Indium(III)-catalyzed tandem reaction with alkynylbenzaldehydes and alkynylanilines to heteroaromatic compounds

Article abstract of DOI:10.1021/jo800474c

(Chemical Equation Presented) Starting from ortho-alkynylbenzaldehydes and ortho-alkynylanilines, In(OTf)₃-catalyzed synthesis of ring-condensed heteroaromatic compounds was developed via a domino intramolecular nucleophilic attack/intermolecular cycloaddition/dehydration reaction.

Full text of DOI:10.1021/jo800474c

SCHEME 1
Indium(III)-Catalyzed Tandem Reaction with
Alkynylbenzaldehydes and Alkynylanilines to
Heteroaromatic Compounds
Reiko Yanada,*,† Kana Hashimoto,† Rie Tokizane,†
Yoshihisa Miwa,† Hideki Minami,† Kazuo Yanada,‡
Minoru Ishikura,§ and Yoshiji Takemoto
Faculty of Pharmaceutical Sciences, Hiroshima International
UniVersity, 5-1-1 Hirokoshingai, Kure, Hiroshima 737-0112,
Japan, Faculty of Pharmaceutical Sciences, Setsunan UniVersity,
Nagaotoge-cho, Hirakata, Osaka 573-0101, Japan, Faculty of
Pharmaceutical Sciences, Health Sciences UniVersity of Hokkaido,
Ishikari-Tobetsu, Hokkaido 061-0293, Japan, and Graduate School
of Pharmaceutical Sciences, Kyoto UniVersity, Yoshida, Sakyo-ku,
Kyoto 606-8501, Japan
ryanada@ps.hirokoku-u.ac.jp
is important for further study. On the other hand, electrophilic
cyclization of phenylacetylenes bearing a carbonyl group or an
imino group in the ortho position is currently a popular research
topic and important method from the viewpoint of synthetic
potential. As shown in Scheme 1, the reaction with ortho-
alkynylcarbonyl compounds 1 usually produces imines 2 in the
presence of amines, and then the coordination of a catalyst to
the alkynyl moiety of 2 occurs to produce 3. The addition of
nucleophiles to 3 results in the formation of 1,2-dihydroiso-
quinolines 4 (route A).3 In the reaction of compound 1 with no
amines, benzannulation would proceed to give compounds 6
via intermediates 5 in the presence of nucleophiles (route B).4
When dienophilic alkynes are added instead of nucleophiles,
Diels-Alder-type cycloaddition reactions would occur with
active dienes 5 to produce naphthyl ketone derivatives 8 via
intermediates 7 (route C).5,6
ReceiVed March 5, 2008
Starting from ortho-alkynylbenzaldehydes and ortho-alky-
nylanilines, In(OTf)3-catalyzed synthesis of ring-condensed
heteroaromatic compounds was developed via a domino
intramolecular nucleophilic attack/intermolecular cycload-
dition/dehydration reaction.
On the basis of these results, we planned to apply π-acidic
metal-catalyzed tandem reaction to rapidly access phenanthridine
structures. We envisaged that Lewis acid catalyzed annulation
of ortho-alkynylbenzaldehydes with ortho-alkynylanilines might
successively proceed to form one carbon-nitrogen and two
carbon-carbon bonds of benzophenanthridine derivatives in one
step. An overview of our strategy is summarized in Scheme 2.
Substituted phenanthridine alkaloids constitute an attractive
class of compounds from the viewpoint of their biological and
pharmaceutical activities, which are attributed to their special
affinity toward DNA. There have recently been a lot of
interesting applications.1 However, a little efficient synthetic
method that is applicable to various phenanthridines has been
developed.2 Development of short and diverse synthetic methods
(3) (a) Su, S.; Porco, J. A., Jr J. Am. Chem. Soc. 2007, 129, 7744. (b) Obika,
S.; Kono, H.; Yasui, Y.; Yanada, R.; Takemoto, Y. J. Org. Chem. 2007, 72,
4462. (c) Asao, N.; Iso, K.; Yudha, S. S. Org. Lett. 2006, 8, 4149. (d) Yanada,
R.; Obika, S.; Kono, H.; Takemoto, Y. Angew. Chem., Int. Ed. 2006, 45, 3822.
(e) Asao, N.; Yudha, S. S.; Nogami, T.; Yamamoto, Y. Angew. Chem., Int. Ed.
2005, 44, 5526.
† Hiroshima International University.
‡ Setsunan University.
§ Health Sciences University of Hokkaido.
Kyoto University.
(4) (a) Barluenga, J.; Va´zquez-Villa, H.; Ballesteros, A.; Gonza´lez, J. M.
J. Am. Chem. Soc. 2003, 125, 9028. (b) Asao, N.; Nogami, T.; Takahashi, K.;
Yamamoto, Y. J. Am. Chem. Soc. 2002, 124, 764.
(1) (a) Zhu, S.; Ruchelman, A. L.; Zhou, N.; Liu, A.; Liu, L. F.; LaVoie,
E. J. Bioorg. Med. Chem. 2005, 13, 6782. (b) Mart´ınez, R.; Chaco´n-Garc´ıa, L.
Curr. Med. Chem. 2005, 12, 127. (c) Leonetti, C.; Amodei, S.; D’Angelo, C.;
Rizzo, A.; Benassi, B.; Antonelli, A.; Elli, R.; Stevens, M. F. G.; D’lncalci, M.;
Zupi, G.; Biroccio, A. Mol. Pharmacol. 2004, 66, 1138. (d) Lewis, W. G.; Green,
L. G.; Grynszpan, F.; Radic´, Z.; Carlier, P. R.; Taylor, P.; Finn, M. G.; Sharpless,
K. B. Angew. Chem., Int. Ed. 2002, 41, 1053. (e) Ishikawa, T. Med. Res. ReV.
2001, 21, 61.
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Menggenbateer; Yamamoto, Y. J. Org. Chem. 2005, 70, 3682. (c) Asao, N.;
Nogami, T.; Lee, S.; Yamamoto, Y. J. Am. Chem. Soc. 2003, 125, 10921. (d)
Dyker, G.; Hildebrandt, D.; Liu, J.; Merz, K. Angew. Chem., Int. Ed. 2003, 42,
4399. (e) Asao, N.; Kasahara, T.; Yamamoto, Y. Angew. Chem., Int. Ed. 2003,
42, 3504. (f) Asao, N.; Takahashi, K.; Lee, S.; Kasahara, T.; Yamamoto, Y.
J. Am. Chem. Soc. 2002, 124, 12650.
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9241. (b) Hilt, G.; Hess, W.; Schmidt, F. Eur. J. Org. Chem. 2005, 2526. (c)
Banwell, M. G.; Lupton, D. W.; Ma, X.; Renner, J.; Sydnes, M. O. Org. Lett.
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(6) Very recently, Iwasawa et al. reported the synthesis of naphthalene
derivatives through platinum(II)-catalyzed reaction of 2-alkynylbenzoate with
vinyl ethers. In this report, they believe the [3 + 2]-cycloaddition mechanism is
reasonable at least in platinum(II)-catalyzed benzannulation. (a) Kusama, H.;
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10.1021/jo800474c CCC: $40.75
Published on Web 05/29/2008
2008 American Chemical Society
J. Org. Chem. 2008, 73, 5135–5138 5135

TABLE 2. Lewis Acid Catalyzed Tandem Cyclization of 9 with 10
SCHEME 2. Synthetic Strategy
TABLE 1. Lewis Acid Catalyzed Tandem Cyclizationa
entry
9
10
Lewis acid
time (h)
11
11b
11b
11b
11c
11d
11e
11f
yield (%)a
entry
Lewis acid
yieldb (%)
1
2
3
4
5
6
7
8
9b
9b
9b
9c
9d
9e
9f
9g
9h
9a
9e
9a
10a
10a
10a
10a
10a
10a
10a
10a
10a
10b
10b
10c
In(OTf)3
Sc(OTf)3
Fe(OTf)3
In(OTf)3
In(OTf)3
In(OTf)3
In(OTf)3
In(OTf)3
In(OTf)3
In(OTf)3
In(OTf)3
In(OTf)3
24
24
24
24
24
13
14
24
24
24
22
72
71
69
25
51
73
62
75
0b
1
2
3
4
5
6
7
8
In(OTf)3
InBr3
93c
76
92
84
85
89
92
13
35
0d
Sc(OTf)3
Sm(OTf)3
Yb(OTf)3
Yb(NTf2)3
Fe(OTf)3
AuClPPh3
AgOTf
Cu(OTf)2
Pd(OAc)2
TfOH
s
s
9
0b
30
54
33,24
9
10
11
12
11g
11h
11a, 11i
10
11
12
0d
0
a Isolated yield. b Complex mixture was formed.
a The reaction was carried out in DMF (3 mL) using 9a (1 mmol) and
10a (1 mmol) in the presence of Lewis acid (10 mol %). b Determined
by 1H NMR using 1,4-di-tert-butylbenzene as an internal standard.
c Isolated yield. d Complex mixture was formed.
10a at 80 °C by In(OTf)3 provided 11b in low yield. However,
this problem was resolved by changing the reaction temperature
from 80 to 120 °C (Table 2, entry 1). Sc(OTf)3 and Fe(OTf)3
catalysts also catalyzed this reaction (entries 2 and 3). We
selected In(OTf)3 as a more effective and lower cost catalyst.
The reactions of aldehydes 9c, 9d, 9e, and 9f with amine 10a
also proceeded smoothly to give 11c, 11d, 11e, and 11f (entries
4-7). Reactions of the substrate bearing an electron-withdraw-
ing substituent on the aromatic ring of aldehyde 9 were faster
than that of an analogous substrate containing an electron-
donating substituent (entries 5-7). The reaction of acetophenone
derivatives 9g and 9h with 10a gave only a complex mixture
(entries 8 and 9). From these results, it is clear that aldehyde
function of compound 9 is important for this reaction. Com-
pound 9a with aniline-bearing butyl-substituted alkyne 10b also
provided the desired compound 11g but in low yield (entry 10).
Therefore, we tried the reaction of aldehyde 9e bearing an
electron-withdrawing group on the aromatic ring with amine
10b. The yield of the desired product was moderately but not
greatly improved (entry 11). The reaction with 9a and trimeth-
ylsilylethynylaniline 10c afforded the desired compound 11i
accompanied by desilylated condensed aromatic compound 11a
in 57% total yield (entry 12).
Various ortho-alkynylbenzaldehydes and ortho-alkynylanilines
can be readily synthesized by Sonogashira reaction. In this
report, we describe a new effective indium(III)-catalyzed tandem
reaction with ortho-alkynylbenzaldehydes and ortho-alkynyl-
anilines to produce ring-condensed heteroaromatic compounds.
In the reaction of ortho-alkynylbenzaldehydes and ortho-
alkynylanilines, there was the possibility that the three routes
A, B, and C in Scheme 1 would occur. First, we turned our
attention to the desired domino reaction in the presence of a
metal catalyst. Fortunately, the reaction of 9a with 10a afforded
benzo[i]phenanthridine 11a2g in 93% yield with 10 mol % of
indium triflate, In(OTf)3, in DMF at 80 °C (Table 1, entry 1).
The structure of compound 11a was unambiguously confirmed
by X-ray crystallography.7 In the absence of In(OTf)3 in DMF,
the reaction did not take place at all. The reaction with In(OTf)3
in water gave 11a (10% yield) and toluene (33% yield). Reaction
with InBr3, Sc(OTf)3, Sm(OTf)3, Yb(OTf)3, Yb(NTf2)3, and
Fe(OTf)3 also produced the condensed aromatic product 11a
in good yields (entries 2-7). In contrast to these results,
AuClPPh3 andAgOTf3a,e gave11ainlowyield,andCu(OTf)2
3e,5c,e
and Pd(OAc)2 were ineffective8 to produce desired product
4b
This indium(III)-catalyzed tandem reaction also allows for
the synthesis of benzophenanthroline derivatives 11j and 11k,
naphthophenanthridine derivative 11l, and naphthonaphthyridine
derivative 11m in moderatly high isolated yields.
but complex mixture (entries 8-11). Brønsted acid, TfOH (30
mol %), did not catalyze this tandem cyclization reaction (entry
12).
With these results in hand, we set out to define the scope of
this methodology. A variety of ortho-alkynylbenzaldehydes 9
and ortho-alkynylanilines 10 were investigated. The reaction
of aldehyde bearing phenyl-substituted alkyne 9b with amine
A proposed mechanism for this indium(III)-catalyzed tandem
reaction is shown in Scheme 3. Coordination of the triple bond
of 9 to In(OTf)3 enhances the electrophilicity of alkyne,9 and
the subsequent nucleophilic attack of the carbonyl oxygen
to the electron-deficient alkyne would result in the formation
of the 6-endo-dig-cyclized pyrylium cation intermediate B.4,5
(7) CCDC 658463 contains the supplementary crystallographic data for this
paper. These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc. cam.ac.uk/data_request/cif.
(8) (a) Zhang, D.; Liu, Z.; Yum, E. K.; Larock, R. C. J. Org. Chem. 2007,
72, 251. (b) Joo, J. M.; Yuan, Y.; Lee, C. J. Am. Chem. Soc. 2006, 128, 14818.
(c) Zhao, J.; Hughes, C. O.; Toste, F. D. J. Am. Chem. Soc. 2006, 128, 7436.
(d) Soriano, E.; Marco-Contelles, J. J. Org. Chem. 2005, 70, 9345. (e) Nakamura,
I.; Yamamoto, Y. Chem. ReV 2004, 104, 2127, and references cited therein. (f)
Nakamura, I.; Bajracharya, G. B.; Mizushima, Y.; Yamamoto, Y. Angew. Chem.,
Int. Ed. 2002, 41, 4328.
(9) (a) Miura, K.; Fujisawa, N.; Toyohara, S.; Hosomi, A. Synlett 2006, 1883.
(b) Sakaki, N.; Annaka, K.; Konakahara, T. Tetrahedron Lett. 2006, 47, 631.
(c) Takita, R.; Yakura, K.; Ohshima, T.; Shibasaki, M. J. Am. Chem. Soc. 2005,
127, 13760. (d) Takita, R.; Fukuta, Y.; Tsuji, R.; Ohshima, T.; Shibasaki, M.
Org. Lett. 2005, 7, 1363. (e) Tsuchimoto, T.; Matsubayashi, H.; Kaneko, M.;
Shirakawa, E.; Kawakami, Y. Angew. Chem., Int. Ed. 2005, 44, 1336. (f)
Nakamura, M.; Endo, K.; Nakamura, E. J. Am. Chem. Soc. 2003, 125, 13002.
5136 J. Org. Chem. Vol. 73, No. 13, 2008

FIGURE 1. 1H NMR spectra (DMF-d6, 300 MHz) of the reaction of
9a with 10a: (a) at 50 °C, 30 min; (b) at 50 °C, 2 h; (c) at 80 °C, 2 h;
(d) at 80 °C, 24 h.
12 would be produced through air oxidation of compound F
formed by the reaction of 9a with 10c through route B in
Scheme 1. This supports the formation of intermediate B.
The Diels-Alder-type cycloaddition of B with ortho-alkynyl-
aniline 10 would occur as shown in C to give the intermediate
D with the same high regioselectivity.5c,e,f The subsequent bond
rearrangement would proceed to afford E with regeneration of
In(OTf)3. Dehydration of E would produce ring-condensed
heteroaromatic compound 11. To obtain further information,
1H NMR spectroscopic analysis between 9 and 11 ppm was
performed using the reaction of 9a with 10a in the presence of
10 mol % of In(OTf)3 in DMF-d6. First, the aldehyde proton
signal (δ 10.5) of 9a gradually decreased, and a new aldehyde
proton signal (δ 10.1) of perhaps compound E (R1 ) H) and
an imine proton signal (δ 9.0) of compound 2 (R1 ) R2 ) H)
gradually increased (Figure 1). After 2 h at 50 °C, the CHN
proton signal (δ 10.2) of the desired cyclic product 11a appeared
in the same proton signal region. The imine proton signal
gradually decreased in conjunction with generation of 11a and
water and then disappeared after 2 h at 80 °C. Finally, after
24 h at 80 °C, there was only the CHN proton signal of 11a,
with no signal of starting aldehyde 9a or aldehyde E.
In conclusion, starting from readily available ortho-alkynyl-
anilines and ortho-alkynylbenzaldehydes, we have developed
a new atom-economical In(OTf)3-catalyzed synthesis of ring-
condensed heteroaromatic compounds via a domino intramo-
lecular nucleophilic attack/intermolecular cycloaddition/dehy-
dration reaction. Further studies on the mechanism and to extend
the scope of synthetic utility are in progress.
Experimental Section
General Procedure for Preparation of Compound 11a. In(OTf)3
(56.2 mg, 0.1 mmol) was added to a solution of ethynylbenzalde-
hyde 9a (130 mg, 1 mmol) with ethynylaniline 10a (117 mg, 1
mmol) in DMF (3 mL), and the mixture was stirred for 24 h at 80
°C. DMF was evaporated under reduced pressure. The mixture was
filtered through a plug of Celite and concentrated in vacuo.
Chromatography over silica gel using 20% AcOEt in hexane
afforded the desired benzo[i]phenanthridine 11a (213 mg, 93%)
as yellow plates.
In the reaction of 9a with 10c (Table 2, entry 12), byproduct
12 was obtained in 4% yield (eq 1). It is thought that byproduct
Benzo[i]phenanthridine (11a).2h Yellow plates; mp 181-182
1
°C (from Hex-AcOEt); H NMR (600 MHz, CDCl3) δ ) 10.23
SCHEME 3. Proposed Mechanism
(s, 1H), 8.91 (d, J ) 8.2 Hz, 1H), 8.66 (d, J ) 8.2 Hz, 1H), 8.60
(d, J ) 8.9 Hz, 1H), 8.28 (d, J ) 7.6 Hz, 1H), 8.18 (d, J ) 8.9 Hz,
1H), 8.02 (d, J ) 8.2 Hz, 1H), 7.81 (dd, J ) 8.2, 6.9 Hz, 1H), 7.79
(dd, J ) 8.2, 6.9 Hz, 1H), 7.73 (dd, J ) 8.2, 6.9 Hz, 1H), 7.69 (dd,
J ) 7.6, 6.9 Hz, 1H); 13C NMR (151 MHz, CDCl3) δ ) 147.8,
145.2, 132.1, 132.0, 130.0, 130.0, 128.9, 128.8, 128.1, 127.1, 127.1,
124.3, 122.7, 122.1, 121.7, 119.8; IR (CHCl3, cm-1) 3011, 1502,
1203, 787, 775, 725, 698; MS (EI) m/z ) 229 (M+, 100); HRMS
(EI) m/z calcd for C17H11N 229.0891, found 229.0885.
5-Phenylbenzo[i]phenanthridine (11b). The residue was chro-
matographed on silica gel [AcOEt-hexane (1:10)] to afford 11b
as yellow prisms: mp 142-144 °C (from Hex-AcOEt); 1H NMR
(600 MHz, CDCl3) δ ) 8.66 (d, J ) 8.2 Hz, 2H), 8.28 (d, J ) 7.6
Hz, 1H), 8.17 (d, J ) 8.9 Hz, 1H), 7.94 (d, J ) 7.6 Hz, 1H),
7.85-7.76 (m, 2H), 7.70 (dd, J ) 7.6, 7.6 Hz, 1H), 7.64-7.60 (m,
2H), 7.54s7.46 (m, 4H), 7.21 (dd, J ) 7.9, 7.9 Hz, 1H); 13C NMR
(151 MHz, CDCl3) δ ) 159.3, 144.5, 144.0, 134.3, 133.2, 132.3,
130.2, 129.9, 129.1, 129.0, 128.8, 128.4, 128.4, 128.3, 126.8, 126.4,
125.8, 123.6, 122.4, 121.4, 119.9; IR (CHCl3, cm-1) 3011, 2965,
1611, 1574, 1558, 1468, 1423, 1362, 1350, 1315, 1298, 1240, 1207,
829, 725, 698; MS (EI) m/z ) 305 (M+, 66.8); HRMS (EI) m/z
calcd for C23H15N 305.1204, found 305.1198.
J. Org. Chem. Vol. 73, No. 13, 2008 5137

5-Butylbenzo[i]phenanthridine (11c). The residue was chro-
matographed on silica gel [AcOEt-hexane (1:10)] to afford 11c
1244, 1223, 1207, 839, 740, 704; MS (EI) m/z ) 319 (M+, 79.9);
HRMS (EI) m/z calcd for C24H17N 319.1361, found 319.1358.
2-Fluoro-5-phenylbenzo[i]phenanthridine (11e). The residue
was chromatographed on silica gel [AcOEt-hexane (1:10)] to afford
11e as yellow prisms: mp 149-150 °C; 1H NMR (600 MHz,
CDCl3) δ ) 8.69 (d, J ) 8.9 Hz, 1H), 8.63 (d, J ) 8.2 Hz, 1H),
8.27 (d, J ) 7.6 Hz, 1H), 8.10 (d, J ) 8.9 Hz, 1H), 7.81-7.75 (m,
2H), 7.72 (dd, J ) 8.2, 8.2 Hz, 1H), 7.63-7.59 (m, 2H), 7.55 (dd,
J ) 8.9, 2.7 Hz, 1H), 7.54-7.50 (m, 3H), 6.96 (td, J ) 10.0, 2.8
Hz, 1H); 13C NMR (151 MHz, CDCl3) δ ) 161.4, 159.7, 144.3,
143.9, 134.6, 133.7, 131.5, 131.4, 130.7, 130.6, 130.0, 129.2, 129.1,
128.8, 128.6, 127.0, 123.4, 122.3, 121.4, 121.1, 115.2, 115.1, 112.1,
112.0; IR (CHCl3, cm-1) 3065, 2963, 1620, 1560, 1516, 1495, 1443,
1431, 1356, 1312, 1294, 1267, 1244, 1207, 1144, 1128, 968, 870,
833, 710, 698, 665; MS (EI) m/z ) 323 (M+, 59.5); HRMS (EI)
m/z calcd for C23H14NF 323.1110, found 323.1112.
1
as yellow prisms: mp 83-84 °C; H NMR (600 MHz, CDCl3) δ
) 8.80 (d, J ) 8.2 Hz, 1H), 8.58 (dd, J ) 7.6, 7.6 Hz, 2H), 8.17
(d, J ) 8.2 Hz, 1H), 8.10 (d, J ) 8.9 Hz, 1H), 8.00 (d, J ) 7.6 Hz,
1H), 7.75 (ddd, J ) 7.5, 7.5, 1.4 Hz, 1H), 7.71 (ddd, J ) 7.5, 7.5,
1.4 Hz, 1H), 7.68-7.61 (m, 2H), 3.70 (t, J ) 7.9 Hz, 2H),
2.12-2.04 (m, 2H), 1.57 (sext, J ) 7.6 Hz, 2H), 1.02 (t, J ) 7.6
Hz, 3H); 13C NMR (151 MHz, CDCl3) δ ) 160.8, 143.9, 133.8,
133.2, 131.7, 130.2, 129.0, 128.9, 128.8, 127.1, 126.8, 126.3, 126.1,
123.2, 122.7, 122.5, 120.3, 41.3, 31.3, 23.0, 14.0; IR (CHCl3, cm-1
)
3063, 3009, 2959, 2932, 2872, 1611, 1562, 1514, 1468, 1454, 1422,
1379, 1360, 1348, 1306, 1279, 1242, 1148, 1132, 1101, 864, 827,
665; MS (EI) m/z ) 285 (M+, 45.0); HRMS (EI) m/z calcd for
C21H19N 285.1517, found 285.1513.
3-Methyl-5-phenylbenzo[i]phenanthridine (11d). The residue
was chromatographed on silica gel [AcOEt-hexane (1:10)] to afford
11d as yellow prisms: mp 142-144 °C; 1H NMR (600 MHz,
CDCl3) δ ) 8.64 (d, J ) 8.2 Hz, 1H), 8.58 (d, J ) 8.9 Hz, 1H),
8.27 (d, J ) 8.2 Hz, 1H), 8.12 (d, J ) 8.2 Hz, 1H), 7.82 (d, J )
8.2 Hz, 1H), 7.77 (dd, J ) 7.6, 7.6 Hz, 1H), 7.69 (ddd, J ) 6.9,
6.9, 1.4 Hz, 1H), 7.62s7.59 (m, 2H), 7.53-7.50 (m, 3H), 7.45 (s,
1H), 7.32 (d, J ) 8.2 Hz, 1H), 2.15 (s, 3H); 13C NMR (151 MHz,
CDCl3) δ ) 159.4, 144.6, 144.0, 135.6, 134.4, 132.1, 131.2, 130.3,
129.9, 129.0, 128.9, 128.8, 128.7, 128.4, 128.3, 128.2, 128.1, 126.7,
123.7, 122.5, 121.1, 118.9, 22.0; IR (CHCl3, cm-1) 3063, 3011,
2963, 2924, 1622, 1612, 1572, 1557, 1468, 1445, 1383, 1356, 1310,
Acknowledgment. We thank Associate Prof. I. Suzuki at
Hiroshima University for donation of Sc(OTf)3, Yb(OTf)3, and
Yb(NTf2)3. We are grateful to Dr. M. Nishi at Setsunan
University for obtaining LRMS and HRMS data.
Supporting Information Available: Experimental details and
spectral data for all new compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
JO800474C
5138 J. Org. Chem. Vol. 73, No. 13, 2008