carbocycles or heterocycles of various ring sizes. The easily
accessible starting materials, simple reaction procedure and mild
conditions make this method attractive for the production of
common- and medium-sized rings.
Table 1 PtCl2-catalyzed cyclization of bis-alkynes
Entry Substrate Reaction time/h Product Ring size Yield (%)
1
2
3
4
5
6
a
1a
1b
1c
1d
1e
1f
3
3
3
12
24
24
2a
2b
2c
2d
2e
2f
6
7
7
8
9
15
67a
89
95
80
13
,5b
We gratefully acknowledge financial support from Fonds der
Chemischen Industrie and the Deutsche Forschungsgemeinschaft
(DFG project DY 12/7-2).
b
0.2 mmol scale. Slightly impure, not fully characterized.
Notes and references
1 (a) G. Illuminati and L. Mandoline, Acc. Chem. Res., 1981, 14, 95–102;
(b) G. A. Molander, Acc. Chem. Res., 1998, 31, 603–609.
2 (a) G. Dyker, D. Hildebrandt, J. Liu and K. Merz, Angew. Chem., 2003,
115, 4536–4538, Angew. Chem., Int. Ed., 2003, 42, 4399–4002; (b)
D. Kadzimirsz, D. Hildebrandt, K. Merz and G. Dyker, Chem.
Commun., 2006, 661–662; (c) G. Dyker and D. Hildebrandt, J. Org.
Chem., 2005, 70, 6093–6096.
3 (a) N. Asao, K. Sato, Menggenbateer and Y. Yamamoto, J. Org.
Chem., 2005, 70, 3682–3685; (b) K. Sato, N. Asao and Y. Yamamoto,
J. Org. Chem., 2005, 70, 8977–8981; (c) N. Kim, Y. Kim, W. Park,
D. Sung, A. K. Gupta and C. H. Oh, Org. Lett., 2005, 7, 5289–5291.
4 For reviews on gold catalysis, see: (a) G. Dyker, Angew. Chem., 2000,
112, 4407–4409, Angew. Chem., Int. Ed., 2000, 39, 4237–4239; (b)
A. S. K. Hashmi, Gold Bull., 2004, 37, 51–65; (c) A. Hoffmann-Ro¨der
and N. Krause, Org. Biomol. Chem., 2005, 3, 387–391. Current
examples of Pt(II) catalysis: (d) H. Kusawa, Y. Miyashita, J. Takaya
and N. Iwasawa, Org. Lett., 2006, 8, 289–292; (e) C. Y. Lo,
M. P. Kumar, H.-K. Chang, S.-F. Lush and R.-S. Liu, J. Org.
Chem., 2005, 70, 10482–10487; (f) E. Soriano and J. Marco-Contelles,
J. Org. Chem., 2005, 70, 9345–9353; (g) A. Fu¨rstner and P. W. Davies,
J. Am. Chem. Soc., 2005, 127, 15024–15025; (h) I. Nakamura,
Y. Mizushima and Y. Yamamoto, J. Am. Chem. Soc., 2005, 127,
15022–15023; (i) C. Nevado and A. M. Echavarren, Chem.–Eur. J.,
2005, 11, 3155–3164; (j) M. P. Mun˜oz, J. Adrio, J. C. Carretero and
A. M. Echavarren, Organometallics, 2005, 24, 1293–1300; (k)
G. B. Bajracharya, I. Nakamura and Y. Yamamoto, J. Org. Chem.,
2005, 70, 892–897; (l) E. Soriano and J. Marco-Contelles, Chem.–Eur. J.,
2005, 11, 521–533.
5 The bis-alkynes are commercially available, except for 1,15-hexadeca-
diyne, which was prepared according to the literature: B. Hellbach,
R. Gleiter and F. Rominger, Synthesis, 2003, 2535–2541.
6 (a) K. Sonogashira, Y. Tohda and N. Hagihara, Tetrahedron Lett.,
1975, 50, 4467–4470; (b) K. R. Roesch and R. C. Larock, J. Org. Chem.,
2002, 67, 86–94.
7 T. H. Chan, M. A. Brook and T. Chaly, Synthesis, 1983, 203–205.
8 B. C. Bales, J. H. Horner, X. Huang, M. Newcomb, D. Crich and
M. M. Greenberg, J. Am. Chem. Soc., 2001, 123, 3623–3629.
9 P. A. Grieco, Y. Yokoyama, G. O. Withers, F. J. Okuniewicz and
C.-L. J. Wang, J. Org. Chem., 1978, 43, 4178–4182.
Scheme 3 Plausible mechanism for annulation reaction.
addition, the yield of annulation product 2e dropped to only 13%,
indicating a limitation of this process. Since the ring strain of
carbocycles generally reaches its maximum in nine-membered
rings, we hoped for higher yields in the cases of macrocycles.
However, an attempt to produce a 15-membered ring from
substrate 1f resulted in a very low yield (Table 1, entry 6).
For comparison, we also tried AuCl3 (5 mol%, 80 uC in
acetonitrile) as a catalyst for the annulation reaction. With 1a and
1e as substrates, we achieved yields of less than 10%, confirming
that PtCl2 is superior.
10 S. Sen, S. Roach, J. Boggs, G. Ewing and J. Magrath, J. Org. Chem.,
1997, 62, 6684–6886.
A plausible mechanism for the platinum(II)-catalyzed annula-
tion reaction is depicted in Scheme 3. The double annulation
process most probably proceeds through the benzopyrylium cation
I, which results from the nucleophilic attack of the carbonyl
oxygen at the alkyne, activated by the Lewis-acidic platinum salt.
A subsequent intramolecular Huisgen-type [3 + 2] cycloaddition of
the second alkyne is assumed to generate intermediate II.13
Rearrangement to III and the formal [4 + 2] cycloaddition product
IV leads to the aromatized final 2b, liberating the active catalyst, in
analogy to the calculations of Straub.13 In the case of FeCl3 as the
Lewis acid, we assume that intermediate II is oxidatively
transformed to 6b.14
11 Crystal data for 6b: C14H12O3, M = 228.24, monoclinic, space group
P21/n, a = 10.592(4), b = 6.912(6), c = 15.076(8) s, b = 94.25(3)u, V =
1100.6(11) s3, Z = 4, T = 100(2) K, m = 0.097 mm21, 8305/1991/1603
reflections collected/unique/observed, Rint = 0.0435, R1 = 0.0521, wR2
(all data) = 0.1172, 154 parameters. All non-hydrogen atoms calculated
anisotropic; positions of the H atoms calculated for idealised positions.
The structure was solved and refined using SHELXTL-97:
G. M. Sheldrick, SHELXTL-97, Program for the solution and refinement
of crystal structures, Universita¨t Go¨ttingen, Germany, 1997. CCDC
299431. For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b602498j.
12 A. K. Gupta, C. Y. Rhim, C. H. Oh, R. S. Mane and S.-H. Han, Green
Chem., 2006, 8, 25–28.
13 For a related Huisgen-type [3 + 2] cycloaddition, which was calculated
by a DFT study, see: B. F. Straub, Chem. Commun., 2004, 1726–1728.
14 A. G. M. Barrett, J. Mortier, M. Sabat and M. A. Sturgess,
Organometallics, 1988, 7, 2553–2561.
The platinum-catalyzed intramolecular domino annulation
reaction of ortho-alkynyl benzaldehydes described herein repre-
sents a versatile approach to naphthalenes with annulated
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