new and general method has been developed for preparation of coumarins and quinolinones by
intramolecular hydroarylation of alkynes. Various aryl alkynoates and alkynanilides undergo fast
intramolecular reaction at room temperature in the presence of a catalytic amount of Pd(OAc)2 in
a mixed solvent containing trifluoroacetic acid (TFA), affording coumarins and quinolinones in
moderate to excellent yields with more than 1000 turnover numbers (TON) to Pd. The methodology
proved to tolerate a number of functional groups such as Br and CHO. On the basis of isotope
experiments, a possible mechanism involving ethynyl chelation-assisted electrophilic metalation
of aromatic C-H bonds by in-situ generated cationic Pd(II) species has been discussed. Also the
involvement of vinylcationic species has been suggested.
In tr od u ction
Coumarins and quinolinones had stimulated a lot of
interest due to their many applications as novel thera-
peutic agents and prompt the development of general and
efficient methods for their preparations.6 Recently, we
have reported the efficient intermolecular hydroarylation
of C-C triple bonds in the presence of Pd and Pt catalysts
by simple arenes (eq 1).
Catalytic activation of aromatic C-H bonds leading to
new and useful reactions such as C-C bond formations
remains a long-term challenge to chemists and is of
considerable interest for the chemical and pharmaceuti-
cal industries.1 It would provide simple, clean, and
economic methods for making many useful aryl-substi-
tuted compounds directly from simple arenes since no
prefunctionalization like halogenation is involved. A few
examples of such reactions have been reported,2,3 the
catalytic hydroarylation of C-C multiple bonds through
the metalation of aromatic C-H bonds by oxidative
insertion of low valent transition metals2a and electro-
philic Pd(II) substitution3d are typical examples, although
there are many stoichiometric reactions of aromatic C-H
bonds with transition-metal compounds.1b,8
We have found that the intramolecular version of this
reaction is much faster than intermolecular one, provid-
ing coumarins and quinolinones in moderate to excellent
yields (eq 2). Although intermolecular and intramolecular
hydroarylation of C-C multiple bonds using aryl halides
has been well developed,4,5,6g to our knowledge, few
intramolecular reactions as shown in eq 2 have been
reported. Herein we report on the novel intramolecular
hydroarylation of activated alkynes, which proceeds with
high efficiency (TON more than 1000 to Pd) and remark-
able chemoselectivity (compatible to various functional
groups) in the presence of a catalytic amount of Pd
catalysts. The present reaction offers a unique, concise
and straightforward route to coumarins and quinolinones
(1) (a) Shilov, E.; Shul’pin, G. B. Chem. Rev. 1997, 97, 2879. (b)
Murai, S., Ed. Activation of Unreactive Bonds and Organic Synthesis;
Springer: New York, 1999; p 48. (c) Fujiwara, Y.; J intoku, T.; Takaki,
K. CHEMTECH 1990, 636. (d) Dyker, G. Angew. Chem., Int. Ed. Engl.
1999, 38, 1698. (e) Trost, B. M. Science 1991, 254, 1471.
(2) (a) Murai, S.;Kakiuchi, F.; Sekine, S.; Tanaka, Y.; Kamatani, A.;
Sonoda, M.; Chatani, N. Nature 1993, 366, 529. (b) Kakiuchi, F.;
Yamamoto, Y.; Chatani, N.; Murai, S. Chem. Lett. 1995, 681 (c) Hong,
P.; Cho, B.; Yamazaki, H. Chem. Lett. 1980, 507. (d) Hong, P.; Cho,
B.; Yamazaki, H.; Chem. Lett. 1979, 339. (e) Boese, W. T.; Goldman,
A. S. Organometallics 1991, 10, 782 (f) Christian, P. L.; Brookhart, M.
J . Am. Chem. Soc. 1999, 121, 6616.
(3) (a) Moritani, I.; Fujiwara, Y. Tetrahedron Lett. 1967, 1119. (b)
Fujiwara, Y.; Moritani, I.; Danno, S.; Teranishi, S. J . Am. Chem. Soc.
1969, 91, 7166. (c) Fujiwara, Y.; Asano, R.; Moritani, I..; Teranishi, S.
J . J . Org. Chem. 1976, 41, 1681. (d) Fujiwara, Y.; Takaki, K.;
Taniguchi, Y. Synlett 1996, 591. (e) J ia, C.; Lu, W.; Kitamura, T.;
Fujiwara, Y. Org. Lett. 1999, 1, 2097. (f) J ia, C.; Piao, D.; Oyamada,
J .; Lu, W.; Kitamura, T.; Fujiwara, Y. Science 2000, 287, 1992. (g) J ia,
C.; Lu, W.; Oyamada, J .; Kitamura, T.; Fujiwara, Y. J . Am. Chem.
Soc. 2000, 122, 7275.
(6) (a) El-Nagdy, S.; Soliman, A. Y.; Bakeer, H. M.; Youssef, A. M.
J . Chem. Soc. Pakistan 1990, 12, 230. (b) Trost, B. M.; Toste F. D. J .
Am. Chem. Soc. 1996, 118, 6305. (c) Nagasawa, K.; Ito, K. Heterocycles
1989, 28, 703. (d) Uno, T.; Ozeki, Y.; Koga, Y.; Chu, G.; Okada, M.;
Tamura, K.; Igawa, T.; Unemi, F.; Kido, M.; Nishi, T. Chem. Pharm.
Bull. 1995, 43, 1724. (e) Lopez-Alvarado, P. Pilar. Synthesis 1998, 188.
(f) Yang, Z.; Xia, Y.; Brosi, A.; Lee, K. Tetrahedron Lett. 1999, 40, 4505.
(g) Arcadi, A.; Cacchi, S.; Fabrizi, G.; Marinelli, F.; Pace, P. Synlett
1996, 568. (h) Kitahara, Y.; Nakahara, S.; Shimizu, M.; Yonezawa, T.;
Kubo, A.; Heterocycles 1993, 36, 1909. (i) Watson, B. T.; Christiansen,
G. E. Tetrahedron Lett. 1998, 39, 9839-9840.
(4) (a) Link, J . T.; Overman, L. E. CHEMTECH 1998, 20. (b) Carri,
W.; Candiani, I. Acc. Chem. Res. 1995, 28, 2. (c) Heumann, A.; Reglier,
M. Tetrahedron 1996, 52, 9289. (d) Heumann, A.; Reglier, M. Tetra-
hedron 1995, 51, 975. (e) Larock, R. C.; Yum, E. K. J . Am. Chem. Soc.
1991, 113, 6689. (f) Larock, R. C. J . Organomet. Chem. 1999, 567, 112.
(5) (a) Li, C.; Liu, R. Chem. Rev. 2000, 100, 3127. (b) Franzen, R.
G. J . Comb. Chem. 2000, 2, 2000. (c) Guillier, F.; Orain, D.; Bradley,
M. Chem. Rev. 2000, 100, 2091. (d) Yet, L. Chem. Rev. 2000, 100, 2963.
(7) The reported procedures are followed for the preparation of aryl
alkynoates or alkynanilides from corresponding acids and phenols or
anilines. (a) Sheehan, J . C.; Hess, G. P. J . Am. Chem. Soc. 1955, 77,
1068. (b). Neises, B.; Steglich, W. Angew. Chem., Int. Ed. Engl. 1978,
17, 523.
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10.1021/jo000861q CCC: $19.00 © 2000 American Chemical Society
Published on Web 10/07/2000

Pd-Catalyzed Hydroarylation of C-C Triple Bonds
J . Org. Chem., Vol. 65, No. 22, 2000 7517
Ta ble 1. Tr a n sition -Meta l-Ca ta lyzed Cycliza tion of
4′-ter t-Bu tylp h en yl P h en ylp r op iola te (1a ) to
4-P h en yl-6-ter t-bu tylcou m a r in (2a )
system Pd(OAc)2/TFA. The representative examples in
Table 2 illustrate the generality of this reaction. In all
cases, the cyclization is highly regioselective, affording
kinetically favored six-membered rings.9 Analysis of the
crude reaction mixture using 1H NMR and 13C NMR
spectra and GC separation indicated no any other re-
gioisomers have been observed. The reaction exhibits
high chemoselectivity with Br, CHO, or heterocyclic
groups in the aromatic moiety (entries 7, 14, and 15 in
Table 2) and with either terminal or internal C-C triple
bonds, which all proved to be compatible. Most of the
reactions (monitored by 1H NMR spectrum) are very fast
and complete within less than 30 min, especially for those
substrates bearing electron-rich aromatic rings (entries
1-9 and 15 in Table 2), showing characteristics of
electrophilic substitutions. Moreover, the reactivity of 3′-,
2′-, and 4′-methylphenyl phenylpropiolates (1i, 1j, and
1k ) decreases in the order 1i > 1j > 1k (entries 9, 10,
and 11), revealing the same characteristics than in
electrophilic substitutions. The slow cyclization reaction
of 1k can be improved by adding more catalysts (5%) to
the reaction mixture (entries 11 and 12).
entry
catalyst (mol %)
time (h)
yielda (%)
1
2
3
4
5
none
Pd(OAc)2 (1)
Pd(OAc)2 (0.06)
Pd(O2CCF3)2(PPh3)2 (1)
Pd(PPh3)4 (1)
24
0.5
60
0.5
1
no reaction
90
32
92
90
6
7
8
PtCl2 (2)/AgOAc (4)
Ni(OAc)2 (2)
Rh2(OAc)4 (2)
Pd(OAc)2 (1)/CF3CO2Na (5)
Pd(O2CCF3)2(PPh3)2 (1)
24
24
24
24
24
46
41
30
trace
trace
9b
10b
a
The general procedure was followed, and the yields were
determined by GC with diethyl phthalate as the internal standard.
Acetic acid was employed as the solvent.
b
from commercially available simple alkynoic acids, phe-
nols, and anilines.
The efficiency of this intramolecular reaction (eq 2) can
be seen from the cyclization of 1f to 2f (eq 4); TON of
1202 can be obtained in the presence of 0.079 mol % of
Pd(OAc)2 in 5 h at room temperature.
Resu lts a n d Discu ssion
Op tim iza tion of Ca ta lytic System s. Initially, we
investigated the cyclization of the 4′-tert-butylphenyl
phenylpropiolate (1a ) to screen the catalytic systems (eq
3).
Compared with intermolecular reaction of phenols with
acetylenes (Scheme 1 and Table 3), which also provide
coumarins, the intramolecular reaction is more than 15
times faster, presumably because the electrophilic meta-
lation of aromatic C-H bonds by Pd(II) species is assisted
by ethynyl coordination. The intermolecular reaction can
be enhanced by addition of trifluoroacetic anhydride
(TFAA) or by using excess of phenol or alkyne (Table 3),
but are generally lower yields.
In connection with the intermolecular addition of
arenes to C-C double bonds investigated recently (eq 1
in Scheme 2), we have found that the equimolar addition
of the electron-rich phenols to 4-methoxycinnamic acid
affords two 3,4-dihydrocoumarins (eqs 2 and 3 in Scheme
2), 3,4-dihydro-4-(4-methoxyphenyl)-5,6,7-trimethoxyl-
coumarin (2r ), and 3,4-dihydro-4-(4-methoxyphenyl)-6,7-
methylenedioxycoumarin (2s) in excellent yields at room
temperature in the presence of 1 mol % Pd(OAc)2. This
reaction supplements our intramolecular reaction as a
route to 3,4-dihydrocoumarins.
Treatment of 1a in the presence of 1 mol % Pd(OAc)2
and trifluoroacetic acid as solvent gave cleanly, within
30 min, 2a as the sole product in 90% yield (entry 2 in
Table 1). No side reaction was observed by analysis of
the reaction mixture using 1H NMR and 13C NMR spectra
and GC. Several transition metals such as Pd(II), Pt(II),
Rh(II), and Ni(II) compounds, which are known to
undergo electrophilic metalation of aromatic C-H bonds
in stoichiometric reactions,1a,3a,b,8 have been selected as
catalysts for this reaction. The results are summarized
in Table 1. Pd catalysts have been found to be the most
active in the reaction (entries 2 and 5 in Table 1). The
reaction with Pt(II), Ni(II), or Rh(II) catalysts is slow and
incomplete within 24 h (entries 6-8 in Table 1). The
catalytic activity of these transition metals decreases in
the order Pd(II) > Pt(II) > Ni (II) > Rh(II) (entries 2, 3,
and 6-8 in Table 1), in accordance with the activity
difference in electrophilic metalation of aromatic C-H
bonds by theses metal ions.1a,8 The reaction is greatly
enhanced by increasing the quantity of Pd(OAc)2 (entries
2 and 3 in Table 1). Almost no reaction was observed in
the absence of either a transition-metal catalyst or TFA
(entries 1, 9, and 10 in Table 1). However, addition of a
small amount of CH2Cl2 (one-third to TFA by volume) to
the reaction system to improve the solubility of reactants
has no detrimental effect on the reaction (Table 2).
Syn th esis of Cou m a r in s. As summarized in Table
2, various aryl alkynoates7 undergo smoothly the in-
tramolecular hydroarylation reactions over the catalytic
Syn th esis of Qu in olin on es. The extension of this
intramolecular addition to the synthesis of nitrogen-
containing heterocycles, 2(1H)-quinolinones, has been
made possible with the same catalytic system (entries
16, 17, and 18 in Table 2). The alkynanilides prepared
from the corresponding alkynoic acid and anilines are
readily cyclized in the presence of 1 mol % Pd(OAc)2 in a
mixed solvent containing TFA at room temperature,
(9) Endo-cyclization for the formation of six-membered rings is one
of the most kinetically favored paths. Baldwin, J . E. J . Chem. Soc.,
Chem. Commun. 1976, 734.

7518 J . Org. Chem., Vol. 65, No. 22, 2000
J ia et al.
Ta ble 2. Syn th esis of Cou m a r in s a n d Qu in olin -2(1H)-on es fr om P d -Ca ta lyzed In tr a m olecu la r Ad d ition Rea ction s of th e
Cor r esp on d in g Ar yl Alk yn oa tes a n d Alk yn a n ilid es
a
b
Isolated yields following the general procedure. The ratio was determined by 1H NMR spectra. c 5% Pd(OAc)2; yield was determined
by 1H NMR. 2% Pd(OAc)2.
d
Ta ble 3. Syn th esis of Cou m a r in s by P d -Ca ta lyzed
In ter m olecu la r Rea ction s (Sch em e 1)
Sch em e 1. F or m a tion of Cou m a r in s via
P d -Ca ta lyzed In ter m olecu la r Ad d ition of Ar en e to
Alk yn e
ratio
R
EWG
CO2H
Me CO2H
Me CO2H
phenol/alkyne time (h) product yielda (%)
Ph
2
2
2
2a
2b
2b
2d
2d
2d
60b
50b
12
2
2
6
24
40
40
40
H
H
H
CO2Et
CO2Et
CO2Et
71
51
62
2
0.5c
a
The reaction was carried out in CH2Cl2/TFA (1 mL/5 mL) using
1 mmol of alkyne and 1% Pd(OAc)2 at room temperature; the yields
b
were based on alkyne. TFAA (1 mmol) added. c Alkyne 5 mmol
was used; yield was based on the phenol.
giving 2(1H)-quinolinones 2o, 2p , and 2q in good yields.
noic acids and anilines did not afford 2(1H)-quinolinones,
On the other hand, the intermolecular reaction of alky-
presumably because the amino groups in anilines are

Pd-Catalyzed Hydroarylation of C-C Triple Bonds
J . Org. Chem., Vol. 65, No. 22, 2000 7519
1
Sch em e 2. Hyd r oa r yla tion of Alk en es
and 2q based on the H NMR spectra of the adducts by
comparison with the adducts from undeuterated TFA.
These results are similar to those in the intermolecular
reactions (eq 1 in Scheme 5),2f,g indicating possible
formation of vinylpalladium complexes such as C in
Scheme 4.
The highly electrophilic cationic palladium species are
expected to be generated in situ through bonding weakly
to trifluoroacetate anions by utilizing TFA as a solvent.11
The cationic species should greatly enhance the metala-
tion of aromatic C-H bonds and at the same time
possibly activate CtC bonds through coordination to
generate the acceptors of aryl nucleophiles. A reasonable
explanation for the requirement of a large excess of TFA
as solvent is the reaction require highly cationic Pd(II)
species to facilitate the formation of stable σ-aryl-Pd
complexes such as B (Scheme 4). It has been proved that
the acid loss from Pd or Pt trifluoroacetate complexes is
irreversible under less acidic conditions,11c thus the
presence of large excess of TFA is necessary to keep
cationic Pd(II) species. Also, a strong acid like TFA would
facilitate the hydrolysis of vinyl-M complexes such as C
to give the final products (route (a) in Scheme 4).12
Recently, we have found that the intermolecular reaction
of phenylacetylene with pentamethylbenzene occurred
without Pd(OAc)2. This suggested that the involvement
of vinylcationic species either generated from cationic Pd
species or strong acid followed by electrophilic cyclization
is also possible in the intramolecular reaction (route (b)
in Scheme 4).16
Sch em e 3. F or m a tion of Qu in olin on es
Exp er im en ta l Section
Gen er a l Meth od s. All the reactions were performed in dry
Pyrex tubes, and only under argon atmosphere when Pd(0)
catalysts were used. All starting materials and solvents were
used as received without further purification unless otherwise
1
indicated. H NMR and 13C NMR spectra were recorded on a
converted in TFA to ammonium ions which act as
electron-withdrawing groups and consequently deactivate
the aromatic rings (Scheme 3). Therefore, the intramo-
lecular addition process offers a unique and efficient
method for the synthesis of 2(1H)-quinolinones.
300 FT-NMR (300 MHz) in CDCl3 solution (TMS as an internal
standard). The methyl protons of sodium 2,2-dimethyl-2-
silapentane-5-sulfonate in a sealed tube containing D2O are
used as an internal standard when the reaction mixture
(containing TFA) was directly subjected to 1H NMR analysis.
IR spectra were recorded either neat or as film on sodium
chloride plates or as KBr pellets. Melting points were mea-
sured with YANACO micro melting apparatus and are uncor-
rected. The GC analysis was performed using a 2.0 m × 3 mm
L stainless steel column packed with Unisole 10T + H3PO4 (5
+ 0.5)% on 80-100 mesh Uniport HP with a flame ionization
detector. For thin-layer chromatography (TLC), Merck pre-
coated aluminum plates were used and detected by a UV lamp.
P ossible Mech a n ism . The trans-intermolecular hy-
droarylation of alkynes with various arenes over the
same catalytic system provides a useful method for the
preparation of cis-arylalkenes. However, the intermo-
lecular reaction is slow in general; the present intramo-
lecular reaction is at least 15 times faster than the
intermolecular one, suggesting the electrophilic substitu-
tion of arenes by Pd(II) cationic species is assisted by the
ethynyl-coordination. In fact, even relatively electron-
deficient aromatic rings, such as those in 4′-tert-bu-
tylphenyl butynoate (1b) and 3′-methylphenyl phenyl-
propiolate (1i), can readily undergo the cyclization
reactions (entries 2 and 9 in Table 2). The formation of
various transition metal-alkyne complexes is well docu-
mented.10 A possible mechanism is outlined in Scheme
4.
(11) (a) Brainard, M. W.; Nutt, W. R.; Lee, T. R.; Whitesides, G. M.
Organometallics 1988, 7, 2379. (b) Clark, F. R. S.; Norman, R. O. C.;
Thommas, C. B.; Willson, J . S. J . Chem. Soc., Perkin Trans. 1 1974,
1289. (c) White, S.; Bennett, B. L.; Roddick, D. M. Organometallics
1999, 18, 2536. (d) Peters, R. G.; Shannon, S.; Roddick, D. M.
Organometallics 1998, 17, 4493. (e) Holtcamp, M. W.; Labinger, J . A.;
Bercaw, J . E. J . Am. Chem. Soc. 1997, 119, 848. (f) Swang, O.; Blom,
R.; Ryan. O.; Faegri, K. J . Phys. Chem. 1996, 100, 17334.
(12) (a) Zeijden, A.; Bosch, H. W.; Berke, H. Organometallics 1992,
11, 563.
(13) Ricci, A.; Buu-Hoi, N. P. Bull. Soc. Chim. Fr. 1967, 3634.
(14) (a) Ito, K.; Maruyama, J . Chem. Pharm. Bull. 1986, 34, 390.
(b) Nagasawa, K.; Higuchi, Y.; Ito, K.; Imamari, M.; Fujii, N. Chem.
Pharm. Bull. 1993, 41, 211. (c) Maruyama, J .; Ito, I. Chem. Pharm.
Bull. 1984, 32, 1178.
The cyclization reactions of 4′-tert-butylphenyl phenyl-
propiolate (1a ) and 3′,4′,5′-trimethoxyl phenylpropyna-
nilides (1q) in CF3CO2D as the solvent (eqs 2 and 3 in
Scheme 5) reveal that deuterium atoms have incorpo-
rated to adducts as vinyl protons at the 3 position of 2a
(15) (a) Rodighiero, P.; Palumbo, M.; Magno, S. M.; Manzini, P.; Gia,
O.; Piro, R.; Guiotto, A. J . Heterocycl. Chem. 1986, 23, 1405. (b)
Ahluwalia, V. K.; Adhikari, R.; Singh, R. P. Acta Chem. Hung. 1987,
124, 427; Chem. Abstr. 1988, 108, 167349.
(10) Patai, S., Ed. The Chemistry of the Carbon-Carbon Triple Bond;
J ohn Wiley & Sons: New York, 1978; Part 1, p 37.
(16) Coldfinger, M. B.; Crawfod, K. B.; Swager, T. M. J . Am. Chem.
Soc. 1997, 119, 4578.

7520 J . Org. Chem., Vol. 65, No. 22, 2000
J ia et al.
Sch em e 4. P ossible Mech a n ism for In tr a m olecu la r Hyd r oa r yla tion of C-C Tr ip le Bon d s
ous NaHCO3 solution, and hexane and then crystallized in a
mixed solvent of hexane/chloroform or hexane/ethanol.
Sch em e 5. Isotop e Rea ction s
A Sp ecific Exa m p le. 4-Methyl-6-tert-butylcoumarin (2b)
was prepared from the cyclization of 4′-tert-butylphenyl bu-
tynoate (1b). In a 25 mL dry Pyrex tube, 1b (0.22 g, 1 mmol),
Pd(OAc)2 (2 mg, 0.01 mmol), TFA (1.5 mL), and CH2Cl2 (0.5
mL) were mixed and stirred at room temperature for 30 min.
The reaction mixture was poured into the saturated NaCl
solution and extracted with ether, and the ethereal layer was
neutralized and washed with saturated NaCl solution, neu-
tralized with NaHCO3, and dried over Na2SO4. Evaporation
of solvent and column chromatography on silica gel with
hexane/EtOAc as the eluent gave 2b (0.198 g, 90%).
In ter m olecu la r Rea ction s of P h en ols w ith Alk yn es (or
w ith Alk en es). To a cold mixture of the phenol, Pd(OAc)2,
TFA (5 mL), and CH2Cl2 (1 mL) on an ice-water bath was
added the alkyne (or alkenes) with stirring. After continuous
stirring at the same temperature for 5 min, the mixture was
warmed to room temperature. Stirring continued until no
further increase of the reaction products or the disappearance
1
of one starting material as monitored by GC, TLC, or H NMR.
When the yield was determined by GC, diethyl phthalate was
added to reaction mixture as an internal standard. The workup
of reaction mixtures was similar to that for an intramolecular
reaction.
Ch a r a cter iza tion . 4-P h en yl-6-ter t-bu tylcou m a r in (2a ):
white crystals; mp 108.3-109.0 °C (n-hexane/EtOAc ) 5:1);
1H NMR (300 MHz, CDCl3) δ 1.27 (s, 9H, tert-butyl), 6.36 (s,
1H, vinyl), 7.35 (d, J ) 8.4 Hz, 1H, aryl), 7.54 (m, 6H, aryl),
7.60 (dd, J ) 2.4, 8.4 Hz, 1H, aryl); 13C NMR (CDCl3, 75 MHz)
δ 31.23, 34.56, 114.99, 116.79, 118.20, 123.15, 128.40, 128.79,
129.47, 129.63, 135.35, 147.19, 152.19, 155.89, 161.00; IR
(CHCl3, cm-1) 1726 (CdO). Anal. Calcd for C19H18O2: C, 81.99;
H, 6.52. Found: C, 81.94; H, 6.55.
4-Meth yl-6-ter t-bu tylcou m a r in (2b): light yellow crystals;
mp 123.5-124.0 °C (lit.13 mp 123 °C); 1H NMR (300 MHz,
CDCl3) δ 1.37 (s, 9H, tert-butyl), 2.46 (d, J ) 1.5 Hz, 3H, CH3),
6.28 (d, J ) 1.5 Hz, 1H, vinyl), 7.27 (d, J ) 8.7 Hz, 1H, aryl),
7.57 (s, 1H, aryl), 7.60 (d, J ) 8.7 Hz, 1H, aryl); 13C NMR
(CDCl3, 75 MHz) δ 18.59, 31.33, 34.59, 114.84, 116.55, 119.20,
120.51, 129.33, 147.17, 151.46, 152.59, 161.01; IR (CHCl3,
cm-1) 1729 (CdO).
Flash column chromatography was carried out on Wako silica
gel, Wakogel C-300, 45-75 µm with hexanes-EtOAc mixtures
(3/1 to 12/1, depending on the polarity of the reaction products)
as eluent. The aryl alkynoates 1a -n were readily prepared
in 63-95% yields from the equimolar reaction of alkynoic acids
and phenols in the presence of 1 equiv of dicyclohexylcarbo-
diimide and 10% of 4-(dimethylamino)pyridine at room tem-
perature according to reported method.7 The alkynanilides
1o-q were prepared in the similar way, but in the absence of
4-(dimethylamino)pyridine. The detailed spectroscopic data for
characterization of the compounds 1a -q are provided in the
Supporting Information.
Gen er a l P r oced u r e for th e P r ep a r a tion of Cou m a r in s
a n d Qu in olin on es. The aryl alkynoate or alkynanilide (1
mmol), a transition-metal catalyst (1-5 mol %), TFA (1.5 mL),
and CH2Cl2 (0.5 mL) were mixed in a 25 mL dry Pyrex tube
and stirred at room temperature. Stirring continued until the
disappearance of the alkynoate as monitored by GC, TLC, or
1H NMR. When the yield was determined by GC, diethyl
phthalate was added to the reaction mixture as an internal
standard. The reaction mixture was poured into a saturated
NaCl aqueous solution and extracted with ether. The ethereal
layer was washed with saturated NaCl solution, neutralized
with NaHCO3 solution, and dried over anhydrous Na2SO4. The
solvent was removed in vacuo, and the products were purified
by flash column chromatography on silica gel and then
recrystallization from the ethyl acetate-hexane mixtures
provided the desired materials.
4-P en tyl-6-ter t-bu tylcou m a r in (2c): 71% yield; colorless
1
crystals; mp 112.6-113.1 °C (hexane/EtOAc ) 3:1); H NMR
(300 MHz, CDCl3) δ 0.94 (t, J ) 7.2 Hz, 3H, CH3), 1.37 (s, 9H,
tert-butyl), 1.42 (m, 4H, 2CH2), 1.73 (m, 2H, CH2), 2.79 (t, J )
7.8 Hz, 2H, CH2), 6.27 (s, 1H, vinyl), 7.27 (d, J ) 8.7 Hz, 1H,
aryl), 7.57 (dd, J ) 2.1, 8.7 Hz, 1H, aryl), 7.60 (s, 1H, aryl);
13C NMR (75 MHz, CDCl3) δ: 13.84, 22.32, 27.72, 31.33, 31.48,
31.55, 34.55, 113.62, 116.73, 118.53, 120.30, 129.10, 147.00,
151.68, 156.49, 161.21; IR (CHCl3, cm-1) 1735 (CdO). Anal.
Calcd for C18H24O2: C, 79.37; H, 8.88. Found: C, 79.38; H,
8.89.
In the preparation of quinolinones, the products were
precipitated by pouring the reaction mixture into the saturated
NaCl solution. The precipitate was washed with water, aque-
6-ter t-Bu tylcou m a r in (2d ): light yellow crystals; mp
76.4-78.0 °C; 1H NMR (300 MHz, CDCl3) δ 1.36 (s, 9H,

Pd-Catalyzed Hydroarylation of C-C Triple Bonds
J . Org. Chem., Vol. 65, No. 22, 2000 7521
t-butyl), 6.41 (d, J ) 9.6 Hz, 1H, vinyl), 7.27 (d, J ) 8.7 Hz,
1H, aryl), 7.45 (d, J ) 2.7 Hz, 1H, aryl), 7.60 (dd, J ) 2.7, 8.7
Hz, 1H, aryl), 7.71 (d, J ) 9.6 Hz, 1H, vinyl); 13C NMR (CDCl3,
75 MHz) δ 31.27, 34.46, 116.31, 116.36, 118.21, 124.08, 129.45,
143.87, 147.53, 151.99, 161.14; IR (CHCl3, cm-1) 1721 (CdO).
Anal. Calcd for C13H14O2: C, 77.20; H, 6.98. Found: C, 77.05;
H, 7.11.
3.68 (m, 1H, CH), 6.25 (s, 1H, vinyl), 6.98 (d, J ) 7.5 Hz, 1H,
aryl), 7.27 (m, 2H, aryl), 7.35 (d, J ) 7.5 Hz, 1H, aryl), 7.45
(m, 3H, aryl); 13C NMR (75 MHz, CDCl3) δ 22.69, 23.28, 26.51,
116.94, 117.62, 127.35, 127.94, 128.42, 128.54, 128.64, 134.63,
134.78, 139.83, 152.13, 157.16, 160.23; IR (CHCl3, cm-1) 1726
(CdO). Anal. Calcd for C19H18O2: C, 81.99; H, 6.52. Found:
C, 81.93; H, 6.51.
4-P h en yl-5,7-d im eth ylcou m a r in (2e): 87% yield; white
crystals; mp 96.3-97.2 °C (n-hexane/EtOAc ) 5:1); H NMR
4-P h en yl-5-m eth oxy-8-for m ylcou m a r in (2m ): 71% yield;
yellow crystals; mp 206.3-208.1 °C; 1H NMR (300 MHz,
CDCl3) δ 3.56 (s, 3H, OCH3), 6.25 (s, 1H, vinyl), 6.78 (d, J )
9.0 Hz, 1H, aryl), 7.28 (m, 2H, aryl), 7.42 (m, 3H, aryl), 8.11
(d, J ) 9.0 Hz, 1H, aryl), 10.62 (s, 1H, CHO); 13C NMR (75
MHz, CDCl3) δ 55.84, 106.69, 108.66, 116.21, 117.66, 126.82,
127.59, 128.27, 132.13, 138.96, 155.10, 157.22, 158.60, 161.91,
186.71. Anal. Calcd for C17H12O4: C, 72.85; H, 4.32. Found:
C, 72.44; H, 4.36.
1
(300 MHz, CDCl3) δ 1.79 (s, 3H, CH3), 2.39 (s, 3H, CH3), 6.18
(s, 1H, vinyl), 6.83 (s, 1H, aryl), 7.09 (s, 1H, aryl), 7.28 (m,
2H, aryl), 7.45 (m, 3H, aryl); 13C NMR (75 MHz, CDCl3) δ
21.27, 23.26, 115.49, 115.81, 116.11, 116.17, 127.35, 128.53,
129.57, 137.03, 139.61, 142.32, 155.19, 156.73, 160.49. IR
(CHCl3, cm-1) 1733 (CdO). Anal. Calcd for C17H14O2: C, 81.58;
H, 5.64. Found: C, 81.55; H, 5.66.
4-P h en yl-5,6,7-tr im eth oxycou m ar in (2f): 91% yield; brown
crystals; mp 146.8-147.7 °C (hexane/EtOAc ) 5:1); H NMR
A mixture of two inseparable regioisomers, 4-m eth yl-2H-
ben zofu r o[3,2-g]-ben zop yr a n -2-on e (2n )15 and 4-m eth yl-
2H-ben zofu r o[2,3-f]-ben zop yr a n -2-on e (2n ′), were isolated
in 75% total yield (2n /2n ′ ) 1/3) from cyclization of 1n : orange
1
(300 MHz, CDCl3) δ 3.26 (s, 3H, OCH3), 3.79 (s, 3H, OCH3),
3.94 (s, 3H, OCH3), 6.06 (s, 1H, vinyl), 6.73 (s, 1H, aryl), 7.32
(m, 2H, aryl), 7.41 (m, 3H, aryl); 13C NMR (75 MHz, CDCl3) δ
56.20, 60.84, 61.02, 96.23, 107.22, 113.97, 127.15, 127.45,
127.97, 138.98, 139.40, 151.03, 151.64, 155.33, 156.85, 160.55;
IR (CHCl3, cm-1) 1726 (CdO). Anal. Calcd for C18H16O5: C,
69.22; H, 5.16. Found: C, 69.25; H, 5.23.
1
crystals; H NMR (300 MHz, CDCl3) δ 2.46 (s, 1H, 0.33CH3),
2.91 (s, 3H, CH3), 6.32 (s, 0.33H, vinyl), 6.36 (s, 1H, vinyl),
6.78 (d, J ) 9.0 Hz, 1H, aryl), 7.33-7.72 (m, 8H, aryl), 7.91
(d, J ) 7.8 Hz, 1H, aryl), 8.27 (d, J ) 8.1 Hz, 1H, aryl); 13C
NMR (75 MHz, CDCl3) δ 18.95, 25.78, 106.09, 107.98, 111.84,
112.33, 114.81, 115.59, 115.93, 116.14, 117.39, 118.94, 119.77,
120.55, 121.52, 122.82, 123.06, 123.19, 124.79, 127.55, 127.77,
129.03, 149.53, 151.32, 152.11, 152.23, 152.36, 152.95, 157.04,
157.65, 160.18, 160.83.
4-P h en yl-5,7-dim eth yl-6-br om ocou m ar in (2g): 85% yield;
yellow crystals; mp 162.3-163.3 °C (hexane/EtOAc ) 3:1); 1H
NMR (300 MHz, CDCl3) δ 1.96 (s, 3H, CH3), 2.52 (s, 3H, CH3),
6.27 (s, 1H, vinyl), 7.29 (m, 2H, aryl), 7.47 (m, 3H, aryl); 13C
NMR (75 MHz, CDCl3) δ 24.72, 24.78, 116.91, 117.40, 117.46,
125.78, 127.14, 128.92, 129.06, 136.88, 139.57, 142.71, 153.63,
156.10, 159.92; IR (CHCl3, cm-1) 1728 (CdO). Anal. Calcd for
4-P en t yl-6,7-m et h ylen ed ioxyqu in olin -2(1H )-on e (2o):
91% yield; white crystals; mp 229.1-230.3 °C (chloroform/
1
hexane ) 1:1); H NMR (300 MHz, CDCl3) δ 0.92 (t, J ) 6.9
C
17H13O2Br: C, 62.03; H, 3.98. Found: C, 62.21; H, 4.18.
1-Meth yl-3H-n a p h th o[2,1-b]p yr a n -3-on e (2h ): 65% yield;
Hz, 3H, CH3), 1.39 (m, 4H, 2CH2), 1.69 (m, 2H, CH2), 2.75 (t,
J ) 7.8 Hz, 2H, CH2), 6.03 (s, 2H, OCH2), 6.47 (s, 1H, vinyl),
6.97 (s, 1H, aryl), 7.07 (s, 1H, aryl), 12.98 (br, 1H, NH, D/H
exchangeable in D2O/ CDCl3); 13C NMR (75 MHz, CDCl3) δ
13.92, 22.47, 28.53, 31.65, 32.78, 96.81, 101.68, 114.38, 116.77,
135.78, 144.43, 150.38, 153.03, 164.46; IR (CHCl3, cm-1) 1654
(CdO). Anal. Calcd for C15H17NO3: C, 69.48; H, 6.61; N, 5.40.
Found: C, 68.85; H, 6.55; N, 5.38.
light yellow crystals; mp 181.0-182.0 °C (hexane/EtOAc ) 5:1)
(lit.14 mp 182.0-183.0 °C); 1H NMR (300 MHz, CDCl3) δ 2.91
(s, 3H, CH3), 6.37 (s, 1H, vinyl), 7.44 (d, J ) 9.0 Hz, 1H, aryl),
7.54 (t, J ) 8.1 Hz, 1H, aryl), 7.64 (t d, 1H, J ) 2.1, 8.1, Hz,
aryl), 7.91 (d, J ) 8.1 Hz, 1H, aryl), 7.93 (d, J ) 8.1 Hz, 1H,
aryl), 8.58 (d, 1H, J ) 9.0 Hz, aryl); 13C NMR (75 MHz, CDCl3)
δ 26.36, 114.43, 116.45, 117.75, 124.97, 125.35, 127.80, 129.65,
130.18, 131.30, 133.60, 154.07, 154.60, 160.32; IR (CHCl3,
cm-1) 1712 (CdO).
4-P en tyl 5,7-d im eth oxyqu in olin -2(1H)-on e (2p ): 85%
yield; light yellow crystals; mp 180.3-181.6 °C (chloroform/
1
hexane ) 3:1); H NMR (300 MHz, CDCl3) δ 0.91 (d, J ) 7.1
A mixture of two inseparable regioisomers, 4-p h en yl-7-
m et h ylcou m a r in (2i) and 4-p h en yl-5-m et h ylcou m a r in
(2i′), was isolated from cyclization of 1i in 78% yield (2i/2i′ )
2/1): yellow crystals; 1H NMR (300 MHz, CDCl3) δ 1.82 (s,
1.5H, 0.5CH3), 2.43 (s, 3H, CH3), 6.21 (s, 0.5H, vinyl), 6.26 (s,
H, vinyl), 6.97-7.51 (m, 12H, aryl); 13C NMR (75 MHz, CDCl3)
δ 21.30, 23.21, 113.60, 113.67, 115.29, 116.20, 116.89, 116.96,
117.10, 125.13, 126.41, 127.06, 128.02, 128.12, 128.37, 128.57,
129.38, 131.05, 135.05, 137.27, 139.13, 142.94, 153.96, 154.74,
155.40, 156.47, 159.89, 160.72. Anal. Calcd for C16H12O2: C,
81.34; H, 5.12. Found: C, 81.22; H, 5.16.
Hz, 3H, CH3), 1.37 (m, 4H, 2CH2), 1.60 (m, 2H, CH2), 2.97 (d,
J ) 7.6 Hz, 2H, CH2), 3.86 (s, 3H, OCH3), 3.86 (s, 3H, OCH3),
6.24 (d, J ) 2.1 Hz, 1H, aryl), 6.30 (s, 1H, vinyl), 6.53 (d, J )
2.1 Hz, 1H, aryl), 12.77 (br, 1H, NH); 13C NMR (75 MHz,
CDCl3) δ 14.08, 22.54, 30.36, 31.97, 37.16, 55.43, 55.65, 91.43,
94.71, 105.86, 116.88, 142.40, 155.41, 158.82, 161.82, 164.50;
IR (CHCl3, cm-1) 1658 (CdO). Anal. Calcd for C16H21NO3: C,
69.79; H, 7.69; N, 5.09. Found: C, 69.52; H, 7.62; N, 5.04.
4-P h en yl 5,6,7-tr im eth oxyqu in olin -2(1H)-on e (2q): 82%
yield; white crystals; mp 262.2-264.2 °C (chloroform/hexane
) 5:1); 1H NMR (300 MHz, CDCl3) δ 3.25 (s, 3H, OCH3), 3.79
(s, 3H, OCH3), 3.96 (s, 3H, OCH3), 6.40 (s, 1H, vinyl), 6.80 (s,
1H, aryl), 7.35 (m, 5H, aryl), 13.17 (br, 1H, NH); 13C NMR (75
MHz, CDCl3) δ 56.25, 60.74, 61.04, 94.46, 108.54, 119.74,
127.22, 127.51, 136.97, 138.63, 141.01, 150.89, 152.58, 156.63,
4-P h en yl-8-m eth ylcou m a r in (2j): 79% yield; white crys-
tals; mp 101.3-102.2 °C (hexane/EtOAc ) 5:1); 1H NMR (300
MHz, CDCl3) δ 2.51 (s, 3H, CH3), 6.37 (s, 1H, vinyl), 7.12 (t, J
) 7.2 Hz, 1H, aryl), 7.32 (d, J ) 8.1 Hz, 1H, aryl), 7.43 (d, J
) 8.1 Hz, 1H, aryl), 7.45 (m, 2H, aryl), 7.52 (m, 3H, aryl); 13
C
163.91; IR (CHCl3, cm-1) 1662 (CdO). Anal. Calcd for C18H17
-
NMR (75 MHz, CDCl3) δ 15.77, 114.87, 118.74, 123.59, 124.77,
126.68, 128.45, 128.77, 129.52, 133.22, 135.57, 152.49, 156.05,
160.89; IR (CHCl3, cm-1) 1724 (CdO). Anal. Calcd for
NO4: C, 69.44; H, 5.50; N, 4.50. Found: C, 68.14; H, 5.61; N,
4.28.
3,4-Dih yd r o-4-(4-m eth oxyp h en yl)-5,6,7-tr im eth oxycou -
m a r in (2r ): 90% yield; off-white crystals; mp 96.7-97.4 °C;
1H NMR (CDCl3, 300 MHz) δ 7.02 (d, J ) 8.7 Hz, 2H, aryl),
6.80 (d, J ) 8.7 Hz, 2H, aryl), 6.51 (s, 1H, aryl), 4.53 (t, J )
4.8 Hz, 1H, CH), 3.86 (s, 3H, OCH3), 3.82 (s, 3H, OCH3), 3.74
(s, 3H, OCH3), 3.67 (s, 3H, OCH3), 2.97 (d, J ) 4.8 Hz, 2H);
13C NMR (CDCl3, 75 MHz) δ 167.42, 158.57, 153.47, 150.38,
147.51, 138.87, 133.67, 127.67, 114.18, 111.20, 96.68, 60.97,
60.86, 55.98, 55.07, 37.25, 34.57; IR (CHCl3, cm-1) 1770 (Cd
O). Anal. Calcd for C19H20O6: C, 66.27; H, 5.91. Found: C,
66.12; H, 5.85.
C
16H12O2: C, 81.34; H, 5.12. Found: C, 80.50; H, 5.13.
4-P h en yl-6-m eth ylcou m a r in (2k ): 50% yield; white crys-
tals; mp 134.7-135.1 °C (hexane/EtOAc ) 5:1); 1H NMR (300
MHz, CDCl3) δ 2.34 (s, 3H, CH3), 6.35 (s, 1H, vinyl), 7.25 (s,
1H, aryl), 7.30 (d, J ) 8.1 Hz, 1H, aryl), 7.36 (dd, J ) 2.1, 8.1
Hz, 1H, aryl), 7.45 (m, 2H, aryl), 7.54 (m, 3H, aryl); 13C NMR
(75 MHz, CDCl3) δ 20.88, 115.18, 117.01, 118.65, 126.66,
128.39, 128.82, 129.55, 132.88, 133.83, 135.35, 152.30, 155.58,
160.93; IR (CHCl3, cm-1) 1724. (CdO). Anal. Calcd for
C
16H12O2: C, 81.34; H, 5.12. Found: C, 81.14; H, 5.11.
4-P h en yl-5-m eth yl-8-isop r op ylcou m a r in (2l): 75% yield;
3,4-Dih yd r o-4-(4-m eth oxyp h en yl)-6,7-m eth ylen ed ioxy-
cou m a r in (2s): 96% yield; white crystals; mp 134.6-135.2 °C;
1H NMR (CDCl3, 300 MHz) δ 7.05 (d, J ) 8.7 Hz, 2H, aryl),
light yellow crystals; mp 139.6-140.4 °C; 1H NMR (300 MHz,
CDCl3) δ 1.32 (d, 6H, J ) 6.9 Hz, 2CH3), 1.79 (s, 3H, CH3),

7522 J . Org. Chem., Vol. 65, No. 22, 2000
J ia et al.
6.86 (d, J ) 8.7 Hz, 2H, aryl), 6.62 (s, 1H, aryl), 6.38 (s, 1H,
aryl), 5.92 (s, 2H, CH2O2), 4.16 (t, J ) 6.3 Hz, 1H, CH), 3.78
(s, 3H, CH3), 2.95 (m, 2H, CH2); 13C NMR (CDCl3, 75 MHz) δ
167.63, 158.90, 147.33, 146.01, 144.29, 132.29, 128.41, 118.31,
114.38, 107.14, 101.59, 98.95, 55.17, 39.71, 37.05; IR (CHCl3,
cm-1) 1768 (CdO). Anal. Calcd for C17H14O5: C, 68.45; H, 4.75.
Found: C, 68.20; H, 4.84.
2′-Eth ylh exyl 3-(2-Meth yl-4,5-m eth ylen ed ioxyp h en yl)-
3-(4-m eth oxyp h en yl)p r op ion a te: light yellow oil; 1H NMR
(CDCl3, 300 MHz) δ 0.80 (t, J ) 7.2 Hz, 3H, CH3), 0.87 (t, J )
7.2 Hz, 3H, CH3), 1.10-1.45 (m, 9H, alkyl), 2.22 (s, 3H, CH3),
2.92 (dd, J ) 1.2, 7.8 Hz, 2H, CH2CdO) 3.74 (s, 3H, OCH3),
3.90 (d, J ) 5.4 Hz, 2H, OCH2), 4.61 (t, J ) 7.8 Hz, 1H, CH),
5.86 (q, J ) 2.4 Hz, 2H, CH2O2), 6.73 (s, 1H, aryl), 6.60 (s, 1H,
aryl), 6.78 (d, J ) 9.0 Hz, 2H, aryl), 7.08 (d, J ) 9.0 Hz, 2H,
aryl); 13C NMR (CDCl3, 75 MHz) δ 10.82, 14.03, 19.61, 22.87,
23.58, 28.83, 30.23, 38.65, 41.39, 42.01, 55.10, 66.68, 100.67,
106.81, 110.74, 113.82, 128.58, 129.10, 134.68, 135.26, 145.58,
145.83, 158.02, 171.99; IR (neat, cm-1) 1734 (CdO). Anal.
Calcd for C26H34O5: C, 73.21; H, 8.03. Found: C, 73.42; H,
8.05.
6-tert-butylcoumarin (2a ) except for the decrease in intensity
of a singlet vinylic resonance at 6.36 ppm based on the
integration of hydrogens of the tert-butyl group: 1.27 (s, 9H,
tert-butyl), 6.36 (s, 0.1H, vinyl, 90% D-incorporated), 7.35 (d,
J ) 8.4 Hz, 1H, aryl), 7.54 (m, 6H, aryl), 7.60 (dd, J ) 2.4, 8.4
Hz, 1H, aryl).
Cycliza tion 3′,4′,5′-Tr im eth oxyl P h en ylp r op yn a n ilid e
(1q) in TF A-d 1. In a 25 mL dry Pyrex tube, 1q (0.22 g, 1
mmol), Pd(OAc)2 (4 mg, 0.01 mmol), TFA-d1 (1.5 mL), and CH2-
Cl2 (0.5 mL) were mixed and stirred at room temperature for
1
30 min. The reaction gave 2q-D in 95% yield based on H NMR
1
spectra with ethyl phthalate as the internal standard. The H
NMR spectrum of 2q-D after workup is similar to that of
4-phenyl 5,6,7-trimethoxyquinolin-2(1H)-one (2q) except for
the decrease in intensity of both a singlet vinylic resonance
at 6.40 ppm and a singlet aryl resonance at 6.80 ppm based
on the integration of hydrogens in methoxyl group: 3.25 (s,
3H, OCH3), 3.79 (s, 3H, OCH3), 3.96 (s, 3H, OCH3), 6.40 (s,
0.3H, vinyl, 70% D-incorporated), 6.80 (s, 0.45 H, aryl, 55%
D-incorporated), 7.35 (m, 5H, aryl), 13.17 (br, 1H, NH).
Cycliza t ion of 4′-ter t-Bu t ylp h en yl P h en ylp r op iola t e
(1a ) in TF A-d 1. In a 25 mL dry Pyrex tube, 1a (0.27 g, 1
mmol), Pd(OAc)2 (2 mg, 0.01 mmol), TFA-d1 (1.5 mL), and CH2-
Cl2 (0.5 mL) were mixed and stirred at room temperature for
30 min. The reaction gave 2b-d in 90% yield based on 1H
NMR spectra with ethyl phthalate as the internal standard.
Su p p or tin g In for m a tion Ava ila ble: Detailed spectro-
scopic data for characterization of starting materials 1a -q.
These materials are available free of charge via the Internet
at http://pubs.acs.org.
1
The H NMR spectrum of 2a -d is similar to that of 4-phenyl-
J O000861Q