Chromium- and tungsten-triggered valence isomerism of cis-1-acyl-2-ethynylcyclopropanes via [3,3] sigmatropy of (2-acylcyclopropyl)vinylidene - Metal intermediates

Article abstract of DOI:10.1021/ja017037j

The reaction of cis vicinal acetylethynylcyclopropanes 1 with a catalytic amount of M(CO)₅(THF) (M = Cr or W) in the presence of Et₃N at room temperature gave ortho-substituted phenols 7 in good yields as valence isomerized products. In the absence of Et₃N the reactions did not work at all. The reaction of a cyclopropane having an ester or an amide instead of an acetyl moiety with M(CO)₅(THF) did not take place, whereas an ethynylvinylcyclopropane gave a mixture of 1- and 2-substituted 1,3,5-cycloheptatrienes. These valence isomerization reactions are assumed to proceed via the formation of vinylidene-metal intermediates 2 from terminal alkynyl moieties followed by [3,3]sigmatropy of 2 to give seven-membered carbene complexes 3. Copyright

Full text of DOI:10.1021/ja017037j

Published on Web 01/04/2002
Chromium- and Tungsten-Triggered Valence Isomerism of
cis-1-Acyl-2-ethynylcyclopropanes via [3,3]Sigmatropy of
(2-Acylcyclopropyl)vinylidene-Metal Intermediates
Kouichi Ohe,* Tomomi Yokoi, Koji Miki, Fumiaki Nishino, and Sakae Uemura*
Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto UniVersity,
Sakyo-ku, Kyoto 606-8501, Japan
Received September 9, 2001; Revised Manuscript Received October 1, 2001
Table 1. Valence Isomerization of 1 (X ) O) with M(CO)5(THF)a
We report herein the novel group 6 metal-triggered [3,3]-
c
sigmatropy of cis vicinal acyl- or vinyl-ethynylcyclopropanes 1 (X
) O, CH2) via cyclopropylvinylidene complexes 2, as shown in
Scheme 1. Vinylidene complexes which can be generated directly
yield
(%)
entry
R in 1
M
additiveb
time (h)
product
1
2
3
4
5
6
7
CH2CH2Ph (1a)
CH2CH2Ph (1a)
CH2CH2Ph (1a)
CH2CH2Ph (1a)
CH2CH2Ph (1a)
OCH2CH2Ph (1b)
morpholino (1c)
Cr
Cr
W
Et3N
-
Et3N
-
Et3N
Et3N
Et3N
24
72
24
72
72
72
72
7a
69
nrd
7a
Scheme 1
72
4
W
nrd
7a
Mo
Cr
Cr
nrd
nrd
a Reactions were carried out at room temperature with 1 (0.2 mmol)
and M(CO)5(THF) prepared by irradiating a solution of M(CO)6 (0.6 mmol)
in THF (20 mL). b 0.6 mmol. c Isolated yield. d 1 was completely recovered.
from terminal alkynes and a variety of transition metals have been
identified as particularly versatile synthetic intermediates during
the past decade.1 We recently reported that group 6 transition metals
undergo pericyclic or pseudopericyclic reaction of (Z)-â-ethynyl
R,â-unsaturated carbonyl compounds 4 via ene-carbonyl-vi-
nylidene complexes 5 to produce 2-pyranylidene complexes 6
(Scheme 2).2 We then decided to extend this pericyclic mode to a
type carbene complex 3a, but an unanticipated product, phenol 7a,
in 69% isolated yield (eq 1). This result shows that valence
isomerization of 1a was promoted by chromium. We next examined
the reaction using other group 6 metal carbonyls and other
cyclopropanes having an alkoxycarbonyl or a carbamoyl group
(Table 1). The reaction of 1a with 3 equiv of W(CO)5(THF) also
gave 7a in 72% yield (entry 3), while Mo(CO)5(THF) was almost
ineffective in the reaction (entry 5). Reactions required the addition
of Et3N and no reactions occurred in the absence of it (entries 2
and 4). Triethylamine seems to facilitate the formation of a
vinylidene complex.12 When reactions of other cyclopropanes such
as an ester 1b and an amide 1c were carried out with 3 equiv of
Cr(CO)5(THF) in the presence of Et3N, no reactions took place
and 1b and 1c were recovered intact (entries 6 and 7). The lack of
reaction of an ester and an amide is in sharp contrast with
pyranylidene-complex formation.
Scheme 2
cyclopropane system having both a vinylidene-metal moiety and
an unsaturated side chain, which could exemplify [3,3]sigmatropy
represented with a [σ2s+π2s+π2s] process. As shown in Scheme
3, [3,3]sigmatropy of cyclopropanes bearing a variety of unsaturated
Scheme 3
As it was found that the group 6 metals induce valence
isomerization of cis-1-acyl-2-ethynylcyclopropanes 1 leading to
phenols 7, catalytic reactions of 1 were next examined. Selected
results on catalytic reactions are shown in Table 2. Both chromium
and tungsten showed the catalytic activity to a similar extent (entries
1 and 2). The use of 5 mol % Cr(CO)5(THF) is enough to induce
catalytic valence isomerization of 1a to give 7a quantitatively (entry
3). Reactions of butyl and p-tolyl ketones gave 7d and 7e in almost
quantitative yields, respectively (entries 4 and 5). While the reaction
of 1-naphthyl ketone 1f gave 7f with much lower yield probably
due to the steric hindrance,13 the reaction of 2-naphthyl ketone 1g
gave the corresponding product 7g in 92% yield (entries 6 and 7).
Heterocycles such as 2-furyl or 2-thienyl were tolerated in the
reactions (entries 8 and 9), but 2-pyridyl substituent slightly
precluded the product formation (entry 10).
substituents, such as vinyl,3 iminyl,3 carbonyl,3 heterocumulenyl,3,4
and metal-carbene,5 heretofore has been well investigated,6 whereas
there has been no report on [3,3]sigmatropy of cyclopropanes
involving a vinylidene-metal moiety (Y ) Cd[M]) as a vinylogous
function. We therefore set out to prepare the vicinal carbonyl- or
vinyl-substituted ethynylcyclopropanes.10
When we carried out the reaction of cis vicinal acylethynylcy-
clopropane 1a (0.2 mmol) under the identical conditions for the
synthesis of 2-pyranylidene-chromium complexes 6 employing 3
equiv of Cr(CO)5(THF)11 in THF (20 mL) in the presence of Et3N
at room temperature, we obtained not a seven-membered Fischer-
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526 VOL. 124, NO. 4, 2002 J. AM. CHEM. SOC.
10.1021/ja017037j CCC: $22.00 © 2002 American Chemical Society

C O M M U N I C A T I O N S
Table 2. Catalytic Valence Isomerization of 1 (X ) O) with
Scheme 5
M(CO)5(THF)a
b
c
entry
R in 1
M
mol %
time (h)
product
yield (%)
1
2
3
CH2CH2Ph (1a)
CH2CH2Ph (1a)
CH2CH2Ph (1a)
n-Bu (1d)
C6H4CH3-p (1e)
1-naphthyl (1f)
2-naphthyl (1g)
2-furyl (1h)
Cr
W
Cr
Cr
Cr
Cr
Cr
Cr
Cr
Cr
20
20
5
5
5
5
5
5
20
30
20
24
24
24
24
24
6
5
17
24
7a
7a
7a
7d
7e
7f
7g
7h
7i
92
99
97
95
95
trace
92
82
92
42
an oxepin and a benzene oxide reacted with Fe(CO)5 under
irradiation to give benzene and phenol together with an (η4-oxepin)-
Fe(CO)3 complex as a minor product.17
4
5
6d
7
In conclusion, we demonstrated the group 6 metal-triggered
valence isomerization of cis vicinal acyl- or vinyl-ethynylcyclo-
propanes in stoichiometric and catalytic processes. This represents
the first example of [3,3]sigmatropy in which a vinylidene-metal
works as a function of a two-π-electron moiety like a ketene.
8
9
2-thienyl (1i)
2-pyridyl (1j)
10d
7j
a 1 (0.5 mmol), Et3N (1.5 mmol), and THF (5 mL) at room temperature.
b Based on the amount of M(CO)6 loaded. c Isolated yield. d At reflux
temperature.
Acknowledgment. This work was supported on Priority Areas
(A) “Exploitation of Multi-Element Cyclic Molecules” from the
Ministry of Education, Culture, Sports and Technology, Japan.
To gain further insight into a mechanism for the group 6 metal
triggering valence isomerism of 1, we next carried out two sets of
experiments. Thus, we undertook the reaction of cis-1-ethynyl-2-
vinylcyclopropane as a carbon analogue, in which a carbonyl
oxygen of 1 was replaced with CH2. The reaction of 1k (0.3 mmol)
with 1 equiv of Cr(CO)5(THF) in THF (10 mL) in the presence of
Et3N at room temperature for 6 h gave a mixture of 1- and
2-substituted 1,3,5-cycloheptatrienes 8k and 9k in 34 and 10%
yields, respectively (eq 2).14 Reaction of vinylcyclopropane 1l also
Supporting Information Available: Experimental procedures and
analytical and spectral data for all new compounds (PDF). This material
is available free of charge via the Internet at http://pubs.acs.org.
References
(1) For reviews on vinylidene transition metal complexes, see: (a) Bruce,
M. I. Chem. ReV. 1991, 91, 197. (b) Bruneau, C.; Dixneuf, P. H. Acc.
Chem. Res. 1999, 32, 311. (c) McDonald, F. E. Chem. Eur. J. 1999, 5,
3103.
(2) Ohe, K.; Miki, K.; Yokoi, T.; Nishino, F.; Uemura, S. Organometallics
2000, 19, 5525. For benzopyranylidene complexes, see: Iwasawa, N.;
Shido, M.; Maeyama, K.; Kusama, H. J. Am. Chem. Soc. 2000, 122, 10226.
Electrocyclizations of dienynes promoted by ruthenium and tungsten
vinylidene complexes have been reported as related reactions, see: Merlic,
C. A.; Pauly, M. E. J. Am. Chem. Soc. 1996, 118, 11319. Maeyama, K.;
Iwasawa, N. J. Org. Chem. 1999, 64, 1344.
(3) For reviews on [3,3]sigmatropic rearrangement of divinylcyclopropanes
and their equivalents, see: (a) Hudlicky, T.; Fan, R. L.; Reed, J. W.;
Gadamasetti, K. G. Org. React. 1992, 41, 1. (b) Hudlicky, T.; Fan, R. L.;
Beckers, D. A.; Kozhushkov, S. I. In Methods of Organic Chemistry
(Houben-Weyl), 4th ed.; de Meijere, A., Ed.; Thieme: Stuttgart, 1997;
Vol. E17c, p 2589.
gave a mixture of cycloheptatrienes 8l (24%) and 9l (7%). The
formation of cycloheptatrienes indicates that [3,3]sigmatropy of a
vinylcyclopropylvinylidene intermediate 2 (X ) CH2) proceeds to
give a seven-membered carbene complex 3 (X ) CH2) as shown
in Scheme 1. Formation of two isomeric 1,3,5-cycloheptatrienes 8
and 9 can be explained by assuming the subsequent [1,5]- and [1,3]-
hydrogen shifts in the complex 3 (X ) CH2) followed by reductive
elimination of pentacarbonylchromium, Cr(CO)5, from hydride
complexes 10 and 11, respectively (Scheme 4). Accordingly,
(4) Bo¨ttcher, G.; Reiâig, H.-U. Synlett 2000, 725.
(5) (a) Herndon, J. W.; McMullen, L. A. J. Am. Chem. Soc. 1989, 111, 6854.
(b) Herndon, J. W. Tetrahedron 2000, 56, 1257 and references therein.
(6) It has been reported that thermal [3,3]sigmatropic rearrangements of 1,2-
diethynylcyclopropanes,7 1-ethynyl-2-vinylcyclopropane,8 and 1-ethynyl-
2-iminyl- or 1-ethynyl-2-formylcyclopropane9 gave rise to seven-
membered diallenic and allenic intermediates. For brevity, limited
references are shown below.
(7) (a) D’Amore, M. B.; Bergman, R. G. J. Am. Chem. Soc. 1969, 91, 5694.
(b) Henry, T. J.; Bergman, R. G. J. Am. Chem. Soc. 1972, 94, 5103. (c)
Bergman, R. G. Acc. Chem. Res. 1973, 6, 25.
(8) Dolbier, W. R.; Garza, O. T.; Al-Sader, B. H. J. Am. Chem. Soc. 1975,
97, 5038.
Scheme 4
(9) (a) Manisse, N.; Chuche, J. J. Am. Chem. Soc. 1977, 99, 1272. (b) B.-
Wargnier, F.; Vincent, M.; Chuche, J. J. Chem. Soc., Chem. Commun.
1979, 584.
(10) All new cyclopropanes prepared gave satisfactory spectral and combustion
analytical data. See Supporting Information.
(11) The solution of Cr(CO)5(THF) (n equiv) used was prepared by irradiating
a solution of a THF solution of Cr(CO)6 (n equiv) at room temperature
for 4 h with a high-pressure Hg lamp.
(12) Similar effects of Et3N have been proposed, see: Ohe, K.; Kojima, M.;
Yonehara, K.; Uemura, S. Angew. Chem., Int. Ed. Engl. 1996, 35, 1823.
Manabe, T.; Yanagi, S.; Ohe, K.; Uemura, S. Organometallics 1998, 17,
2942.
isomerism of cis-1-acyl-2-ethynylcyclopropane 1 (X ) O) also can
be explained by assuming a multistep pathway as shown in Scheme
5. Thus, [1,5]-H shift from CH2 in a seven-membered ring of 1-oxa-
2,5-cycloheptadien-7-ylidene complex 3 (X ) O) to a metal and
the subsequent reductive elimination of M(CO)5 from 12 give rise
to the formation of an oxepin 13 as a primary product. The oxepin
13, which is in equilibrium with the arene oxide 14,15 cannot be
isolated, but it is converted into phenol 7 under the present reaction
conditions.16 It has been reported that an equilibrium mixture of
(13) Isomerization of 1f to trans-1-ethynyl-2-(1-naphthoyl)cyclopropane (20%)
was observed in this reaction.
(14) Structures of 8 and 9 were confirmed by comparing their NMR spectra
in two regions of δ 1.0-2.5 and 5.0-7.0 ppm with those of 1- and
2-methyl-1,3,5-cycloheptatrienes reported, see: Egger, K. W.; Moser, W.
R. J. Phys. Chem. 1967, 71, 3699. See Supporting Information.
(15) (a) Vogel, E.; Gu¨nther, H. Angew. Chem., Int. Ed. Engl. 1967, 6, 385. (b)
Bruice, T. C.; Bruice, P. Y. Acc. Chem. Res. 1976, 9, 378.
(16) Triethylamine and/or M(CO)5 seem to be presumably responsible for
isomerization of 14 to 7.
(17) Aumann, R.; Averbeck, C.; Kruger, C. Chem. Ber. 1975, 108, 3336.
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