C O M M U N I C A T I O N S
Table 2. One-pot Construction of Polycyclic Framework Catalyzed
by Gold(l) Species
the second allylic cation E, and ultimately produces the observed
oxacyclic product 19 through an intramolecular alkenation reaction.
For intermediate E′ given from allylsilane nucleophile, the alkena-
tion preferably occurs at the remote allylic carbon to give the
observed compound 16.10
In summary, AuPPh3SbF6 efficiently catalyzes11 the cyclization
of cis-2,4-dien-1-als with two nucleophiles at room temperature,
which leads to a 1,4-double addition to the newly formed cyclo-
pentene ring. The use of this cyclization is reflected not only by
its compatibility with a wide scope of nucleophiles, but also by a
facile construction of complex frameworks in diversified annulation
approaches. Studies toward the synthesis of bioactive molecules
are in progress.
Acknowledgment. The authors wish to thank the National
Science Council, Taiwan, for supporting this work.
Supporting Information Available: Catalyst screening (Table S1
and S2), cyclization of aldehydes 1-3 and s6 with nucleophiles (Table
S3), spectral data, and NMR spectra of compounds 1-38 and s4-5.
This material is available free of charge via the Internet at http://
pubs.acs.org.
References
(1) For metal-catalyzed cyclizations with the addition of water or alcohols,
see selected examples: (a) Trost, B. M.; Rudd, M. T. J. Am. Chem. Soc.
2003, 125, 11516. (b) Trost, B. M.; Brown, R. E.; Toste, F. D. J. Am.
Chem. Soc. 2000, 122, 5877. (c) Nieto-Oberhuber, C.; Munoz, M. P.;
Lopez, S.; Jimenez-Nunez, E.; Nevado, C; Herrero-Gomez, E.; Raducan,
M.; Echavarren, A. M. Chem.sEur. J. 2006, 12, 1677. (d) Yao, T.; Zhang,
X.; Larock, R. C. J. Am. Chem. Soc. 2004, 126, 11164. (e) Odedra, A.;
Wu, C.-J.; Pratap, T. B.; Huang, C.-W.; Ran, Y. F.; Liu, R.-S. J. Am.
Chem. Soc. 2005, 127, 3406.
a Nucleophile (1.1 equiv), CH2Cl2, 20 °C, 1 h, 4 mol % ClAuPPh3/
AgSbF6. b Products were purified from a silica column. c Species 15 and
16 were isolated in 17% and 14% yields, respectively.
Scheme 2
(2) For metal-catalyzed cyclization with addition of carbon nucleophiles, see
selected examples: (a) Shintani, R.; Okamoto, K.; Otomaru, Y.; Ueyama,
K.; Hayashi, T. J. Am. Chem. Soc. 2005, 127, 54. (b) Miura, T.; Shimada,
M.; Murakami, M. J. Am. Chem. Soc. 2005, 127, 1094. (c) Cauble, D. F.;
Gipson, J. D.; Krische, M. J. J. Am. Chem. Soc. 2003, 125, 1110. (d)
Lautens, M.; Mancuso, J. J. Org. Chem. 2004, 69, 3478.
(3) Okamura, W. H.; De Lera, A. R. ComprehensiVe Organic Synthesis; Trost,
B. M., Ed.; Pergamon: Oxford, 1991; Vol. 5, 699.
(4) (a) Miller, A. K.; Banghart, M. R.; Beaudry, C. M.; Suh, J. M.; Trauner,
D. Tetrahedron, 2003, 59, 8919. (b) Lo, C.-Y.; Lin, C.-C.; Cheng, H.-
M.; Liu, R.-S. Org. Lett. 2006, 8, 3153. (c) Kundu, K.; McCullagh, J. V.;
Morehead, A. T., Jr. J. Am. Chem. Soc. 2005, 127, 16042.
(5) Selected examples for PPh3Au+-catalysis: (a) Zhang, L.; Sun, S.; Kozmin,
S. A. AdV. Synth. Catal. 2006, 348, 2271. (b) Nieto-Oberhuber, C.; Mun˜oz,
M. P.; Bun˜uel, E.; Nevado, C.; Ca´rdenas, D. J.; Echavarren, A. M. Angew.
Chem., Int. Ed. 2004, 43, 2402. (c) Wang, S.; Zhang, L. J. Am. Chem.
Soc. 2006, 128, 14274. (d) Luzung, M. R.; Markham, J. P.; Toste, F. D.
J. Am. Chem. Soc. 2004, 126, 10858. (e) Brouwer, C.; He, C. Angew.
Chem., Int. Ed. 2006, 45, 1744. (f) Lian, J.-J.; Chen, P.-C.; Lin, Y.-P.;
Liu, R.-S. J. Am. Chem. Soc. 2006, 128, 11372.
alcohol, giving desired oxacyclic compounds 28A and 28B in 65%
and 16% yields, respectively. The same cyclization of cis-2,4-dien-
1-al 29 (0.50 M) with 3-buten-1-ol (3 equiv) gave cyclopentene
product 30 in 75%, and its subsequent metathesis reaction (25 °C
in CH2Cl2, 8 h) provided oxacyclic compound 31 in 88% yield.
(6) The screening of these acid catalysts were performed with allylsilane and
MeOH; the results were provided in Tables S1 and S2, respectively (see
Supporting Information).
(7) Table S3 shows additional products 32-38 given from the cyclization of
these nucleophiles with aldehydes 1-3 and acyclic aldehyde s6.
(8) The structures of oxacyclic compounds 19 and 21 were deduced by 1H
NOE, HMBC, and HMQC, respectively. These spectra are provided in
Supporting Information.
(9) In a separate experiment, treatment of 1,4-bis(phenoxy)cyclopentene 7
with AuPPh3SbF6 (5 mol%) in dilute CH2Cl2 (0.01 M, 25 °C, 6 h) provided
oxacyclic compound 20 in 91% yield. This information suggests that
formation of 20 is probably caused by rearrangement of kinetically favored
product F according to the mechanism below.
Scheme 2 shows a working mechanism to rationalize the catalytic
chemoselectivity, which reveals that PPh3Au+ activates the ene-
aldehyde coupling of species 2 to generate an allylic cation B.
Addition of 3-methyl-2-buten-1-ol to species B proceeds through
an oxygen-attack opposite the n-butyl substituent, giving O-linked
alloxy species C and releasing a proton. We proposed that this free
proton cleaves the C-OAu bond of species C to regenerate an
allylic alcohol D, which undergoes H+-assisted ionization to form
(10) The mechanistic discussion with the cyclization of aldehyde 2 with two
allysilane molecules is provided in Supporting Information.
(11) The 31P NMR signal of AuPPh3SbF6 appeared at δ 30.7 in CDCl3, which
was shifted completely to δ 44.9 upon the addition of cis-dienal 3 (10
equiv); this information supports that this cationic gold species can bind
to aldehyde to initiate the catalytic cyclization.
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