Catalytic [2 + 2 + 2] and thermal [4 + 2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes

Article abstract of DOI:10.1021/jo0624546

We have determined that a cationic rhodium(I)/Segphos complex catalyzes an enantio- and diastereoselective intermolecular [2 + 2 + 2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes with various monoalkynes at room temperature to give axially chiral 1,4-t

Full text of DOI:10.1021/jo0624546

RhCl(PPh3)3,6 which are widely used for the [2 + 2 + 2]
cycloadditions of R,ω-diynes with monoalkynes, were found
to catalyze the [2 + 2 + 2] cycloaddition in refluxing n-octane7
or refluxing ethanol,8 respectively. However, these catalytic
systems require high reaction temperature (60-130 °C), and
the product yields were not satisfactory (5-77%). Recently,
highly efficient Cp*RuCl(cod)-catalyzed [2 + 2 + 2] cycload-
dition of terminal and methyl-substituted internal 1,2-bis-
(propiolyl)benzenes with monoalkynes was reported.9 Although
this catalyst system realized mild reaction conditions (room
temperature) and high product yields (33-92%), 1,2-bis-
(phenylpropiolyl)benzene could not be employed as a result of
the formation of a stable ruthenacycle.9,10
Catalytic [2 + 2 + 2] and Thermal [4 + 2]
Cycloaddition of 1,2-Bis(arylpropiolyl)benzenes
Ken Tanaka,*,† Takeshi Suda,† Keiichi Noguchi,‡ and
Masao Hirano†
Department of Applied Chemistry, Graduate School of
Engineering, and Instrumentation Analysis Center, Tokyo
UniVersity of Agriculture and Technology, Koganei,
Tokyo 184-8588, Japan
tanaka-k@cc.tuat.ac.jp
We reported previously that cationic rhodium(I)/modified-
BINAP complexes are highly effective catalysts for chemo- and
regioselective [2 + 2 + 2] cycloadditions.11 These catalysts were
further extended to enantioselective [2 + 2 + 2] cycloadditions
for the construction of axial chiralities.12 Herein, we describe a
cationic rhodium(I)/(S)-Segphos [(4,4′-bi-1,3-benzodioxole)-5,5′-
diylbis(diphenylphosphine)]13 complex-catalyzed enantio- and
diastereoselective intermolecular [2 + 2 + 2] cycloaddition of
1,2-bis(arylpropiolyl)benzenes with monoalkynes at room tem-
perature leading to axially chiral 1,4-teraryls possessing an
anthraquinone structure. We also describe a thermal intramo-
lecular [4 + 2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes
leading to aryl-substituted naphthacenediones.
We first examined various rhodium(I) and iridium(I) com-
plexes [10% based on 1,2-bis(phenylpropiolyl)benzene (1a)] for
their ability to catalyze the [2 + 2 + 2] cycloaddition of 1a
with internal monoalkyne 2a as shown in Table 1. The use of
Segphos and H8-BINAP [2,2′-bis(diphenylphosphino)-
5,5′,6,6′,7,7′,8,8′-octahydro-1,1′-binaphthyl]14 as ligands, which
ReceiVed NoVember 30, 2006
We have determined that a cationic rhodium(I)/Segphos
complex catalyzes an enantio- and diastereoselective inter-
molecular [2 + 2 + 2] cycloaddition of 1,2-bis(arylpropi-
olyl)benzenes with various monoalkynes at room temperature
to give axially chiral 1,4-teraryls possessing an anthraquinone
structure in good yields with good enantio- and diastereo-
selectivities. We have also determined that a thermal
intramolecular [4 + 2] cycloaddition of 1,2-bis(arylpropi-
olyl)benzenes proceeds at 60 °C to give aryl-substituted
naphthacenediones in moderate to good yields.
(6) Recent review, see: Fujiwara, M.; Ojima, I. In Modern Rhodium-
Catalyzed Organic Reactions; Evans, P. A., Ed.; Wiley-VCH: Weinheim,
2005; Chapter 7, pp 129-150.
(7) Hillard, R. L., III; Vollhardt, K. P. C. J. Am. Chem. Soc. 1977, 99,
4058-4069.
Transition-metal-mediated [2 + 2 + 2] cycloaddition1 of 1,2-
bis(propiolyl)benzene derivatives with monoalkynes is a valu-
able transformation for the synthesis of substituted anthraquino-
nes. Such a transformation was achieved by cycloadditions of
isolated naphthoquinone-fused rhodacyclopentadiene complexes
with monoalkynes2 and of 1,2-bis(phenylpropiolyl)benzene with
monoalkynes using a large excess of highly toxic Ni(CO)4.3
After these reports, several catalytic methods were developed.
The first catalytic reaction was realized by using 5-25% Ni-
(PPh3)2(CO)2 as a precatalyst at 60-130 °C.4 CpCo(CO)25 and
(8) McDonald, F. E.; Zhu, H. Y. H.; Holmquist, C. R. J. Am. Chem.
Soc. 1995, 117, 6605-6506.
(9) (a) Yamamoto, Y.; Hata, K.; Arakawa, T.; Itoh, K. Chem. Commun.
2003, 1290-1291. (b) Yamamoto, Y.; Saigoku, T.; Ohgai, T.; Nishiyama,
H.; Itoh, K. Chem. Commun. 2004, 2702-2703. (c) Yamamoto, Y.; Saigoku,
T.; Nishiyama, H.; Ohgai, T.; Itoh, K. Org. Biomol. Chem. 2005, 3, 1768-
1775.
(10) Yamamoto, Y.; Arakawa, T.; Itoh, K. Organometallics 2004, 23,
3610-3614.
(11) Our first report on the cationic rhodium(I)/modified-BINAP-
catalyzed inter- and intramolecular [2 + 2 + 2] cycloadditions, see: (a)
Tanaka, K.; Shirasaka, K. Org. Lett. 2003, 5, 4697-4699. Application to
the synthesis of cyclophanes, see: (b) Tanaka, K.; Toyoda, K.; Wada, A.;
Shirasaka, K.; Hirano, M. Chem. Eur. J. 2005, 11, 1145-1156. (c) Tanaka,
K.; Sagae, H.; Toyoda, K.; Noguchi, K. Eur. J. Org. Chem. 2006, 3575-
3581. Application to the synthesis of nitrogen heterocycles, see: (d) Tanaka,
K.; Wada, A.; Noguchi, K. Org. Lett. 2005, 7, 4737-4739. (e) Tanaka, K.;
Wada, A.; Noguchi, K. Org. Lett. 2006, 8, 907-909. (f) Tanaka, K.; Suzuki,
N.; Nishida, G. Eur. J. Org. Chem. 2006, 3917-3922.
† Department of Applied Chemistry.
‡ Instrumentation Analysis Center.
(1) Recent reviews, see: (a) Kotha, S.; Brahmachary, E.; Lahiri, K. Eur.
J. Org. Chem. 2005, 4741-4767. (b) Yamamoto, Y. Curr. Org. Chem.
2005, 9, 503-519. (c) Varela, J.; Saa´, C. Chem. ReV. 2003, 103, 3787-
3802. (d) Malacria, M.; Aubert, C.; Renaud J. L. In Science of Synthesis:
Houben-Weyl Methods for Molecular Transformations; Lautens, M., Trost,
B. M., Eds.; Georg Thieme Verlag: New York, 2001; Vol. 1, pp 439-
530. (e) Saito, S.; Yamamoto, Y. Chem. ReV. 2000, 100, 2901-2915.
(2) Mu¨ller, E. Synthesis 1974, 761-774.
(3) Wagner, F.; Meier, H. Tetrahedron 1974, 30, 773-779.
(4) Mu¨ller, E.; Scheller, A.; Winter, W.; Wagner, F.; Meier, H. Chem.-
Ztg. 1975, 99, 155-157.
(5) Recent review, see: Gandon, V.; Aubert, C.; Malacria, M. Chem.
Commun. 2006, 2209-2217.
(12) (a) Tanaka, K.; Nishida. G.; Wada, A.; Noguchi, K. Angew. Chem.,
Int. Ed. 2004, 43, 6510-6512. (b) Tanaka, K.; Nishida, G.; Ogino, M.;
Hirano, M.; Noguchi, K. Org. Lett. 2005, 7, 3119-3121. (c) Nishida, G.;
Suzuki, N.; Noguchi, K.; Tanaka, K. Org. Lett. 2006, 8, 3489-3492. (d)
Tanaka, K.; Takeishi, K.; Noguchi, K. J. Am. Chem. Soc. 2006, 128, 4586-
4587.
(13) Saito, T.; Yokozawa, T.; Ishizaki, T.; Moroi, T.; Sayo, N.; Miura,
T.; Kumobayashi, H. AdV. Synth. Catal. 2001, 343, 264-267.
(14) Zhang, X.; Mashimo, K.; Koyano, K.; Sayo, N.; Kumobayashi, H.;
Akutagawa, S.; Takaya, H. Tetrahedron Lett. 1991, 32, 7283-7286.
10.1021/jo0624546 CCC: $37.00 © 2007 American Chemical Society
Published on Web 02/09/2007
J. Org. Chem. 2007, 72, 2243-2246
2243

TABLE 1. Screening of Catalysts for [2 + 2 + 2] Cycloaddition of
TABLE 3. Rhodium-Catalyzed Enantio- and Diastereoselective
[2 + 2 + 2] Cycloaddition of 1,2-Bis(arylpropiolyl)benzenes with
Monoalkynesa
1,2-Bis(phenylpropiolyl)benzene with Monoalkynea
% yieldb
(dr)
ee
entry
1
2
R1
R2
3
(%)c
entry
catalyst
conv (%)
yield (%)b
1d
2
3
4
5
1b 2h Et
1b 2c n-Pr
1b 2i Me
Et
(+)-3bh
(+)-3bc
(+)-3bi
78 (4:1)
75 (6:1)
80 (8:1)
70 (2:1)
97
98
97
97
87
89
85
1
2
3
4
5
6
7
[Rh(cod)2]BF4/Segphos
[Rh(cod)2]BF4/H8-BINAP
[Rh(cod)2]BF4/BINAP
[Rh(cod)2]BF4/dppb
[Rh(cod)2]BF4/dppf
[Rh(cod)Cl]2/Segphos
[Ir(cod)2]BF4/Segphos
100 (46c)
76 (33c)
n-Pr
n-C5H11
100 (28c)
77 (18c)
60
22
39
11
11
36
11
19
<5
0
1b 2a CH2OMe CH2OMe (-)-3ba
1b 2b Me
1b 2d Me
1c 2c n-Pr
CH2OH
CO2Et
n-Pr
(R,R)-(-)-3bb 68 (3:1)
6
(-)-3bd
(+)-3cc
93 (3:1)
71 (3:1)
7e
a [Rh(cod)2]BF4 (0.015 mmol), Segphos (0.015 mmol), 1 (0.15 mmol),
2 (0.165 mmol, 1.1 equiv), and CH2Cl2 (1.5 mL) were used. b Isolated yield.
c ee (%) of major diastereomers. d 2h (0.30 mmol, 2 equiv) was used.
e CH2Cl2 (3.0 mL) was used.
a Catalyst (0.015 mmol), 1a (0.15 mmol), 2a (0.165 mmol, 1.1 equiv),
and CH2Cl2 (1.5 mL) were used. b Isolated yield. c Catalyst: 5%.
TABLE 2. Rhodium-Catalyzed [2 + 2 + 2] Cycloaddition of
1,2-Bis(phenylpropiolyl)benzene with Monoalkynesa
thraquinones 3aa-3ad in good to high yields (entries 1-4).
Not only internal alkynes but also terminal alkynes can be
employed for this reaction. Methoxymethyl-, alkyl-, and phenyl-
substituted terminal alkynes cleanly afforded the corresponding
substituted anthraquinones 3ae-3ag in high yields (entries
5-7).
The [2 + 2 + 2] cycloaddition of 1,2-bis(propiolyl)benzenes,
bearing an ortho-substituted phenyl group at both alkyne termini,
with monoalkynes would install two axial chiralities during the
formation of benzene rings.15-18 Recently, Shibata et al. reported
the highly efficient enantio- and diastereoselective synthesis of
axially chiral 1,4-teraryl compounds via [IrCl(cod)]2/MeDU-
PHOS [1,2-bis(2,5-dimethylphospholano)benzene]-catalyzed [2
+ 2 + 2] cycloaddition of electron rich R,ω-diynes, bearing an
ortho-substituted phenyl group at both alkyne termini, with
electron-rich oxygen-functionalized monoalkynes.18 However,
our experiments revealed that iridium(I) complexes did not
catalyze the [2 + 2 + 2] cycloaddition of electron-deficient
diketodiyne substrates. As shown in Table 3, the reaction of
2-methylphenyl-substituted diketodiyne 1b with 3-hexyne 2h
using [Rh(cod)2]BF4/(S)-Segphos furnished 1,4-teraryl 3bh in
78% yield with good diasereoselectivity (dl-isomer was obtained
as a major isomer, dl:meso ) 4:1) and high enantioselectivity
(97% ee, dl-isomer) (entry 1).19 Interestingly, increasing the
length of the alkyl chain improved the diastereoselectivities
(entries 2 and 3). Not only unfunctionalized alkyl-substituted
entry
2 (equiv)
R1
R2
3
yield (%)b
1
2
3
4
5c
6
7
2a (1.1)
2b (1.1)
2c (1.1)
2d (1.1)
2e (2.0)
2f (2.0)
2g (2.0)
CH2OMe
CH2OMe
CH2OH
n-Pr
CO2Et
CH2OMe
n-Bu
3aa
3ab
3ac
3ad
3ae
3af
76
95
86
64
82
78
96
Me
n-Pr
Me
H
H
H
Ph
3ag
a [Rh(cod)2]BF4 (0.015 mmol), Segphos (0.015 mmol), 1a (0.15 mmol),
2 (0.165 mmol, 1.1 equiv or 0.30 mmol, 2.0 equiv), and CH2Cl2 (1.5 mL)
were used. b Isolated yield. c Reaction time: 24 h.
are effective for our previous [2 + 2 + 2] cycloaddition of
electron-deficient alkynes with monoalkynes,12 furnished the
desired diphenyl-substituted anthraquinone 3aa in good yields
(entries 1 and 2). On the other hand, other conventional bidentate
phosphine ligands (BINAP, dppb, and dppf) were found to be
less effective (entries 3-5). The catalytic activities of cationic
rhodium(I)/Segphos and H8-BINAP complexes were examined
with low catalyst loading (5%), which revealed that Segphos
showed catalytic activity higher than that of H8-BINAP (entries
1 and 2). Importantly, the use of a cationic rhodium(I) complex
is essential for the present [2 + 2 + 2] cycloaddition. The use
of neutral rhodium(I)/Segphos complex furnished 3aa in <5%
yield, and the cationic iridium(I)/Segphos complex did not
catalyze this reaction at all (entries 6 and 7). Unfortunately, the
[2 + 2 + 2] cycloaddition of methyl-substituted internal 1,2-
bis(propiolyl)benzene with monoalkynes did not proceed under
the present optimal reaction conditions.
(15) For pioneering work on the synthesis of biaryls through alkyne
cyclotrimerization, see: Sato, Y.; Ohashi, K.; Mori, M. Tetrahedron Lett.
1999, 40, 5231-5234.
(16) For pioneering work on the synthesis of 1,4-teraryls and oligo-p-
phenylenes through alkyne cyclotrimerization, see: McDonald, F. E.;
Smolentsev, V. Org. Lett. 2002, 4, 745-748.
(17) Gutnov, A.; Heller, B.; Fischer, C.; Drexler, H.-J.; Spannenberg,
A.; Sundermann, B.; Sundermann, C. Angew. Chem., Int. Ed. 2004, 43,
3795-3797.
(18) (a) Shibata, T.; Fujimoto, T.; Yokota, K.; Takagi, K. J. Am. Chem.
Soc. 2004, 126, 8382-8383. (b) Shibata, T.; Tsuchikama, K. Chem.
Commun. 2005, 6017-6019. (c) Shibata, T.; Tsuchikama, K.; Otsuka, M.
Tetrahedron: Asymmetry 2006, 17, 614-619. (d) Shibata, T.; Arai, Y.;
Takami, K.; Tsuchikama, K.; Fujimoto, T.; Takebayashi, S.; Takagi, K.
AdV. Synth. Catal. 2006, 348, 2475-2483.
A series of monoalkynes 2a-g were subjected to the above
optimal reaction conditions as shown in Table 2. Methoxy-
methyl-, hydroxymethyl-, alkyl-, and ethoxycarbonyl-substituted
internal alkynes afforded the corresponding substituted an-
(19) The use of other BINAP-type ligands (BINAP, tol-BINAP, H8-
BINAP) gave a meso- or cis-isomer as a major product.
2244 J. Org. Chem., Vol. 72, No. 6, 2007

TABLE 4. Thermal [4 + 2] Cycloaddition of
SCHEME 1
1,2-Bis(arylpropiolyl)benzenesa
internal alkynes 2h,c,i and 2-methylphenyl-substituted diketo-
diyne 1b but also both electron-rich and electron-deficient
oxygen-functionalized internal alkynes 2a,b,d and 1-naphthyl-
substituted diketodiyne 1c can be employed for this reaction,
although enantio- and/or diastereoselectivities decreased (entries
4-7). Importantly, good enantio- and diastereoselectivities were
observed by using both symmetrical (entries 1, 2, 4, and 7) and
unsymmetrical (entries 3, 5, and 6) monoalkynes. The absolute
configuration of 4-bromobenzoate of (-)-3bb was determined
to be the (R,R)-form by the anomalous dispersion method.
Scheme 1 depicts a plausible mechanism for the selective
formation of (R,R)-(-)-3bb. Both enantio- and diastereoselec-
tivities are determined by preferential formation of intermediate
A, due to the steric interaction between the two methyl groups
of 1b and the two axial PPh2 groups of (S)-Segphos, and
sterically less demanding coordination of monoalkyne 2b to
rhodium. Reductive elimination of rhodium gives (R,R)-(-)-
3bb and regenerates the rhodium catalyst.
It is well-established that aryl alkynyl ketones exhibit
enhanced reactivity toward thermal intramolecular [4 + 2]
cycloaddition, and thus the reaction can be carried out at
relatively lower temperature.20,21 Indeed, when the rhodium-
catalyzed cycloaddition of 1 with 2 was carried out at elevated
temperature (60-80 °C), both intermolecular [2 + 2 + 2]
cycloaddition of 1 with 2 and intramolecular [4 + 2] cyclo-
addition of 1 proceeded concurrently to give substituted
anthraquinone 3 and substituted naphthacenedione 4, respec-
tively.22
a Reactions were conducted using 1 (0.10 mmol) in (CH2Cl)2 (60-80
°C) or xylene (140 °C) (2.0 mL). b Isolated yield. c NMR yield.
thyl-substituted diketodiynes 1b and 1c also furnished the
corresponding substituted naphthacenediones 4b and 4c in 52%
and 59% isolated yields, respectively (entries 4 and 5).
In conclusion, we have established that a cationic rhodium-
(I)/Segphos complex catalyzes an enantio- and diastereoselective
intermolecular [2 + 2 + 2] cycloaddition of 1,2-bis(arylpropi-
olyl)benzenes with various monoalkynes at room temperature
to give axially chiral 1,4-teraryls possessing the anthraquinone
structure in good yields with good enantio- and diastereoselec-
tivities. We have also established that a thermal intramolecular
[4 + 2] cycloaddition of 1,2-bis(arylpropiolyl)benzenes proceed
at 60 °C to give aryl-substituted naphthacenediones in moderate
to high yields. These [2 + 2 + 2] and [4 + 2] cycloadditions
of 1,2-bis(arylpropiolyl)benzenes represent a versatile new
method for the preparation of aryl-substituted anthraquinone and
naphthacenedione structures.
The effect of reaction temperature and the scope of aryl-
substituted diketodiyne substrates for this thermal intramolecular
[4 + 2] cycloaddition were examined in the absence of rhodium
catalysts as shown in Table 4. Increasing the reaction temper-
ature decreased the yield of 4a, although it shortened the reaction
times (entries 1-3). The highest yield of 4a was obtained at
60 °C for 48 h using (CH2Cl)2 as a solvent (entry 3). Under
this optimal reaction conditions, 2-methylphenyl- and 1-naph-
Experimental Section
Representative Procedure for Catalytic [2 + 2 + 2] Cycload-
ditions of 1,2-Bis(arylpropiolyl)benzenes with Monoalkynes
(Table 2, entry 1). Under an Ar atmosphere, a CH2Cl2 (0.5 mL)
solution of Segphos (9.2 mg, 0.015 mmol) was added to a CH2Cl2
(0.5 mL) solution of [Rh(cod)2]BF4 (6.1 mg, 0.015 mmol) at room
temperature, and the mixture was stirred for 5 min. The resulting
solution was stirred under H2 (1 atm) at room temperature for 0.5
h, concentrated to dryness, and dissolved in CH2Cl2 (0.5 mL). To
this solution was added a CH2Cl2 (0.5 mL) solution of 1,2-bis-
(phenylpropiolyl)benzene10 (1a, 50.1 mg, 0.15 mmol) and 1,4-
dimethoxy-2-butyne (2a, 18.8 mg, 0.165 mmol), and remaining
substrates were washed away by using CH2Cl2 (0.5 mL). The
solution was stirred at room temperature for 16 h. The resulting
solution was concentrated and purified by silica gel chromatography
(hexane/Et3N ) 15:1), which furnished 2,3-dimethoxymethyl-1,4-
diphenylanthraquinone (3aa, 51.3 mg, 0.114 mmol, 76% yield) as
a yellow solid.
(20) For pioneering work on the intramolecular [4 + 2] cycloadditions
of conjugated arenynes, see: Michael, A.; Bucher, J. E. Chem. Ber. 1895,
28, 2511-2512.
(21) (a) Rodr´ıguez, D.; Navarro-Va´zquez, A.; Castedo, L.; Dom´ınguez,
D.; Saa´, C. Org. Lett. 2000, 2, 1497-1500. (b) Rodr´ıguez, D.; Navarro-
Va´zquez, A.; Castedo, L.; Dom´ınguez, D.; Saa´, C. J. Am. Chem. Soc. 2001,
123, 9178-9179. (c) Rodr´ıguez, D.; Navarro-Va´zquez, A.; Castedo, L.;
Dom´ınguez, D.; Saa´, C. Tetrahedron Lett. 2002, 43, 2717-2720. (d)
Rodr´ıguez, D.; Navarro-Va´zquez, A.; Castedo, L.; Dom´ınguez, D.; Saa´, C.
J. Org. Chem. 2003, 68, 1938-1946. (e) Rodr´ıguez, D.; Mart´ınez-Esperon,
M. F.; Castedo, L.; Dom´ınguez, D.; Saa´, C. Synlett 2003, 1524-1526. (f)
Rodr´ıguez, D.; Mart´ınez-Espero´n, M. F.; Navarro-Va´zquez, A.; Castedo,
L.; Dom´ınguez, D.; Saa´, C. J. Org. Chem. 2004, 69, 3842-3848.
(22) Saa´ and co-workers reported that attempted intramolecular [4 + 2]
cycloadditions of diketodiyne 1a under thermal or catalyzed conditions led
to its decomposition; see: Rodr´ıguez, D.; Castedo, L.; Dom´ınguez, D.; Saa´,
C. Org. Lett. 2003, 5, 3119-3121.
2,3-Dimethoxymethyl-1,4-diphenylanthraquinone (3aa). Yel-
low solid; mp 160.0-160.8 °C; IR (neat) 2875, 1670, 1320, 1250,
1
1090 cm-1; H NMR (CDCl3, 300 MHz) δ 7.98 (dd, J ) 5.7 and
J. Org. Chem, Vol. 72, No. 6, 2007 2245

3.3 Hz, 2H), 7.63 (dd, J ) 5.7 and 3.3 Hz, 2H), 7.42-7.54 (m,
6H), 7.20-7.31 (m, 4H), 4.20 (s, 4H), 3.16 (s, 6H); 13C NMR
(CDCl3, 75 MHz) δ 183.9, 144.7, 142.8, 140.0, 133.9, 133.6, 132.8,
128.2, 127.8, 126.9, 126.7, 68.0, 58.8; HRMS (FAB) calcd for
C30H25O4 [M + H]+ 449.1753, found 449.1759.
stirred at 60 °C for 48 h. The resulting solution was concentrated
and purified by silica gel chromatography (hexane/CH2Cl2 ) 2:1),
which furnished 6-phenylnaphthacene-5,12-dione (4a, 25.7 mg,
0.077 mmol, 77% yield) as an orange solid.
6-Phenylnaphthacene-5,12-dione (4a).22 Yellow solid; mp
282.2-282.8 °C; 1H NMR (CDCl3, 300 MHz) δ 9.01 (s, 1H), 8.31-
8.41 (m, 1H), 8.08-8.23 (m, 2H), 7.41-7.84 (m, 8H), 7.18-7.34
(m, 2H); 13C NMR (CDCl3, 75 MHz) δ 183.4, 183.2, 144.2, 139.7,
136.2, 135.7, 134.6, 134.2, 133.6, 130.2, 130.1, 129.3, 129.1, 128.9,
128.5, 128.4, 127.7, 127.2, 126.9.
(+)-2,3-Dipropyl-1,4-di-o-tolylanthraquinone [(+)-3bc, dl:
meso ) 6:1]. Pale yellow solid; mp 132.5-135.4 °C; [R]25D +83.7°
[CHCl3, c2 .19, dl:meso ) 6:1, 98% ee (dl-isomer)]; IR (neat) 2900,
1670, 1310, 1250, 730 cm-1; 1H NMR (CDCl3, 300 MHz) δ 7.91-
8.02 (m, 2H), 7.55-7.64 (m, 2H), 7.22-7.43 (m, 6H), 6.99-7.11
(m, 2H), 2.38-2.58 (m, 2H), 2.14-2.32 (m, 2H), 2.03 (m, 6H),
1.19-1.42 (m, 4H), 0.72 (t, J ) 7.2 Hz, 6H), methyl protons of
meso-3bc: 2.00 (s, 6H); 13C NMR (CDCl3, 75 MHz) δ 184.34,
184.28, 147.8, 147.6, 142.1, 140.93, 140.85, 135.2, 135.0, 134.1,
134.0, 133.2, 130.7, 129.6, 129.5, 127.93, 127.86, 127.0, 126.5,
126.4, 125.6, 125.5, 32.7, 32.5, 24.0, 23.6, 20.2, 20.0, 14.72, 14.66;
HRMS (FAB) calcd for C34H33O2 [M + H]+ 473.2481, found
473.2458; CHIRALPAK AD-H, hexane/2-PrOH ) 98:2, 0.8 mL/
min, tR 4.48 min (minor dl-isomer), 6.07 min (meso-isomer), and
6.75 min (major dl-isomer).
Acknowledgment. This work was partly supported by Asahi
Glass Fundation. We thank Takasago International Corporation
for the gift of Segphos and H8-BINAP.
Supporting Information Available: Experimental procedure
for the synthesis of diynes (1a, 1b, and 1c), compound characteriza-
tion data (1a, 1b, 1c, 3ab, 3ac, 3ad, 3ae, 3af, 3ag, 3ba, 3bb, 3bd,
3bh, 3bi, 3cc, 4-bromobenzoate of (R,R)-(-)-3bb, 4b, and 4c), 1H
NMR spectra of all compounds, and X-ray crystallographic files
for 4-bromobenzoate of (R,R)-(-)-3bb in CIF format. This material
is available free of charge via the Internet at http://pubs.acs.org.
Representative Procedure for Thermal Intramolecular [4 +
2] Cycloadditions of 1,2-Bis(arylpropiolyl)benzenes (Table 4,
entry 3). Under an Ar atmosphere, a (CH2Cl)2 (2.0 mL) solution
of 1,2-bis(phenylpropiolyl)benzene (1a, 33.4 mg, 0.10 mmol) was
JO0624546
2246 J. Org. Chem., Vol. 72, No. 6, 2007