A new reagent system for modified Ullmann-type coupling reactions: NiCl2(PPh3)2/PPh3/Zn/NaH/toluene

Full text of DOI:10.1021/jo001563w

J . Org. Chem. 2001, 66, 2877-2880
2877
zopyran-4-one (2), it was observed that the isolated yield
of A using NiCl2(PPh3)2/PPh3/Zn in DMF was elevated
when K2CO3 was present as a base in the reaction
mixture, while employing Cu1 (either with DMF, PhNO2,
or pyridine as solvent) or Ni(0) as catalyst under the
standard conditions,4b the isolated yield of A was nor-
mally less than 15%. In addition, the ratio of A/B was
A New Rea gen t System for Mod ified
Ullm a n n -Typ e Cou p lin g Rea ction s:
NiCl2(P P h 3)2/P P h 3/Zn /Na H/Tolu en e
Guo-qiang Lin* and Ran Hong
Shanghai Institute of Organic Chemistry, Chinese Academy
of Sciences, 354 Fenglin Road, Shanghai, 200032, China
lingq@pub.sioc.ac.cn
Received November 3, 2000
In tr od u ction
Compared with the classical Cu-mediated1 Ullmann
reaction, other transition metal (such as Pd and Ni)-
catalyzed2-5 coupling reactions are generally milder and
more efficient, tolerate a large variety of functional
groups, and may furnish biaryls in excellent yields.
However, the homocoupling reactions promoted by these
transition metals are sensitive to the substrates bearing
free OH groups and bisortho substitutents.6 It is noticed2-5
that polar solvents facilitate the solvation of nickel(II)
complexes formed in the oxidative addition steps and
thus promote the coupling process, and meanwhile, the
aryl radicals7 generated in the reaction tend to abstract
hydrogen from the conventionally reported polar solvents
(such as THF and DMF) and, thus, result in hydro-
genolysis product of the aryl halides. It is therefore often
hard to offer satisfactory yield while running such
reaction in a polar solvent. During the course of the total
synthesis of bibenzopyran-4-ol (1), a natural product
isolated8 from the root of Aloe barbadensis, we found a
new reagent system for coupling arylhalides and vinyl-
halides. Herein, we wish to report some unprecedented
results.
improved toward more of the former (Table 1, entries 1
and 2), although B was still formed as major product. In
polar solvents, arylnickel neutral species can be proto-
nated or abstract hydrogen from the solvent to form
cationic hydrides.9 The Bro¨nsted acidity of nickel hydride
intermediate [ArNiLnH]+ requires the powerful base
(such as NaH, LiH) to remove the proton, and the
reductive elimination process can thus be retarded.3b
To find a better scavenger for the acidic proton,9 several
bases and solvents were examined (Table 1). It shows
that if large excess of sodium hydride was present in the
reaction system, the ratio of A/B reversed from 40:60 to
80:20 in favor of the formation of the coupling product A
(entries 3 vs 2). An increase of NaH from 10 equiv to 20
equiv caused a drop in the ratio of A/B (entries 4 vs 3).
Replacement of DMF with THF had no practical effects
(entries 5 vs 3). In addition, the reaction did not occur
when NaH was utilized as sole reductant in THF.
Therefore, NaH functioned as a base in polar solvent in
the absence of other additives.11 When benzene was
employed as the reaction media, the yield of coupling
product increased dramatically (up to 91.9%, entry 6).
Even better selectivities (97.8% and >99%) were observed
when toluene was used as the solvent (entries 7 and 8,
respectively). The catalyst loading affected the selectivity,
possibly due to the hydrogenolysis of substrates by the
nickel hydride species.11,12 On the other hand, the results
from the presence of NaOtBu or NaBH4 were not encour-
aging (entries 9 and 10), and compound D was obtained
as the major undesired product in the Ni(0)-NaOtBu
system (entry 9).
Resu lts a n d Discu ssion
In an attempt to prepare compound A (a potential
precursor to 1) by homocoupling of 3-iodo-6-methoxyben-
(1) Fanta, P. E. Sythesis 1974, 9. For recent applications, see:
Meyers, A. I. J . Heterocycl. Chem. 1998, 35, 991.
(2) (a) Sainsbury, M. Tetrahedron 1980, 36, 3327. (b) Bringmann,
G.; Walter, R. Angew Chem., Int. Ed. Engl. 1990, 29, 977. (c) Stanforth,
S. P. Tetrahedron 1998, 54, 263.
(3) (a) Semmelhack, M. F.; Helquist, P. M.; J ones, L. D. J . Am.
Chem. Soc. 1971, 93, 5908. (b) Semmelhack, M. F.; Helquist, P. M.;
J ones, L. D.; Keller, L.; Mendelson, L.; Ryono, L. S.; Smith, J . G.;
Stauffer, R. D. J . Am. Chem. Soc. 1981, 103, 6460.
(4) (a) Zembayashi, M.; Tamao, K.; Yoshida, J .; Kumada, M.
Tetrahedron Lett. 1977, 4089. (b) Colon, I.; Kelsey, D. R. J . Org. Chem.
1986, 51, 2627 and references therein. (c) Iyoda, M.; Otsuka, H.; Sato,
K.; Nisato, N.; Oda, M. Bull. Chem. Soc. J pn. 1990, 63, 80 and
references therein.
To the best of our knowledge, the combination of metal
Zn and NaH in toluene as the reductive system has never
been reported, even though each of them acts as a good
reductant in polar solvents.4b,12 Further scrutiny with the
same reaction shown in Table 1 revealed that (Table 2):
(a) higher temperature accelerated coupling reaction
(entries 1 vs 2, 3 vs 4, 7 vs 8); (b) the presence of excess
(5) (a) Miura, M.; Hashimoto, H.; Itoh, K.; Nomura, M. Chem. Lett.
1990, 459. (b) Clark, F. R. S.; Norman, R. O. C.; Thomas, C. B. J . Chem.
Soc., Perkin Trans.
1 1975, 121. (c) Uchiyama, M.; Suzuki, T.;
Yamakazi, Y. Chem. Lett. 1983, 1165. (d) Torii, S.; Tamaka, H.;
Morisaki, K. Tetrahedron Lett. 1985, 26, 1655. (e) J utand, A.; Negri,
S.; Mosleh, A. J . Chem. Soc., Chem. Commun. 1992, 1729. (f) Hennings,
D. D.; Iwama, T.; Rawal, V. H. Org. Lett. 1999, 1, 1205.
(6) Knight, D. W. In Comprehensive Organic Chemistry; Trost, B.
M., Fleming, I., Eds.; Pergamon: Oxford, U.K., 1991; Vol. 3, p 499.
The Ullmann-type coupling reactions of those haloarenes with carboxlic
acids were not successful under Caubere’s NiCRA11c or Ni(COD)2
developed by Semmelhack’s group with the fashion of carboxylate
salts.3b
(7) (a) Tsou, T. T.; Kochi, J . K. J . Am. Chem. Soc. 1979, 101, 6319,
7574. (b) Percec, V.; Bae, J .-Y.; Zhao, M.; Hill, D. H. J . Org. Chem.
1995, 60, 176.
(8) Saleem, R.; Faizi, S.; Deeba, F.; Siddiqui, B. S.; Qazi, M. H.
Planta Med. 1997, 63, 454.
(9) Pearson, R. G. Chem. Rev. 1985, 85(1), 41.
(10) Scho¨nberg, A.; Sina, A. J . Am. Chem. Soc. 1950, 72, 3396.
(11) (a) Caubere, P. Angew Chem., Int. Ed. Engl. 1983, 22, 599. (b)
Vanderesse, R.; Brunet, J . J .; Caubere, P. J . Organomet. Chem. 1984,
264, 263. (c) Lourak, M.; Vanderesse, R.; Fort, Y.; Caubere, P. J . Org.
Chem. 1989, 54, 4840. (d) Fort, Y.; Becker, S.; Caubere, P. Tetrahedron
1994, 50, 11893. (e) More recently, activated LiH was used as an
effective reducing agent in the catalytic cycle; see: Massicot, F.;
Schneider, R.; Fort, Y. J . Chem. Res., Synop. 1999, 664 and references
therein.
(12) Colon, I. J . Org. Chem. 1982, 47, 2622 and references therein.
10.1021/jo001563w CCC: $20.00 © 2001 American Chemical Society
Published on Web 03/20/2001

2878 J . Org. Chem., Vol. 66, No. 8, 2001
Ta ble 1. Resu lts of Mod ified Ni(0)-Ca ta lyzed Hom ocou p lin g of Com p ou n d 2a
Notes
entry
solvent
additive
A
B
C
yield (%)
1
2
3
4
5
6
7
8
9
DMF
DMF
DMF
DMF
no
30
40
80
60
72
91.9
97.8
70
60
20
35
20
8.1
2.2
<1
15
67
quant
quant
quant
quant
quant
quant
quant
quant
30c
K2CO3
NaH
NaHb
NaH
5
8
THF
benzene
toluene
toluene
benzene
benzene
NaH
NaH
NaH
>99
NaOtBu
NaBH4
10
33
97
a
The reactions were performed using 1 equiv of NiCl2(PPh3)2, 2 equiv of PPh3, 4 equiv of Zn, and 8 equiv of additive except entry 8,
in which 0.5 equiv of nickel catalyst was used. 20 equiv of NaH was used. c In this entry, D, as an intermediate for the synthesis of
b
benzopyranone (see ref 10), was the major side product through the hydrolysis of compound B.
Ta ble 2. Va r ieties of Rea ction Con d ition s (in Tolu en e)a
PPh3
(2 equiv)
Zn
(4 equiv)
NaH
(8 equiv)
entry
T (°C)
time (h)
convn (%)
yield (%)
ratio (A/B)b
1
2
3
4
5
6
+
+
+
+
+
+
+
+
+
+
+
+
90
rt
90
rt
90
rt
6
21
18
24
24
3
100
<10
100
49
97
97
99
99
97
99
95
99
98
e
97.8:2.2
20:80
90:10
94:6
+
+
59
81:19
82c
95d
66.5
40
47:53c
40:60d
44:56
7
8
9
+
+
90
rt
90
24
24
6
82:18
+
+
a
All reactions were run using 1 equiv of NiCl2(PPh3)2 in toluene at rt or 90 °C. “+” represents this component being present in the
b
reaction mixture. For example, in entry 1, the ratio of NiCl2(PPh3)2/PPh3/Zn/NaH/substrate is 1:2:4:8:1. The yields and the ratios were
determined by HPLC. c Determined by HPLC. Traces of the substrate were detected. The yield and the ratio were determined by 1H
d
NMR (300 MHz). e No products were detected.
Sch em e 1. P r op osed Mech a n ism for th e
F or m a tion of C a n d E in a P ola r Solven t
ligand PPh3 favored the formation of coupling product A
(entries 1 vs 5, 3 vs 7, 4 vs 8); and (c) the reaction was
accelerated in the presence of metallic Zn (entries 1 vs
3, 6 vs 8). Although the function of Zn dust is still
unclear,13 all of the components are necessary for our new
reagent system to obtain the current excellent results.
Several different mechanisms have been proposed in
the literature4b,7a,11c,14-16 for the nickel(0)-catalyzed ho-
mocoupling reactions of arylhalides. As no dibenzyl was
found among the reaction products (monitored by GC-
might be from the same intermediate, such as 316c,17,18
in Scheme 1. In addition, increasing the content of THF
in toluene to 20% led to the formation of C and E;
MS), a free radical mechanism6 can be ruled out. We
presume a different potential mechanism as shown in
Scheme 1. Under our conditions, compound E was formed
simultaneously with C (Table 1, entries 4 and 5), and
because C and E are not obtained from the hydrogenation
of A and B, respectively, thus, the formation of C and E
(16) There are established examples of hydride and aryl groups as
bridging ligands. The transition state (or intermediate) for such an
inner-sphere electron transfer process can be depicted as singly bridged
or doubly bridged; see: (a) Basolo, F.; Pearson, R. G. Mechanisms of
Inorganic Reactions; Wiley: New York, 1967; pp 482. (b) Wilkins, R.
G. Kinetics and Mechanisms of Transition Metal Complexes; Allyn and
Bacon: Boston, 1974. (c) Yamamoto, Y.; Wakabayashi, S.; Osakada,
K. J . Organomet. Chem. 1992, 428, 223. (d) Kristja´nsdo´ttir, S. S.;
Norton, J . R. J . Am. Chem. Soc. 1991, 113, 4366 and references therein.
(17) For a σ-phenylpalladium hydride species, see: Grushin, V. V.;
Alper, H. J . Am. Chem. Soc. 1995, 117, 4305.
(13) Some unpublished results show that the ratio of coupling
product to reductive product is dependent on the ratio of Zn dust to
nickel catalyst. The function of zinc may be reminiscent of the reported
hypothesis.15
(14) Amatore, C.; J utand, A. Organometallics 1988, 7, 2203.
(15) A hypothesis explained that the nickelate intermediate could
form a bridged Zn complex (heteronuclear complex) on the zinc surface
and facilitate electron-transfer reaction. This process might occur in
polar solvents such as DMAc; see ref 4b.
(18) Burch, R. R.; Muetterties, E. L.; Teller, R. G.; Williams, T. M.
J . Am. Chem. Soc. 1982, 104, 4257.

Notes
J . Org. Chem., Vol. 66, No. 8, 2001 2879
case of 4f, no enyne and diyne products were observed.19
Although the coupling yield and selectivity of â-bro-
mostyrene 4g were moderate, the coupling product could
not be detected in the absence of NaH.20a
Ta ble 3. Hom ocou p lin g of Som e Su bstr a tes u n d er Th is
Con d ition a
It was generally considered that the limitations as-
sociated with nickel-based approaches are the free hy-
droxyl groups (such as OH, COOH) and the steric effects
of ortho substitutents, especially bisortho substi-
tutents.3b,6,11c Under our conditions, halobenzoic acids 4h ,i
and bisortho-substituted halobenzenes 4j,k could also be
coupled successfully with good yields. The homocoupling
of these three kinds of substrates were hardly successful
under other reported Ni-catalyzed Ullmann-type coupling
conditions.3b,6,11c,18,22 It is difficult for aryl halide bearing
bisortho-substitutents to add oxidatively to the ArNi(I)-
L3 to give an Ar2Ni(III)L2 complex.6 The formed 2,2′,6,6′-
tetrasubstituted biaryls are prone to the dinickel hydride
intermediates.
In summary, we have developed a powerful coupling
system involving Zn and NaH for nickel(0)-catalyzed
Ullmann-type reactions, especially for bisortho-substi-
tuted halobenzenes and halobenzoic acids. It is the first
time the nickel-modified Ullmann-type reaction has been
performed in a nonpolar solvent while the catalyst is
generated in situ. As demonstrated in the text, the
nonpolar solvent and the hydride as bridging ligand may
play a significant role. Current work in our laboratory is
focused on the further elucidation of the mechanism as
well as the scope of this new reagent system.
Exp er im en ta l Section
Gen er al Meth ods. Toluene was freshly distilled from sodium-
benzophenone ketyl. Zn dust22 was activated according to the
literature. NiCl2(PPh3)2,23 4d ,24 4e,24 4j,25 and 4k 26 were pre-
pared by literature procedures. NaH was washed twice with dry
1
hexane under N2. H NMR (300 MHz) spectra were recorded in
CDCl3, and chemical shifts are given in Hz. Column chroma-
tography was performed with 300-400 mesh silica gel using
flash column techniques. Elemental analyses were performed
by EA-MOD 7106. Low-resolution mass spectra were recorded
on a Finigan-4201 spectrometer, IR on FTS-185. The melting
points were not corrected. 1H NMR spectral data of 5a ,27 5b,28
5c,28 5f,16 5g,17 5h ,27 5i,27 5j,25 and 5k 29 are in agreement with
published data.
Gen er a l P r oced u r e. The Schlenk flask was charged with
NiCl2(PPh3)2 (0.5 mmol), PPh3 (1 mmol), Zn dust (3 mmol), NaH
(8 mmol, oil-free), and aryl halide (1 mmol), sealed with a rubber
septum, evacuated, and filled with argon several times (vacuum
line). Freshly distilled toluene (5 mL) was added via a syringe.
The mixture was stirred at 70-90 °C for 2-6 h, cooled,and then
quenched with 5% HCl (aq). The organic layer was extracted
a
All reactions were run using 0.5 equiv of nickel catalyst.
b
Different methods were reported in the literature, like as
(20) (a) Takagi, K.; Mimura, H.; Inokawa, S. Bull. Chem. Soc. J pn.
1984, 57, 3517. (b) Determined by GC in the reference: Leadbeater,
N. E.; Resouly, S. M. Tetrahedron Lett. 1999, 40, 4243.
(21) When a simple aryl halide, p-OMeC6H4I, was treated, the yield
of coupling product was 47% and the major side product was
p-OMeC6H4Ph (35%).
(22) Shriner, R. L.; Neumann, F. W. Organic Syntheses; Wiley: New
York, 1955; Collect. Vol. III, p 74.
(23) Venanzi, L. M. J . Chem. Soc. 1958, 722.
(24) J ohnson, C. R.; Adams, J . P.; Braun, M. P.; Senanayake, C. B.
W.; Workulich, P. M.; Uskokovic, M. R. Tetrahedron Lett. 1992, 33,
917.
(25) Kanoh, S.; Muramoto, H.; Kobayashi, N.; Motoi, M.; Suda, H.
Bull. Chem. Soc. J pn. 1987, 60, 3659.
(26) Kajigaesshi, S.; Kakinami, T.; Okamoto, T.; Nakamura, H.;
Fujikawa, M. Bull. Chem. Soc. J pn. 1987, 60, 4187.
(27) Cadogan, J . I. G., Ley, S. V., Pattenden, G., Raphael, R. A.,
Rees, C. W., Eds. Dictionary of Organic Compounds, 6th ed.; Chapman
& Hall: London, U.K., 1996; Vol. 1.
Ni(PPh3)4/DMF, Ni(COD)2/DMF, and “NiCRA”. c TLC detected a
trace of reductive product.
therefore, the two hydrogen atoms added to C may be
taken from NaH and the polar solvent, respectively.
Compound B can also be formed through the reductive
elimination of the mononickel complex [ArNiHL2].
To explore the scope and limitations of this coupling
conditions, reactions of haloarene 4a , R-iodo-R,â-unsatur-
ated ketones 4b-e, haloalkenes 4f,g, halobenzoic acid
4h ,i, and bisortho-substituted halobenzene 4j,k were
investigated (Table 3). Most of them could be coupled
smoothly in high yields with excellent selectivities. In the
(19) Vanderesse, R.; Fort, Y.; Becker, S.; Caubere, P. Tetrahedron
Lett. 1986, 27, 3517.
(28) Eiden, F.; Prielipp, L. Arch Pharm. (Weinheim) 1977, 310, 109.
(29) Gottarelli, G.; Spada, G. P. J . Org. Chem. 1991, 56, 2096.

2880 J . Org. Chem., Vol. 66, No. 8, 2001
Notes
with CHCl3 and dried over Na2SO4. Upon removal of of the
solvent, the corresponding biaryl was obtained after flash
chromatography on silica gel (CH2Cl2/EtOAc) and recrystalli-
zation from CH2Cl2/MeOH.
3,3′-Bis(6-m eth oxych r om on e) (A): mp 257-258 °C; MS 350
(M+), 349 (M + H), 348, 335, 322, 307; FT-IR (cm-1) 3080, 2976,
1645, 1567, 1484, 1313, 1150, 870, 817, 788, 711; 1H NMR
(CDCl3, 300 MHz) δ 8.86 (s, 2H, H-2), 7.65 (d, J ) 3.0 Hz, 2H,
H-5), 7.47 (d, J ) 9.2 Hz, 2H, H-7), 7.30 (dd, J ) 9.2, 3.0 Hz,
H-8), 3.92 (s, 6H, OCH3). Anal. Calcd for C20H14O6: C, 68.57; H,
4.03. Found: C, 68.58; H, 3.98.
3-Iod o-6-m eth oxych r om on e (2): mp 118-119 °C; MS 302
(M+), 303 (M + H), 287, 272, 119, 107, 79; FT-IR (cm-1) 3072,
1653, 1616, 1565, 867, 823, 715, 566, 479; 1H NMR (CDCl3, 300
MHz) δ 8.29 (s, 1H, H-2), 7.58 (d, J ) 3.0 Hz, 1H, H-5), 7.41 (d,
J ) 9.2 Hz, 1H, H-8), 7.29 (dd, J ) 9.0, 3.0 Hz, 1H, H-7), 3.91
(s, 3H, OCH3). Anal. Calcd for C20H14O6: C, 39.76; H, 2.34; I,
42.01. Found: C, 39.76; H, 2.27; I, 42.09.
3-Iod o-6-m eth ylch r om on e (4b): mp 129-131 °C; MS 286
(M+), 258, 159, 103; FT-IR (cm-1) 1644, 1614, 1598, 1558, 1482,
867, 817, 778, 543, 472; 1H NMR (CDCl3, 300 MHz) δ 8.28 (s,
1H, H-2), 8.03 (d, J ) 2.0 Hz, 1H, H-5), 7.52 (dd, J ) 8.3, 2.0
Hz, 1H, H-7), 7.37 (d, J ) 8.3 Hz, 1H, H-8), 2.47 (s, 3H, CH3).
Anal. Calcd for C10H7IO2: C, 41.97; H, 2.47; I, 44.38. Found: C,
42.03; H, 2.41; I, 44.48.
3 -( 6 -M e t h o x y c h r o m o n e -3 ) -6 -m e t h o x y -2 , 3 -2 H -
ch r om on e (C): mp 205-206 °C; MS 352 (M+), 351 (M - H),
335 (M - 15), 321, 201, 150; FT-IR (cm-1) 2925, 1683, 1640, 1590,
1494, 1165, 843, 826, 796, 744; 1H NMR (CDCl3, 300 MHz) δ )
7.87 (s, 1H, H-2), 7.56 (d, J ) 3.0 Hz, 1H, H-5), 7.42 (d, J ) 3.0
Hz, 1H, H-5′), 7.41 (d, J ) 9.0 Hz, 1H, H-8), 7.28 (dd, J ) 9.0,
3.0 Hz, 1H, H-7), 7.14 (dd, J ) 9.0, 3.0 Hz, 1H, H-7′), 6.96 (d, J
) 9.0 Hz, 1H, H-8′), 4.69 (t, J ) 11.4 Hz, 1H, H-3′), 4.56 (dd, J
) 11.4, 5.3 Hz, 1H, H-2′), 4.21 (dd, J ) 11.4, 5.3 Hz, 1H, H-2′),
3.88, 3.82 (each s, 6H, 2 × OCH3). Anal. Calcd for C20H16O6: C,
68.18; H, 4.58. Found: C, 68.40; H, 4.47.
P r ep a r a tion of 3-Iod o-6-m eth oxych r om on e (2). To a
stirred suspension of powered sodium (2.38 g, 103 mmol) in dry
ether (60 mL) was added dropwise a well-cooled solution of 2′-
methoxy-5′-hydroxyacetophenone (4.08 g, 24.6 mmol) in freshly
distilled ethylformate (8 mL, 100 mmol) and dry ether (200 mL).
The reaction mixture was stirred for 4 h in an ice bath and then
overnight at rt. Twenty millilters of ethylformate-ether mixture
(1:10) was added, and the reaction mixture was refluxed for 1
h. On cooling, water (100 mL) was added carefully, and the
alkaline layer was separated. The alkaline layer was acidified
by 50% H2SO4 (pH < 1) and refluxed for 1 h. It was cooled and
extracted with CHCl3 (30 mL × 3). The combined organic layers
were washed with brine and dried over Na2SO4. 5-Methoxy-
chromone was obtained as yellowish solid after the solvent was
evaporated. The crude product 5-methoxychromone and piperi-
dine (6.2 mL, 62.5 mmol) were refluxed in methanol (50 mL)
for 3 h. Rotary evaporation gave a yellow solid, which was
dissolved in CHCl3 (40 mL). Pyridine (2 mL, 25 mmol) and iodide
(12.7 g, 50 mmol) were added into the solution in one portion.
The reaction mixture was stirred overnight and quenched with
15 mL of saturated Na2S2O3 (aq). After the mixture was
vigorously stirred at room temperature over 30 min, the organic
layer was separated. The water layer was extracted with CHCl3
(30 mL × 3). The combined organic layers were washed with
brine and dried over Na2SO4. The white solid (6.83 g, 22.6 mmol)
was obtained in 92% yield after flash column chromatography
on silica gel (CH2Cl2/EtOAc 85/15).
3-Iod o-ch r om on e (4c): mp 95-96 °C; MS 272 (M+), 244, 145,
89; FT-IR (cm-1) 1646, 1609, 1597, 1556, 868, 833, 765, 540, 514;
1H NMR (CDCl3, 300 MHz): δ ) 8.31 (s, 1H, H-2), 8.25 (dd, J )
8.5, 1.4 Hz, 1H, H-5), 7.72 (td, J ) 8.5, 1.4 Hz, 1H, H-7), 7.27-
7.50 (m, 2H, H-6, 8). Anal. Calcd for C9H6IO2: C, 39.71; H, 1.84;
I, 46.69. Found: C, 39.76; H, 1.84; I, 46.31.
2,2′-Bis(2-cycloh exen -1-on e) (5d ): mp 109-110 °C; MS 302
(M+), 303 (M + H), 287, 272, 119, 107, 79; FT-IR (cm-1) 3072,
1653, 1616, 1565, 867, 823, 715, 566, 479; 1H NMR (CDCl3, 300
MHz) δ 8.29 (s, 1H, H-2), 7.58 (d, J ) 3.0 Hz, 1H, H-5), 7.41 (d,
J ) 9.2 Hz, 1H, H-8), 7.29 (dd, J ) 9.0, 3.0 Hz, 1H, H-7), 3.91
(s, 3H, OCH3). Anal. Calcd for C20H14O6: C, 39.76; H, 2.34; I,
42.01. Found: C, 39.76; H, 2.27; I, 42.09.
2,2′-Bis(4-t er t -b u t yld ip h e n ylsilyloxy-2-cycloh e xe n -1-
on e) (5e): MS 698 (M+), 641, 563, 199, 135, 77; FT-IR (cm-1
)
2960, 2859, 1893, 1683, 1590, 1106; 1H NMR (CDCl3, 300 MHz)
δ 7.69 (m, 8H, Ph), 7.35-7.49 (m, 12H, Ph), 6.61 (d, J ) 2.4 Hz,
0.6 × 2H, H3,3′), 6.57 (d, J ) 1.6 Hz, 0.4 × 2H, H3,3′), 4.51-4.58
(m, 2H, H4,4′), 2.48-2.55 (m, 2H, H6,6′), 2.16-2.28 (m, 2H, H6,6′),
2.05-2.08 (m, 4H, H5,5′), 1.09 (s, 18H).
Ack n ow led gm en t. We acknowledge the financial
assistance by the NSFC (079201) and the major basic
research development program (G2000 077506). We
thank Prof. T.-Y. Luh (National Taiwan University,
Taiwan) for helpful discussions and Mr. Rob Hoen (Rijks
Universiteit Groningen) for reading the manuscript. We
1
also thank Dr. Hao Huang and Mr. Keming Xia for H
NMR and HPLC performances, respectively.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra for
A, C, 2, 4b,c, and 5d ,e are provided. This material is available
free of charge via the Internet at http://pubs.acs.org.
J O001563W