Metal-catalyzed carbocyclization by intramolecular reaction of allylsilanes and allylstannanes with alkynes [4]

Full text of DOI:10.1021/ja993524b

J. Am. Chem. Soc. 2000, 122, 1221-1222
1221
Scheme 1
Metal-Catalyzed Carbocyclization by Intramolecular
Reaction of Allylsilanes and Allylstannanes with
Alkynes
Carolina Ferna´ndez-Rivas, Mar´ıa Me´ndez, and
Antonio M. Echavarren*
Departamento de Qu´ımica Orga´nica
UniVersidad Auto´noma de Madrid
Cantoblanco, 28049 Madrid, Spain
ReceiVed October 1, 1999
Transition-metal-catalyzed carbocyclizations of R,ω-enynes can
proceed by three major pathways (Scheme 1). Thus, insertion of
a metal hydride species M-H into the alkyne gives I, which may
evolve by insertion and elimination to give the regioisomeric
dienes II and III resulting in an overall cycloisomerization of
the enyne (Scheme 1, pathway a).1 Alternatively, an oxidative
metallacycloaddition to form metalacycle IV followed by â-hy-
dride elimination1,2 may give rise to a mixture of II and III
(pathway b). A more complex pathway has recently been
uncovered in the reaction of enynes with electrophilic metal
complexes that involves a rearrangement initiated by a complex
of type V to afford metathesis-type products VI (pathway c).3,4
However, transition-metal-catalyzed carbocyclizations by in-
tramolecular attack of mild nucleophilic reagents such as allyl-
silanes or allylstannanes (VII, M ) SiR3, SnR3) onto alkynes to
form dienes III are unknown,5 although a stoichiometric process
using HgCl2 as an electrophile in the presence of a base has
recently been developed.6,7 Interestingly, strong Lewis acids such
as HfCl4 promote the endo-dig cyclization of allylsilanes VII (M
) SiR3).8 Here we report that allylsilanes9,10 and allylstannanes11
cyclize readily upon treatment with several electrophilic Pt(II),
Pd(II), Ru(II), and Ag(I) metal salts as catalysts.
Scheme 2
Scheme 3
(1) Reviews of metal-catalyzed carbocyclizations: (a) Ojima, I.; Tzama-
rioudaki, M. L. Z.; Donovan, R. J. Chem. ReV. 1996, 96, 635. (b) Negishi,
E.; Cope´ret, C.; Ma, S.; Liou, S.-Y.; Liu, F. Chem. ReV. 1996, 96, 365. (c)
Trost, B. M. Chem. Eur. J. 1998, 4, 2405.
(2) (a) Trost, B. M.; Lautens, M.; Chan, C.; Jebaratnam, D. J.; Mueller, T.
J. Am. Chem. Soc. 1991, 113, 636 and references therein. (b) Trost, B. M.;
Haffner, C. D.; Jebaratnam, D. J., Krische, M. J.; Thomas, A. P. J. Am. Chem.
Soc. 1999, 121, 6183. (c) Trost, B. M.; Krische, M. J. J. Am. Chem. Soc.
1999, 121, 6131. (d) For an alternative pathway see: Trost, B. M.; Toste, F.
D. J. Am. Chem. Soc. 1999, 121, 9728.
(3) Reaction catalyzed by palladacyclopentadiene complexes: (a) Trost,
B. M.; Tanoury, G. J. J. Am. Chem. Soc. 1988, 110, 1636. (b) Trost, B. M.;
Trost, M. K. J. Am. Chem. Soc. 1991, 113, 1850. (c) Trost, B. M.; Trost, M.
K. Tetrahedron Lett. 1991, 32, 3647. (d) Trost, B. M.; Yanai, M.; Hoogsteen,
K. A. J. Am. Chem. Soc. 1993, 115, 5294. (e) Trost, B. M.; Hashmi, A. S. K.
Angew. Chem., Int. Ed. Engl. 1993, 32, 1085. (f) Trost, B. M.; Hashmi, A. S.
K. J. Am. Chem. Soc. 1994, 116, 2183. (g) See also: Fu¨rstner, A.; Szillat, H.;
Gabor, B.; Mynott, R. J. Am. Chem. Soc. 1998, 120, 8305.
(4) Reaction catalyzed by Ru complexes or Pt salts: (a) Chatani, N.;
Morimoto, T.; Muto, T.; Murai, S. J. Am. Chem. Soc. 1994, 116, 6049. (b)
Blum, J.; Berr-Kraft, H.; Badrieh, Y. J. Org. Chem. 1995, 60, 5567. (c)
Chatani, N.; Furukawa, N.; Sakurai, H.; Murai, S. Organometallics 1996, 15,
901. (d) Chatani, N.; Kataoka, K.; Sakurai, H.; Murai, S.; Furukawa, N.; Seki,
Y. J. Am. Chem. Soc. 1998, 120, 9104.
Certain Ru(II) complexes react with terminal alkynes to form
vinylidenes.12 In this process, it has been proposed that the Ru(II)
coordinates with the alkyne to form a η2-alkyne complex.13 Thus,
we hypothesized that reaction of the alkyne with a Ru(II) complex
could promote the nucleophilic attack of the allylsilane or stannane
(Scheme 2). Alternatively, intermediate VIII could give rise to
vinyl cation IX. An anti attack of the allyl nucleophile onto the
η2-alkyne metal complex or the metal-stabilized vinyl cation
would then give cycle X. We have found that this process could
be carried out catalytically with a variety of electrophilic metal
complexes.
Heating a solution of allylsilane 1 in the presence of CpRuCl-
(PPh3)2 (5 mol %) and NaPF6 (10 mol %) in MeOH, conditions
known to readily form vinylidene ruthenium complexes with
terminal akynes,13 gave cleanly carbocycle 2 in high yield
(Scheme 3 and Table 1, entry 1). This transformation was also
carried out with RuCl3 under the same conditions (entry 2).
Interestingly, Pd(II), Pt(II), and Ag(I) salts also triggered the
carbocyclization reaction (entries 3-9). The best results were
(5) Palladium-catalyzed intramolecular reaction of allylsilanes with
dienes: (a) Castan˜o, A. M.; Ba¨ckvall, J.-E. J. Am. Chem. Soc. 1995, 117, 560.
(b) Castan˜o, A. M.; Persson, B. A.; Ba¨ckvall, J.-E. Chem. Eur. J. 1997, 3, 482.
(6) Huang, H.; Forsyth, C. J. J. Am. Chem. Soc. 1997, 62, 88595.
(7) Reviews of organoallylmetalation of alkynes: (a) Knochel, P. In
ComprehensiVe Organic Synthesis; Trost, B. M., Fleming, I., Eds.; Perga-
mon: Oxford, 1991; Vol. 4, Chapter 4.4. (b) Yamamoto, Y.; Naoki, A. Chem.
ReV. 1993, 93, 2007. (c) Normat, J. F.; Alexakis, A. Synthesis 1981, 841.
(8) (a) Imamura, K.; Yoshikawa, E.; Gevorgyan, V.; Yamamoto, Y. J. Am.
Chem. Soc. 1998, 120, 5339. (b) Asao, N.; Yoshikawa, E.; Yamamoto, Y. J.
Org. Chem. 1996, 61, 4874. (c) Yoshikawa, E.; Gevorgyan, V.; Asao, N.;
Yamamoto, Y. J. Am. Chem. Soc. 1997, 119, 6781. (d) Asao, N.; Matsukawa,
Y.; Yamamoto, Y. J. Chem. Soc., Chem. Commun. 1996, 1513.
(9) (a) Patai, S.; Rappoport, Z., Eds. The Chemistry of Organic Silicon
Compounds; Wiley: Chichester, 1998; Part 2. (b) Fleming, I.; Barbero, A.;
Walter, D. Chem. ReV. 1997, 97, 2063.
(11) (a) Davies, A. G. Organotin Chemistry; VCH: Weinheim, 1997. (b)
Synthesis of allylstannanes from allyl carboxylates: Lipshutz, B. H.; Ellsworth,
E. L.; Dimock, S. T.; Reuter, D. C. Tetrahedron Lett. 1989, 30, 2065.
(12) Review: Bruce, M. I. Chem. ReV. 1991, 91, 197.
(13) Pilette, D.; Ouzzine, K.; Le Bozec, H.; Dixneuf, P. H. Organometallics
1992, 11, 809.
(10) Synthesis of allylsilanes from allyl carboxylates: (a) Tsuji, Y.; Funato,
M.; Ozawa, M.; Ogiyama, H.; Kajita, S.; Kawamura, T. J. Org. Chem. 1996,
61, 5779. (b) Tsuji, Y.; Kajita, S.; Isobe, S.; Funato, M. J. Org. Chem. 1993,
58, 3607.
10.1021/ja993524b CCC: $19.00 © 2000 American Chemical Society
Published on Web 01/26/2000

1222 J. Am. Chem. Soc., Vol. 122, No. 6, 2000
Communications to the Editor
exocyclic alkene with a Z-configuration,15 and 17,15 the product
of a formal metal-catalyzed ene-cyclization.3
Table 1. Metal-Catalyzed Cyclization of Enynes VII (Schemes 3
and 4)a
To ascertain the mechanism of the metal-catalyzed cyclization,
the reaction of allylsilane 1 was carried out using methanol-d4 as
the solvent. Under the conditions of entry 8, 1 gave exclusively
2-d1.16 This result indicates that the metal probably coordinates
the alkyne as shown in VIII, thus triggering an anti attack of the
allyl nucleophile. Cleavage of the carbon-metal bond of X (W
) PtCl) by methanol-d4 accounts for the formation of 2-d1. The
entry enyne
catalyst (mol %)
CpRuCl(PPh3)2 (5)b
RuCl3 (5)
PdCl2 (5)
Pd(MeCN)2Cl2 (5)
Pd(MeCN)4(BF4)2 (5) MeOH
PtCl2 (5)
PtCl2 (5)
solvent product yield (%)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
1
1
1
1
1
1
1
1
1
3
3
3
5
6
6
8
MeOH
MeOH
MeOH
MeOH
2
2
2
2
2
2
2
2
2
4
4
4
4
7
7
9
9
9
9
92
53
47
65
82
94
83
95
54
50
82
81
62
81
43
48
79
32
31
87
79
acetone
acetonec
MeOH
dioxane
MeOH
MeOH
acetonec
MeOH
MeOH
MeOHd
MeOH
MeOH
dioxane
Pt(MeCN)2Cl2 (5)
AgOTf (5)
CpRuCl(PPh3)2 (20)b
PtCl2 (5)
PtCl2 (5)
PtCl2 (5)
isolation of Z-configured 12 and 16 is also consistent with an
anti attack of the allyl nucleophile to the η2-coordinated complex
VIII or a vinyl cation IX. On the other hand, the formation of
14 in the cyclization of 13 can be explained by an attack of the
allylstannane anti to the more sterically hindered trimethylsilyl
substituent of the vinyl cation, in agreement with that proposed
for a similar cyclization mediated by HgCl2.6
Trapping of intermediate alkeny-metal complex X (W ) [M])
could lead to the formation of an additional C-C bond. Thus, it
could be conceived that insertion of allyl chloride into the
alkenyl-Pd bond followed by elimination of PdCl2 could give
an allylated derivative.17 In the event, performing the cyclization
of 1 with Pd(MeCN)2Cl2 as the catalyst (5 mol %) in THF in the
presence of excess allyl chloride and 4 Å molecular sieves led
stereoselectively to 18 (43%),15 along with 2 (19%).18
CpRuCl(PPh3)2 (20)b
PtCl2 (5)
PtCl2 (2)
10 PtCl2 (2)
10 AgOTf (28)
10 Pd(MeCN)4(BF4)2 (20) dioxane
11 PtCl2 (5)
13 CpRuCl(PPh3)2 (50)
15 PtCl2 (5)
MeOH 12
MeOH 14
MeOH 16 (+17) 50 (+43)
a Unless otherwise stated, all reactions were carried out under
refluxing conditions for 17 h. b 2 equiv (based on Ru) of NaPF6 were
also added. c Reaction temperature ) 23 °C. d Reaction time ) 48 h.
Scheme 4
In summary, we have found that the cyclization of allylsilanes
and allylstannanes with alkynes proceeds catalytically in the
presence of a variety of electrophilic metal salts. The use of PtCl2
in methanol or acetone gives rise to the best results in most cases.
This reaction is regio-complementary to that promoted by Lewis
acids.8 Metathesis-type products, which are the major products
in the cyclization of enynes with electrophilic metal salts,4,5 are
not formed in this metal-catalyzed cyclization.19 Since allylsilanes
and allylstannanes are readily available from allyl carboxylates,10,11b
this new carbocyclization offers a synthetically useful alternative
to the cyclization-carbonylation of allyl halides or carboxylates
with alkynes catalyzed by nickel or palladium.20 The stereose-
lective formation of ene-type product 17 in the cyclization of 15
is also of interest and suggests that further optimization of the
catalysts by the use of appropriate ligands2 could lead to a general
synthesis of functionalized carbocycles.
obtained by using PtCl2 or Pt(MeCN)2Cl2 as the catalysts in
acetone or MeOH as the solvents (entries 6-8). The cyclization
could not be promoted by proton or Lewis acids.14 Similarly,
silane 3 reacts in the presence of CpRuCl(PPh3)2 (entry 10) or
PtCl2 (entries 11 and 12) to give 4. Allylstanannes 5 and 6 also
react under these conditions to furnish 4 and 7, respectively
(entries 13-15). Cyclization of allylsilane 8 with PtCl2 catalyst
in refluxing MeOH proceeded rather sluggishly to give six-
membered-ring carbocycle 9 (entry 16). The corresponding
allylstannane 10 was more reactive, furnishing 9 in good yield
with PtCl2 as the catalyst (entry 17).
Acknowledgment. We are grateful to the DGES (Project PB97-0002)
for support and to the MEC (predoctoral fellowships to C.F.-R. and M.M.)
We acknowledge Johnson Matthey PLC for a generous loan of RuCl3,
PdCl2, and PtCl2 and Dr. J. M. Cuerva for early experiments.
Supporting Information Available: Experimental details, charac-
terization data, and copies of the 1H and 13C NMR spectra for new
carbocycles (PDF). This material is available free of charge via the Internet
at http://pubs.acs.org.
JA993524B
Substituted alkynes also react with electrophilic metal catalysts
to give the corresponding carbocycles (Scheme 4). Thus, phenyl-
substituted alkyne 11 reacted uneventfully in the presence of PtCl2
to give selectively Z-12 (Table 1, entry 20).15 The cyclization of
trimethylsilyl-substituted alkynes proceeded more slowly and had
to be carried out with the more reactive allylstannane in the
presence of CpRuCl(PPh3)2 (50 mol %). Under these conditions,
13 gave exclusively 14 with an E configuration on the trimeth-
ylsilyl-substituted alkene (entry 21).15 Substrate 15, bearing an
alkyne activated with an electron-withdrawing group, reacted in
the presence of PtCl2 to give a 1:1 mixture of 16, with the
(16) The configuration of 2-d1 was determined by the absence of the signal
corresponding to the methylidene E-hydrogen (4.96 ppm) of 2. See the
Supporting Information for details.
(17) Yanagihara, N.; Lambert, C.; Iritani, K.; Utimoto, K.; Nozaki, H. J.
Am. Chem. Soc. 1986, 108, 2753.
(18) When the reaction was carried out in MeOH, 18 was obtained in only
9% yield, along with 2 (84%).
(19) (a) Interestingly, the simple enyne dimethyl (propargyl)(allyl)malonate,
which gives methathesis products with other metal catalysts,4a,c reacted with
CpRuCl(PPh3)2 (20 mol %) and NaPF6 (20 mol %) in MeOH (reflux, 17 h)
reacts by a different pathway to give known dimethyl 3-formyl-4-methyl-3-
cyclopenten-1,1-dicarboxylate (54%).19b (b) Parsons, W. H.; Kuehne, M. E.
J. Org. Chem. 1977, 42, 3408.
(20) (a) Page`s, L.; Llebaria, A.; Camps, F.; Molins, E.; Moreto´, J. M. J.
Am. Chem. Soc. 1992, 114, 10449. (b) Ihle, N.; Heathcock, C. H. J. Org.
Chem. 1993, 58, 560. (c) Oppolzer, W. In ComprehensiVe Organometallic
Chemistry II; Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon:
Oxford, 1995; Vol. 12, Chapter 8.3.
(14) No cyclization was observed with: (a) NaPF6, MeOH, reflux; (b) BF3‚
OEt2, reflux. The reaction in the presence of TsOH led to decomposition.
(15) The configuration of this compound has been determined by NOEDIFF
or NOESY experiments. See the Supporting Information for details.