3+ Complexes - American Chemical Society

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Organometallics 2010, 29, 3876–3886 DOI: 10.1021/om100564v

Cationic Planar Chiral (η6-Arene)Mn(CO)3þ Complexes: Resolution, NMR Study in Chiral-Oriented Solvents, and Applications to the Enantioselective Synthesis of 4-Substituted Cyclohexenones and (η6-Phosphinoarene)Mn(CO)3þ Complexes Antoine Eloi,† Franc-oise Rose-Munch,*,† Eric Rose,*,† Ariane Pille,† Philippe Lesot,*,‡ and Patrick Herson§ †

Equipe Chimie Organique et Organom etallique, UPMC Universit e Paris 06, IPCM, CNRS UMR 7201, Case 181, 4 Place Jussieu, 75252 Paris Cedex 05, France, ‡RMN en Milieu Orient e, Universit e Paris Sud 11, ICMMO, CNRS UMR 8182, B^ atiment 410, F-91405 Orsay Cedex, France, and §Centre de R esolution de Structures, UPMC Universit e 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 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)3þ 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 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 complexes, and among them, Cr complexes have been extensively studied.1 More recently, the isoelectronic cationic [(η6arene)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. [email protected]; [email protected]; [email protected]. (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. (2) (a) McDaniel, K. F. Comprehensive Organometallic Chemistry II; Abel, E. W.; Stone, F. G. A.; Wilkinson, G., Eds.; Pergamon Press: Oxford, 1995; Vol. 6, p 93. (b) Pape, A. R.; Kaliappan, K. P.; K€ undig, 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. pubs.acs.org/Organometallics

Published on Web 08/17/2010

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 complexes, thus providing an easy access to the corresponding η6 complexes after rearomatization by exo-hydride abstraction at the sp3 carbon atom (Scheme 1).

(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) RoseMunch, 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. (4) Auffrant, A.; Prim, D.; Rose-Munch, F.; Rose, E.; Schouteeten, 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, 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 2010 American Chemical Society

Article Scheme 1. Functionalization of (η5-Cyclohexadienyl)Mn(CO)3 Complexes

One of the common features of (η6-arene)-Cr(CO)3 and -Mn(CO)3þ complexes is their planar chirality, which has 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 enantioselective methods.1d,8 In contrast, only two specific examples of nonracemic planar chiral cationic η6 Mn complexes have so far been reported to the best of our knowledge, starting from (p-cresol)Mn(CO)3þ derivatives.9 As for η5-cyclohexadienyl-Mn complexes, only a few syntheses of nonracemic planar chiral (η5cyclohexadienyl)Mn(CO)3 derivatives have been achieved by diastereoselective addition of nucleophiles to cationic η6-arene-Mn complexes.10,11 In the last three years, two enantioenriched 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 phosphinosubstituted η5 complex through the formation of a chiral palladium 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-areneMn complexes and apply it to a range of substrates with fruitful prospects in the field of enantioselective synthesis. 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) K€ undig, E. P. Topics in Organometallic Chemistry; Springer: Berlin, 2004; Vol. 7. (7) (a) Bolm, C.; Muniz, K. Chem. Soc. Rev. 1999, 28, 51. (b) Salzer, A. Coord. Chem. Rev. 2003, 242, 59. (8) K€ undig, 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 η6arene-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-substituted 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. (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 communication: Eloi, A.; Rose-Munch, F.; Rose, E. J. Am. Chem. Soc. 2009, 131, 14178.

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Scheme 2. Addition of Bromo- and Chloro-Ester Carbanions to an η6-Arene-Mn Complex

Scheme 3. Methodology Applied for the Resolution of (η6Arene)Mn(CO)3þ Complexes Using a Chiral Nucleophile “Round Trip”

preliminary communication.13 The synthetic strategy proposed 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 carbanions add easily to the arene ring of η6-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 diastereoisomeric 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 method, which should be efficient but nevertheless mild enough in order to be compatible with η5 and η6 complexes. Choice of the Chiral Enantiopure Enolate. In our preliminary 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. We then turned our attention to a more rigid chiral auxiliary, namely, camphor enolate, which comes from a (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.

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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.

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 chirality: (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 chromatography 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 diffusion 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 diastereoisomer A and (S,2pS)-2a for B. The chirality of the complexes has been conventionally described by the configuration at the C9 center (R or S), together with the corresponding 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 fraction, F2. Each fraction was submitted to the action of K2CO3 (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 information, the absolute stereochemical assignments of (1pR)-1a and (-)-4c are thus confirmed. (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.

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 experimental 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 corresponding 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). Consequently, 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)-camphor 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 diastereoisomers (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 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 rearomatization of η5 complexes have been described in the literature. The first one, generally using either N-bromosuccinimide or DDQ, involves an oxidative rearomatization with the loss of the Mn(CO)3 entity.10b,19-21 The second (18) Alternatively, to avoid the recrystallization step, each diastereoisomer, 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.

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Figure 3. Representation of the stereochemical composition of the mixture of diastereoisomers before and after epimerization. Scheme 5. Purification and Rearomatization of η5-Mn Complexes

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 carbon atom, and the corresponding η6 complex is obtained with BF4 as counteranion.4,22,23 Under the experimental conditions 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 conditions, the presence of a silicium derivative favors the enolate trapping by formation of a silylated enolate ether, while the BF4- anion plays the role of the counteranion, stabilizing the cationic species after the chiral auxiliary elimination. Alternatively, another method, avoiding the expensive silver salt AgBF4, involved the addition of a slight excess of [HBF4, OMe2] in a CH2Cl2 solution of the η5 complex. Addition of Et2O in the crude mixture allowed the precipitation of the corresponding cationic η6 complex. Thus, complexes (1pR)1a and (1pS)-1a were successfully isolated in 94% and 96% yield, respectively and >98% ee each (Scheme 5), assuming that the ee kept the same value as the de value of the parent η5 complex. In order to confirm this hypothesis, we have tested a specific example by deuterium 2D NMR spectroscopy in a chiral liquid crystal (vide infra). Using the same experimental (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.

Figure 4. Molecular structure of the diastereoisomer (R,2pR)-2a depicting the absolute configuration of both chirality elements. Scheme 6. Synthesis of Enantiopure m-Chloro and -Bromoanisole Complexes

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 from 91% to 99%, with >98% ee each. Knowing the absolute configuration of the (R,2pR)-2a complex thanks to the X-ray analysis, we recrystallized the corresponding cationic η6-arene complex (1pR)-1a, whose X-ray analysis unambiguously confirmed its absolute configuration (Figure 5).16 Thus, during the rearomatization process, the planar chirality stayed unchanged.24 2.2. NMR Study in Chiral-Oriented Solvents. Whereas the de value was easily determined for each η5 complex by 1H NMR spectroscopy, the usual analytical methods for the determination of ee’s failed when applied to the chiral cationic η6 complexes. Indeed neither the europium chiral (24) For diastereoselective nucleophilic addition to chiral-at-the-metal η5-cyclohexadienyl Mnþ 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.

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Figure 5. Molecular structure of the enantiomer (1pR)-1a depicting 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 complexes 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 complexes 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 overcome 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 discrimination 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 trimethylsilyl complex as starting material, namely, the ortho-trimethylsilyl-anisole derivative complex 1d bearing the silyl group ortho to the methoxy substituent (Scheme 7). Under the same experimental conditions as those previously 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 (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.

Figure 6. 2H quadrupolar doublets of (a) (rac)-1e, (b) (-)-1e (86% ee), and (c) (þ)-1e (77% ee) obtained without recrystallization 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 resonance deconvolution.

was unsuccessful here due to rather broad 13C resonances (vide infra), thus preventing the possibility to spectrally discriminate the charged enantiomers on the basis of carbon-13 chemical shift anisotropy difference.26a,b As a possible alternative, 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-Lglutamate (PBLG).26,28 In this emerging and powerful analytical technique, enantiomers-d1 are spectrally discriminated on the basis of differences of 2H 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 (28) Lesot, P.; Courtieu, J. Prog. NMR Spectrosc. 2009, 55, 128.

Article

pointing out the shape recognition of mirror-image complexes by the mesophase. 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 2 H 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 experiments 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 polypeptide 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 mechanisms by decreasing the T1 and T2 relaxation times, leading to additional 2H lineshape broadening.31 The very short longitudinal 2H relaxation time of the aromatic deuterium site assessed using an inversion-recovery sequence (T1 = 21 ms) confirms these arguments. The low-resolution 1H 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 55 Mn nuclei, which are not favorable for recording highresolution 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 ( 98% obtained after recrystallization 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. 2.3. Applications to Organic and Organometallic Enantioselective Syntheses. The potential of the enantiopure η6 complexes in the field of enantioselective syntheses of 4-substituted 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 (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. 2004, 171, 135. (31) Levitt, M. H. In Spin Dynamics; Wiley & Sons: Chichester, 2007.


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η6-arene-Cr series and represents an efficient tool for the synthesis of functionalized alicyclic molecules,2b in the η6arene-Mn series, only very few studies have been reported.6 The most direct route to manganese-mediated dearomatization 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 cyclohexadienes 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 resulting 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 methoxy-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 obtained. 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 substituent. 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 complex intermediate by replacement of a CO ligand with NOþ. Upon treatment of complex (þ)-3c with another carbanion such as diphenylmethane carbanion, bromocyclohexenone (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. (41) As far as we are aware, very few reports of nucleophile additions to alkoxy-substituted (η6-arene)Mn(CO)3þ complexes have been published 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 alkoxysubstituted (η6-arene)Cr(CO)3 as well as from dihapto-coordinated complexes of Os.

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Scheme 8. Synthesis of Enantiopure Cyclohexenones 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 monosubstituted complex has no planar chirality. Addition of isobutyronitrile, diphenylmethyl, triphenylmethyl, and dimethylacetate carbanions delivered the enantiopure cyclohexenones (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 nucleophiles. 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, 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 confirms 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, which rules 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 addition 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. η6-Phosphinoarene Complexes. Chiral ligands based on planar chiral tricarbonyl metal complexes represent an original 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 (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.

Figure 7. ORTEP views of complex (þ)-1c and the corresponding 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-C5 2.161(4); Mn-C6 2. 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).

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 Fe.47 No ligand containing a planar chiral (η6-arene)Mn(CO)3þ complex was described so far, and the first example of an enantiopure planar chiral ligand built on a (η5-cyclohexadienyl)Mn(CO)3 complex skeleton was only reported in 200912 and involves a resolution procedure using a chiral palladium complex 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 the cationic meta-disubstituted (η6-phosphinoanisole)Mn(CO)3þ 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 formation of the arene coordinated to the cationic Mn(CO)3 entity. To the best of our knowledge, this represents the first example of a (44) M€ uniz, K. Topics in Organometallic Chemistry; K€undig, 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. (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. Organometallics 2009, 28, 5757.

Article


Scheme 9. Syntheses of Enantiopure (η6-Phosphinoanisole)Mn (CO)3+ Complexes

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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.

Experimental Section

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 rearomatization of complex (-)-3f easily occurred with CPh3BF4 to deliver the cationic ortho-disubstituted (η6-phosphinoanisole) Mn(CO)3þ complex (-)-1g in 95% yield. Again, the set of signals between 2.74 and 4.22 ppm characterizing the η5-cyclohexadienyl π system of (-)-3f is shifted downfield between 7.27 and 6.25 ppm in the rearomatized compound (-)-1g.

3. Conclusion This paper reports on the first resolution of cationic orthoand meta-disubstituted arenetricarbonylmanganese complexes through (D)-(þ)-camphor enolate addition, isomerization 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 cationic 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 unambiguously that the rearomatization step occurred with a total conservation of the stereochemical information. This resolution method based on the “round trip” of a cheap, commercially available chiral nucleophile is a general approach. It involves only the intrinsic electrophilic properties of the coordinated 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 nucleophilic addition to the enantiopure (η6-meta-bromoanisole)Mn (CO)3þ. Finally, the synthesis of the first η5- and η6-phosphi(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.

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 spectrometer 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 tetrahydrofuran 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 F254 plates (0.25 mm). Compounds were visualized by UV irradiation. Flash column chromatography was carried out using forced flow of the indicated solvent on Roth Kieselgel 60 (0.020.045 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. Crystallographic data were collected on an Enraf-Nonius Cad-4 diffractometer. High-resolution mass spectral analyses were performed by the Groupe de Spectrometrie de Masse (UMR 7613, UPMC). Elemental analyses were performed by Le Service de Microanalyses 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. 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 = 44%. 1H 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 1.34 (m, 4H, camphyl CH2), 1.42 (m, 1H, H9), 1.46 (3H, s, η5 Me),

3884


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 (camphyl 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. Calcd: C, 61.15; H, 6.11. Found: C, 61.11; H, 6.05. [R]20D = -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): δ 0.42 (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 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 least polar): m = 195 mg, Y = 45%. 1H 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 C20H22ClO5MnNaþ 455.0434, found 455.0429. [R]20D = -62 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%. 1H NMR (400 MHz, 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

Eloi et al. 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 C20H22BrO5MnNaþ 498.9929, found 498.9932. [R]20D = -46 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, benzened6): 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 (camphyl 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 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]20D = -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. 13 C 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]20D = þ102 cm3 g-1 dm-1 (CHCl3, c 0.253 g/100 mL). Diastereoisomeric η5 Complexes 2e. First diastereoisomer (the least polar): m = 189 mg, Y = 40%. 1H NMR (200 MHz, benzened6): 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 (camphyl 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): ν 1731 (camphyl CO), 1911 (Mn(CO)3), 2009 (Mn(CO)3) cm-1. HRMS: calcd for C23H30DO5MnSiNaþ 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 (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 complexes 1a-e see the Supporting Information. Synthesis of Cyclohexenones 4. Typical Procedures for Compound (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): δ 1.57 (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): ν 1681 (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)-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, and H6), 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), 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): δ 1.99 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. 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


3885

(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. 13C 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 = 11.4 Hz), 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. 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, 2.8 Hz, 10.4 Hz), 6.82 (dt, 1H, H3, J = 2.0 Hz, 10.4 Hz) ppm. 13C NMR (100 MHz, CDCl3): δ 14.5 (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.

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 concentrated 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, H6exo, 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. 13C NMR (100 MHz, CDCl3): δ 28.3 (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.

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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 (Mn(CO)3) cm-1. [R]20D = -80 cm3 g-1 dm-1 (CHCl3, c 1.000 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.

Eloi et al. 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. Complex (-)-1g. m = 227 mg, Y = 95%. 1H 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.

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.

3+ Complexes - American Chemical Society

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