A novel [5+2] cycloaddition reaction using a dicobalt acetylene complex [6]

Full text of DOI:10.1021/ja001003e

6116
J. Am. Chem. Soc. 2000, 122, 6116-6117
Scheme 1
A Novel [5+2] Cycloaddition Reaction Using a
Dicobalt Acetylene Complex
Keiji Tanino,*,† Tadashi Shimizu,‡ Motoki Miyama,‡ and
Isao Kuwajima*,§
DiVision of Chemistry, Graduate School of Science
Hokkaido UniVersity, Sapporo 060-0810, Japan
Department of Chemistry
Tokyo Institute of Technology
Meguro, Tokyo 152-8551, Japan
Scheme 2
Laboratory for Natural Products Chemistry
Kitasato UniVersity, S-105 1-15-1
Kitasato, Sagamihara 228-8555, Japan
ReceiVed March 21, 2000
Cycloheptane derivatives are found in a wide range of natural
products,1 and various synthetic methods of these compounds have
been explored.2 From the viewpoint of efficiency, a cycloaddition
approach which produces two C-C bonds in one stage is
advantageous. In this regard, [4+3]-type annulation reactions of
dienes and allyl cationic species have been widely examined,3
while much less attention has been given to a [5+2] cycloaddition
approach.4-6
Scheme 3
In relation with the [3+2] cycloaddition reactions using a
3-(alkylthio)allyl cationic species as a three-carbon unit,7 we have
been interested in a [5+2] type cycloaddition reaction using a
vinylogue of the allyl cationic species. However, there are serious
problems in using a pentadienyl cation as a five-carbon unit, that
is, (1) the geometry of the pentadienyl cation should be controlled
as (Z) and (2) the pentadienyl cation with cis configuration would
undergo an intramolecular cyclization reaction to give a cyclo-
pentene derivative (Scheme 1).8 The most reasonable and practical
solution to these problems is the use of an oxidopyrylium as a
five-carbon unit,5 which was employed in total synthesis of some
natural products.9
of a “tandem cyclization-rearrangement strategy”.10 In this novel
transformation, use of a hexacarbonyldicobalt acetylene complex,
which has considerably large C(acetylenic)-C(acetylenic)-
C(propargylic) angles,11 was quite effective for selective cycliza-
tion to a seven-membered ring.12 These results led us to design a
new [5+2] cycloaddition reaction using a hexacarbonyldicobalt
propargyl cation13 as an equivalent of a pentadienyl cation
(Scheme 2).
The five-carbon unit was prepared from ester 114 as shown in
Scheme 3. Several enol triisopropylsilyl ethers15 were subjected
to the [5+2] cycloaddition reaction with 4, and the desired
On the other hand, we have reported a powerful methodology
for constructing a highly strained ingenane skeleton on the basis
† Hokkaido University.
‡ Tokyo Institute of Technology.
§ Kitasato University.
(1) (a) Heathcock, C. H.; Graham, S. L.; Pirrung, M. C.; Pavoac, F.; White,
C. T. In Total Synthesis of Natural Products; Apsimon, J., Ed.; John Wiley
and Sons: New York, 1983; Vol. 5, pp 333-393. (b) Fraga, B. M. Natural
Prod. Rep. 1996, 13, 307-326.
(2) For a review, see: Ho, T. L. Carbocycle Construction in Terpene
Synthesis; VCH Publishers: New York, 1988.
(3) For reviews of [4+3] cycloaddition reactions, see: (a) Hosomi, A.;
Tominaga, Y. In ComprehensiVe Organic Synthesis; Trost, B. M., Fleming,
I., Eds.; Pergamon: Oxford, 1991; Vol. 5, Chapter 5.1, pp 593-615. (b)
Hoffman, H. M. R. Angew. Chem., Int. Ed. Engl. 1984, 23, 1-19. (c) Mann,
J. Tetrahedron 1986, 42, 4611-4659. (d) Noyori, R.; Hayakawa, Y. Org.
React. 1983, 29, 163-344. (e) Harmata, M. Tetrahedron 1997, 53, 6235-
6280.
(4) For metal-catalized [5+2] cycloaddition reactions, see: (a) Wender,
P. A.; Takahashi, H.; Witulski, B. J. Am. Chem. Soc. 1995, 117, 4720-4721.
(b) Wender, P. A.; Glorius, F.; Husfeld, C. O.; Langkopf, E.; Love, J. A. J.
Am. Chem. Soc. 1999, 121, 5348-5349 and references therein.
(5) For oxidopyrylium cycloadditions, see: (a) Sammes, P. G. Gazz. Chim.
Ital. 1986, 116, 109-114. (b) West, F. In AdVances in Cycloaddition; Lautens,
M., Ed.; JAI Press: Greenwich, 1997; Vol. 4, pp 1-40. (c) Wender, P. A.;
Mascaren˜as, J. L. Tetrahedron Lett. 1997, 33, 2115-2118 and references
therein.
(9) For examples, see: (a) Wender, P. A.; Lee, H. Y.; Wilhelm, R. S.;
Williams, P. D. J. Am. Chem. Soc. 1989, 111, 8954-8957. (b) Wender, P.
A.; Kogen, H.; Lee, H. Y.; Munger, J. D., Jr.; Wilhelm, R. S.; Williams, P.
D. J. Am. Chem. Soc. 1989, 111, 8957-8958. (c) Wender, P. A.; Rice, K. D.;
Schnute, M. E. J. Am. Chem. Soc. 1997, 119, 7897-7898. (d) Wender, P. A.;
Jesudason, C. D.; Nakahira, H.; Tamura, N.; Tebbe, A. L.; Ueno, Y. J. Am.
Chem. Soc. 1997, 119, 12976-12977.
(10) Nakamura, T.; Matsui, T.; Tanino, K.; Kuwajima, I. J. Org. Chem.
1997, 62, 3032-3033.
(11) Cotton, F. A.; Jamerson, J. D.; Stults, B. R. J. Am. Chem. Soc. 1976,
98, 1774-1779.
(12) For selected examples of seven-membered dicobalt acetylene complexs,
see: (a) Schreiber, S. L.; Sammakia, T.; Crowe, W. E. J. Am. Chem. Soc.
1986, 108, 3128-3130. (b) Yenjai, C.; Isobe, M. Tetrahedron 1998, 54, 2509-
2520. (c) Brook, M. A.; Urschey, J.; Stradiotto, M. Organometallics 1998,
17, 5342-5346. (d) Patel, M. M.; Green, J. R. Chem. Commun. 1999, 509-
510. (e) Iwasawa, N.; Satoh, H. J. Am. Chem. Soc. 1999, 121, 7951-7952.
(13) For reviews of synthetic utility of cobalt-complexed propargyl cations,
see: (a) Nicholas, K. M. Acc. Chem. Res. 1987, 20, 207-214. (b) Caffyn, A.
J. M.; Nicholas, K. M. In ComprehensiVe Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford, 1995;
Vol. 12, pp 685-702.
(6) Stepwise cycloaddition reactions of “allylsilane-acetal bifunctional
reagents” with enol silyl ethers including [5+2]-type annulation were
reported: (a) Lee, T. V.; Boucher, R. J.; Rockell, C. J. M. Tetrahedron Lett.
1988, 29, 689-692. (b) Lee, T. V.; Boucher, R. J.; Porter, J. R.; Rockell, C.
J. M. Tetrahedron 1989, 45, 5887-5894. (c) Lee, T. V.; Cregg, C. Synlett
1990, 317-319.
(7) (a) Takahashi, Y.; Tanino, K.; Kuwajima, I. Tetrahedron Lett. 1996,
37, 5943-5946. (b) Masuya, K.; Domon, K.; Tanino, K.; Kuwajima, I. J.
Am. Chem. Soc. 1998, 120, 1724-1731. (c) Mizuno, H.; Domon, K.; Masuya,
K.; Tanino, K.; Kuwajima, I. J. Org. Chem. 1999, 64, 2648-2656 and
references therein.
(14) Earl, R. A.; Townsend, L. B. In Organic Synthesis; Freeman, J. P.,
Ed.; John Wiley and Sons: New York, 1990; Collect. Vol. VII, pp 334-338.
(15) The yield of the cycloadducts depends on the bulkiness of the silyl
group. For example, the reaction of 1-(trimethylsiloxy)cyclohexene afforded
the desired product in only 12% yield.
(8) Habermas, K. L.; Denmark, S. E. Org. React. 1994, 45, 1-158.
10.1021/ja001003e CCC: $19.00 © 2000 American Chemical Society
Published on Web 06/08/2000

Communications to the Editor
J. Am. Chem. Soc., Vol. 122, No. 25, 2000 6117
Table 1. [5+2] Cycloaddition Reaction of Enol Silyl Ethers
Scheme 4
Scheme 5
a Method A: A mixture of an enol silyl ether and 1.2 equiv of 4 in
CH2Cl2 was treated with 2.4 equiv of Me2AlCl at -23 °C. Method
B: A mixture of an enol silyl ether and 1.2 equiv of 4 in ClCH2CH2Cl
was treated with 2.4 equiv of Et2All at -23 °C. b Structures of major
diastereomers are depicted. c Diastereomeric ratio determined by proton
NMR spectra.
orbital overlap between the oxonium ion and the allylsilane
moiety.17,7a It should be noted that the configuration of the major
product is consistent with TS-1 in the reactions of both acyclic
and cyclic enol silyl ethers.
While ceric ammonium nitrate (CAN) is generally used to
regenerate an alkyne from the corresponding dicobalt hexa-
carbonyl complex,18 it is not the case for these cycloaddition
products. Thus, treatment of acetylene complex 5 with an excess
amount of CAN in acetone-water yielded a maleic anhydride
derivative in good yield.19 This novel transformation involves
incorporation of two carbonyl groups on both of the acetylenic
carbons, but the reaction mechanism is not clear at this point.
In conclusion, a [5+2] cycloaddition reaction of a new five-
carbon unit with an enol silyl ether was developed on the basis
of a dicobalt hexacarbonyl propargyl cation species. The high
stereoselectivity of the cycloaddition reaction as well as the novel
transformation of the cyclization product show promise for natural
product synthesis.
cycloadducts were obtained in good to high yields (Table 1). In
certain cases (entries 5, 8, and 9), use of Et2AlI in place of
Me2AlCl proved to give better results.
Several stereochemical features of the reactions have been
noted:16 (1) Both of the geometrical isomers of 1-(triisopropyl-
siloxy)propene afforded the same diastereomer 5 as a major
product (entries 1 and 2), and similar behavior was observed
in the reactions of 3-(triisopropylsiloxy)-3-pentene (entries 3
and 4). (2) Cyclic enol silyl ethers afforded the corresponding
trans-fused bicyclic compounds predominantly. (3) Complete
diastereofacial selection was achieved by a methyl group at the
allylic position of the cyclohexene ring (entry 7).
Such high stereoselectivity of the [5+2] cycloaddition reaction
is remarkable enough to attract much attention from both the
synthetic and mechanistic viewpoints. Since the annulation
reaction proceeds in a stepwise fashion involving a silyloxonium
ion intermediate, the stereochemistry of the products should be
determined in the intramolecular cyclization step. Taking into
account the rigidity as well as the bulkiness of the dicobalt
hexacarbonyl acetylene moiety, two transition state models, in
which the acetylene complex moiety is perpendicular to the
silyloxonium ion moiety, can be depicted (Scheme 4). In these
models, the antiperiplanar transition state (TS-1) may be favored
over the synclinal transition state (TS-2) because of the greater
Acknowledgment. This work was partially supported by grants from
the Ministry of Education, Science, Sports, and Culture of the Japanese
Government.
Supporting Information Available: Experimental procedures and
characterization data for 2-16 and ORTEP drawings of 14 and 16;
ORTEP drawings of the derivative of 12 and 15 (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
JA001003E
(17) Fleming, I.; Dunogues, J.; Smithers, R. Org. React. 1989, 37, 57-
575.
(18) Seyferth, D.; Nestle, M. O.; Wehman, A. T. J. Am. Chem. Soc. 1975,
97, 7417-7426.
(16) The stereochemistry of 5, 6, 9, and 11 was established by X-ray
crystallographic structure determination of the corresponding derivatives
(Supporting Information). The stereochemistry of 8 and 10 was suggested
from the analogy to that of 9 and 11.
(19) A similar transformation of an acyclic acetylene dicobalt hexacarbonyl
complex was reported: Schottelius, M. J.; Chen, P. HelV. Chim. Acta 1998,
81, 2341-2347.