Cationic planar chiral (η6-Arene)Mn(CO)3 + complexes: Resolution, NMR study in chiral-oriented solvents, and applications to the enantioselective synthesis of 4-substituted cyclohexenones and (η6-Phosphinoarene)Mn(CO)3+ complexes

Article abstract of DOI:10.1021/om100564v

An easy round-trip of (D)-(+)-camphor enolate to a racemic mixture of cationic (η⁶-arene)Mn(CO)₃⁺ complexes is the base of the strategy adopted for the first resolution of such complexes. X-ray structures of one of the (η⁵-cyclohexadienyl)Mn(CO) ₃ diastereoisomers obtained after addition of the chiral auxiliary as well as of the corresponding enantiopure η⁶ cationic complex after rearomatization have been established. Proton-decoupled deuterium 2D NMR in chiral polypeptide liquid crystals proved to be an efficient tool for the determination of the enantiomeric purity of such planar chiral cationic η⁶ complexes. The potential of this unprecedented resolution is exemplified by enantioselective syntheses in organic and organometallic fields. Thus, starting from the enantiopure (η⁶-meta-halogenoanisole) Mn(CO)₃⁺ complexes, enantiopure 2,4-disubstituted cyclohexenones were easily generated through a Mn-assisted dearomatization process, and the first examples of enantiopure η⁵- and η⁶-phosphino-substituted Mn complexes were obtained through lithiation/electrophilic quench sequence.

Full text of DOI:10.1021/om100564v

3876 Organometallics 2010, 29, 3876–3886
DOI: 10.1021/om100564v
þ
Cationic Planar Chiral (η6-Arene)Mn(CO)3 Complexes: Resolution,
NMR Study in Chiral-Oriented Solvents, and Applications to the
Enantioselective Synthesis of 4-Substituted Cyclohexenones and
þ
(η6-Phosphinoarene)Mn(CO)3 Complexes
Antoine Eloi,† Franc-oise Rose-Munch,*,† Eric Rose,*,† Ariane Pille,†
Philippe Lesot,*,‡ and Patrick Herson§
†Equipe Chimie Organique et Organomeꢀtallique, UPMC Universiteꢀ Paris 06, IPCM, CNRS UMR 7201,
‡
Case 181, 4 Place Jussieu, 75252 Paris Cedex 05, France, RMN en Milieu Oriente, Universite Paris Sud 11,
ꢀ
ꢀ
§
^
ꢀ
ICMMO, CNRS UMR 8182, Batiment 410, F-91405 Orsay Cedex, France, and Centre de Resolution de
Structures, UPMC Universiteꢀ Paris 06, IPCM, CNRS UMR 7201, Case 42, 4 Place Jussieu, 75252 Paris
Cedex 05, France
Received June 8, 2010
An easy round-trip of (D)-(þ)-camphor enolate to a racemic mixture of cationic (η6-arene)Mn-
(CO)3þ complexes is the base of the strategy adopted for the first resolution of such complexes. X-ray
structures of one of the (η5-cyclohexadienyl)Mn(CO)3 diastereoisomers obtained after addition of
the chiral auxiliary as well as of the corresponding enantiopure η6 cationic complex after rear-
omatization have been established. Proton-decoupled deuterium 2D NMR in chiral polypeptide
liquid crystals proved to be an efficient tool for the determination of the enantiomeric purity of such
planar chiral cationic η6 complexes. The potential of this unprecedented resolution is exemplified by
enantioselective syntheses in organicþand organometallic fields. Thus, starting from the enantiopure
(η6-meta-halogenoanisole)Mn(CO)3 complexes, enantiopure 2,4-disubstituted cyclohexenones
were easily generated through a Mn-assisted dearomatization process, and the first examples of
enantiopure η5- and η6-phosphino-substituted Mn complexes were obtained through lithiation/
electrophilic quench sequence.
1. Introduction
thanks to the development of cine and tele nucleophilic
substitutions3 and to recent general functionalization methods
of their (η5-cyclohexadienyl)Mn(CO)3 derivatives, which are
obtained by addition of a nucleophile R1 (Scheme 1). Indeed
palladium-catalyzed cross-coupling reactions,4 as well as
lithiation/electrophilic quench sequences,5 lead to efficient
syntheses of a large variety of diversely substituted η5 com-
plexes, thus providing an easy access to the corresponding η6
complexes after rearomatization by exo-hydride abstraction at
the sp3 carbon atom (Scheme 1).
The electrophilicity of an arene is dramatically enhanced by
coordination to a tricarbonyl-metal entity, M(CO)3 (M =
Cr, Mnþ), allowing several transformations that cannot be
carried out on the metal-free arene ring. Thus there has been
widespread interest in the chemistry of arene-metal com-
plexes, and among them, Cr complexes have been extensively
studied.1 More recently, the isoelectronic cationic [(η6-
arene)Mn(CO)3]þ complexes have been taking a growing place
in organometallic chemistry as well as in organic syntheses2
*To whom correspondence should be addressed. E-mail: francoise.
rose@upmc.fr; eric.rose@upmc.fr; philippe.lesot@u-psud.fr.
(3) Mn complexes: (a) Balssa, F.; Gagliardini, V.; Rose-Munch, F.;
Rose, E. Organometallics 1996, 15, 4373. Cr complexes: (b) Boutonnet,
J. C.; Rose-Munch, F.; Rose, E. Tetrahedron Lett. 1985, 26, 3989. (c) Rose-
Munch, F.; Rose, E.; Semra, A. J. Chem. Soc., Chem. Commun. 1986, 1108.
(d) Rose-Munch, F.; Rose, E.; Semra, A. J. Chem. Soc., Chem. Commun.
1986, 1551. (e) Rose-Munch, F.; Rose, E.; Semra, A. J. Chem. Soc., Chem.
Commun. 1987, 942. (f) Boutonnet, J. C.; Rose-Munch, F.; Rose, E. Bull.
Soc. Chim. Fr. 1987, 640. (g) Rose-Munch, F.; Rose, E.; Semra, A.; Bois, C.
J. Organomet. Chem. 1989, 363, 103. (h) Djukic, J. P.; Rose-Munch, F.;
Rose, E. Organometallics 1995, 14, 2027.
(1) (a) Semmelhack, M. F. Comprehensive Organometallic Chemistry
II; Wilkinson, G.; Abel, Stone, F. G. A., Eds.; Pergamon Press: Oxford, UK,
1995; Vol. 2.4, p 517. (b) Rose-Munch, F.; Rose, E. Curr. Org. Chem.
1999, 3, 445. (c) McGlinchey, M. J.; Ortin, Y.; Seward, C. M. Comprehensive
Organometallic Chemistry III, Crabtree, R. H.; Mingos, D. M. P., Eds.;
Elsevier Science Ltd: Oxford, 2006; Vol. 5, p 201. (d) Rosillo, M.;
ꢀ
Dominguez, G.; Perez-Castells, J. Chem. Soc. Rev. 2007, 36, 1589.
(e) Astruc, D. Organometallic Chemistry and Catalysis; Springler: Heidelberg,
2007; Chapter 21, p 490.
(4) Auffrant, A.; Prim, D.; Rose-Munch, F.; Rose, E.; Schouteeten,
(2) (a) McDaniel, K. F. Comprehensive Organometallic Chemistry II;
Abel, E. W.; Stone, F. G. A.; Wilkinson, G., Eds.; Pergamon Press: Oxford,
S.; Vaissermann, J. Organometallics 2003, 22, 1898.
(5) (a) Jacques, B.; Chavarot, M.; Rose-Munch, F.; Rose, E. Angew.
Chem. 2006, 118, 3561. ; Angew. Chem., Int. Ed. 2006, 45, 3481.
(b) Jacques, B.; Chanaewa, A.; Chavarot-Kerlidou, M.; Rose-Munch,
€
1995; Vol. 6, p 93. (b) Pape, A. R.; Kaliappan, K. P.; Kundig, E. P. Chem.
Rev. 2000, 100, 2917. (c) Rose-Munch, F.; Rose, E. Eur. J. Inorg. Chem.
2002, 1269. (d) Prim, D.; Andrioletti, B.; Rose-Munch, F.; Rose, E.; Couty, F.
Tetrahedron 2004, 60, 3325. (e) Sweigart, D. A.; Reingold, J. A.; Son, S. U.
Comprehensive Organometallic Chemistry III; Crabtree, R. H.; Mingos,
D. M. P., Eds.; Elsevier Science Ltd: Oxford, 2006; Vol. 5, p 761.
ꢀ
F.; Rose, E.; Gerard, H. Organometallics 2008, 27, 626. (c) Jacques, B.;
ꢀ
Eloi, A.; Chavarot-Kerlidou, M.; Rose-Munch, F.; Rose, E.; Gerard, H.;
Herson, P. Organometallics 2008, 27, 2505. (d) Eloi, A.; Rose-Munch, F.;
ꢀ
Rose, E.; Chavarot-Kerlidou, M.; Gerard, H. Organometallics 2009, 28, 925.
r
pubs.acs.org/Organometallics
Published on Web 08/17/2010
2010 American Chemical Society

Article
Organometallics, Vol. 29, No. 17, 2010 3877
Scheme 1. Functionalization of (η5-Cyclohexadienyl)Mn(CO)3
Complexes
Scheme 2. Addition of Bromo- and Chloro-Ester Carbanions to
an η6-Arene-Mn Complex
One of the common features of (η6-arene)-Cr(CO)3 and
þ
-Mn(CO)3 complexes is their planar chirality, which has
Scheme 3. Methodology Applied for the Resolution of (η6-
Arene)Mn(CO)3þ Complexes Using a Chiral Nucleophile
“Round Trip”
been intensively investigated particularly for Cr complexes.
Thus, planar chiral η6-arene-Cr complexes have been applied
in numerous examples as highly valuable starting materials for
asymmetric synthesis of complex natural products or bioactive
compounds5 as well as ligands for asymmetric catalysis.1d,7
Hence, the preparation of enantiomerically pure planar chiral
η6-arene-Cr complexes is an important task, and various
approaches are now available. They can be obtained by
resolution, by diastereoselective syntheses, or by enantioselec-
tive methods.1d,8 In contrast, only two specific examples of
nonracemic planar chiral cationic η6 Mn complexes have so far
been reporþted to the best of our knowledge, starting from (p-cresol)-
Mn(CO)3 derivatives.9 As for η5-cyclohexadienyl-Mn com-
plexes, only a few syntheses of nonracemic planar chiral (η5-
cyclohexadienyl)Mn(CO)3 derivatives have been achieved by
diastereoselective addition of nucleophiles to cationic η6-are-
ne-Mn complexes.10,11 In the last three years, two enantioen-
riched η5-cyclohexadienyl-Mn complexes, substituted by either
a formyl or a phosphino group, have been obtained: (i) by
resolution of a planar chiral formyl-substituted η5 complex
through the formation of the corresponding aminal from a chiral
diamine;5a,c (ii) by resolution of a planar chiral phosphino-
substituted η5 complex through the formation of a chiral palla-
dium complex.12 In this specific context, it was highly valuable to
develop an efficient and easy methodology, as general as possible,
to prepare enantiomerically pure planar chiral cationic η6-arene-
Mn complexes and apply it to a range of substrates with fruitful
prospects in the field of enantioselective synthesis.
preliminary communication.13 The synthetic strategy pro-
posed is completed by the development of a direct analysis
method of the enantiomeric purity of the η6-arene-Mn
complexes using proton-decoupling deuterium (2H{1H})
2D NMR in chiral polypeptide oriented solvents.
2. Results and Discussion
2.1. Resolution of Cationic η6-Complexes. Stabilized car-
banions addeasilytothearene ringofη6-arene-Mn complexes,
giving the corresponding η5-cyclohexadienyl-Mn derivatives.2
For bromo- or chloro-ester carbanions, we have pointed out that
the corresponding neutral η5-Mn complexes in the presence of an
acid were not stable and restored the starting material under
harsh conditions such as a mixture of CF3CO2H and HPF6 used
to provide the counteranion (Scheme 2).14a Ideally we tried to
take advantage of this reactional “reversibility” by choosing
adequate chiral enantiopure carbanions that could form diaster-
eoisomeric η5 complexes stable enough to be separated on silica
gel column chromatography.
A rearomatization process by elimination of the chiral
auxiliary (from which the name “round trip”) would give
access to enantiopure cationic η6 complexes (see Scheme 3).
This strategy addressed two important points: (i) the nature
of the enantiopure carbanion; (ii) the rearomatization meth-
od, which should be efficient but nevertheless mild enough in
order to be compatible with η5 and η6 complexes.
We report in the present work the first method for the
resolution of ortho- and meta-disubstituted planar chiral
racemic η6-arene-Mn complexes using (D)-(þ)-camphor
enolate as the chiral auxiliary as well as several examples of
applications in enantioselective organic and organometallic
syntheses. Part of this work has been the subject of a
€
(6) Kundig, E. P. Topics in Organometallic Chemistry; Springer:
Berlin, 2004; Vol. 7.
Choice of the Chiral Enantiopure Enolate. In our prelimin-
ary attempts, we chose as chiral auxiliary four primary
carbanions issued from the methyl groups of either amide,
esters, or ketone (see Figure 1), thus avoiding the formation
of another chiral element by addition to the η6 complex. Two
diastereoisomers were obtained in each case. Unfortunately,
they had exactly the same polarity, and hence, they could not
be separated by silica gel chromatography. Furthermore 1H
NMR spectra recorded at 400 MHz (and even at higher field)
have shown almost the same patterns, and so this approach
failed to afford any information on the selectivity.
(7) (a) Bolm, C.; Muniz, K. Chem. Soc. Rev. 1999, 28, 51. (b) Salzer, A.
Coord. Chem. Rev. 2003, 242, 59.
(8) Kundig, E. P.; Pache, S. Science of Synthesis; Noyori, R.; Imamoto,
T., Eds.; Thieme Verlag, 2002; Vol. 2, p 155.
(9) Son, S. U.; Park, K. H.; Lee, S. J.; Seo, H.; Chung, Y. K. Chem.
Commun. 2002, 1230.
€
(10) For addition of chiral nonracemic nucleophiles to achiral η6-
arene-Mn complexes, see for example: (a) Miles, W. H.; Brinkman,
H. R. Tetrahedron Lett. 1992, 33, 589. (b) Miles, W. H.; Smiley, P. M.;
Brinkman, H. R. J. Chem. Soc., Chem. Commun. 1989, 1897.
(11) For addition of achiral nucleophiles to chiral auxiliary-substi-
tuted η6 arene-Mn complexes, see for example: (a) Pearson, A. J.; Zhu,
P. Y.; Youngs, W. J.; Bradshaw, J. D.; Mc Conville, D. B. J. Am. Chem.
Soc. 1993, 115, 10376. (b) Pearson, A. J.; Gontcharov, A. V.; Zhu, P. Y.
Tetrahedron 1997, 53, 3849.
We then turned our attention to a more rigid chiral
auxiliary, namely, camphor enolate, which comes from a
(12) Cetiner, D.; Jacques, B.; Payet, E.; Chavarot-Kerlidou, M.;
Rose-Munch, F.; Rose, E.; Tranchier, J.-P.; Herson, P. Dalton Trans.
2009, 27.
(13) Part of this work has been the subject of a preliminary commu-
nication: Eloi, A.; Rose-Munch, F.; Rose, E. J. Am. Chem. Soc. 2009,
131, 14178.
(14) (a) Balssa, F. Ph.D. Thesis, University of Paris 6 (France), 1995,
unpublished results. (b) Balssa, F.; Gagliardini, V.; Rose-Munch, F.;
Rose, E. Organometallics 1996, 15, 4373.

3878 Organometallics, Vol. 29, No. 17, 2010
Eloi et al.
Figure 1. Structures of the Amide, Esters, and Ketone Chosen
As Chiral Auxiliaries.
Scheme 4. Addition of Camphor Enolate to m-Methylanisole
Complex
Figure 2. ORTEP view of the mixture of diastereoisomers 2a of F1.
in MeOH in order to epimerize the exo isomer at the C9
carbon into the more stable endo isomer.
The crude mixture of each experiment presented two spots
on TLC plates with exactly the same polarities and for which
the 1H NMR spectra had the same fingerprint. These experi-
mental observations are compatible with the schematic
description proposed in Figure 3. Thus we can qualitatively
explain the presence of the two spots as well as the corre-
sponding stereochemical composition after epimerization,
which is not complete due to the equilibrium limit of the
transformation of the exo/endo isomers (i.e., 10/90). Conse-
quently, in each experiment a small quantity of diastereoisomers
(S,2pS)-2a and (S,2pR)-2a remains present (Figure 3).
Knowing precisely the behavior of the compounds in each
fraction during the epimerization process, we proposed the
following optimized protocol. A solution of (D)-(þ)-cam-
phor enolate was added to complex (rac)-1a, giving a mixture
of two pairs of diastereoisomers, (R,2pR)-, (S,2pS)- and
(R,2pS)-, (S,2pR)-2a, in the ratio 30:70. Epimerization was
then achieved upon transferring a saturated solution of
K2CO3 in MeOH to the crude mixture, affording diastereoi-
somers (R,2pR)- and (S,2pS)-2a in an excellent ratio, >90:10,
and (R,2pS)- and (S,2pR)-2a in a ratio of >92:8. Purification by
chromatography afforded two diastereoisomers, (R,2pR) and
(R,2pS), in 44% and 48% yield, with >80% and 84% de,
respectively (measured by 1H NMR). After recrystallization, the
complexes (R,2pR)-2a and (R,2pS)-2a were isolated with >98%
de each (Scheme 5).18
commercially available, enantiopure compound.15 Addition
of camphor enolate to meta-methylanisole-Mn(CO)314b in
THF at low temperature should lead to the formation of four
diastereoisomers due to the presence of two types of chir-
ality: (i) the planar chirality of the η5 complexes; (ii) the new
stereogenic center C9 formed at the carbon R to the carbonyl
of the camphyl group with formation of the endo and exo
isomers (Scheme 4).
After completion of the reaction, the analysis of the crude
mixture by thin-layer chromatography plates (petroleum ether/
diethyl ether, 70/30) showed only two spots clearly distinguished
with a high degree of separation (Rf values: 0.4 and 0.6).
Purification of the mixture by silica gel column chroma-
tography led to two fractions, whose the analysis of 1H NMR
spectra fortunately indicated the presence of four different η5
complexes, two in each fraction.
Crystals of the less polar fraction (called F1) were readily
obtained from a diethyl ether solution by a two-well diffu-
sion procedure (petroleum ether in the outer well). Their
X-ray analysis16 (Figure 2) clearly shows the presence of four
molecules in the cell, but only two are different with a change
of both chiralities at the same time: (R,2pR)-2a for diaster-
eoisomer A and (S,2pS)-2a for B. The chirality of the
complexes has been conventionally described by the config-
uration at the C9 center (R or S), together with the corre-
sponding configuration at the chiral plane (2pR or 2pS).17
In light of these results, it was easy to deduce the (R,2pS) þ
(S,2pR) diastereoisomeric composition of the second frac-
tion, F2. Each fraction was submitted to the action of K2CO3
The assignment of the absolute configuration of the planar
chiral η5-cyclohexadienyl moiety was determined through
X-ray analysis of suitable crystals of the diastereoisomer
(R,2pR)-2a (see Figure 4).16
New Method of Rearomatization by Elimination of the
Chiral Auxiliary. Up to now, only two methods of rear-
omatization of η5 complexes have been described in the
literature. The first one, generally using either N-bromosuc-
cinimide or DDQ, involves an oxidative rearomatization
with the loss of the Mn(CO)3 entity.10b,19-21 The second
(15) The camphyl group has been shown to provide an interesting
asymmetric environment in Cr complexes; see: Paramahamsan, H.; Pearson,
A. J.; Pinkerton, A. A.; Zhurova, E. A. Organometallics 2008, 27, 900.
(16) Details of the X-ray structure analyses of F1, (R,2pR)-2a, (1pR)-
1a, (þ)-1c, and (-)-4c are compiled in Table 1 in the Supporting
Information. It is worth noting that the Flack parameters of (R,2pR)-
2a and (þ)-1c complexes are better than those of (1pR)-1a and (-)-4c
complexes. But as the two last complexes are derived from (R,2pR)-2a
and (þ)-1c with procedures that maintain the stereochemical informa-
tion, the absolute stereochemical assignments of (1pR)-1a and (-)-4c are
thus confirmed.
(18) Alternatively, to avoid the recrystallization step, each diaster-
eoisomer, after purification by column chromatography, could be
submitted to a second epimerization step.
(19) Pearson, A. J.; Bruhn, P. R. J. Org. Chem. 1991, 56, 7092.
(20) Pearson, A. J.; Shin, H. Tetrahedron 1992, 48, 7527.
(21) Pearson, A. J.; Lee, S. H.; Gouzoules, F. J. Chem. Soc., Perkin
Trans. 1 1990, 2251.
(17) The planar chirality was assigned according to the extending
Cahn-Ingold-Prelog rules described in: Gibson, S. E.; Ibrahim, H.
Chem. Commun. 2002, 2465.

Article
Organometallics, Vol. 29, No. 17, 2010 3879
Figure 3. Representation of the stereochemical composition of the mixture of diastereoisomers before and after epimerization.
Scheme 5. Purification and Rearomatization of η5-Mn Com-
plexes
Figure 4. Molecular structure of the diastereoisomer (R,2pR)-2a
depicting the absolute configuration of both chirality elements.
one, only applied to the case of η5 complexes substituted at
the sp3 carbon atom by two hydrogen atoms, uses trityl
tetrafluoroborate to abstract the exo hydride of the sp3
Scheme 6. Synthesis of Enantiopure m-Chloro and -Bromoani-
sole Complexes
carbon atom, and the corresponding η6 complex is obtained
with BF4 as counteranion.4,22,23 Under the experimental con-
ditions used in a previous study,14 the complex (R,2pR)-2a
was refluxed for 24 h in CF3COOH, and the expected
cationic η6 complex was isolated in a moderate yield of
30% after addition of HPF6. A much more convenient and
efficient method was identified. This consisted of stirring
complex (R,2pR)-2a in CH2Cl2 at room temperature in the
presence of a AgBF4/SiMe3Cl mixture. Under these condi-
tions, the presence of a silicium derivative favors the enolate
trapping by formation of a silylated enolate ether, while the
conditions, we achieved the resolution of meta-chloro (rac)-
1b and meta-bromo (rac)-1c, and we obtained (1pR)-1b,
(1pS)-1b, (1pR)-1c, and (1pS)-1c (Scheme 6) in yields ranging
BF4- anion plays the role of the counteranion, stabilizing the
cationic species after the chiral auxiliary elimination. Alter-
from 91% to 99%, with >98% ee each.
natively, another method, avoiding the expensive silver salt
Knowing the absolute configuration of the (R,2pR)-2a
AgBF4, involved the addition of a slight excess of [HBF4,
complex thanks to the X-ray analysis, we recrystallized the
OMe2] in a CH2Cl2 solution of the η5 complex. Addition of
corresponding cationic η6-arene complex (1pR)-1a, whose
Et2O in the crude mixture allowed the precipitation of the
X-ray analysis unambiguously confirmed its absolute con-
corresponding cationic η6 complex. Thus, complexes (1pR)-
1a and (1pS)-1a were successfully isolated in 94% and 96%
figuration (Figure 5).16 Thus, during the rearomatization
process, the planar chirality stayed unchanged.24
2.2. NMR Study in Chiral-Oriented Solvents. Whereas the
yield, respectively and >98% ee each (Scheme 5), assuming
that the ee kept the same value as the de value of the parent η5
1
de value was easily determined for each η5 complex by H
complex. In order to confirm this hypothesis, we have tested
NMR spectroscopy, the usual analytical methods for the
a specific example by deuterium 2D NMR spectroscopy in a
determination of ee’s failed when applied to the chiral
chiral liquid crystal (vide infra). Using the same experimental
cationic η6 complexes. Indeed neither the europium chiral
(22) Pauson, P. L.; Segal, J. A. J. Chem. Soc., Dalton Trans. 1975,
1677.
(23) (a) Jacques, B.; Tranchier, J.-P.; Rose-Munch, F.; Rose, E.;
Stephenson, G. R.; Guyard-Duhayon, C. Organometallics 2004, 23, 184.
(b) Schouteeten, S.; Tranchier, J.-P.; Rose-Munch, F.; Rose, E.; Auffrant, A.;
Stephenson, G. R. Organometallics 2004, 23, 4308. (c) Cetiner, D.; Tranchier,
J.-P.; Rose-Munch, F.; Rose, E.; Herson, P. Organometallics 2008, 27, 784.
(24) For diastereoseþlective nucleophilic addition to chiral-at-the-metal
η5-cyclohexadienyl Mn species see: Pike, R. D.; Ryan, W. J.; Carpenter,
G. B.; Sweigart, D. A. J. Am. Chem. Soc. 1989, 111, 8535. In this paper,
authors used the lithium enolate of (-)-bornylacetate as chiral auxiliary to
produce enantiomerically pure dienes after reactivation of the η5 complex with
NOPF6.

3880 Organometallics, Vol. 29, No. 17, 2010
Eloi et al.
Figure 5. Molecular structure of the enantiomer (1pR)-1a de-
picting the absolute configuration due to the planar chirality.
Scheme 7. Resolution of o-Trimethylsilylanisole Complexes 1d
and 1e
shift reagents nor chiral HPLC was successful, mainly due to
the instability and the insolubility of these cationic com-
plexes in polar organic solvents. In the literature, only two
approaches have been reported: (i) derivatization by anion
exchange with TRISPHAT25 (but this requires preparation
and isolation of the [chiral cation][TRISPHAT] salts prior to
the analysis); (ii) nucleophilic addition to obtain η5 com-
plexes that could be analyzed by HPLC.9 In this second case
the disadvantage is that each example requires a new reaction
whose yield and conversion need to be quantitative. To over-
come this recurrent problem in the field of the chiral molecule
analysis, we turned our attention toward a direct spectroscopic
tool: NMR in polypeptide chiral liquid crystals (CLCs).26 This
approach is a very efficient tool for analyzing a wide range of
chiral compounds including metal complexes, and recently it
showed to be a valuable method for the enantiomeric discri-
mination of planar chiral (η6-arene)Cr(CO)3 complexes.27 In
order to address the possible problem of solubility of cationic
complexes in liquid-crystalline solvents, we chose a trimethyl-
silyl complex as starting material, namely, the ortho-trimethyl-
silyl-anisole derivative complex 1d bearing the silyl group ortho
to the methoxy substituent (Scheme 7).
Figure 6. 2H quadrupolar doublets of (a) (rac)-1e, (b) (-)-1e
(86% ee), and (c) (þ)-1e (77% ee) obtained without recrystalli-
zation of the parent η5 complex and (d) (þ)-1e (>98% ee)
isolated after recrystallization of the parent η5 complex. These
doublets are extracted from the 92.1 MHz 2H Q-COSY Fz map
recorded in PBLG/CHCl3 mesophases after the tilt procedure.
The ee’s were determined by both peak integration and reso-
nance deconvolution.
was unsuccessful here due to rather broad 13C resonances
(vide infra), thus preventing the possibility to spectrally discri-
minate the charged enantiomers on the basis of carbon-13
chemical shift anisotropy difference.26a,b As a possible alterna-
tive, we turned our attention to 2H{1H} NMR using isotopically
enriched analytes. This option was highly valuable as far as the
synthesis of the labeled analyte was simple to reach. This is the
case here because the synthesis of the labeled complex (rac)-1e
was easily achieved by complexation of the free deuterated
trimethylsilylanisole. The corresponding diastereoisomeric η5
complexes were formed by addition of the enolate and isolated
in 40% and 42% yield with >86 and 77% de, respectively. After
recrystallization, the η5 complexes (R,pR)-2e and (R,pS)-2e
were obtained with >98% de each. Their rearomatization
yielded the (1pR)-1e and (1pS)-1e η6 complexes (Scheme 7).
Deuterated η6 complexes in racemic and enantioenriched series
obtained before and after recrystallization of the η5 parent
complexes were analyzed using 2H{1H} 2D-NMR experiments
in a chiral liquid crystal (CLC) made of poly-γ-benzyl-L-
glutamate (PBLG).26,28 In this emerging and powerful analy-
tical technique, enantiomers-d1 are spectrally discriminated on
Under the same experimental conditions as those pre-
viously described, the diastereoisomeric η5 complexes were
formed and isolated in 42% and 43% yield with >86 and
77% de, respectively. After recrystallization, complexes (R,
pR)-2d and (R,pS)-2d were isolated with >98% de each.
Rearomatization by elimination of the chiral enolate gave
rise to the formation of enantiopure (1pR)-1d and (1pS)-1d
η6 complexes (>98% ee).
In contrast to the neutral chiral η6-arene Cr complexes,27
the natural abundance 13C{1H} NMR analysis in CLCs
2
the basis of differences of H quadrupolar splittings (ΔνQ’s),
yielding two distinct quadrupolar doublets (centered generally)
on the same δ2H, one for each enantiomeric complex (see
Figure 6a).26 Such a spectral situation is observed for (rac)-1e
when dissolved in the PBLG/CHCl3 system at 305 K, thus
(25) Planas, J. G.; Prim, D.; Rose, E.; Rose-Munch, F.; Monchaud,
D.; Lacour, J. Organometallics 2001, 20, 4107.
(26) (a) Lesot, P.; Merlet, D.; Meddour, A.; Loewenstein, A.; Courtieu,
J. J. Chem. Soc., Faraday Trans. 1995, 91, 1371. (b) Sarfati, M.; Lesot, P.;
Merlet, D.; Courtieu, J. Chem. Commun. 2000, 2069. (c) Lesot, P.; Sarfati, M.;
Courtieu, J. Chem. Eur. J. 2003, 9, 1724.
(27) Lafon, O.; Lesot, P.; Rivard, M.; Chavarot, M.; Rose-Munch,
F.; Rose, E. Organometallics 2005, 24, 4021.
(28) Lesot, P.; Courtieu, J. Prog. NMR Spectrosc. 2009, 55, 128.

Article
Organometallics, Vol. 29, No. 17, 2010 3881
pointing out the shape recognition of mirror-image complexes
by the mesophase.
η6-arene-Cr series and represents an efficient tool for the
synthesis of functionalized alicyclic molecules,2b in the η6-
arene-Mn series, only very few studies have been reported.6
The most direct route to manganese-mediated dearomatiza-
tion reactions requires the treatment of cationic (η6-arene)-
Mn(CO)3þ complexes with two nucleophiles, which can be either
hydride32 or a C-nucleophile.33 Decomplexation to cyclohexa-
dienes is simply achieved by stirring the mixture in the presence of
oxygen. Very little work has been described in this area, whereas
the most extensive study is related to an indirect route that
involves reactivation of the neutral η5-manganese complex result-
ing from the first nucleophilic addition by replacement of a CO
ligand with NOþ.34-39 This situation motivated us to determine
whether double nucleophilic addition to the enantiopure meth-
oxy-substituted η6 complexes could provide a synthetic route to
enantiopure 4-substituted cyclohexenones.40,41
Regioselective meta addition of LiAlH4 to the enantiopure
m-chloro- and m-bromoanisole complexes (-)-1b and (-)-1c
yielded neutral complexes (-)-3b and (þ)-3c, in 70% and
72% yield, respectively. Dearomatization by addition of a
second nucleophile, LiCMe2CN, to the complexes (-)-3b
and (þ)-3c led to the formation of the anionic η4-Mn
intermediates formed by an exo attack with respect to the
Mn(CO)3 entity to the C5 carbon atom by the second
nucleophile (Scheme 8). After oxidative demetalation, an
acidic hydrolysis generated the corresponding enantiopure
3-chloro- and 3-bromocyclohexenones (þ)-4b and (þ)-4c in
different yields according to the methods of oxidation used.
Indeed, in the presence of iodine or oxygen bubbling, only
moderate yields of 40% and 60%, respectively, were ob-
tained. However when FeCl3 was tested as oxidant,10a,24
both halogenated cyclohexenones were isolated in 76%
yield, and hence this oxidant was chosen in further examples.
At this stage, it could be assumed that the remarkable
efficiency and regioselectivity of the second nucleophilic
attack, ortho with respect to the halogen group, was certainly
due to the inductive effect of the bromide or chloride sub-
stituent. To our knowledge, this synthesis represents the first
example of double nucleophilic addition to a η6-anisole
derivative Mn complex without reactivation of the η5 com-
plex intermediate by replacement of a CO ligand with NOþ.
Upon treatment of complex (þ)-3c with another carbanion
such as diphenylmethane carbanion, bromocyclohexenone
To avoid possible destabilization of the CLC by the
presence of cationic entities, we dissolved a very small
amount of complexes (∼5-10 mg). This simple solution is,
however, not always favorable from a spectral point of view
because the increase of solute ordering leads to rather large
2H splittings, accompanied by a broadening of linewidths
(proportional to ΔνQ).29 This effect originates from both the
residual magnetic field and mesophase inhomogeneities, but
it can be partially avoided using the Q-COSY Fz 2D experi-
ments due to the refocusing of the inhomogeneities by the
sequence.26b,30,31 In the case of 1e, the magnitude of ΔνQ’s is
unusually large (over 1300 Hz), and linewidths are around 40
Hz, while the half difference of ΔνQ’s is about 70 Hz. In
regard to the good fluidity of the PBLG NMR samples
obtained, these spectral features suggest strong electrostatic
interactions between these charged complexes and the poly-
peptide molecule, thus slowing the molecular tumbling of the
former. Besides, the close proximity of the 55Mn atom (I = 5/2)
that possesses a large nuclear quadrupole moment (0.55 ꢀ
10-28 m2) could also participate in the relaxation mechan-
isms by decreasing the T1 and T2 relaxation times, leading to
additional 2H lineshape broadening.31 The very short long-
2
itudinal H relaxation time of the aromatic deuterium site
assessed using an inversion-recovery sequence (T1 = 21 ms)
1
confirms these arguments. The low-resolution H and 13C-
{1H} spectra recorded in the same could also result from the
presence of 55Mn atom. Consequently, considering the spin
number (I = 5/2) and magnitude of Q associated with the
55Mn nuclei, which are not favorable for recording high-
resolution spectra, 55Mn{1H} NMR spectroscopy in the
PBLG mesophases has not been explored in this work.
Figure 6 shows both the 2H doublets obtained for racemic
(a) and enantioenriched mixtures (b-d) and extracted from
the tilted 2D Q-COSY Fz spectrum. This process allows the
extraction of columns corresponding to each inequivalent
deuterium site.28 As expected, the use of a 2D sequence
reduces significantly the linewidths of 2H resonances (<25 Hz),
thus allowing the spectral discrimination until the spectral
baseline of signals, contrarily to the 1D spectra. This resolution
improvement is crucial to measure scalemic mixtures with high
ee. Thus we were able to evaluate very accurately the ee of chiral
η6 complexes before and after recrystallization of the corre-
sponding η5 complexes. The ee > 98% obtained after recrys-
tallization proves conclusively that no racemization occurs
during the rearomatization step, in good agreement with our
initial assumption. Furthermore, this new result shows, for the
first time, that NMR in the chiral mesophase can be efficiently
used for analyzing chiral charged metallic complexes. This
statement was far from being obvious initially considering the
polarity of those cationic arene-manganese complexes.
(32) Brookhart, M.; Lukacs, A. J. Am. Chem. Soc. 1984, 106, 4164.
(33) Roell, B. C.; McDaniel, K. F.; Vaughan, W. S.; Macy, T. S.
Organometallics 1993, 12, 224.
(34) Pike, R. D.; Sweigart, D. A. Synlett 1990, 565.
(35) Chung, Y. K.; Sweigart, D. A.; Connelly, N. G.; Sheridan, J. B.
J. Am. Chem. Soc. 1985, 107, 2388.
(36) Lee, T. Y.; Kang, Y. K.; Chung, Y. K.; Pike, R. D.; Sweigart,
D. A. Inorg. Chim. Acta 1993, 214, 125.
(37) Pike, R. D.; Ryan, W. J.; Lennhoff, N. S.; Van Epp, J.; Sweigart,
D. A. J. Am. Chem. Soc. 1990, 112, 4798.
(38) Sheridan, J. B.; Padda, R. S.; Chaffee, K.; Wang, C.; Huang, Y.
J. Chem. Soc., Dalton Trans. 1992, 1539.
(39) Pearson, A. J.; Gontcharov, A. V.; Zhu, P. Y. Tetrahedron 1997,
53, 3849.
(40) Enantiopure cyclohexenones are useful building blocks for a
wide variety of natural products and for synthetic transformations. See
for example: Evarts, J.; Torres, E.; Fuchs, P. L. J. Am. Chem. Soc. 2002,
124, 11093.
2.3. Applications to Organic and Organometallic Enantio-
selective Syntheses. The potential of the enantiopure η6
complexes in the field of enantioselective syntheses of 4-sub-
stituted cyclohexenones and (η6-phosphinoarene)Mn-
(CO)3þ complexes was next investigated.
Cyclohexenone Synthesis. Whereas the metal-mediated
dearomatization process has been extensively studied in the
(41) As far as we are aware, very few reports of nucleophile additions
to alkoxy-substituted (η6-arene)Mn(CO)3 complexes have been pub-
þ
(29) Lesot, P.; Lafon, O.; Aroulanda, C.; Dong, R. Y. Chem. Eur. J.
2008, 14, 4082.
(30) Lafon, O.; Lesot, P.; Merlet, D.; Courtieu, J. J. Magn. Reson.
lished to deliver 5-substituted cyclohexenones: Pearson, A. J.; Vickerman,
R. J. Tetrahedron Lett. 1998, 39, 5931. See also ref 11. It may be noted that
formation of cyclohexenones has been developed starting from alkoxy-
substituted (η6-arene)Cr(CO)3 as well as from dihapto-coordinated com-
plexes of Os.
2004, 171, 135.
(31) Levitt, M. H. In Spin Dynamics; Wiley & Sons: Chichester, 2007.

3882 Organometallics, Vol. 29, No. 17, 2010
Eloi et al.
Scheme 8. Synthesis of Enantiopure Cyclohexenones 4
Figure 7. ORTEP views of complex (þ)-1c and the correspond-
˚
ing enone (-)-4c. Selected bond lengths (A) for (þ)-1c: Mn-C1
2.184(4); Mn-C2 2.198(4); Mn-C3 2.247(4); Mn-C4 2.201(4);
Mn-C52.161(4);Mn-C62. 168(4);C1-Br 1.884(5). For (-)-4c:
C2-C3 1.318(4); C2-C1 1.463(4); C1-C6 1.494(5); C6-C5
1.525(4); C5-C4 1.536(4); C3-C4 1.507(4); C1-01 1.219(4);
C10-N 1.133(4).
(þ)-4d was obtained in an excellent yield of 92%. Treatment of
(þ)-3c with one equivalent of BuLi followed by hydrolysis
gave the enantiopure (η5-2-methoxycyclohexadienyl)Mn-
(CO)3 complex (-)-3d in 96% yield, a key organometallic
chiral synthon that cannot be obtained through the resolution
of the (η6-anisole)Mn(CO)3þ parent complex since this mono-
substituted complex has no planar chirality. Addition of
isobutyronitrile, diphenylmethyl, triphenylmethyl, and di-
methylacetate carbanions delivered the enantiopure cyclohex-
enones (þ)-4e, (þ)-4f, (þ)-4g, and (þ)-4h in 75%, 80%, 82%,
and 74% yield, respectively and with 98% ee (Scheme 8). Thus,
even without any halogen substituent, η5-Mn complex (-)-3d
was sufficiently activated by the Mn(CO)3 tripod toward
nucleophilic addition. Interestingly, the regioselectivity at the
C5 carbon atom is entirely determined by the presence of the
electro-donor methoxy group that deactivates sterically and
electronically the C1 carbon atom toward addition of nucleo-
philes. We were lucky enough to obtain nice crystals suitable
for X-ray diffraction studies not only of the enantiopure
complex (þ)-1c but also of the corresponding enone (-)-4c
obtained by hydride then isobutyronitrile carbanion addition
to complex (þ)-1c.16 The main information given by the first
structure is the absolute configuration (1pS)-1c of the η6
complex. The ORTEP view of compound (-)-4c indicates
the presence of the ketone function conjugated to the C2-C3,
modulator in the metal coordination sphere.43 Most of the
examples of such non-metallocenic structures reported to date
rely on a planar chiral (η6-arene)Cr(CO)3 complex,7,17,44 and
very few examples are based on different transition metals
involving Mn45 (in cymantrene-derived complexes), Re,46 or
þ
Fe.47 No ligand containing a planar chiral (η6-arene)Mn(CO)3
complex was described so far, and the first example of an
enantiopure planar chiral ligand built on a (η5-cyclohexadie-
nyl)Mn(CO)3 complex skeleton was only reported in 200912 and
involves a resolution procedure using a chiral palladium com-
plex intermediate. Consequently, we decided to determine
whether the enantiopure cationic η6 complexes now available
by resolution could be interesting building blocks for the
versatile synthesis of η5 and η6 enantiopure new Mn-based
ligands by functionalization using halogen-metal exchange48
or lithiation/electrophilic quench method.5 For this purpose, we
chose complex (þ)-3c as starting material. Treatment with BuLi
formed the lithiated intermediate by halogen-metal exchange
reaction,48 which is quenched with PPh2Cl to deliver complex
(-)-3e in 69% yield (Scheme 9). The regioselectivity of the
functionalization is unambigously confirmed by the upfield shift
of the H3 proton signal from 6.17 ppm for complex (þ)-3c to
5.40 ppm for complex (-)-3e. Encouragingly, abstraction of
hydride with CPh3BF4 allowed rearomatization to isolate thþe
cationic meta-disubstituted (η6-phosphinoanisole)Mn(CO)3
complex (-)-1f in 85% yield. Signals corresponding to the
protons of the η5-cyclohexadienyl π system of (-)-3e between
2.24 and 5.40 ppm and the singlet of the methoxy group at 3.34
ppm are replaced by a set of signals between 5.96 and 7.18 ppm
and a singlet at 4.16 ppm in the spectrum of (-)-1f, in good
agreement with the expected downfield shift due to the forma-
tion of the arene coordinated to the cationic Mn(CO)3 entity. To
the best of our knowledge, this represents the first example of a
˚
whose the 1.318(4) A length suggests a double bond. More
important, the configuration of the C4 carbon atom that
added the second nucleophile, namely, the isobutyronitrile
carbanion, could be attributed, and its R configuration con-
firms the mechanism of this addition. Indeed this is in perfect
agreement with an attack exo to the Mn(CO)3 tripod of the
(η5-1-bromo-3-methoxycyclohexadienyl)Mn(CO)3, whichrules
out the possibility of an endo migration from an alkylmanganese
intermediate formed by addition of the carbanion to the metal
atom. Such an endo migration was observed in the reaction of
phenyl- or methyllithium with (η5-cyclohexadienyl)Mn(CO)3
complexes.37 Indeed, acylmetalates were formed by ready addi-
tion of the carbanions to the manganese carbonyl ligands of the
η5 complexes, and endo-substituted cyclohexenyl complexes
were obtained after phenyl or methyl migration from the acyl
group to the endo face of the six-membered-ring ligand.
€
€
(44) Muniz, K. Topics in Organometallic Chemistry; Kundig, E. P., Ed.;
Springer, 2004; Vol. 7, p 205
(45) For cymantrene derivatives see: (a) Kudis, S.; Helmchen, G.
Angew. Chem., Int. Ed. 1998, 37, 3047. (b) Son, S. U.; Park, K. H.; Lee, S. J.;
Chung, Y. K.; Sweigart, D. A. Chem. Commun. 2001, 1290. (c) Deschamps,
B.; Ricard, L.; Mathey, F. J. Organomet. Chem. 2004, 689, 4647.
(d) Wechsler, D.; Rankin, M. A.; McDonald, R.; Ferguson, M. J.; Schatte,
G.; Stradiotto, M. Organometallics 2007, 26, 6418.
η6-Phosphinoarene Complexes. Chiral ligands based on
planar chiral tricarbonyl metal complexes represent an ori-
ginal family of ligands for enantioselective catalysis.42 The
“spectator” transition metal fragment not only creates the
planar chirality but may also act as a steric and electronic
(46) For (η5-Cp)Re(CO)3 derivatives see: (a) Bolm, C.; Kesselgruber,
M.; Hermanns, N.; Hildebrand, J. P.; Raabe, G. Angew. Chem., Int. Ed.
2001, 40, 1488. (b) Eichenseher, S.; Delacroix, O.; Kromm, K.; Hampel, F.;
Gladysz, J. A. Organometallics 2005, 24, 245.
(47) For an (η4-diene)Fe(CO)3 fragment see: Okamoto, K.; Kimachi,
T.; Ibuka, T.; Takemoto, Y. Tetrahedron: Asymmetry 2001, 12, 463.
(48) Eloi, A.; Rose-Munch, F.; Rose, E.; Lennartz, P. Organometal-
lics 2009, 28, 5757.
(42) Delacroix, O.; Gladysz, J. A. Chem. Commun. 2003, 665.
(43) Jones, G. B.; Chapman, B. J.; Mathews, J. E. J. Org. Chem. 1998,
63, 2928.

Article
Organometallics, Vol. 29, No. 17, 2010 3883
Scheme 9. Syntheses of Enantiopure (η6-Phosphinoanisole)Mn
no-substituted complexes through a lithiation-electrophilic
quench sequence serves to demonstrate the potential of this
method for generating new enantiopure ligands for transition
metal complexes.
(CO)3+ Complexes
Experimental Section
NMR in PBLG Solvent. The composition of oriented NMR
samples are 10 ( 1 mg of solute, 100 ( 1 mg of PBLG with DP =
768, and 100 mg and 552 ( 1 mg of dry chloroform. Details on
the oriented sample preparation and the potential of the NMR
spectroscopy in PBLG can be found in ref 25. The Q-COSY Fz
2D spectra were recorded on a 14.1 T Avance II Bruker spectro-
meter equipped with a 2H cryoprobe, using a data 2D matrix of
3000 (t2) ꢀ 512 (t1) points and 8 scans for each t1. Exponential
filtering (1.5 Hz) is applied in both spectral dimensions. 1H
signals are decoupled by the Waltz-16 sequence.
General Remarks. All reactions were performed in oven-dried
glassware under an inert atmosphere (nitrogen). Reagent-grade
dichloromethane was distilled over calcium hydride, and tetrahy-
drofuran was dried over benzophenone ketyl and distilled. All the
arenes were distilled over calcium hydride prior to use. Analytical
thin-layer chromatography was performed on Merck silica gel 60
cationic (η6-phosphinoarene)Mn(CO)3 complex,49 which is, in
addition, enantiopure. Subjecting complex (-)-3d to the same
experimental conditions (BuLi then PPh2Cl quenching) resulted
in the isolation of the ortho-substituted regioisomer (-)-3f in
68% yield. The regioselective substitution at the C3 carbon atom
is confirmed by the disappearance of the H3 proton signal at
5.83 ppm, together with an upfield shift of the H4 proton signal
(4.86 and 4.22 ppm for 3d and 3f, respectively). The rear-
omatization of complex (-)-3f easily occurred with CPh3BF4
to deliver the cationic ortho-disubstituted (η6-phosphinoanisole)
F254 plates (0.25 mm). Compounds were visualized by UV irradia-
tion. Flash column chromatography was carried out using forced
flow of the indicated solvent on Roth Kieselgel 60 (0.02-
0.045 mm). 1H and 13C NMR spectra were recorded on a Bruker
AC 200 MHz and a Bruker ARX 400 MHz, with chemical shifts
referenced to the internal standard CDCl3. Infrared spectra were
measured on a Nicolet-Avatar 320 FT-IR spectrometer. Crystal-
lographic data were collected on an Enraf-Nonius Cad-4 diffract-
ometer. High-resolution mass spectral analyses were performed by
þ
Mn(CO)3 complex (-)-1g in 95% yield. Again, the set of
signals between 2.74 and 4.22 ppm characterizing the η5-cyclo-
hexadienyl π system of (-)-3f is shifted downfield between 7.27
and 6.25 ppm in the rearomatized compound (-)-1g.
ꢀ
the Groupe de Spectrometrie de Masse (UMR 7613, UPMC).
Elemental analyses were performed by Le Service de Microanalyses
3. Conclusion
ꢀ
de l’Universite P. et M. Curie (Paris). Optical rotations were
measured on a Perkin-Elmer 343 polarimeter at 589 nm. GC
analyses were performed on a Varian CP3380 instrument, equipped
with a Cyclodex B fused silica column (50 m ꢀ 0.25 mm).
Preparation of racemic cationic (η6-arene)Mn(CO)3 complexes,
see the Supporting Information.
This paper reports on the first resolution of cationic ortho-
and meta-disubstituted arenetricarbonylmanganese com-
plexes through (D)-(þ)-camphor enolate addition, isomeriza-
tion of the newly formed C9 stereogenic center, separation of
the corresponding η5-cyclohexadienyl diastereoisomers, and
then elimination of the chiral auxiliary by a quantitative
method of rearomatization. To overcome the failure of usual
methods to determine the enantiomeric purity of chiral catio-
nic η6 complexes, we have demonstrated that deuterium 2D
NMR in chiral-oriented solvents is a very adequate tool for
investigating this class of compounds. Thus we have been able
to directly evaluate the ee value of one of the new enantiopure
η6 cationic complexes and thus experimentally prove unam-
biguously that the rearomatization step occurred with a total
conservation of the stereochemical information. This resolu-
tion method based on the “round trip” of a cheap, commer-
cially available chiral nucleophile is a general approach. It
involves only the intrinsic electrophilic properties of the co-
ordinated ring, simply implying two changes of hapticity: η6 to
η5 for the addition step and η5 to η6 for the elimination one. A
wide range of applications may now be envisioned in the field
of organic as well as organometallic enantioselective synthesis,
mainly due to the compatibility with the presence of halides
and alkoxy groups on the arene moiety. Thus, a short and
versatile route to a series of enantiopure 3,4-disubstituted
cyclohexenones has been tested involving a double nucleophi-
lic addition to the enantiopure (η6-meta-bromoanisole)Mn
(CO)3þ. Finally, the synthesis of the first η5- and η6-phosphi-
Synthesis of Complexes 2a-e. Typical Procedure for the Addition
of the Chiral Nucleophile. To a suspension of 1a (1 mmol) in THF
(5 mL) cooled at -78 °C was added a solution of camphor enolate
(1.2 mmol in 5 mL of THF). After 5 min stirring at -78 °C, the
mixture was slowly warmed to room temperature and quenched by
the addition of H2O. After extraction with Et2O the combined
organic layers were washed with a saturated aqueous solution of
NaCl and dried over MgSO4. After concentration in vacuo, a yellow
oil was obtained, which was stirred for epimerization with a
saturated solution of K2CO3 in MeOH (5 mmol in 20 mL) for
24 h. Usual workup afforded a mixture of the diastereoisomers 2a,
which were separated by flash chromatography on silica gel (eluent:
100:1, EP/Et2O).
(R,2pR)-2a (the least polar diastereoisomer): m = 181 mg, Y =
1
44%. H NMR (400 MHz, benzene-d6): δ 0.38 (s, 3H, camphyl
Me), 0.56 (s, 3H, camphyl Me), 0.74 (s, 3H, camphyl Me), 0.92 to
(49) The first (η6-phosphinoarene)Cr(CO)3 was described more than 30
years ago: Rausch, M. D.; Gloth, R. E. J. Organomet. Chem. 1978, 153, 59.
1.34 (m, 4H, camphyl CH2), 1.42 (m, 1H, H9), 1.46 (3H, s, η5 Me),

3884 Organometallics, Vol. 29, No. 17, 2010
Eloi et al.
1.55 (m, 1H, H14), 2.39 (d, 1H, H5 or H1, J = 6.0 Hz), 2.72 (dd, 1H,
H6, J = 6.0 Hz and J = 9.8 Hz), 3.10 (s, 3H, OMe), 3.59 (d, 1H, H1
or H5, J = 6.0 Hz), 5.39 (s, 1H, H3) ppm. 13C NMR (100 MHz,
benzene-d6): δ 9.5 (camphyl Me), 18.8 (camphyl Me), 19.1 (cam-
phyl Me), 20.8 (camphyl CH2), 22.1 (η5 Me), 30.5 (camphyl CH2),
38.3 (C6), 43.8 (C14), 44.1 (C1 or C5), 45.0 (Cquat), 54.0 (C5 or C1),
54.2 (OMe), 58.3 (Cquat), 61.4 (C9), 71.9 (C3), 107.8 (C4), 142.0 (C2),
216.7 (camphyl CO) ppm. IR (ATR Diamant): ν 1727 (camphyl
CO), 1907 (Mn(CO)3), 2002 (Mn(CO)3) cm-1. HRMS (ESIþ):
calcd for C21H25O5MnNaþ 435.0980, found 435.0975. Anal.
CO), 1927 (Mn(CO)3), 2016 (Mn(CO)3) cm-1. HRMS: calcd for
C20H22BrO5MnNaþ 498.9929, found 498.9933. Anal. Calcd for
C20H22BrO5Mn: C, 50.34; H, 4.65. Found: C, 50.41; H, 4.61.
[R]20D = þ2 cm3 g-1 dm-1 (CHCl3, c 0.99 g/100 mL).
Second diastereoisomer (the most polar): m = 200 mg, Y =
42%. 1H NMR (400 MHz, benzene-d6): δ 0.33 (s, 3H, camphyl
Me), 0.51 (s, 3H, camphyl Me), 0.72 (s, 3H, camphyl Me), 0.84 to
1.44 (m, 4H, camphyl CH2), 1.52 (m, 2H, H9 and H14), 2.54 (d,
1H, H1, J = 5.7 Hz), 2.68 (m, 1H, H6), 2.79 (s, 3H, OMe), 4.10
(d, 1H, H5, J = 5.7 Hz), 5.75 (s, 1H, H3) ppm. 13C NMR (100
MHz, benzene-d6): δ 10.1 (camphyl Me), 19.3 (camphyl Me),
19.7 (camphyl Me), 21.3 (camphyl CH2), 31.3 (camphyl CH2),
40.5 (C1), 40.9 (C6), 44.7 (C14), 45.7 (Cquat), 54.7 (OMe), 59.1
(Cquat), 62.1 (C9), 64.5 (C5), 73.1 (C3), 100.3 (C4), 140.8 (C2),
216.5 (camphyl CO) ppm. IR (ATR Diamant): ν 1731 (camphyl
CO), 1924 (Mn(CO)3), 2015 (Mn(CO)3) cm-1. HRMS: calcd for
Calcd: C, 61.15; H, 6.11. Found: C, 61.11; H, 6.05. [R]20
=
D
-107 cm3 g-1 dm-1 (CHCl3, c 0.293 g/100 mL).
(R,2pS)-2a (the most polar diastereoisomer): m = 198 mg, Y =
48%. 1H NMR (400 MHz, benzene-d6): δ0.42 (s, 3H, camphyl Me),
0.54 (s, 3H camphyl Me), 0.74 (s, 3H, camphyl Me), 0.95 to 1.30 (m,
4H, camphyl CH2), 1.48 (m, 1H, H9), 1.57 (s, 3H, η5 Me), 1.61 (m,
1H, H14), 2.69 to 2.81 (m, 2H, H1 or H5 and H6), 2.90 (s, 3H, OMe),
3.58 (d, 1H, H5 or H1, J = 5.4 Hz), 5.24 (s, 3H, H3) ppm. 13C NMR
(100 MHz, benzene-d6): δ 10.2 (camphyl Me), 19.4 (camphyl Me),
19.7 (camphyl Me), 21.4 (camphyl CH2), 22.9 (camphyl Me), 31.2
(camphyl CH2), 39.0 (C6), 40.1 (C5 or C1), 44.7 (C14), 45.7 (Cquat),
54.4 (OMe), 59.1 (Cquat), 61.8 (C1 or C5), 62.5 (C9), 70.7 (C3), 108.1
(C4), 142.3 (C2), 216.9 (camphyl CO) ppm. IR (ATR Diamant): ν
C20H22BrO5MnNaþ 498.9929, found 498.9932. [R]20 = -46
D
cm3 g-1 dm-1 (CHCl3, c 1.000 g/100 mL).
Diastereoisomeric η5 Complexes 2d. First diastereoisomer (the
least polar): m = 198 mg, Y = 42%. 1H NMR (200 MHz, benzene-
d6): δ 0.32 (s, 3H, camphyl Me), 0.42 (s, 9H, SiMe3), 0.53 (s, 3H,
camphyl Me), 0.73 (s, 3H, camphyl Me), 0.94 to 1.34 (m, 4H,
camphyl CH2), 1.48 (m, 1H, H9), 1.51 (m, 1H, H14), 2.57 (t, 1H, H5,
J = 6.5 Hz), 2.74 (dd, 1H, H6, J= 6.5 Hz, J= 10.8 Hz), 3.07 (s, 3H,
OMe), 3.64 (d, 1H, H1, J = 6.5 Hz), 4.53 (d, 1H, H4, J = 6.5 Hz)
ppm. 13C NMR (100 MHz, benzene-d6): δ 0.8 (SiMe3), 10.1
(camphyl Me), 19.4 (camphyl Me), 19.5 (camphyl Me), 21.4 (cam-
phyl CH2), 31.1 (camphyl CH2), 37.8 (C6), 44.4 (C14), 45.5 (C1), 45.6
(Cquat), 54.9 (OMe), 57.4 (C5), 59.0 (Cquat), 62.3 (C9), 75.9 (C3), 97.6
(C4), 147.2 (C2), 217.5 (camphyl CO) ppm. IR (ATR Diamant): ν
1732 (camphyl CO), 1901 (Mn(CO)3), 2005 (Mn(CO)3) cm-1
.
HRMS (ESIþ): calcd for C21H25O5MnNaþ 435.0980, found
435.0971. [R]20D = þ11 cm3 g-1 dm-1 (CHCl3, c 0.240 g/100 mL).
Diastereoisomeric η5 Complexes 2b. First diastereoisomer (the
1
least polar): m = 195 mg, Y = 45%. H NMR (400 MHz,
benzene-d6): δ 0.31 (s, 3H, camphyl Me), 0.50 (s, 3H, camphyl
Me), 0.69 (s, 3H, camphyl Me), 0.86 to 1.23 (m, 4H, camphyl
CH2), 1.42 (dd, 1H, H9, J = 3.8 Hz, J = 10.1 Hz), 1.54 (t, 1H,
H14, J = 3.8 Hz), 2.69 (dt, 1H, H6, J = 5.8 Hz, J = 10.8 Hz),
2.86 (dt, 1H, H1, J = 1.8 Hz, J = 5.8 Hz), 2.97 (s, 3H, OMe),
3.41 (dt, 1H, H5, J = 1.8 Hz, J = 5.8 Hz), 5.77 (t, 1H, H3, J =
1.8 Hz) ppm. 13C NMR (100 MHz, benzene-d6): δ 10.1 (camphyl
Me), 19.3 (camphyl Me), 19.5 (camphyl Me), 21.3 (camphyl
CH2), 31.1 (camphyl CH2), 40.1 (C6), 44.4 (C14), 45.1 (C5), 45.6
(Cquat), 59.0 (C1 and OMe), 61.6 (Cquat), 66.4 (C9), 72.3 (C3),
113.8 (C4), 140.5 (C2), 217.0 (camphyl CO) ppm. IR (ATR
Diamant): ν 1731 (camphyl CO), 1914 (Mn(CO)3), 2021 (Mn
(CO)3) cm-1. HRMS: calcd for C20H22ClO5MnNaþ 455.0434,
found 455.0429. Anal. Calcd: C, 55.55; H, 5.13. Found: C, 55.61;
H, 5.21. [R]20D = -58 cm3 g-1 dm-1 (CHCl3, c 0.207 g/100 mL).
Second diastereoisomer (the most polar): m = 212 mg, Y =
49%. 1H NMR (400 MHz, benzene-d6): δ 0.34 (s, 3H, camphyl
Me), 0.51 (s, 3H, camphyl Me), 0.72 (s, 3H, camphyl Me), 0.85 to
1.32 (m, 4H, camphyl CH2), 1.52 (m, 2H, H9 and H14), 2.51 (d,
1H, H1, J = 5.7 Hz), 2.71 (m, 1H, H6), 2.80 (s, 3H, OMe), 4.04
(d, 1H, H5, J = 5.7 Hz), 5.66 (s, 1H, H3) ppm. 13C NMR (100
MHz, benzene-d6): δ 10.1 (camphyl Me), 19.3 (camphyl Me),
19.7 (camphyl Me), 21.3 (camphyl CH2), 31.3 (camphyl CH2),
40.3 (C6), 40.5 (C1), 44.7 (C14), 45.7 (Cquat), 54.8 (OMe), 59.1
(Cquat), 62.1 (C9), 62.5 (C5), 70.5 (C3), 113.4 (C4), 140.4 (C2),
216.5 (camphyl CO) ppm. IR (ATR Diamant): ν 1732 (camphyl
CO), 1914 (Mn(CO)3), 2011 (Mn(CO)3) cm-1. HRMS: calcd for
1731 (camphyl CO), 1911 (Mn(CO)3), 2009 (Mn(CO)3) cm-1
.
HRMS: calcd for C23H31O5MnSiNaþ 493.1219, found 493.1214.
Anal. Calcd: C, 58.71; H, 6.65. Found: C, 58.64; H, 6.59. [R]20
=
D
-151 cm3 g-1 dm-1 (CHCl3, c 0.360 g/100 mL).
Second diastereoisomer (the most polar): m = 202 mg, Y =
43%. 1H NMR (400 MHz, benzene-d6): δ 0.40 (s, 12H, SiMe3 and
camphyl Me), 0.57 (s, 3H, camphyl Me), 0.75 (s, 3H, camphyl Me),
0.96 to 1.36 (m, 4H, camphyl CH2), 1.52 to 1.58 (m, 2H, H9 and
H14), 2.67 (d, 1H, H1, J = 4.8 Hz), 2.72 (s, 3H, OMe), 2.77 (m, 1H,
H6), 3.76 (t, 1H, H5, J = 7.0 Hz), 4.57 (d, 1H, H4, J = 7.0 Hz) ppm.
13C NMR (100 MHz, benzene-d6): δ 0.7 (SiMe3), 10.2 (camphyl
Me), 19.4 (camphyl Me), 19.6 (camphyl Me), 21.4 (camphyl CH2),
31.3 (camphyl CH2), 37.7 (C6), 39.7 (C1), 44.9 (C14), 45.7 (Cquat),
54.2 (OMe), 59.2 (Cquat), 62.8 (C9), 63.8 (C5), 76.1 (C3), 97.9 (C4),
146.9 (C2), 216.8 (camphyl CO) ppm. IR (ATR Diamant): ν 1726
(camphyl CO), 1908 (Mn(CO)3), 2003 (Mn(CO)3) cm-1. HRMS:
calcd for C23H28O5MnSiNaþ 493.1219, found 493.1214. [R]20
þ102 cm3 g-1 dm-1 (CHCl3, c 0.253 g/100 mL).
=
D
Diastereoisomeric η5 Complexes 2e. First diastereoisomer (the
least polar): m = 189 mg, Y = 40%. 1H NMR (200 MHz, benzene-
d6): δ 0.32 (s, 3H, camphyl Me), 0.42 (s, 9H, SiMe3), 0.53 (s, 3H,
camphyl Me), 0.73 (s, 3H, camphyl Me), 0.80 to 1.26 (m, 4H,
camphyl CH2), 1.44 (dd, 1H, H9, J = 4.2 Hz, J = 10.8 Hz), 1.53 (t,
1H, H14, J = 4.2 Hz), 2.56 (t, 1H, H5, J = 6.5 Hz), 2.75 (dd, 1H, H6,
J = 6.5 Hz, J = 10.8 Hz), 3.06 (s, 3H, OMe), 4.53 (d, 1H, H4, J =
6.5 Hz) ppm. 13C NMR (100 MHz, benzene-d6): δ 0.8 (SiMe3), 10.1
(camphyl Me), 19.4 (camphyl Me), 19.5 (camphyl Me), 21.4 (cam-
phyl CH2), 31.1 (camphyl CH2), 37.7 (C6), 44.4 (C14), 45.5 (C1), 45.6
(Cquat), 54.9 (OMe), 57.4 (C5), 59.0 (Cquat), 62.3 (C9), 75.9 (C3), 97.6
(C4), 147.2 (C2), 217.5 (camphyl CO) ppm. IR (ATR Diamant):
C20H22ClO5MnNaþ 455.0434, found 455.0429. [R]20 = -62
D
cm3 g-1 dm-1 (CHCl3, c 0.253 g/100 mL).
Diastereoisomeric η5 Complexes 2c. First diastereoisomer (the
least polar): m = 196 mg, Y = 41%. H NMR (400 MHz,
1
benzene-d6): δ 0.32 (s, 3H, camphyl Me), 0.50 (s, 3H, camphyl
Me), 0.69 (s, 3H, camphyl Me), 0.81 to 1.31 (m, 4H, camphyl
CH2), 1.44 (dd, 1H, H9, J = 3.8 Hz, J = 10.1 Hz), 1.59 (t, 1H,
H14, J = 3.8 Hz), 2.67 (dt, 1H, H6, J = 5.8 Hz, J = 10.8 Hz),
2.93 (m, 1H, H1), 2.94 (s, 3H, OMe), 3.44 (dt, 1H, H5, J = 1.8
Hz, J = 5.8 Hz), 5.87 (t, 1H, H3, J = 1.8 Hz) ppm. 13C NMR
(100 MHz, benzene-d6): δ 10.1 (camphyl Me), 19.3 (camphyl
Me), 19.6 (camphyl Me), 21.3 (camphyl CH2), 31.1 (camphyl
CH2), 40.7 (C6), 44.5 (C14), 45.2 (C5), 45.6 (Cquat), 55.2 (OMe),
57.2 (C1), 59.0 (Cquat), 61.7 (C9), 74.9 (C3), 100.8 (C4), 140.9 (C2),
217.0 (camphyl CO) ppm. IR (ATR Diamant): ν 1735 (camphyl
ν 1731 (camphyl CO), 1911 (Mn(CO)3), 2009 (Mn(CO)3) cm-1
.
HRMS: calcdforC23H30DO5MnSiNaþ 494.1280, found: 494.1285.
[R]20D = -150 cm3 g-1 dm-1 (CHCl3, c 0.280 g/100 mL).
Second diastereoisomer (the most polar): m = 198 mg, Y =
42%. 1H NMR (400 MHz, benzene-d6): δ 0.40 (m, 12H, SiMe3
and camphyl Me), 0.56 (s, 3H, camphyl Me), 0.75 (s, 3H,
camphyl Me), 0.96 to 1.40 (m, 4H, camphyl CH2), 1.50 to 1.61
(m, 2H, H9 and H14), 2.71 (s, 3H, OMe), 2.78 (dd, 1H, H6, J =
7.0 Hz, J = 10.8 Hz), 3.76 (t, 1H, H5, J = 7.0 Hz), 4.57 (d, 1H,
H4, J = 7.0 Hz) ppm. 13C NMR (100 MHz, benzene-d6): δ 0.7

Article
Organometallics, Vol. 29, No. 17, 2010 3885
(SiMe3), 10.2 (camphyl Me), 19.4 (camphyl Me), 19.6 (camphyl
Me), 22.4 (camphyl CH2), 31.3 (camphyl CH2), 37.7 (C6), 39.7 (C1),
44.9 (C14), 45.7 (Cquat), 54.2 (OMe), 59.2 (Cquat), 62.8 (C9), 63.8 (C5),
76.1 (C3), 97.9 (C4), 146.9 (C2), 216.8 (camphyl CO) ppm. IR (ATR
Diamant): ν 1726 (camphyl CO), 1908 (Mn(CO)3), 2003 (Mn(CO)3)
cm-1. HRMS: calcd for C23H27DO5MnSiNaþ 494.1280, found:
494.1282 . [R]20D = þ103 cm3 g-1 dm-1 (CHCl3, c 0.223 g/100 mL).
Typical Procedure for the Rearomatization. To a suspension of
AgBF4 (4 mmol in 10 mL of CH2Cl2) was added ClSiMe3
(4 mmol) at room temperature. After 10 min of stirring at room
temperature, a white solid precipitated and a solution of one of the
diastereoisomers 2a (1 mmol in 10 mL of CH2Cl2) was added. After
10 min, the crude mixture was filtered and the solvents were
evaporated under nitrogen flush, giving a yellow solid. This solid
was dissolved in the minimum CH2Cl2 volume, and after addition of
100 mL of Et2O, a yellow powder precipitated, which was filtered to
give the corresponding complex (ent)-1a: (-)-(1pR)-1a or (þ)-(1pS)-
1a in 96% (334 mg) or 98% (341 mg) yield, respectively. For yields
and [R]20D values of enantiopure cationic (η6-arene)Mn(CO)3 com-
plexes 1a-e see the Supporting Information.
(m, 1H, H5), 2.21 to 2.29 (m, 1H, H5), 2.38 to 2.43 (m, 1H, H6),
2.58 to 2.66 (m, 2H, H6 and H4), 6.16 (ddd, 1H, H2, J = 1.0 Hz,
2.0 and 10.4 Hz), 6.95 (dt, 1H, H3, J = 2.0 and 10.4 Hz) ppm. 13
C
NMR (100 MHz, CDCl3): δ 24.1 (Me), 24.6 (Me), 24.8 (C5), 35.3
(C7), 37.2 (C6), 44.5 (C4), 124.3 (C10), 132.1 (C2), 148.0 (C3),
198.3 (C1) ppm. IR (ATR Diamant): ν 1683 (CO), 2234 (CN)
cm-1. [R]20D = þ31 cm3 g-1 dm-1 (CHCl3, c 1.000 g/100 mL).
HRMS: calcd for C10H13NONaþ 186.0895, found 186.0892.
Anal. Calcd: C, 73.59; H, 8.03. Found: C, 73.55; H, 8.06. GC
analysis: cyclodex B fused silica column (50 m ꢀ 0.25 mm),
140 °C for 1 h and 200 °C (20 °C/mn), tR racemic mixture: 64.179
and 64.292 min; tR compound 4e: 64.179 min.
Cyclohexenone (þ)-4f. m = 315 mg, Y = 80%. 1H NMR (400
MHz, CDCl3): δ 1.59 to 2.05 (m, 2H, H5), 2.29 to 2.55 (m, 2H, H6),
3.31 (1H, m, H4), 3.78 (d, 1H, H7,J=11.4Hz),5.96(dd,1H,H2,J=
2.4 and 10.3 Hz), 6.76 (dd, 1H, H3 J = 2.4 and 10.3 Hz), 7.18 to 7.42
(m, 10H, HPh) ppm. 13C NMR (100 MHz, CDCl3): δ 28.5 (C5), 37.2
(C6), 40.3 (C4), 56.8 (C7), 127.0 to 130.2 (CPh and C2), 142.6 (CPh),
142.8 (CPh), 153.2 (C3), 200.0 (C1) ppm. IR (ATR Diamant): ν 1699
(CO) cm-1. [R]20D = þ35 cm3 g-1 dm-1 (CHCl3, c 1.000 g/100 mL).
HRMS: calcd for C19H18NaOþ 285.1250, found 285.1257. Anal.
Calcd: C, 86.99; H, 6.92. Found: C, 86.92; H, 6.97.
Synthesis of Cyclohexenones 4. Typical Procedures for Com-
pound (þ)-4b. To a solution of lithium diisopropylamide (2.6 mmol,
1.3 equiv) in THF (15 mL) was added methyl-2-propionitrile
(2.8 mmol, 0.3 mL, 1.4 equiv) at -78 °C. After 15 min of stirring,
the solution was warmed to -65 °C and 0.45 mL (3 equiv) of HMPA
was added. After 10 min, a solution of complex (-)-3b (1.5 mmol,
1 equiv) in 4 mL of THF was slowly transferred in the reaction
mixture, which was cooled again at -78 °C. The solution was
warmed to room temperature after 30 min and stirred for 2 h. FeCl3
(1.3 g, 4 equiv) was then added and the resulting mixture stirred for
1 h. Then 10 mL of an HCl solution (2 M) was added, and the
solution was stirred for 10 min before being extracted with Et2O
(20 mL). The combined organic layers were washed with a solution of
HCl (1 M) and then with a saturated aqueous solution of NaCl, dried
over MgSO4, and concentrated in vacuo. Flash chromatography on
silica gel allowed purifying the final product (eluent: 50/50 EP/Et2O),
and the cyclohexenone (þ)-4b was obtained as a white shiny solid:
m = 225 mg, Y = 76%. 1H NMR (400 MHz, CDCl3): δ1.57 (s, 3H,
Me), 1.59 (s, 3H, Me), 2.26 to 2.44 (m, 3H, H5, H5, and H6), 2.68 to
2.76 (m, 2H, H4 and H6), 6.40 (s, 1H, H2)ppm. 13C NMR (100 MHz,
CDCl3): δ 25.8 (C5), 26.8 (Me), 27.5 (Me), 33.3 (C6), 35.7 (C7), 49.2
(C4), 124.3 (C10), 132.1 (C2), 156.0 (C3), 196.0 (C1) ppm. IR (ATR
Diamant): ν1681 (CO), 2233 (CN) cm-1. [R]20D =þ20 cm3 g-1 dm-1
(CHCl3, c 1.000 g/100 mL). HRMS: calcd for C10H12ClNNaOþ
220.0500, found 220.0508. Anal. Calcd: C, 60.76; H, 6.12. Found: C,
60.72; H, 6.19. GC analysis: cyclodex B fused silica column (50 m ꢀ
0.25 mm), 160 °C for 1 h and 200 °C (20 °C/mn), tR racemic mixture:
63.438 and 63.682 min; tR compound 4b: 63.682 min.
Cyclohexenone (þ)-4g. m = 416 mg, Y = 82%. 1H NMR (400
MHz, CDCl3): δ 1.47 (m, 1H, H5), 2.16 to 2.29 (m, 2H, H5 and
H6), 2.45 (m, 1H, H6), 4.31 (1H, m, H4), 5.87 (dd, 1H, H2,
J = 2.8 and 10.5 Hz), 7.07 (dd, 1H, H3, J = 2.8 and 10.5 Hz),
7.20 to 7.48 (m, 15H, HPh) ppm. 13C NMR (100 MHz, CDCl3): δ
27.1 (C5), 38.1 (C6), 42.1 (C4), 126.7 to 130.5 (C2 and CPh), 153.3
(C3), 199.7 (C1) ppm. IR (ATR Diamant): ν 1675 (CO) cm-1
.
[R]20D = þ26 cm3 g-1 dm-1 (CHCl3, c 0.467 g/100 mL). HRMS:
calcd for C25H22NaOþ 361.1563, found 361.1569. Anal. Calcd: C,
83.08; H, 6.14. Found: C, 83.15; H, 6.09.
Cyclohexenone (þ)-4h. m = 233 mg, Y = 74%. 1H NMR (400
MHz, CDCl3): δ 1.19 (s, 3H, H11 or H12), 1.21 (s, 3H, H12 or H11),
1.26 (t, 3H, H10,J= 7.1 Hz), 1.76 (m, 1H, H5), 2.01 (m, 1H, H5), 2.36
(m, 1H, H6), 2.52 (m, 1H, H6), 2.80 (ddd, 1H, H4, J= 2.5 Hz, 4.7 Hz,
11.3 Hz), 4.16 (q, 2H, H9, J = 7.1 Hz), 6.02 (ddd, 1H, H2, J = 1.0
Hz,2.8Hz,10.4Hz),6.82(dt, 1H, H3, J= 2.0 Hz, 10.4 Hz) ppm. 13
C
NMR (100 MHz, CDCl3): δ14.5 (C10), 22.4 (C11 or C12), 22.8 (C12 or
C11), 24.7 (C5), 37.9 (C6), 44.1 (C4), 45.2 (C7), 61.1 (C9), 130.6 (C2),
151.6 (C3), 176.9 (C8), 199.5 (C1) ppm. IR (ATR Diamant): ν 1722
(CO ester), 1683 (CO) cm-1. [R]20D = þ37 cm3 g-1 dm-1 (CHCl3, c
1.000 g/100 mL). HRMS: calcd for C12H18NaO3þ 233.1148, found
233.1141. Anal. Calcd: C, 61.79; H, 7.78. Found: C, 61.71; H, 7.82.
Synthesis of η6 Phosphinoarene Complexes.
Cyclohexenone (þ)-4c. m = 276 mg, Y = 76%. 1H NMR (400
MHz, CDCl3): δ 1.55 (s, 3H, Me), 1.58 (s, 3H, Me), 2.17 to 2.48 (m,
3H, H5, H5,andH6), 2.64 to 2.82 (m, 2H, H4 and H6), 6.63 (s, 1H, H2)
ppm. 13C NMR (100 MHz, CDCl3): δ 26.5 (C5), 27.5 (Me), 27.8
(Me), 33.0 (C6), 36.1 (C7), 50.6 (C4), 124.2 (C10), 136.3 (C2), 146.9 (C3),
Complex (-)-3e. To a solution of n-BuLi in THF (1.6 mmol,
3 equiv, in 3 mL) at -78 °C was added a solution of complex (þ)-3c
in THF (0.548 mmol in 5 mL). After 10 min of stirring at -78 °C,
ClPPh2 (1.951, 3.6 equiv) was added and the solution slowly warmed
to room temperature. After hydrolysis and extractions with diethyl
ether, combined organic layers were washed with water, then with a
saturated aqueous solution of NaCl, dried over MgSO4, and con-
centrated in vacuo. Flash chromatography on silica gel allowed
purifying the final product (eluent: 50/50 EP/Et2O), and the η5
phosphino complex (-)-3e was obtained as a yellow powder. m =
237 mg, Y = 69%. 1H NMR (400 MHz, CDCl3): δ 2.24 (d, 1H,
195.0 (C1) ppm. IR (ATR Diamant): ν 1678 (CO), 2233 (CN) cm-1
.
[R]20D = þ50 cm3 g-1 dm-1 (CHCl3, c 1.000 g/100 mL). HRMS:
calcd for C10H12BrNNaOþ 263.9994, found 263.9989. Anal. Calcd:
C, 49.61; H, 5.00. Found: C, 49.69; H, 5.02. GC analysis: cyclodex B
fused silica column (50 m ꢀ 0.25 mm), tR racemic mixture: 70.602 and
70.844 min; tR compound 4c: 70.844 min.
Cylohexenone (þ)-4d. m = 471 mg, Y = 92%. 1H NMR (400
MHz, CDCl3): δ1.99 to 2.20 (m, 4H, 2H5 and 2H6), 3.62 (ddd, 1H, H4,
J = 8.0 Hz, 5.0 and 2.9 Hz), 4.44 (d, 1H, H7, J = 8.0 Hz), 6.51 (s, 1H,
H2), 7.25 to 7.31 (m, 10H, HPh)ppm. 13C NMR (100 MHz, CDCl3): δ
26.1 (C5), 32.7 (C6), 47.8 (C4), 54.2 (C7), 127.0 to 129.2 (CPh), 134.0
(C2), 142.0 (CPh), 154.6 (C3), 196.0 (C1) ppm. IR (ATR Diamant): ν
1669 (CO) cm-1. [R]20D = þ127 cm3 g-1 dm-1 (CHCl3, c 1.000 g/100
mL). HRMS: calcd for C19H17BrNaOþ 363.0355, found 363.0351.
Anal. Calcd: C, 62.65; H, 4.70. Found: C, 62.56; H, 4.75.
H
6exo, J = 11.8 Hz), 2.86 (m, 3H, H1 H5 and H6endo), 3.34 (s, 3H,
OMe),5.40(s,1H,H3), 7.24 to 7.55 (m, 10, HPh)ppm.13CNMR(100
MHz, CDCl3): δ28.3 (C6), 36.7 (C5), 52.3 (C1), 54.4 (OMe), 71.6 (C3),
109.1 (C2), 128.9 to 133.7 (CPh), 142.7 (C4) ppm. 31P NMR (162
MHz, CDCl3): -3.40 ppm. IR (ATR Diamant): ν 1929 (Mn(CO)3),
2020 (Mn(CO)3) cm-1. [R]20D = -35 cm3 g-1 dm-1 (CHCl3, c 1.000
g/100 mL). HRMS: calcd for C22H18MnNaO4Pþ 455.0215, found
455.0219. Anal. Calcd: C, 58.04; H, 3.99. Found: C, 58.19; H, 3.82.
Cylohexenone (þ)-4e. m = 176 mg, Y = 72%. 1H NMR (400
MHz, CDCl3): δ 1.42 (s, 3H, Me), 1.45 (s, 3H, Me), 1.82 to 1.94

3886 Organometallics, Vol. 29, No. 17, 2010
Eloi et al.
Complex (-)-3f. To a solution of (-)-3d (0.863 mmol, 1 equiv)
and TMEDA (1.294 mmol, 1.5 equiv) in THF (10 mL) at -78 °C
was added nBuLi (1.294 mmol, 1.5 equiv). After 1 h of stirring at -78 °C,
ClPPh2 (1.381 mmol, 1.6 equiv) was added, and the solution slowly
warmed to room temperature. After hydrolysis and extractions with
diethyl ether, combined organic layers were washed with water, then
with a saturated aqueous solution of NaCl, dried over MgSO4, and
concentrated in vacuo. Flash chromatography on silica gel allowed
purifying the final product (eluent: 50/50 EP/Et2O), and the η5
phosphino complex (-)-3f was obtained as a yellow powder. m =
373 mg, Y = 69%. 1H NMR (400 MHz, CDCl3): δ 2.23 (d, 1H,
H6exo), J = 12.4 Hz), 2.74 (m, 2H, H5 þ H6endo), 2.77 (m, 1H, H1),
3.21 (s, 1H, OMe), 4.22 (d, 1H, H4,J= 7.2 Hz), 7.16 to 7.70 (m, 10H,
HPh) ppm. 13C NMR (100 MHz, CDCl3): δ 27.1 (C6), 36.2 (C1), 51.8
(C5), 54.8 (OMe), 80.9 (C3), 97.3 (C4), 128.7 to 134.4 (CPh), 134.5
(C2), 138.2 (CPh), 146.4 (CPh) ppm. 31P NMR (162 MHz, CDCl3):
-17.09 (PPh2) ppm. IR (ATR Diamant): ν 1917 (Mn(CO)3), 2000
Complex (-)-1f. m = 203 mg, Y = 85%. 1H NMR (400 MHz,
CDCl3): δ 4.16 (s, 3H, OMe), 5.96 (m, 1H, H6), 6.19 (m, 1H, H2),
6.53 (dt, 1H, H4, J = 4.9 Hz, 9.6 Hz), 7.18 (t, 1H, H5, J = 9.6
Hz), 7.60 to 7.71 (m, 10H, HPh) ppm. 13C NMR (100 MHz,
CDCl3): δ 59.5 (OMe), 83.6 (C6), 86.8 (C2), 93.3 (C4), 105.9 (C5),
126.3 (C1), 131.1 to 136.1 (CPh), 150.8 (C3) ppm. 31P NMR (162
MHz, CDCl3): -3.76 (PPh2) ppm. IR (ATR Diamant):
ν 2002 (Mn(CO)3), 2081 (Mn(CO)3) cm-1. [R]20D = -140 cm3
g-1 dm-1 (CH3OH, c 1.000 g/100 mL). HRMS: calcd for
C22H17MnO4Pþ 431.0239, found 431.0235. Anal. Calcd: C,
61.27; H, 3.97. Found: C, 61.23; H, 3.91.
1
Complex (-)-1g. m = 227 mg, Y = 95%. H NMR (400
MHz, CDCl3): δ 4.20 (s, 3H, OMe), 6.25 (m, 2H, H5 and H6),
6.63 (dd, 1H, H3, J = 2.0 Hz, 6.0 Hz), 7.27 (m, 1H, H4), 7.55 to
7.66 (m, 10, HPh) ppm. 13C NMR (100 MHz, CDCl3): δ 59.9
(OMe), 80.0 (C3), 90.8 (C5), 106.8 (C4), 108.2 (C6), 130.6 to 131.6
(CPh and C1), 153.4 (C2) ppm. 31P NMR (162 MHz, CDCl3):
-13.08 (PPh2) ppm. IR (ATR Diamant): ν 2004 (Mn(CO)3),
2074 (Mn(CO)3) cm-1. [R]20D = þ38 cm3 g-1 dm-1 (CH3OH, c
1.000 g/100 mL). HRMS: calcd for C22H17MnO4Pþ 431.0239,
found 431.0238. Anal. Calcd: C, 61.27; H, 3.97. Found: C, 61.29;
H, 3.99.
(Mn(CO)3) cm-1. [R]20 = -80 cm3 g-1 dm-1 (CHCl3, c 1.000
D
g/100 mL). HRMS: calcd for C22H18MnNaO4Pþ 455.0215, found
455.0218. Anal. Calcd: C, 58.04; H, 3.99. Found: C, 58.11; H, 3.88.
Typical Procedure for the Rearomatization of η5 Phosphinoarene
Complexes. To a solution of (-)-3e (0.461 mmol, 1 equiv) in
dichloromethane (10 mL) at room temperature was added CPh3BF4
(1.381 mml, 3 equiv). After 1 h of stirring at room temperature, the
yellow solution was concentrated and diethyl ether (30 mL) was added,
leading to the formation of a pale yellow solid. After filtration, complex
(-)-1f was isolated as a pale yellow solid.
Acknowledgment. We thank the Ecole Normale
ꢀ
Superieure (Paris) for financial support to A.E. and CNRS
for financial support.
Supporting Information Available: Tables listing detailed
X-ray crystallographic data of compounds F1, (R,2pR)-2a,
(1pR)-1a, (þ)-1c, and (-)-4c, experimental procedures, and
spectroscopic data for the new compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.