Synthesis of enantiopure ruthenium tricarbonyl complexes of a bicyclic cyclopentadienone derivative

Article abstract of DOI:10.1002/ejic.200800174

(-)-Menthone was converted stereoselectively into 3-menthylpropargyl alcohol 8 in several steps and subsequently converted into enantiopure cyclopentadienone ruthenium carbonyl complexes. In the malonate cases, ruthenacycle 15 was also formed during the cyclization reaction. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800174

SHORT COMMUNICATION
DOI: 10.1002/ejic.200800174
Synthesis of Enantiopure Ruthenium Tricarbonyl Complexes of a Bicyclic
Cyclopentadienone Derivative
Min-soo Kim,[a] Jun Won Lee,[a] Jae Eun Lee,[a] and Jahyo Kang*[a]
Keywords: Carbonylation / Cyclopentadienyl ligands / Half-sandwich complexes / Ruthenium
(–)-Menthone was converted stereoselectively into 3-men-
thylpropargyl alcohol 8 in several steps and subsequently
converted into enantiopure cyclopentadienone ruthenium
carbonyl complexes. In the malonate cases, ruthenacycle 15
was also formed during the cyclization reaction.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
Thus, the chiral cycloalkyl groups on the opposite side
of the cyclopentadienone ligand would provide a C2-sym-
metric environment around the ligand, which may be uti-
lized in asymmetric synthesis. The underlying assumption
is that both of the methine hydrogens on the side-chain ring
point away from the carbonyl oxygen atom (as in B) be-
cause of the unfavorable interaction of the side-chain ring
with the allylic hydrogens (as in C).
Incidentally, the cyclopentadienone–Ru complexes are
also important intermediates for the Shvo complex, which
is used as a catalyst in the racemization of optically active
alcohols.[9]
Introduction
Cyclopentadienones are useful synthetic intermediates[1]
for polycyclic compounds[2] and polymers.[3] Additionally,
transition-metal complexes containing chiral cyclopen-
tadienyl ligands are widely used in asymmetric catalysis and
olefin polymerization reactions.[4] In general, transition-
metal-mediated alkyne–alkyne–CO couplings with metal
carbonyl[5] compounds provides a direct and effective syn-
thesis of cyclopentadienones, which are potentially useful
owing to their occurrence in a diverse range of natural
product molecules.[6] In this homocoupling reaction, two al-
kynes react with Fe(CO)5 under a CO atmosphere to give
the symmetrically substituted cyclopentadienone–Fe(CO)3
complexes.[7]
Results and Discussion
Herein is reported a general approach to cyclopenta-
dienone–ruthenium carbonyl complexes of chiral cyclo-
(–)-Menthone was treated at –78 °C for 1 h with the
pentadienone derivatives, which may be useful in asymmet- lithio derivative of the tert-butyldimethylsilyl ether of pro-
ric synthesis, by cross-coupling of tethered diynes by pargyl alcohol in THF, which was generated by the reaction
Ru3(CO)12-promoted cyclocarbonylation (Scheme 1).[8]
of the corresponding alkyne with n-butyllithium at –40 °C
Scheme 1. The cyclopentadienone–Ru complex.
and subsequently at 0 °C (1 h). The product was purified
by distillation (b.p. 142–144 °C/0.9–1.0 Torr) to give 90%
yield of the diastereomeric mixture (≈2:1 preference for the
axial alcohol) of the known epimeric alcohols 2[10]
(Scheme 2).
[a] Department of Chemistry, Sogang University, Mapo-gu,
Seoul 121-742, Korea
Fax: +82-2-701-0967
E-mail: kangj@sogang.ac.kr
Supporting information for this article is available on the
WWW under http://www.eurjic.org/ or from the author.
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Enantiopure Ru Complexes of a Bicyclic Cyclopentadienone Derivative
diphenylsilane in CH2Cl2 in the presence of 2,6-lutidine[7b]
(r.t., 8 h). Additionally, propargyl alcohol 8 was converted
into the corresponding propargylic bromide in 76% yield
by using phosphorus tribromide in pyridine, and it was then
condensed with the sodio derivative of dimethyl malonate
in DMF at 0 °C to give diyne compound 11 in 69% yield
(Scheme 3).
Scheme 3. Preparation of diynes 9–11.
Finally, a mixture of diyne compound 9 or 10 and triru-
thenium dodecacarbonyl (0.5 mol/mol of the diyne, 50%
excess) was heated to reflux in toluene for 5–10 h[11] to une-
ventfully provide cyclopentadienone–ruthenium tricarbonyl
Scheme 2. Preparation of propargylic alcohol 8.
The tertiary hydroxy group of diastereomeric propargylic complex 12 or 13 as brown foams after purification by flash
alcohol 2 was reduced stereoselectively to give the corre- chromatography in ca. 30 and 24% yields, respectively
sponding trans alcohol 8 in a series of three consecutive (Scheme 4).
reactions. Thus, propargylic alcohol 2 was first treated with
dicobalt octacarbonyl in CH2Cl2 at room temperature for
6 h to give the corresponding dicobalt hexacarbonyl com-
plex of alkyne 3. Subsequently, the more easily ionizable
tertiary propargylic hydroxy group of monosilyl ether 3 was
reduced by borane–dimethyl sulfide complex (hydride
source) in the presence of boron trifluoride–diethyl ether
(Lewis acid) at –78 °C. After aqueous workup and
chromatography, the pure cobalt complex of propargylic
ether 5 was isolated in 53% yield along with ca. 10% yield
of completely reduced alkyne 6. Evidently, the trans geome-
Scheme 4. Preparation of bicyclic cyclopentadienone–ruthenium
tricarbonyl complexes 12 and 13.
try resulted from the axial delivery of the hydride to incipi-
The reaction of dimethyl malonate 11 with Ru3(CO)12
ent carbocation 4 (the stereochemistry of propargylic provided two ruthenium-containing compounds: the usual
alcohol 5 was later confirmed by 1H–13C hetero COSY, 1H– cyclopentadienone adduct 14 [Rf = 0.33 (10% EtOAc/n-
1H homo COSY, and proton NOESY on the corresponding hexane); 36% yield after column chromatography and
benzoate of alcohol 8). Subsequent demetalation of cobalt recrystallization] as colorless crystals and a slightly less-
complex 5 with ceric ammonium nitrate at 0 °C provided a polar material [Rf = 0.41 (10% EtOAc/n-hexane)] as yellow-
mixture of silyl ether 7 (15% yield), and desilylated alcohol ish crystals, which exhibited almost the same NMR spectra
8 (43% yield). Silyl ether 7 could be independently desi- but later was shown to be ruthenacylopentadiene[12] 15
lylated by tetrabutylammonium fluoride in THF at 0 °C to (18% yield after column chromatography and recrystalli-
furnish pure propargylic alcohol 8 in 92% yield (Scheme 2). zation) by X-ray crystallography (Scheme 5). However, the
Gratifyingly, without purification of intermediates, the met- more reactive tris(acetonitrile) complex Ru3(CO)9-
[13]
alation with dicobalt octacarbonyl, reduction, and final (MeCN)3
did not give a significant increase in yield of
demetalation of the cobalt residue (2Ǟ5) could be ac- cyclopentadienone adduct 14 (ca. 40% yield) or the forma-
complished in 23% overall yield for the three steps.
tion of ruthenacycle 15.
With propargylic alcohol 8 in hands, various types of
The structural features of bicyclic cyclopentadienone–ru-
diyne compounds for the synthesis of the bicyclic ruthe- thenium tricarbonyl complex 14 are quite informative. The
nium tricarbonyl complexes were prepared. Acetone ketal cyclopentadienone carbonyl (C4–O4) approximately
9 was prepared by the reaction of 2-methoxypropene with eclipses one of the terminally coordinated carbonyl ligands
propargylic alcohol 8 in the presence of pyridinium p-tolu- (C1–O1) on the ruthenium atom. This steric effect is re-
enesulfonate (ppts) in CH2Cl2 at 0 °C (87% yield). The cor- flected in the lengthening of the Ru–C1 bond [1.933(5) Å].
responding bis(diphenylsilyl) ether 10 was prepared in 78% Thus, one may assume that the effect of this eclipsing would
yield by the reaction of propargylic alcohol 8 with dichloro- make the eclipsing carbonyl ligand on the ruthenium atom
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M.-s. Kim, J. W. Lee, J. E. Lee, J. Kang
SHORT COMMUNICATION
Scheme 5. Preparation of bicyclic ruthenium tricarbonyl complexes 14 and 15.
be more susceptible to dissociation, which is required step
Conclusions
for the initiation of the catalytic cycle of the complex,[14]
even though the fluxional behavior of this kind of complex
in solution is expected.[15] As expected, both of the menthyl
rings in bicyclic cyclopentadienone–ruthenium tricarbonyl
complex 14 assume a chair conformation. The methine hy-
drogens on the connecting carbon atoms (C12 and C22) on
each menthyl ring lie almost in the same plane as the diene
We prepared various enantiopure bicyclic cyclopenta-
dienone–ruthenium carbonyl complexes with menthyl side
chains that reside on the opposite side of the cyclopenta-
dienone ring. The complexes were derived stereoselectively
from (–)-menthone in several steps.
Supporting Information (see footnote on the first page of this arti-
unit (–21.2 and –160.0°), which was expected. More import- cle): Experimental procedures.
antly, both of the two isopropyl groups on the menthyl rings
are pushed away from the ruthenium metal center, despite
the increased steric interaction of the menthyl ring with the
Acknowledgments
allylic hydrogens (Scheme 1, C; Figure 1),[16] which was
contrary to our initial expectation. It is also interesting that
This work was supported by the Special Research Grant of Sogang
the overall structure of bicyclic diruthenium ruthenacycle
complex 15 is similar to that of bicyclic cyclopentadienone–
ruthenium tricarbonyl complex 14 except for the fact that
the carbonyl group of complex 14 is replaced by one
Ru(CO)3 unit (Figure 2).[16]
University. Assistance in X-ray crystallography by Professor
Myoung Soo Lah at Hanyang University, Ansan, is appreciated.
[1] Review: M. Ogliaruso, M. G. Romanelli, E. I. Becker, Chem.
Rev. 1965, 65, 261–367.
[2] a) A. Gamba, R. Gandolfi, R. Oberti, N. Sardone, Tetrahedron
1993, 49, 6331–6348; b) T. Jikyo, M. Eto, K. Harano, Tetrahe-
dron 1999, 55, 6051–6066; c) J. D. Rainier, J. E. Imbriglio, Org.
Lett. 1999, 1, 2037–2039; d) A. J. Pearson, J. B. Kim, Tetrahe-
dron Lett. 2003, 44, 8525–8527.
[3] U. Kumer, T. X. Meenan, Macromolecules 1995, 28, 124–130.
[4] a) A. H. Hoveyda, J. P. Morken, Angew. Chem. Int. Ed. Engl.
1996, 35, 1262–1284; b) R. L. Halterman, Chem. Rev. 1992, 92,
965–994.
[5] Reviews on transition-metal-catalyzed cycloadditions: a) I.
Ojima, M. Tzamarioudaki, Z. Li, R. J. Donovan, Chem. Rev.
1996, 96, 635–662; b) H.-W. Frühauf, Chem. Rev. 1997, 97,
523–596.
[6] a) G. Mehta, J. D. Umarye, Org. Lett. 2002, 4, 1063–1066; b)
V. B. Birman, S. Danishefsky, J. Am. Chem. Soc. 2002, 124,
2080–2081; c) B. B. Snider, N. A. Hawryluk, Org. Lett. 2001,
3, 569–572.
Figure 1. X-ray crystal structure of chiral bicyclic cyclopenta-
dienone–ruthenium Complex 14; hydrogen atoms have been omit-
ted for clarity.
[7] a) A. C. Filippou, T. Rosenauer, Angew. Chem. Int. Ed. 2002,
41, 2393–2396; b) A. J. Pearson, J. B. Kim, Org. Lett. 2002, 4,
2837–2840; c) A. J. Pearson, A. Perosa, Organometallics 1995,
14, 5178–5183; d) H.-J. Knölker, E. Baum, J. Heber, Tetrahe-
dron Lett. 1995, 36, 7647–7650.
[8] a) Y. Yamamoto, Y. Miyabe, K. Itoh, Eur. J. Inorg. Chem. 2004,
3651–3661; b) M. I. Bruce, J. R. Knight, J. Organomet. Chem.
1968, 12, 411–413.
[9] a) F. F. Huerta, A. B. E. Minidis, J.-E. Bäckvall, Chem. Soc.
Rev. 2001, 30, 321–331; b) M.-J. Kim, Y. Ahn, J. Park, Bull.
Korean Chem. Soc. 2005, 26, 515–522.
[10] C. Spino, C. Beaulieu, J. Lafrenière, J. Org. Chem. 2000, 65,
7091–7097.
Figure 2. X-ray crystal structure of chiral bicyclic diruthenium
ruthenacycle complex 15; hydrogen atoms have been omitted for
clarity.
[11] a) G. Cetini, O. Gambino, E. Sappa, M. Valle, J. Organomet.
Chem. 1969, 17, 437–443; b) Y. Blum, Y. Shvo, Isr. J. Chem.
1984, 24, 144–148.
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Enantiopure Ru Complexes of a Bicyclic Cyclopentadienone Derivative
[12] a) G. Gervasio, D. Marabello, E. Sappa, A. Secco, J. Or-
ganomet. Chem. 2005, 690, 3730–3736; b) E. Sappa, J. Or-
ganomet. Chem. 1999, 573, 139–155.
[13] P. Grenouillet, C. de Bellefon, J. Organomet. Chem. 1996, 513,
155–162.
[14] a) Y. Blum, Y. Shvo, D. F. Chodosh, Inorg. Chim. Acta 1985,
97, L25–L26; b) B. Schneider, I. Goldberg, D. Reshef, Z. Stein,
Y. Shvo, J. Organomet. Chem. 1999, 588, 92–98.
[15]
L. Kruczynski, J. Takats, Inorg. Chem. 1976, 15, 3140–3147.
[16] CCDC-677374 (for 14) and -677375 (for 15) contain the sup-
plementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Received: February 15, 2008
Published Online: April 25, 2008
Eur. J. Inorg. Chem. 2008, 2510–2513
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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