Cobalt-mediated intermolecular allyl/alkyne [3 + 2 + 2] cycloaddition reactions. A practical metal template for convergent synthesis of functionalized seven-membered rings [12]

Full text of DOI:10.1021/ja982010u

9702
J. Am. Chem. Soc. 1998, 120, 9702-9703
Scheme 1
Cobalt-Mediated Intermolecular Allyl/Alkyne [3 + 2
+ 2] Cycloaddition Reactions. A Practical Metal
Template for Convergent Synthesis of Functionalized
Seven-Membered Rings
Nola Etkin,1a Trevor L. Dzwiniel, Kathy E. Schweibert,1b and
Jeffrey M. Stryker*
Department of Chemistry, UniVersity of Alberta
Edmonton, Alberta T6G 2G2, Canada
In this communication, we report that unsaturated permethyl-
cyclopentadienylcobalt(III) allyl complexes react with alkynes to
give substituted η5-cycloheptadienyl complexes by metal-mediated
intermolecular [3 + 2 + 2] cycloaddition. Subsequent nucleo-
philic alkylation/decomplexation procedures provide functional-
ized organic cycloheptadienes in a highly regioselective and
stereoselective manner, providing convergent new methodology
for the construction of synthetically valuable seven-membered-
ring systems.
ReceiVed June 9, 1998
Transition metal-mediated cycloaddition reactions provide
synthetic access to important organic ring systems inaccessible
by traditional cycloaddition methodology.2 Seven-membered-ring
synthesis is prominent among these efforts, with important recent
advances in two-component cycloadditions and intramolecular
cyclization methodology.3 Our investigation is focused on the
development of metal-mediated allyl/alkyne cycloaddition reactiv-
ity patterns, targeting intermolecular three-component cyclization
processes.4 η3-Allyl alkyne coupling reactions proceed via vinyl
olefin intermediates and typically provide open-chain η5-penta-
dienyl complexes5 (path a) or η5-cyclopentadienyl complexes6
(path b) from reaction with a single alkyne (Scheme 1).
Incorporation of two alkynes has also been reported, leading to
the formation of η1,η4-methanocyclohexadiene complexes (path
c).7 By controlling the regiochemistry of the migratory insertion
that determines ring size in the double alkyne reactions, we
recently established the first allyl/alkyne cycloaddition reactions
to yield seven-membered-ring systems with high selectivity (path
d).8,9 To exploit the synthetic potential of that iridium-mediated
reactivity pattern, less expensive and more reactive organometallic
systems were sought for the development of organic methodology.
The required cobalt(III) η3-allyl complexes can be generated
in several ways compatible with the development of synthetic
organic methodology.10 The neutral η3-allylcobalt triflate com-
plexes 2 are particularly convenient precursors, with good thermal
stability, high solubility, and a highly labile triflate ligand (eq
1). The unsubstituted allyl triflate complex 2a is prepared in high
(1)
(1) Current locations: (a) Department of Chemistry, University of Prince
Edward Island, Charlottetown, PE C1A 4P3, Canada. (b) Central Research
and Development, E. I. DuPont de Nemours and Co., Wilmington, DE 19880.
(2) Recent reviews: (a) Lautens, M.; Klute, W.; Tam, W. Chem. ReV. 1996,
96, 49. (b) Rigby, J. H.; Pigge, F. C. Org. React. 1997, 51, 351. Rigby, J. H.
Org. React. 1997, 49, 331. (c) Shore, N. E. Chem. ReV. 1988, 88, 1081. (d)
See also: Harmata, M. Tetrahedron 1997, 53, 6235.
(3) Recent and lead references: (a) Dyker, G. Angew. Chem., Int. Ed. Engl.
1995, 34, 2223. (b) Trost, B. M.; Higuchi, R. I. J. Am. Chem. Soc. 1996, 118,
10094. (c) Negishi, E.-I.; Ma, S.; Sugihara, T.; Noda, Y. J. Org. Chem. 1997,
62, 1922. (d) Wender, P. A.; Husfeld, C. O.; Langkopf, E.; Love, J. A. J. Am.
Chem. Soc. 1998, 120, 1940. Wender, P. A.; Takahashi, H.; Witulski, B. J.
Am. Chem. Soc. 1995, 117, 4720. (e) Davies, H. M. L.; Stafford, D. G.; Doan,
B. D.; Houser, J. H. J. Am. Chem. Soc. 1998, 120, 3326. (f) Harvey, D. F.;
Grenzer, E. M.; Gantzel, P. K. J. Am. Chem. Soc. 1994, 116, 6719. (g)
Barluenga, J.; Tomas, M.; Rubio, E.; Lopez-Pelegrin, J. A.; Garcia-Grande,
S.; Pertierra, P. J. Am. Chem. Soc. 1996, 118, 695. (h) Huffman, M. A.;
Liebeskind, L. S. J. Am. Chem. Soc. 1993, 115, 4895. (i) Kreiter, C. G.; Fiedler,
C.; Frank, W.; Reiss, G. J. J. Organomet. Chem. 1995, 490, 133. (j) Wang,
C.; Sheridan, J. B.; Chung, H.-J.; Cote, M. L.; Lalancette, R. A.; Rheingold,
A. L. J. Am. Chem. Soc. 1994, 116, 8966. See also the citations contained
within refs 3a-j.
yield by treatment of allyl alcohol with (C5Me5)Co(ethylene)2 (1)11
and triflic acid. The red-brown inner-sphere triflate complex 2a
thus formed can be used in situ or isolated in 85-90% yield.12,13
Substituted η3-allyl derivatives are best prepared from the 1,3-
diene by thermal exchange followed by protonation, without
isolation of the intermediate diene complex (eq 1). Thus, η3-
crotyl and η3-1,2-dimethylallyl triflate complexes 2b and 2c12-14
are formed in near-quantitative yield and can be isolated in
crystalline form in yields in excess of 80%.
Consistent with a previous report,6b permethylcyclopentadi-
enylcobalt η3-allyl complexes react with alkynes in THF to yield
substituted cyclopentadienyl complexes by dehydrogenative [3
+ 2] cycloaddition, even in the presence of excess alkyne. By
using a noncoordinating solvent, however, the reaction is diverted
to the higher-order cycloaddition, producing seven-membered-
ring complexes from incorporation of two equivalents of alkyne
(Table 1). Thus, treatment of allyl, crotyl, and 1,2-dimethylallyl
complexes 2a-c in dichloromethane with excess acetylene affords
(4) Seven-membered-ring synthesis via three- or four-component cyclization
is very rare: (a) Grevels, F.-W.; Schnieder, K. Angew. Chem., Int. Ed. Engl.
1981, 20, 410. (b) Binger, P. Bu¨ch, H. B. Top. Curr. Chem. 1987, 135, 77.
(c) Herndon, J. W.; Zora, M.; Patel, P. P.; Chatterjee, G.; Matasi, J. J.; Turner,
S. U. Tetrahedron 1993, 49, 5507. (d) Cooke, J.; Takats, J. J. Am. Chem.
Soc. 1997, 119, 11088.
(5) See: Betz, P.; Jolly, P. W.; Kruger, C.; Zakrzewski, U. Organometallics
1991, 10, 3520 and references therein. For a comprehensive list of allyl/alkyne
coupling reactions, see the citations in ref 8.
(6) (a) Lutsenko, Z. L.; Aleksandrov, G. G.; Petrovskii, P. V.; Shubina, E.
S.; Andrianov, V. G.; Struchkov, Yu. T.; Rubezhov, A. Z. J. Organomet.
Chem. 1985, 281, 349. (b) Nehl, H. Chem. Ber. 1993, 126, 1519.
(7) Lutsenko, Z. L.; Petrovskii, P. V.; Bezrukova, A. A.; Rubezhov, A. Z.
Bull. Acad. Sci. USSR. DiV. Chem. Sci. 1988, 37, 735.
(8) Schwiebert, K. E.; Stryker, J. M. J. Am. Chem. Soc. 1995, 117, 8275.
(9) Mn(allyl)3-/R,ω-diyne cycloaddition gives mixtures of six- and seven-
membered-ring dienes: Tang, J.; Shinokubo, H.; Oshima, K. Organometallics
1998, 17, 290. In contrast, iridium-mediated allyl/R,ω-diyne cycloaddition
provides seven-membered-ring formation exclusively.8
(10) (a) Allyl halide/(C5Me5)Co(ethylene)2, followed by Ag(I) ionization:
Brestensky, D. M. Ph.D. Dissertation, Indiana University, 1992. (b) Oxidation
or oxidative halogenolysis/Ag(I) ionization of cobalt(II) allyl complexes:
Reference 6b.
(11) Nicholls, J. C.; Spencer, J. L. Inorg. Synth. 1990, 28, 278. Frith, S.
A.; Spencer, J. L. Inorg. Synth. 1985, 23, 15.
(12) Complete experimental, spectroscopic, and analytical data are provided
in the Supporting Information.
(13) Triflate complexes 2 show solvent-dependent infrared spectroscopy12
similar to that observed for the isostructural inner-sphere iridium triflate
complex: Schwiebert, K. E.; Stryker, J. M. Organometallics 1993, 12, 600.
(14) The allyl ligands are assigned the exo configuration based on difference
NOE spectroscopy.12
S0002-7863(98)02010-1 CCC: $15.00 © 1998 American Chemical Society
Published on Web 09/02/1998

Communications to the Editor
J. Am. Chem. Soc., Vol. 120, No. 37, 1998 9703
Table 2. Synthesis of Functionalized Cycloheptadienes
Table 1. [3 + 2 + 2] Allyl/Alkyne Cycloadditiona
tionalized diene complexes 412 with complete stereoselectivity.20-22
Demetallation is more difficult than in the less-electron-rich
cyclopentadienylcobalt systems19 but is accomplished in reason-
able yields by using ferricenium salts and a two-phase solvent
system.12 The dienes are obtained without positional isomeriza-
tion as the exclusive organic product; the material balance consists
of intractable material and the known dication [(C5Me5)Co-
(NCCH3)3]2+(PF6-)2.23 It is noteworthy that the trans stereo-
chemical relationship observed for the cycloheptadiene substit-
uents in 5b, 5c, and 5g is complementary to that obtained by
conventional metal-mediated functionalization sequences starting
from the unsubstituted η5-cycloheptadienyl ring.18
η5-cycloheptadienyl complexes 3a-c as air-stable solids in good
yield (entries 1-3).12 No formation of η5-cyclopentadienyl or
η1,η4-methanocyclohexadiene products is observed, nor are
significant amounts of regioisomeric η5-cycloheptadienyl com-
plexes detected in the crude product. The endo stereochemistry
of the methyl substituent in complexes 3b and 3c is assigned by
spectroscopic correlation with the structure and stereochemistry
of bicyclic complex 3f, which was confirmed unambiguously by
X-ray crystallography.12 The use of terminal alkynes also leads
to the formation of η5-cycloheptadienyl complexes (entries 4 and
5), although phenylacetylene and 3,3-dimethyl-1-butyne provide
regioisomeric substitution patterns in complexes 3d and 3e.15,16
Synthetically interesting bicyclic complexes 3f and 3g can also
be prepared, starting from readily available five- and six-
membered-ring precursors (entries 6 and 7). In these cases,
oxidative addition is used to prepare the η3-allyl complexes, which
are converted without isolation by in situ ionization and treatment
with acetylene.
Acknowledgment. Financial support from the Natural Sciences and
Engineering Research Council of Canada and the University of Alberta
is gratefully acknowledged. We also thank Dr. Robert McDonald of the
Department of Chemistry Structure Determination Laboratory for X-ray
crystallography.
Supporting Information Available: Experimental procedures, com-
plete spectroscopic and analytical data, tables of comparative NMR
spectroscopy, and details of the crystal structure determination for complex
3f (40 pages, print/PDF). See any current masthead page for ordering
information and Web access instructions.
JA982010U
(18) The synthetic organic chemistry of η5-cycloheptadienyl iron complexes
has been developed, starting with a preformed seven-membered ring: (a)
Pearson, A. J. Iron Compounds in Organic Synthesis; Academic Press: New
York, 1994; Chapter 5. (b) Pearson, A. J.; Kole, S. L. Ray, T. J. Am. Chem.
Soc. 1984, 106, 6060.
Conversion of η5-cycloheptadienyl complexes 3 to organic
cycloheptadiene derivatives is accomplished by nucleophilic
alkylation17,18/oxidative decomplexation (Table 2).19 Sodium
dimethylmalonate, for example, adds regioselectively to the
unsubstituted end of the pentadienyl fragment, providing func-
(19) Oxidative decomplexation of cobalt η4-cycloalkadiene complexes:
Gesing, E. R. F.; Tane, J. P.; Vollhardt, K. P. C. Angew. Chem., Int. Ed.
Engl. 1980, 19, 1023. Tane, J. P.; Vollhardt, K. P. C. Angew. Chem., Int. Ed.
Engl. 1982, 21, 617. Macomber, D. W.; Verma, A. G.; Rogers, R. D.
Organometallics 1988, 7, 1241.
(15) The use of propyne produces an inseparable mixture of η5-cyclohep-
tadienyl isomers; the use of trimethylsilylacetylene produces only desilylated
η5-cyclopentadienyl complex. Dimethyl acetylenedicarboxylate appears not
to coordinate to the electrophilic cobalt center.
(20) Malonate anion deprotonates sterically hindered complex 3e, producing
the η4-1,4-di-tert-butylcycloheptatriene complex.
(16) Disubstituted alkynes undergo more complicated transformations,
which will be discussed in a separate account: Dzwiniel, T. L.; Etkin, N. E.;
Stryker, J. M., in preparation.
(21) The potential for sequential polyalkylation procedures is demonstrated
by the conversion of diene complex 4a to [(C5Me5)Co(6-malonyl-η5-
-
-
cycloheptadienyl)]+BF4 upon treatment with Ph3C+BF4 (CH2Cl2, room
(17) Nucleophilic additions to [(C5H5)Co(η5-cycloheptadienyl)]+: (a) Salzer,
A.; Bigler, P. Inorg. Chim. Acta 1981, 48, 199. (b) Maguire, L. A. P.;
Mouncher, P. A.; Salzer, A. J. Organomet. Chem. 1988, 347, 383. (c) Wieser,
M.; Karaghiosoff, K.; Beck, W. Chem. Ber. 1993, 126, 1081.
temperature, 60%).12,18
(22) The addition of LiEt3BH (THF, -78 °C) to 3a-c provides noncon-
jugated η4-cyclohepta-1,4-diene complexes.17a
(23) Fairhurst, C.; White, C. J. Chem. Soc., Dalton Trans. 1979, 1524.