Rhodium-catalyzed intramolecular silylcarbotricyclization (SiCaT) of triynes [7]

Full text of DOI:10.1021/ja9815529

3230
J. Am. Chem. Soc. 1999, 121, 3230-3231
Table 1. SiCaT Reactions of Triynes 7 Catalyzed by Rh and
Rhodium-Catalyzed Intramolecular
Silylcarbotricyclization (SiCaT) of Triynes
Rh-Co Complexesa
Iwao Ojima,* An T. Vu, James V. McCullagh, and
Atsushi Kinoshita1
Department of Chemistry
State UniVersity of New York at Stony Brook
Stony Brook, New York 11794-3400
ReceiVed May 5, 1998
Transition metal-catalyzed cyclotrimerization of acetylenes has
attracted considerable interest as a powerful method for construc-
tion of highly substituted and/or functionalized benzene deriva-
tives and has found many applications to the syntheses of natural
and unnatural products of interest.2 We describe here a novel
silicon-initiated intramolecular cyclotrimerization, i.e., “silylcar-
botricyclization (SiCaT)”, of dodec-1,6,11-triynes, tridec-1,6,12-
triyne, and tetradec-1,7-13-triyne catalyzed by rhodium com-
plexes, which proceeds through three consecutive carbometalations.
In the course of our studies on the silylcarbocyclization (SiCaC)
reactions of alkenynes and alkynals (eq 1),3,4 we have found that
the alkyl-rhodium intermediate 2 (X ) CH2) can be further
trapped by another alkyne moiety in alkenyne 4 to give bis-
(methylenecyclopentyl) 6, stereospecifically (eq 2).5 Although
(1)
(2)
carbometalation of the vinylsilane moiety with the vinyl-[Rh]
species in the same molecule to form the corresponding fused
tricyclic skeleton is conceptually possible in this reaction, such a
cyclization has not taken place. Instead, a simple reductive
elimination occurred to give 6. This result may well be attributable
to the rotational freedom about the bond connecting the two
cyclopentyl units.
We anticipated that restricting this rotational freedom by
introducing a carbon-carbon double bond would generate a rigid
framework that would facilitate the subsequent carbometalation
to realize the third carbocyclization, i.e., SiCaT reaction. This
anticipation led us to investigate the cascade SiCaC reaction of
dodec-1,6,11-triynes.6 Representative results are summarized in
Table 1.
The reaction of triyne 7a (0.5 mmol) with PhMe2SiH (1.0
mmol) catalyzed by Rh(acac)(CO)2 (1 mol %) in toluene (6 mL)
under carbon monoxide atmosphere7 at 70 °C for 24 h afforded
tetrahydro-as-indacenes, 8a and 9a, as the major products and
bis(silylmethylcyclopentenyl) 10a as the minor product in 94%
yield (8a:9a:10a ) 2:2:1) (Table 1, entry 1). The efficacy of
various rhodium catalysts was also examined. The use of rhodium
dimers such as [Rh(NBD)Cl]2 and [Rh(COD)Cl]2 (entries 2-3)
gives substantially higher selectivity in the formation of SiCaT
products, 8a and 9a. The use of rhodium and rhodium-cobalt
clusters such as Rh4(CO)12 and Rh2Co2(CO)128 enables the SiCaT
reaction of 7a to take place at 22 °C, giving 8a as the predominant
product (entries 4-6). It should be noted that the use of 5 equiv
of PhMe2SiH in the Rh4(CO)12-catalyzed reaction rather decreases
the relative yield of 8a (entry 5). A number of other hydrosilanes
are also effective for this reaction (entries 7-12), providing 8a
predominantly. Reactions with reactive hydrosilanes such as
(EtO)2MeSiH and (EtO)3SiH (entries 7-8) occur much faster than
those with alkyl and arylsilanes such as Et3SiH, t-BuMe2SiH, and
(1) Visiting graduate student on leave from Faculty of Pharmaceutical
Sciences, Hokkaido University, supported by the Japan Society for Promotion
of Science Fellowship in 1997.
(2) For recent reviews on metal-catalyzed acetylene cyclotrimerizations,
see: (a) Grotjahn, D. B. In ComprehensiVe Organometallic Chemistry II;
Hegedus, L. S., Ed.; Pergamon/Elsevier Science: Kidlington, 1995; Vol. 12,
p 741. (b) Vollhardt, K. P. C. Angew. Chem., Int. Ed. Engl. 1984, 23, 539. (c)
Lautens, M.; Klute, W.; Tam, W. Chem. ReV. 1996, 96, 49. (d) Ojima, I.;
Tzamarioudaki, M.; Li, Z.; Donovan, R. J. Chem. ReV. 1996, 96, 635.
(3) (a) Ojima, I.; Donovan, R. J.; Shay, W. R. J. Am. Chem. Soc. 1992,
114, 4, 6580. (b) Ojima, I.; Tzamarioudaki, M.; Tsai, C.-Y. J. Am. Chem.
Soc. 1994, 116, 3643. (c) Ojima, I.; Fracchiolla, D. A.; Donovan, R. J.; Banerji,
P. J. Org. Chem. 1994, 59, 7594. (d) Ojima, I.; Kass, D. F.; Zhu, J.
Organometallics 1996, 15, 5191. (e) Ojima, I.; Zhu, J.; Vidal, E. S.; Kass, D.
F. J. Am. Chem. Soc. 1998, 120, 6690.
(4) Matusda, I.; Ishibashi, H.; Ii, N. Tetrahedron Lett. 1995, 36, 241.
(5) Ojima, I.; McCullagh, J. V.; Shay, W. R. J. Organomet. Chem. 1996,
521, 421.
(6) Doyle and Shanklin reported an unexpected cyclotrimerization of but-
3-yn-2-one and methyl propynoate, giving the corresponding trisubstituted
benzenes under silylformylation9 conditions using Rh2(pfb)4 (pfb ) perfluo-
robutyrate) and Et3SiH under ambient pressure of CO. See ref 9m.
(7) CO atmosphere appears to be necessary to stabilize the active catalyst
species. Reactions under N2 were sluggish and gave lower yields.
(8) (a) Horva´th, I. T.; Bor, G.; Garland, M.; Pino, P. Organometallics 1986,
5, 1441. (b) Ojima, I.; Clos, N.; Donovan, R. J.; Ingallina, P. Organometallics
1991, 10, 3211.
10.1021/ja9815529 CCC: $18.00 © 1999 American Chemical Society
Published on Web 03/20/1999

Communications to the Editor
J. Am. Chem. Soc., Vol. 121, No. 13, 1999 3231
Scheme 1
cascade carbometalations to form the common intermediate I.
Subsequent carbocyclization followed by â-hydride elimination
leads to the formation of the normal SiCaT product 8. Alterna-
tively, I can undergo Z-E isomerization10 to generate intermediate
II. High reaction temperatures and the presence of heteroatoms
in the substrate’s backbones enhance the Z-E isomerization. The
carbocyclization of II then yields intermediate V, in which the
metal and the C-4 hydrogen are trans to each other, precluding
the occurrence of â-hydride elimination. Thus, â-silyl elimination
takes place instead to give nonsilylated SiCaT product 9.11 In the
presence of excess hydrosilane, reductive elimination occurs to
generate conjugated triene III. The fate of the triene III is
governed by the substituent Y. When Y is a hydrogen, highly
regioselective 1,6-hydrosilylation3e of III occurs to give 10, while
III undergoes a disrotatory electrocyclic reaction to yield 11 when
Y is a methyl group. The steric hindrance caused by the exo-
methyl group can be ascribed to the suppression of 1,6-hydro-
silylation (see eq 3).
The observed high selectivity for the formation of 8 in reactions
employing rhodium clusters as catalyst precursors may be
attributed to the generation of a highly active catalyst species,
probably a dinuclear complex. The highly active Rh-Co mixed
dinuclear species has been proposed and characterized under the
silylformylation conditions in these laboratories.9a,f
Although various metal-catalyzed acetylene [2 + 2 + 2]
cyclotrimerizations are known,2 the SiCaT reaction is unique in
that the reaction is initiated by Si-[M] species and proceeds in a
cascade manner. The SiCaT reaction provides rapid access to
functionalized tricyclic skeletons including those of 5-6-6 and
6-6-6 ring systems. Further studies on the scope of the SiCaT
reaction and its applications to organic synthesis are actively
underway.
Ph2MeSiH (entries 9-11). The reaction with bulky Ph3SiH also
takes place, albeit in lower yield (entry 12).
The SiCaT reaction is also applicable to substrates containing
dioxane and ether functionalities (entries 13-15), yielding
silylated product 8 selectively. For triynes with heteroatoms in
the backbones, 7e-g, the reactions catalyzed by Rh(acac)(CO)2
proceed much faster than that of 7a at 22 °C, giving predominantly
tetrahydroindacenes 9e-g accompanied by none or a small
amount of 4-silyl-2,7-bisaza(or oxa)tetrahydroindacenes 8e-g in
good to excellent total yields (entries 17, 20, and 23). Reactions
of 7e-g at 22 °C (entries 17-18, 20-21, and 23-24) give higher
yields than those run at higher temperatures (entries 16, 19, and
22). Note that the formation of 4-silyl-2,7-dioxa-tetrahydroin-
dacene 8g is only observed when the reaction of 7g was run at
22 °C (entry 23-24). These results have important implications
on the mechanism of the SiCaT reaction (vide infra). The use of
Rh4(CO)12 in the reaction of 7g slightly enhances the formation
of silylated product 8g (entry 24).
Acknowledgment. This research was supported by grants from the
National Institutes of Health (NIGMS) and the National Science Founda-
tion. Generous support from Mitsubishi Chemical Corp. is gratefully
acknowledged. A.T.V. is grateful to NIGMS for his NIH Postdoctoral
Fellowship (NRSA).
The reaction of 7h, in which one of the terminal alkyne moieties
is substituted with a methyl group, catalyzed by Rh4(CO)12 (0.5
mol %) proceeded cleanly at 22 °C to give 4-methyl-5-silyltetra-
hydroindacene 8h, 4-methyltetrahydroindacene 9h and 4-methyl-
5-silylhexahydroindacene 11 in quantitative yield by H NMR
analysis (eq 3). The formation of 8h and 11 clearly indicates that
1
Supporting Information Available: Experimental procedures, spec-
tral data for all new compounds 7a-c, 7e, 8-14 (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.
JA9815529
(9) Examples of silicon-initiated reactions are SiCaC (see ref 3-5) and
silylformylation reactions. For silylformylation reaction, see: (a) Ojima, I.;
Ingallina, P.; Donovan, R. J.; Clos, N. Organometallics 1991, 10, 38. (b) Ojima,
I.; Donovan, R. J.; Ingallina, P.; Clos, N.; Shay, W. R.; Eguchi, M.; Zeng,
Q.; Korda, A. J. Cluster Sci. 1992, 3, 423. (c) Eguchi, M.; Zeng, Q.; Korda,
A.; Ojima, I. Tetrahedron Lett. 1993, 34, 915. (d) Ojima, I.; Donovan, R. J.;
Eguchi, M.; Shay, W. R.; Ingallina, P.; Korda, A.; Zeng, Q. Tetrahedron 1993,
49, 5431. (e) Ojima, I.; Vidal, E.; Tzamarioudaki, M.; Matsuda, I. J. Am.
Chem. Soc. 1995, 117, 6797. (f) Ojima, I.; Li, Z.; Donovan, R. J.; Ingallina,
P. Inorg. Chim. Acta 1998, 270, 279. (g) Ojima, I.; Li, Z. In Catalysis by Di-
and Polynuclear Metal Complexes; Adams, R. A., Cotton. F. A., Eds.; John
Wiley & Sons: Chichester, 1998; Chapter 9, pp 307-343. For contributions
from other laboratories, see: (h) Matsuda, I.; Ogiso, A.; Sato, S.; Izumi, Y.
J. Am. Chem. Soc. 1989, 111, 2332. (i) Matsuda, I.; Ogiso, A.; Sato, S. J.
Am. Chem. Soc. 1990, 112, 6120. (j) Matsuda, I.; Sakakibara, J.; Nagashima,
H.; Tetrahedron Lett. 1991, 32, 7431. (k) Matsuda, I.; Sakakibara, J.; Inoue,
H.; Nagashima, H. Tetrahedron Lett. 1992, 33, 5799. (l) Doyle, M. P.;
Shanklin, M. S. Organometallics 1993, 12, 11. (m) Doyle, M. P.; Shanklin,
M. S. Organometallics 1994, 13, 1081. (n) Wright, M. E.; Cochran, B. B. J.
Am. Chem. Soc. 1993, 115, 2059. (o) Zhou, J. Q.; Alper, H. Organometallics
1994, 13, 1586. (p) Monteil, F.; Matsuda, I.; Alper, H. J. Am. Chem. Soc.
1995, 117, 4419. (q) Leighton, J. L.; Chapman, E. J. Am. Chem. Soc. 1997,
119, 12416. (r) Matsuda, I.; Fukuta, Y.; Tsuchihashi, T.; Nagashima, H.; Itoh,
K. Organometallics 1997, 16, 4327. (s) Maruoka, T.; Matsuda, I.; Itoh, K.
Tetrahedron Lett. 1998, 39, 7325.
the reaction is initiated from the less hindered acetylene terminus
of 7h.
The formation of products with different ring sizes is also
realized for the SiCaT reaction (eq 4). The reaction of 12a
catalyzed by Rh4(CO)12 gives mainly the silylated product 13a
as a 1:1 mixture of two regioisomers (56%), along with nonsi-
lylated product 14a (29%). For 12b, the reaction does not occur
at room temperature but at 50 °C gives a 1:1 mixture of 13b and
14b in 82% total yield.
The most plausible mechanism for the SiCaT reaction that can
accommodate all of the observed results is proposed in Scheme
1. As illustrated, the reaction proceeds through a silicon-initiated9
(10) (a) Ojima, I.; Clos, N.; Donovan, R. J.; Ingallina, P. Organometallics
1990, 9, 3127. (b) R. Tanke; R. H. Crabtree J. Am. Chem. Soc., 1990, 112,
7984-7989.
(11) Metallacycles may also be proposed as intermediates for the formation
of 9. However, control experiments clearly indicate the necessity of a
hydrosilane to promote SiCaT reaction, i.e., in absence of a hydrosilane
reaction gives only small amount of 9.