Reactions of iodinated vinylidene complexes generated from 1-Iodo-1-alkynes and W(CO)5(thf)

Article abstract of DOI:10.1021/ja0113091

We have succeeded in generating iodinated tungsten vinylidene complexes from 1-iodo-1-alkynes and W(CO)₅(thf), and have employed these complexes for two types of synthetically useful reactions, that is, 6π-electrocyclization for o-(iodoethynyl)

Full text of DOI:10.1021/ja0113091

Published on Web 01/05/2002
Reactions of Iodinated Vinylidene Complexes Generated from
1-Iodo-1-alkynes and W(CO)5(thf)
Tomoya Miura and Nobuharu Iwasawa*
Department of Chemistry, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, 152-8551
Received May 30, 2001
Scheme 1
In this contribution, we report the first example of the generation
of iodinated vinylidene complexes of pentacarbonyltungsten (0) by
the reaction of 1-iodo-1-alkynes with W(CO)5(thf), and the use of
these complexes in two types of synthetically useful reactions, that
is, the 6π-electrocyclization of o-(iodoethynyl)styrenes and endo-
selective cyclization of ω-iodoacetylenic silyl enol ethers.
Recently transition-metal vinylidene complexes have become the
center of great interest in organic and organometallic chemistry,
due, not only to their facile generation from terminal alkynes, but
also to their unique reactivities.1 Whereas several synthetically
useful reactions utilizing the vinylidene complexes generated from
terminal alkynes have been developed over the past decade,2
reactions of vinylidene complexes derived from alkynes possessing
a labile substituent at the terminus involving 1,2-migration of that
substituent have hardly been studied.3-5
Table 1. Synthesis of Iodo-Substituted Naphthalene Derivatives
We have previously reported several synthetic reactions using
vinylidene complexes of group 6 metals derived from terminal
alkynes, that is, the W(CO)5(thf)-catalyzed endo-selective cycliza-
tion of ω-acetylenic silyl enol ethers,6 and the 6π-electrocyclization
of o-ethynylstyrenes7 and o-ethynylphenyl ketones.8 However, it
is not possible, by these procedures, to introduce a substituent onto
the olefinic part derived from the terminal alkyne. The development
of a method allowing us to manipulate this position effectively is
highly desirable. For this purpose, we decided to examine the
possibility of generating iodinated vinylidene complexes from
1-iodo-1-alkynes using W(CO)5(thf), expecting that cyclizations
similar to those described above could be achieved along with
introduction of an iodine atom into the olefinic part of the products.
To our knowledge, only one example has been reported for the
preparation of iodinated vinylidene complexes from 1-iodo-1-
alkynes using CpMn(CO)2(thf), and no synthetic utility has been
reported for such complexes.5a
First we examined 6π-electrocyclization of o-(iodoethynyl)-
styrenes2h,7 using a stoichiometric amount of W(CO)5(thf). When
1-(iodoethynyl)-2-(1-methylethenyl)benzene 1 was treated with 1.0
M amount of preformed W(CO)5(thf) at room temperature, it was
completely consumed within 4 h and 1-iodo-4-methylnaphthalene
2 was obtained in 95% yield. The position of the iodine atom is
confirmed by the presence of two doublets at δ ) 7.02 and 7.96,
corresponding to the Ha and Hb protons, respectively.9 Furthermore,
this reaction could be carried out successfully even with only a
catalytic amount (as little as 0.1 M amount) of W(CO)5(thf) to give
the same product in good yield. The reaction is thought to proceed
as follows: treatment of 1 with W(CO)5(thf) would give an alkyne-
W(CO)5 π-complex, which gradually isomerizes to the iodinated
vinylidene intermediate A via 1,2-migration of the iodo group; then
6π-electrocyclization occurs forming the carbene intermediate B,
which affords the iodo-substituted naphthalene by 1,2-hydrogen
migration with regeneration of W(CO)5(thf) (Scheme 1).9,10
The scope of the reaction is summarized in Table 1. Not only
iodo-substituted aromatic enynes 3-6 but also the nonaromatic
a 0.1 M amount of W(CO)5(thf) was used. b 0.2 M amount of W(CO)5(thf)
was used.
dienyne derivative 7 were cyclized to afford the corresponding iodo-
substituted naphthalene and benzene derivatives 8-12. Use of a
stoichiometric amount of W(CO)5(thf) generally gives the product
in good yield, while the yield of the catalytic reaction varies
depending on the structure and the substituents of the substrate. In
particular, the difference in reactivity between R-siloxy derivative
4 and R-methoxycarbonyl derivative 5 suggests that this cyclization
proceeds smoothly when the electron density at the â-position of
the olefin is high.11
We next studied intramolecular nucleophilic attack of a silyl enol
ether onto the iodinated vinylidene complex.6 When an ω-io-
doacetylenic silyl enol ether 13 was treated with a 1.0 M amount
of W(CO)5(thf) in the presence of 3.0 M amounts of H2O, the
reaction again proceeded smoothly at room temperature to give an
iodo-substituted cyclopentene derivative 14 in 65% yield. The
position of iodine atom, confirmed by an NOE experiment, supports
the hypothesis that this reaction also proceeds through the iodinated
vinylidene complex D. The carbene carbon of the complex is
expected to be highly electrophilic, and thus nucleophilic attack of
the silyl enol ether occurs here to give the vinylmetallic species E,
which is protonated by H2O to give the corresponding iodo-
substituted â,γ-unsaturated ketone 14 (Scheme 2). Reactions of
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518 VOL. 124, NO. 4, 2002 J. AM. CHEM. SOC.
10.1021/ja0113091 CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
Scheme 2
making them very versatile substrates for further coupling reactions.
Further studies to expand the synthetic utility of iodinated vinylidene
complexes are in progress in our laboratory.
Acknowledgment. This research was partly supported by the
Toray Science Foundation and a Grant-in-Aid for Scientific
Research from the Ministry of Education, Science, Sports and
Culture of Japan. We also thank Central Glass Co., Ltd. for generous
gift of trifluoromethanesulfonic acid. T.M. has been granted a
Research Fellowship of the Japan Society for the Promotion of
Science for Young Scientists.
Supporting Information Available: Preparative methods and
spectral and analytical data of compounds 1-33 (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
Table 2. Cyclization of ω-Iodoacetylenic Silyl Enol Ethers Using a
Stoichiometric Amount of W(CO)5(thf)
References
(1) For a review on vinylidene complexes, see: (a) Bruneau, C.; Dixneuf, P.
H. Acc. Chem. Res. 1999, 32, 311. (b) Bruce, M. I. Chem. ReV. 1991, 91,
197. (c) Bruce, M. I.; Swincer, A. G. AdV. Organomet. Chem. 1983, 22,
59.
(2) For recent synthetic use of vinylidene complexes, see: (a) Ohmura, T.;
Yamamoto, Y.; Miyaura, N. J. Am. Chem. Soc. 2000, 122, 4990. (b)
McDonald, F. E.; Reddy, K. S.; D´ıaz, Y. J. Am. Chem. Soc. 2000, 122,
4304. (c) Trost, B. M.; Rhee, Y. H. J. Am. Chem. Soc. 1999, 121, 11680.
(d) McDonald, F. E. Chem. Eur. J. 1999, 5, 3103. (e) Tokunaga, M.;
Wakatsuki, Y. Angew. Chem., Int. Ed. 1998, 37, 2867. (f) Bruneau, C.;
Dixneuf, P. H. J. Chem. Soc., Chem. Commun. 1997, 507. (g) Ohe, K.;
Kojima, M.; Yonehara, K.; Uemura, S. Angew. Chem., Int. Ed. Engl. 1996,
35, 1823. (h) Merlic, C. A.; Pauly, M. E. J. Am. Chem. Soc. 1996, 118,
11319. (i) Trost, B. M. Chem. Ber. 1996, 129, 1313. (j) Wang, Y.; Finn,
M. G. J. Am. Chem. Soc. 1995, 117, 8045.
(3) For examples of migration of a trialkylsilyl group, see: (a) Katayama,
H.; Onitsuka, K.; Ozawa, F. Organometallics 1996, 15, 4642. (b) Naka,
A.; Okazaki, S.; Hayashi, M.; Ishikawa, M. J. Organomet. Chem. 1995,
499, 35. (c) Connelly, N. G.; Geiger, W. E.; Lagunas, M. C.; Metz, B.;
Rieger, A. L.; Rieger, P. H.; Shaw, M. J. J. Am. Chem. Soc. 1995, 117,
12202. (d) Sakurai, H.; Fujii, T.; Sakamoto, K.; Chem. Lett. 1992, 339.
(e) Werner, H.; Schneider, D. Angew. Chem., Int. Ed. Engl. 1991, 30,
700.
a 18 was a 3:2 mixture of E and Z isomers. b 22 was a 1:2 mixture of
syn and anti isomers.
(4) For example of migration of alkylthio group, see: Miller, D. C.; Angelici,
R. J. Organometallics 1991, 10, 79.
(5) For example of migration of the iodo group, see: (a) Lo¨we, C.; Hund,
H.-U.; Berke, H. J. Organomet. Chem. 1989, 371, 311. For iodinated
dinuclear vinylidene complexes, see: (b) Bruce, M. I. Koutsantonis, G.
A.; Liddell, M. J.; Nicholson, B. K. J. Organomet. Chem. 1987, 320,
217. (c) Horva´th, I. T.; Pa´lyi, G.; Marko´, L. J. Chem. Soc., Chem.
Commun. 1979, 1054.
Scheme 3
(6) Maeyama, K.; Iwasawa, N. J. Am. Chem. Soc. 1998, 120, 1928.
(7) Maeyama, K.; Iwasawa, N. J. Org. Chem. 1999, 64, 1344.
(8) (a) Iwasawa, N.; Shido, M.; Maeyama, K.; Kusama, H J. Am. Chem. Soc.
2000, 122, 10226. See also: (b) Ohe, K.; Miki, K.; Yokoi, T.; Nishino,
F.; Uemura, S. Organometallics 2000, 19, 5525.
(9) The signals corresponding to Ha and Hb were confirmed by the following
deuterium experiment. When 1 deuterated at both positions of the alkene
terminus was treated with W(CO)5(thf), the two doublets at δ ) 7.02 and
7.96 in the 1H NMR spectra of the product 2 completely disappeared.
This result also supports that 1,2-hydrogen migration occurs from the
carbene intermediate B to give the product.
(10) We monitored the reaction of 1 with W(CO)5(thf)-d8 by NMR in THF-
d8. During the course of the reaction, only the starting material and the
cyclized product were observed and none of the possible intermediates
could be detected.
(11) The reaction time necessary for consumption of the starting material under
the stoichiometric conditions was 1 h for 4 and 2 h for 5. The reaction of
5 with 0.2 M amount of W(CO)5(thf) gave a substantial amount of
polymerization products judging from the presence of broadened peaks
in the 1H NMR spectrum of the crude product.
(12) On the basis of deuterium exchange experiments we have previously
proposed that for the similar reaction of terminal alkynes the cyclization
takes place through both π-alkyne complexes (like C) and vinylidene
complexes (like D).6 In contrast, it is noted that this reaction for 1-iodo-
1-alkynes occurs through the vinylidene complexes alone.
(13) For other recent examples of nucleophilic endo-selective cyclization onto
alkynes, see: (a) Kim, K.; Okamoto, S.; Sato, F. Org. Lett. 2001, 3, 67.
(b) Imamura, K.; Yoshikawa, E.; Gevorgyan, V.; Yamamoto, Y. Tertra-
hedron Lett. 1999, 40, 4081. (c) Imamura, K.; Yoshikawa, E.; Gevorgyan,
V.; Yamamoto, Y. J. Am. Chem. Soc. 1998, 120, 5339.
(14) Under the catalytic conditions, complex mixtures of products including
the product starting material hydrolysis were obtained.
(15) Crabtree, R. H.; Habib, A. In ComprehensiVe Organic Synthesis; Trost,
B. M., Ed.; Pergamon Press: Oxford, 1991; Vol. 7, Chapter 1.1.
(16) It is noteworthy that the iodo-substituted products are easily oxidized by
molecular oxygen, as the corresponding hydrogen-substituted products
are air-stable for a longer period of time.
some representative substrates are summarized in Table 2. In every
case, the reaction proceeds readily at room temperature to give the
iodo-substituted â,γ-unsaturated ketone, the endo-cyclized product,
in good yield without formation of the alternative iodine positional
isomer.12,13 Although one would expect that the reaction should
proceed with only a catalytic amount of W(CO)5(thf), in fact these
conditions gave only a poor yield of the product.14
We also found that these cyclized products were gradually
oxidized by air to provide R,â-unsaturated diketones in good yield.
For example, when the bicyclic compound 20 was kept in an open
vessel without solvent for 1 week at room temperature, the diketone
derivative 23 was obtained in 76% yield. Under similar conditions
the monocyclic compound 22 was also transformed to the corre-
sponding product 24 in 82% yield. We assume that this reaction
proceeds through allylic oxidation by molecular oxygen to give an
R,â-unsaturated γ-peroxy ketone as the initial product, which is
converted to the enedione.15,16
In conclusion, we have succeeded in generating iodinated
tungsten vinylidene complexes from 1-iodo-1-alkynes, and have
employed these complexes in two types of synthetically useful
reaction. The iodine is retained in the products of these reactions,
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