Reactions of propargyl metallic species generated by the addition of alkynyllithiums to Fischer-type carbene complexes

Full text of DOI:10.1021/ja962173n

1486
J. Am. Chem. Soc. 1997, 119, 1486-1487
Scheme 1
Reactions of Propargyl Metallic Species Generated
by the Addition of Alkynyllithiums to Fischer-Type
Carbene Complexes
Nobuharu Iwasawa,* Katsuya Maeyama, and
Masatoshi Saitou
Department of Chemistry, Graduate School of Science
The UniVersity of Tokyo
Hongo, Bunkyo-ku, Tokyo 113, Japan
ReceiVed June 27, 1996
The 1,2-addition reaction of highly nucleophilic organome-
tallics such as alkyllithiums or Grignard reagents to Fischer-
type carbene complexes would produce carbon-elongated group
6 organometallic intermediates, which could be employed for
further manipulations.1 However, most such reactions reported
so far have been confined to additions to phenyl-substituted
carbene complexes, and the addition intermediates have not been
employed for further carbon-carbon bond formation.2 Fur-
thermore, carbene complexes having a primary or secondary
alkyl substituent on the carbene carbon have never been
successfully employed in this type of reaction, because depro-
tonation of the R-proton has taken place preferentially.3 In this
paper we would like to report that a new type of propargyl
metallic species is generated by the addition reaction of
alkynyllithiums to Fischer-type carbene complexes including
those having R-hydrogens, and that these species can be
employed for several useful carbon-carbon bond-forming
reactions.4
When phenylethynyllithium was added to pentacarbonyl[1-
methoxy-2-methyl-1-propylidene]tungsten(0) (1a; R1 ) i-Pr) at
-78 °C in THF, a smooth addition reaction to the carbene
complex 1a was observed, and the complete consumption of
1a indicated that deprotonation of R-proton did not occur under
these conditions. Furthermore, neutral aqueous workup with
pH 7 phosphate buffer at -78 °C followed by mild acid
treatment gave the R,â-unsaturated ketone 2a (R1 ) i-Pr, R2 )
Ph) in 86% yield,5 while acidic workup such as quenching with
2 M HCl or CF3COOH at -78 °C gave the enyne 3a (R2 )
Ph, R′ ) R′′ ) Me) with no detectable formation of 2a.
The difference in reaction pathway depending on the quench-
ing conditions can be explained as follows: The addition
reaction of phenylethynyllithium to 1a occurs at -78 °C to give
the addition intermediate 4a. When strong acid is added to 4a,
elimination of methanol occurs to produce an unstable carbene
Table 1. The Addition Reactions of Alkynyllithiums to Tungsten
Carbene Complexes
conditions Aa,b
(yield of 2/%)
conditions Ba
(yield of 3/%)
R1
R2
Ph
n-Hex
Ph
n-Hex
Ph
n-Hex
i-Pr (1a)
i-Pr
n-Bu (1b)
n-Bu
Ph (1c)
Ph
86 (2a)
80
79
51
97
85 (R′ ) R′′ ) Me) (3a)
59 (R′ ) R′′ ) Me)
68 (R′ ) n-Pr, R′′ ) H)c
34 (R′ ) n-Pr, R′′ ) H)c
d
d
78 (2c)
a Conditions A: The reaction is quenched with pH 7 buffer at -78
°C and then 2 M HCl is added to hydrolyze the vinyl ether completely.
Conditions B: The reaction is quenched with 2 M HCl or CF3COOH
at -78 °C. b Obtained as a mixture of (E) and (Z) isomers. c (Z)-Enynes
were obtained in about 10:1 ratio in these cases. d Enones 2 were
obtained as major products.
intermediate 6a, which gives the enyne 3a by 1,2-hydrogen
migration. On the other hand, when the reaction is quenched
with pH 7 buffer, the addition intermediate 4a behaves like a
propargyl metallic species to give, on γ-protonation, a methyl
1,2-propadienyl ether 5a, which is hydrolyzed to give enone
2a.6 The results of the reaction of various tungsten carbene
complexes and alkynyllithiums are summarized in Table 1. Even
in the reactions of the primary alkyl-substituted carbene complex
1b, the addition reaction occurs preferentially to the deproto-
nation reaction, and the products are obtained in moderate to
good yields. It should be emphasized that in control experiments
reaction of 1b with n-octyllithium or phenyllithium gave none
of the corresponding addition product and 1b was recovered.
Thus the use of alkynyllithiums is essential for the success of
the addition reaction.
The production of R,â-unsaturated ketones indicates that the
one-carbon homologation of alkynyllithiums to propargyl metal-
lic species can be achieved by using the Fischer-type carbene
complexes. Hence, it was expected that the propargylic metallic
species could be applied to further carbon-carbon bond
formation reactions.7 Most of the previously known types of
propargyl metallic species are in equilibrium with allenyl
metallic species, and in their reaction with aldehydes, a mixture
of acetylenic and allenic alcohols is usually obtained,8 selective
preparation of allenyl products being limited to several specific
combinations of substrates and metals.9
(1) For reviews on the chemistry of Fischer-type carbene complexes,
see: (a) Wulff, W. D. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon: Oxford, 1995;
Vol. 12, Chapter 5.3. (b) Hegedus, L. S. In ComprehensiVe Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.;
Pergamon: Oxford, 1995; Vol. 12, Chapter 5.4. (c) Wulff, W. D. In
ComprehensiVe Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Pergamon
Press: Oxford, 1991; Vol. 5, Chapter 9.2. (d) Brown, F. J. Prog. Inorg.
Chem. 1980, 27, 1.
(2) For examples, see: (a) Casey, C. P.; Brunsvold, W. R. J. Organomet.
Chem. 1974, 77, 345. (b) Fischer, E. O.; Held, W. J. Organomet. Chem.
1976, 112, C59. (c) Casey, C. P.; Burkhardt, T. J.; Bunnell, C. A.; Calabrese,
J. C. J. Am. Chem. Soc. 1977, 99, 2127. (d) Iwasawa, N.; Saitou, M. Chem.
Lett. 1994, 231. (e) Barluenga, J.; Bernad, P. L., Jr.; Concello´n, J. M.
Tetrahedron Lett. 1994, 50, 9471. Several other examples are cited therein.
(3) For examples, see: (a) Kreiter, C. G. Angew. Chem., Int. Ed. Engl.
1968, 7, 390. (b) Casey, C. P.; Anderson, R. L. J. Am. Chem. Soc. 1974,
96, 1230. (c) Wulff, W. D.; Gilbertson, S. R. J. Am. Chem. Soc. 1985, 107,
503. (d) Wulff, W. D.; Anderson, B. A.; Toole, A. J. J. Am. Chem. Soc.
1989, 111, 5485 and references cited therein.
(6) Casey and Brunsvold reported that the reaction of vinyllithium and
phenylmethoxycarbene complex, followed by treatment with anhydrous HCl,
gave 1-methoxy-1-phenylpropene as a major product instead of the desired
vinylphenylcarbene complex. They proposed that protonation occurred at
the γ-position of the addition intermediate.2a
(4) A similar type of propargylic species is proposed to be formed in
the following examples: (a) Fischer, H.; Meisner, T.; Hofmann, J. Chem.
Ber. 1990, 123, 1799. (b) Do¨tz, K. H.; Christoffers, C.; Knochel, P. J.
Organomet. Chem. 1995, 489, C84.
(5) Formation of dienyl ethers and R,â-unsaturated ketones was reported
by the thermal reaction of Fischer-type carbene complexes and alkynes via
metallacyclobutene intermediates. (a) Macomber, D. W. Organometallics
1984, 3, 1589. (b) Harvey, D. F.; Neil, D. A. Tetrahedron 1993, 49, 2145
and references cited therein.
(7) For reactions of propargyl transition metal species, see for example:
Shu, H.-G.; Shiu, L.-H.; Wang, S.-H.; Wang, S.-L.; Lee, G.-H.; Peng, S.-
M.; Liu, R.-S. J. Am. Chem. Soc. 1996, 118, 530 and references cited therein.
(8) Yamamoto, H. In ComprehensiVe Organic Synthesis; Trost, B. M.,
Fleming, I., Eds.; Pergamon Press: New York, 1991; Vol. 2, Chapter 9.2.
S0002-7863(96)02173-7 CCC: $14.00 © 1997 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 119, No. 6, 1997 1487
Table 2. Preparation of Various Furans and Pyrroles
Scheme 2
R1
R2
R3
yield of 8/%
yield of 10/%
Ph
Ph
Ph
Ph
i-Pr
n-Bu
n-Hex
n-Hex
n-Hex
n-Hex
n-Hex
Ph
Ph
i-Pr
PhCHdCH
COOEt
Ph
86 (8m)
72 (8n)
67
80
82
75
64
85a
Ph
62
a The molybdenum complex was employed in this case, better yield
being obtained than with the corresponding tungsten complex.
In the first place, we examined the reactions of the addition
intermediates 4 with various aldehydes. When benzaldehyde
was added to the addition intermediate derived from phenyl
carbene complex 1c and n-octynyllithium, the reaction pro-
ceeded at -78 °C and a furan derivative 8m (R1 ) R3 ) Ph,
R2 ) n-Hex), which was thought to be formed by cyclization
of the allenyl intermediate 7m,10 was obtained in 82% yield
after aqueous workup. However, the corresponding reaction
with isobutyraldehyde induced extensive self-condensation of
the aldehyde, and the furan 8n (R1 ) Ph, R2 ) n-Hex, R3 )
i-Pr) was obtained in only 12% yield together with the enone
2c in 59% yield. We next examined the addition of Lewis acids
to 4 to activate the aldehyde. Among several Lewis acids
examined, BF3‚OEt2 was the most effective and the desired furan
8n was obtained in 72% yield. We also examined the possibility
of preparing pyrrole derivatives by employing aldimines instead
of aldehydes. After several trials, the intermediate propargyl
metallic species were found to react with imines, in particular
sulfonyl imines, in the presence of BF3‚OEt2 giving pyrrole
derivatives 10 in good yields. As summarized in Table 2, a
variety of 2,3,5-trisubstituted furans or pyrroles are obtained in
which three substituents on the furans or pyrroles are derived
from the substituents of the carbene complexes, alkynes, and
aldehydes or imines, respectively. This reaction affords a unique
three-component coupling approach to substituted furans or
pyrroles. It should be noted that formation of the regioisomeric
acetylenic product was not observed in these reactions.Carbon
dioxide also reacts with these propargyl metallic species to give
Table 3. Preparation of Various Butenolides
R1
R2
yield of 12/%
R1
R2
yield of 12/%
i-Pr
i-Pr
i-Pr
Ph
n-Hex
SiMe3
64
75
66
n-Bu
Ph
Ph
Ph
Ph
n-Hex
63
63
72
the carboxylated compounds in good yields.11 Thus, after the
addition of alkynyllithiums to the carbene complexes, gaseous
carbon dioxide was introduced to the reaction mixture. After
acidic workup, butenolides 12 were obtained in good yield.12
As shown in Table 3, this carboxylation reaction shows wide
generality and various butenolides can be synthesized by this
procedure.
In conclusion, a new type of propargyl metallic intermediate
is generated by the addition reaction of alkynyllithiums with
Fischer-type carbene complexes. This intermediate reacts
regioselectively and in good yields with aldehydes, imines, and
CO2 to give respectively furans, pyrroles, and butenolides
containing various substituents.
Acknowledgment. We are grateful to Professor Koichi Narasaka
(the University of Tokyo) for helpful discussions and encouragement
during this work. This research was supported in part by a grant from
the Ministry of Education, Science and Culture of Japan and the
Fujisawa Foundation.
(9) See for examples: (a) Daniels, R. G.; Paquette, L. A. Tetrahedron
Lett. 1981, 22, 1579. (b) Ishiguro, M.; Ikeda, N.; Yamamoto, H. Chem.
Lett. 1982, 1029. (c) Kobayashi, S.; Nishino, K. J. Am. Chem. Soc. 1995,
117, 6392 and references cited therein.
Supporting Information Available: Experimental procedures and
spectral data for compounds 2, 3, 8, 10, and 12 (12 pages). See any
current masthead page for ordering and Internet access instructions.
(10) There is another possible mechanism where 1,2-migration of the
pentacarbonylmetal portion occurs during the reaction as shown below. See
the following references for related mechanisms: (a) Barluenga, J.; Toma´s,
M.; Rubio, E.; Lo´pez-Pelegr´ın, J. A.; Garc´ıa-Granda, S.; Pertierra, P. J.
Am. Chem. Soc. 1996, 118, 695. (b) Barluenga, J.; Toma´s, M.; Ballesteros,
A.; Santamar´ıa, J.; Carbajo, R. J.; Lo´pez-Ortiz, F.; Garc´ıa-Granda, S.;
Pertierra, P. Chem. Eur. J. 1996, 2, 88. See also ref 4.
JA962173N
(11) There are a few examples of a CO2 insertion reaction involving
anionic tungsten-carbon derivatives: (a) Darensbourg, D. J.; Rokicki, A.
J. Am. Chem. Soc. 1982, 104, 349. (b) Darensbourg, D. J.; Grotsch, G. J.
Am. Chem. Soc. 1985, 107, 7473.
(12) Formation of butenolides as a minor product was reported on the
thermal reaction of Fischer-type carbene complex and alkynes under a CO
atomosphere. (a) Chan, K. S.; Peterson, G. A.; Brandvold, T. A.; Faron, K.
L.; Challener, C. A.; Hyldahl, C.; Wulff, W. D. J. Organomet. Chem. 1987,
334, 9. (b) Bao, J.; Wulff, W. D.; Dragisich, V.; Wenglowsky, S.; Ball, R.
G. J. Am. Chem. Soc. 1994, 116, 7616. See also: Hoye, T. R.; Rehberg, G.
M. J. Am. Chem. Soc. 1990, 112, 2841.