2958
C. Li et al. / Tetrahedron Letters 50 (2009) 2956–2959
Table 3
which is followed by elimination of acetic acid in the presence of
base.
Gold(I)-catalyzed isomerization of cyclopropene derivatives 1a–f
R
In summary, we have reported a highly efficient gold(I)-cata-
lyzed isomerization of cyclopropene to indene. Gold vinyl carbe-
noid is suggested to be the reactive intermediate. Further
exploration of these transformations is under way and will be re-
ported in due course.
AuPPh3Cl (2 mol%)
Ph
Ph
R
AgOTf (2 mol%)
Ph
CH2Cl2, rt, time
Ph
Ph
1a-f
2a-f
Acknowledgments
Entry
1, R
Time
2, Yielda (%)
1
2
3
4
5
6
1a, H
30 min
15 min
40 min
20 min
6 h
2a, 99
2b, 97
2c, 98
2d, 97
2e, 54b
2f, 99
The project is generously supported by Natural Science Founda-
tion of China (Grant Nos. 20832002, 20772003, and 20821062), the
Ministry of Education of China, and National Basic Research Pro-
gram of China (973 Program, No. 2009CB825300).
1b, Me
1c, n-Bu
1d, Ph
1e, PhC„C
1f, PhCH2CH2CH2
30 min
a
Supplementary data
Isolated yield.
An unknown product was isolated together with 2e.
b
Supplementary data associated with this paper can be found, in
References and notes
OAc
1. For recent reviews on cyclopropenes, see: (a) Padwa, A. Acc. Chem. Res. 1979, 12,
310–317; (b) Baird, M. S. Chem. Rev. 2003, 103, 1271–1294; (c) Walsh, R. Chem.
Soc. Rev. 2005, 34, 714–732; (d) Rubin, M.; Rubina, M.; Gevorgyan, V. Synthesis
2006, 1221–1245; (e) Rubin, M.; Rubina, M.; Gevorgyan, V. Chem. Rev. 2007,
107, 3117–3179; (f) Marek, I.; Simaan, S.; Masarwa, A. Angew. Chem., Int. Ed.
2007, 46, 7364–7376.
OAc
Au
A
2. Back, R. D.; Dmitrenko, O. J. Am. Chem. Soc. 2004, 126, 4444–4452.
3. For recent examples, see: (a) Semmelhack, M. F.; Ho, S.; Steigerwald, M.; Lee, M.
C. J. Am. Chem. Soc. 1987, 109, 4397–4399; (b) Semmelhack, M. F.; Ho, S.; Cohen,
D.; Steigerwald, M.; Lee, M. C.; Lee, G.; Gilbert, A. M.; William, D. W.; Ball, R. G. J.
Am. Chem. Soc. 1994, 116, 7108–7122; (c) Ma, M.; Zhang, J. J. Am. Chem. Soc.
2003, 125, 12386–12387; (d) Shao, L.-X.; Zhang, Y.-P.; Qi, M.-H.; Shi, M. Org.
Lett. 2007, 9, 117–120; (e) Chuprakov, S.; Gevorgyan, V. Org. Lett. 2007, 9, 4463–
4466.
6a
OAc
Au
Au
B
4. (a) Padwa, A.; Blacklock, T. J.; Loza, R. J. Am. Chem. Soc. 1981, 103, 2404–2405;
(b) Padwa, A.; Blacklock, T. J.; Loza, R. J. Org. Chem. 1982, 47, 3712–3721; (c)
Cho, S. H.; Liebeskind, L. S. J. Org. Chem. 1987, 52, 2631–2634; (d) Padwa, A.;
Kassir, J. M.; Xu, S. L. J. Org. Chem. 1997, 62, 1642; (e) Müller, P.; Pautex, N.;
Doyle, M. P.; Bagheri, V. Helv. Chim. Acta 1990, 73, 1233–1241; (f) Padwa, A.;
Kassir, J. M.; Xu, S. L. J. Org. Chem. 1991, 56, 6971–6972; (g) Müller, P.;
Gränicher, C. Helv. Chim. Acta 1993, 76, 521–534; (h) Müller, P.; Gränicher, C.
Helv. Chim. Acta 1995, 78, 129–144.
5. For recent reviews, see: (a) Jiménez-Núñez, E.; Echavarren, A. M. Chem.
Commun. 2007, 333–346; (b) Fürstner, A.; Davies, P. W. Angew. Chem., Int. Ed.
2007, 46, 3410–3449; (c) Hashmi, A. S. K. Chem. Rev. 2007, 107, 3180–3211; (d)
Li, Z.; Brouwer, C.; He, C. Chem. Rev. 2008, 108, 3239–3265; (e) Arcadi, A. Chem.
Rev. 2008, 108, 3266–3325; (f) Jiménez-Núñnez, E.; Echavarren, A. M. Chem.
Rev. 2008, 108, 3326–3350; (g) Gorin, D. J.; Sherry, B. B. D.; Toste, F. D. Chem.
Rev. 2008, 108, 3351–3378.
OAc
OAc
OAc
Au
Au
F
C
D
-HOAc
DBU
OAc
Au
5a
6. Zhu, Z.-B.; Shi, M. Chem. Eur. J. 2008, 14, 10219–10222.
E
7. Bauer, J. T.; Hadfield, M. S.; Lee, A.-L. Chem. Commun. 2008, 6405–6407.
8. In the presence of Rh2(pfb)4, the products were (Z)-2,3-diphenylbuta-1,3-
dienyl acetate and (2-phenyl-1H-inden-3-yl)methyl acetate. The selectivity of
the reaction was rather poor.
Scheme 3.
OAc
The scope of the reaction was further demonstrated by the reac-
tion of 1,2,3-triphenylcycloprop-1-ene derivatives 1a–f under the
optimized reaction conditions (Table 3). In most cases, the reaction
afforded the corresponding indene derivatives in high yields. The
only exception was when C3 substituent is alkynyl group, in which
case the reaction took long time and the corresponding indene
product 2e was isolated in only moderate yield (entry 5).
The reaction mechanism is proposed as shown in Scheme 3. The
cationic Au catalyst coordinates with the double bond of cyclopro-
pene, leading to the formation of cyclopropyl cation regioselec-
tively with Au at the less substituted carbon and the cation at
the benzyl position. Subsequent ring-opening results in the forma-
tion of vinyl Au carbene species C and D.10 C and D can equilibrate
through the common resonance structure of Au-attached allylic
cation species E. Direct aromatic C–H insertion by Au carbene D
or Freidel–Crafts-type reaction of carbon cation E gives indene F,
42%
7
+
Rh2(tfa)4
(1 mol%)
OAc
H
H
CH2Cl2
rt, 2h
OAc
H
5e
54%
8
9. Typical experiment procedures: To CH2Cl2 (2 mL) were added AuClPPh3 (3.3 mg,
0.0067 mmol) and AgOTf (1.7 mg, 0.0067 mmol). The resulting mixture was
stirred for 5 min at room temperature. 1,2,3-Triphenyl-3-phenylpropyl
cyclopropene 1f (130 mg, 0.34 mmol), which was dissolved in CH2Cl2 (5 mL),
was then added to the solution. The solution turned to yellow immediately. The
reaction was monitored with TLC. After the substrate was consumed, the