tion was reported by Trost, who used Pd(II), palladacycles,
as the catalyst.4a When enynes bearing an ester group on
the acetylenic carbon and a cis substituent on the terminal
olefinic carbon were used, type I products were selectively
formed. In the case of a terminal alkyne entity, a mixture of
types I and II was obtained. We subsequently found that
even more practical and simple metal halides, such as [RuCl2-
(CO)2]2, show a high catalytic activity for the skeletal
reorganization of enynes having a terminal acetylenic moiety
leading to type I products.3a Since this report, various metal
halides or cation complexes have been used in the skeletal
reorganization. Substrates applicable to the skeletal reorga-
nization depend on the nature of catalysts. Enynes having
an alkyl or phenyl group on the acetylenic carbon can be
used only with Pt complexes. The Pt-catalyzed reaction of
enynes bearing a substituent, such as methyl or phenyl, on
the acetylenic carbon gave type I product as a main product,
and the substitution of an ester group gave type II product
selectively.6b Several mechanisms have been proposed,
including a nonstabilized carbene mechanism and a nonclas-
sical carbocation mechanism,5 and various types of new
cycloisomerization reactions have been explored on the basis
of these reaction mechanisms. Proposed carbene intermedi-
ates were trapped by intramolecular olefins.4l,n,6 The skeletal
reorganization of enynes was extended to the cycloisomer-
ization of yne-benzenes.7 Other new types of reactions which
are initiated by electrophilic interaction of metal halides with
alkynes have recently been studied mostly with PtCl2 or
AuCl3.8 The driving force for the catalysis is the high
electrophilic affinity of the metal complexes toward an
acetylene moiety. InCl3 has recently been reported to have
a high affinity toward acetylenic bonds.9 This prompted us
to examine its use as a catalyst in the cycloisomerization
reactions of enynes. We wish to report here on an unusual
type of skeletal reorganization of enynes catalyzed by InCl3.
In an initial investigation, it was found that InCl3 can also
be used to effect skeletal reorganization. Treatment of 1 with
InCl3 (10 mol %) in toluene at 80 °C resulted in a skeletal
reorganization to give 1-vinylcyclopentene 2 along with a
six-membered cycloisomerization product 3 (eq 2).
The reactions of some 1,6- and 1,7-enynes with terminal
acetylenic moieties were next examined (eqs 3-9).10 The
reaction proceeded smoothly to afford the expected skeletal
reorganization products in good to high yields.3,4 In the case
of 1,6-enynes, six-membered cycloisomerization products
were also formed.11 On the other hand, no corresponding
seven-membered cycloisomerization products were formed
in the case of 1,7-enynes (eqs 8 and 9). The reaction of
enynes containing a mono-substituent at the olefinic carbon
was found to proceed in a stereospecific manner with respect
to the geometry of the olefin moiety (eqs 4, 5, 8, and 9).
(3) (a) Ru(II): Chatani, N.; Morimoto, T.; Muto, T.; Murai, S. J. Am.
Chem. Soc. 1994, 116, 6049-6050. (b) Pt(II): Chatani, N.; Furukawa, N.;
Sakurai, H.; Murai, S. Organometallics 1996, 15, 901-903. (c) Ir(I):
Chatani, N.; Inoue, H.; Morimoto, T.; Muto, T.; Murai, S. J. Org. Chem.
2001, 66, 4433-4436. (d) Ga(III): Chatani, N.; Inoue, H.; Kotsuma, T.;
Murai, S. J. Am. Chem. Soc. 2002, 124, 10294-10295.
(4) Pd: (a) Trost, B. M.; Tanoury, G. J. J. Am. Chem. Soc. 1988, 110,
1636-1638. (b) Trost, B. M.; Trost, M. K. J. Am. Chem. Soc. 1991, 113,
1850-1852. Pt: (c) Trost, B. M.; Chang, V. K. Synthesis 1993, 824-832.
(d) Fu¨rstner, A.; Szillat, H.; Gabor, B.; Mynott, R. J. Am. Chem. Soc. 1998,
120, 8305-8314. (e) Trost, B. M.; Doherty, G. A. J. Am. Chem. Soc. 2000,
122, 3801-3810. (f) Fu¨rstner, A.; Szillat, H.; Stelzer, F. J. Am. Chem. Soc.
2000, 122, 6785-6786. (g) Fu¨rstner, A.; Stelzer, F.; Szillat, H. J. Am. Chem.
Soc. 2001, 123, 11863-11869. (h) Oi, S.; Tsukamoto, I.; Miyano, S.; Inoue,
Y. Organometallics 2001, 20, 3704-3709. (i) Oh, C. H.; Bang, S. Y.; Rhim,
C. Y. Bull. Korean Chem. Soc. 2003, 24, 887. (j) Mamane, V.; Gress, T.;
Krause, H.; Fu¨rstner, A. J. Am. Chem. Soc. 2004, 126, 8654-8655. (k)
Bajracharya, G. B.; Nakamura, I.; Yamamoto, Y. J. Org. Chem. 2005, 70,
892-897. Au: (l) Nieto-Oberhuber, C.; Mun˜oz, M. P.; Bunuel, E.; Nevado,
C.; Ca´rdenas, D. J.; Echavarren, A. M. Angew. Chem., Int. Ed. 2004, 43,
2402-2406. (m) Me´zailles, N.; Ricard, L.; Gagosz, F. Org. Lett. 2005, 7,
4133-4136. (n) Nieto-Oberhuber, C.; Mun˜oz, M. P.; Lo´pez, S.; Jime´nez-
Nu´n˜ez, E.; Nevado, C.; Herrero-Go´mez, E.; Raducan, M.; Echavarren, A.
M. Chem. Eur. J. 2006, 12, 1677-1693. Ru: (o) Madhushaw, R. J.; Lo,
C.-Y.; Hwang, C.-W.; Su, M.-D.; Shen, H.-C.; Pal, S.; Shaikh, I. R.; Liu,
R.-S. J. Am. Chem. Soc. 2004, 126, 15560-15565.
(5) (a) Echavarren, A. M.; Nevado, C. Chem. Soc. ReV. 2004, 33, 431-
436. (b) Soriano, E.; Ballesteros, P.; Marco-Contelles, J. Organometallics
2005, 24, 3172-3181. (c) Nieto-Oberhuber, C.; Lo´pez, S.; Mun˜oz, M. P.;
Ca´rdenas, D. J.; Bun˜uel, E.; Nevado, C.; Echavarren, A. M. Angew. Chem.,
Int. Ed. 2005, 44, 6146. (d) Soriano, E.; Marco-Contelles, J. J. Org. Chem.
2005, 70, 9345-9353. See also refs 3d and 4f.
Surprisingly, an unusual type of product was obtained
when enynes containing an alkyl group on the acetylenic
carbon were employed. The reaction of ethyl-substituted
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Org. Lett., Vol. 8, No. 10, 2006