Perrhenate Esters in New Catalytic Reactions - Wiley Online Library

DOI: 10.1002/cctc.200900206

Perrhenate Esters in New Catalytic Reactions Stphane Bellemin-Laponnaz*[a] Dedicated to Professor Alain Dedieu on the occasion of his retirement

There has been tremendous interest in the use of alkyltrioxorhenium complexes as catalysts for various organic transformations. Although such applications are now well known and, indeed, have been widely studied, other organorhenium oxide families, namely the perrhenate esters O3ReOR, have received

much less attention. In this review, such ReVII species are shown to be very promising catalysts and several recent examples are presented, with the aim of shedding light on their synthetic potential as a new tool for organic chemists.

Introduction Organometallic rhenium oxides in high oxidation states have found widespread applications in chemistry as synthetic reagents or catalysts, and also in materials science.[1] Among them, methyltrioxorhenium (MTO) has proven to be an excellent catalyst for various organic transformations, such as oxidation catalysis, aldehyde olefination, and olefin metathesis.[2] MTO offers numerous advantages besides its catalytic activity, including facile synthesis using cheap and environmentally benign reagents [3] and stability, as well as handling, in air without any special care. For all of these reasons, the development of chemistry related to methyltrioxorhenium has been the subject of intensive research during the last three decades and remains an ongoing effort. Surprisingly, the success of MTO has overshadowed another organorhenium oxide family, namely the perrhenate esters O3ReOR, which are precursors in the synthesis of MTO. Such rhenium(VII) complexes are characterized by the presence of a labile ligand, usually OSiR3, which alters the complex’s reactivity with organic molecules, thus providing manifold opportunities for the development of new catalytic reactions. Although a few examples were reported in the 1990s, chemists have only recently become interested in the use of this system for the development of new processes. Recent reports in this area indicate a bright future for this rhenium oxo family.[4] Although the chemistry of methyltrioxorhenium (Figure 1 a) has previously been described in several reviews,[1, 2] a similar survey on perrhenate esters (Figure 1 b) has not been carried

out to date, despite the interesting results reported in this area over the past few years The present contribution thus reviews recent catalytic applications involving these metal oxo complexes.

Why Perrhenate Esters May Be of Interest in Catalysis The MTO complex features an unusually stable alkyl–metal bond, which implies that usually only the oxo ligands are involved in catalytic reactions. Conversely, as perrhenate esters contain a labile alkoxide ligand, facile reactions, in particular with alcohols, become feasible (Scheme 1 a)[5] Transesterification reactions proceed most likely according to transition state A, in which the rhenium entity may be seen as a ReO3 + unit. In addition, significant polarization of the carbon–oxygen bond may occur in the resultant O3ReO R’ species, mainly because of the high oxidation state of the metal and the presence of three strongly electron-withdrawing oxo ligands. Such a strong polarization may induce the formation of ion-pair intermediate B (Scheme 1 b), thus yielding ReO4 species with concomitant rearrangement of the R’ group. Overall, these two simple steps, combined with the potential reactivity of the oxo ligands (Re=O), are usually involved in perrhenate estercatalyzed reactions, as detailed in the present contribution.[6]

Isomerization of Allylic Alcohols The isomerization of an allylic alcohol, consisting of a [1,3]-shift of the alcohol and the concomitant displacement of the double bond, is a useful reaction because one regioisomer may be more difficult to prepare than another. Such a reaction requires the presence of a catalyst, which has traditionally

Figure 1. a) Methyltrioxorhenium (MTO). b) Perrhenate ester.

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[a] S. Bellemin-Laponnaz Institut de chimie, CNRS-Universit de Strasbourg 1, rue Blaise Pascal, 67000 Strasbourg (France) Fax: (+ 33) 368-851637 E-mail: [email protected]

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Scheme 1. a) Reactivity of rhenium(VII) O3ReOR species with alcohol substrate, with proposed intermediate A; b) polarization leading to formation of ion-pair intermediate B.

been a Brønsted acid, albeit with low selectivity.[7] First Scheme 3. Selected examples of applications of rhenium perrhenates as conducted efficiently with vanadium oxides at high temperacatalyst for the isomerization of allylic alcohols: a) Isomerization of tertiary tures,[8] Osborn and co-workers reported in 1998 that allylic alcohols to primary alcohols; b) isomerization of enantiomerically enriched cyanohydrin to the corresponding tertiary allylic alcohol; c) [1,3]ReO3OSiR3 species were efficient catalytic systems for this rearrangement of a cis-oriented vinyl boronate. [9, 10] However, reaction, even at low temperatures (Scheme 2). the catalyzed reaction led to a thermodynamic equilibrium between substrate and product. To broaden the scope of the isomerized by ReVII oxo catalysts, as reported by the Osborn reaction, Grubbs and co-workers developed an isomerization and co-workers.[17, 18] Finally, Floreancig and co-workers carried out the Re-catalyzed isomerization of chiral allylic alcohols procedure that employed N,O-bis(trimethylsilyl)acetamide (Scheme 4), which led to the expected hemiacetal product in (BSA) to promote quantitative isomerization of tertiary allylic alcohols to primary alcohols (Scheme 3 a).[11] Efficient deprotection of the silylated products led to the formation of allylic alcohols incorporating trisubstituted alkenes in high yield. This method was recently used in the syntheses of (+)-6’-hydroxyarenarol[12] and ( )-apratoxin.[13–15] The problem of chirality transfer was also addressed, since such Scheme 4. Rhenium(VII) stereoselective isomerization of allylic alcohol applied in the formal synthesis of leucascandrolide A. a rearrangement process may be a useful way to prepare 69 % yield. The reaction was found to occur through a highly chiral secondary and, more interestingly, chiral tertiary allylic alstereoselective suprafacial migration. The intermediate was cohols. For example, under optimal conditions, enantiomerithen converted in two steps into leucascandrolide A, a potent cally enriched cyanohydrin (99 % ee) was isomerized to the corcytotoxic and antifungal macrolide.[19] responding tertiary allylic alcohol with excellent yield and ee [11] (Scheme 3 b). Independently, Hansen and Lee reported an elThe groups of Osborn,[9] Dedieu,[20] and others[11b, 15b] have egant regiochemical control in the [1,3]-rearrangement by investigated the mechanism of the rhenium oxo-catalyzed using the oxygen affinity of a cis-oriented vinyl boronate to rearrangement of allylic alcohols, and their conclusions are trap the hydroxy group (Scheme 3 c).[16] The resulting vinyl borconsistent with the original proposal by Chabardes, who suggested that reactions with such oxo complexes occurred via a onic acids were found to be excellent coupling partners in cyclic transition state similar to the [1,3]-dioxa-Cope rearrangeSuzuki coupling reactions. Notably, the substrate does not rement.[21] Scheme 5 displays the proposed mechanistic model quire deprotection, since allylic silyl ethers are also efficiently for the rhenium-catalyzed isomerization. The first step is an exchange of the substrate with the labile ligand of the perrhenate precatalyst to generate the active species. A migration of the allyl group to a metal–oxo unit, via transition state C, then takes place to form the rearranged alcohol after an exchange step between the new alkoxo species and the substrate. Scheme 2. Isomerization of allylic alcohols catalyzed by ReVII catalyst.

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Perrhenate Esters in New Catalytic Reactions The product is then released after an exchange step with the starting hemiacetal.

Synthesis of Phosphoric Acid Monoesters

Scheme 5. Proposed mechanism for the isomerization of allylic alcohols.

Ishihara et al. used perrhenic acid (ReO3OH) to catalyze the condensation of phosphoric acid with an alcohol, yielding the corresponding phosphoric acid monoesters (Scheme 8).[24] Such products are important substances in materials and medicinal chemistry and are currently synthesized on an industrial scale. Importantly, no successful methods for the synthesis of such molecules by direct condensation of the two components were previously known. The use of perrhenic acid as catalyst therefore opened a route to a useful method for an environmentally friendly synthesis of phosphoric acid monoesters. A 1:1 N-methylpyrrolidone/o-xylene solvent mixture and

The Prins Reaction The Prins reaction is an efficient way to synthesize tetrahydropyran rings from homoallylic alcohols and aldehydes.[22] The reaction usually requires superstoichiometric use of Brønsted or Lewis acids because the acid counterion is trapped in the product. However, the rhenium complex ReO3OSiPh3 is an effi- Scheme 7. Proposed mechanism for the Prins cyclization reaction catalyzed by ReVII. cient catalyst for this transformation with aromatic or a,b-unsaturated aldehydes (Scheme 6).[23] Thus, 4-hydroxytetrahydropyrans are formed stereoselectively under mild conditions (typically 5 mol % catalyst, CH2Cl2, room temperature) The proposed mechanism (Scheme 7) states that the reaction of the hemiacetal with the rhenium catalyst leads to a perrhenate ester, which undergoes a rearrangement via intermediate D.

Scheme 8. Direct condensation of phosphoric acid with alcohols catalyzed by O3ReOH.

Scheme 6. Prins cyclization reaction.

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20 mol % of dibutylamine in the presence of 1 mol % of ReO3OH were used for the dehydration under azeotropic reflux. Although the exact role of the amine remains unclear, it is known to contribute to the stabilization of the rhenium catalyst. Thus, in the proposed mechanism, a plausible intermediate would be a mixed anhydride and a nucleophilic substitution of the latter by an alcohol would 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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catalyst for the synthesis of 1,1-dihydroperoxides [R1R2C(OOH)2] by peroxyacetalization of ketones, aldehydes, or acetals with H2O2 (Scheme 12 a).[27] A typical procedure involves 5 mol % of

Scheme 9. Plausible intermediate for the dehydrative condensation of phosphoric acid.

Dehydration of Amides and Aldoximes Perrhenic acid has also been found to catalyze the dehydration of primary amides and aldoximes to nitriles.[25] This dehydration was originally performed by using stoichiometric reagents; it is only in the early 1990s that chemists developed transition metal-catalyzed processes, albeit in presence of stoichiometric additives. In search of an efficient catalyst for the dehydration in the absence of any additives, Yamamoto et al. screened various metal alkoxides and found that ReVII–oxo species were promising candidates. The optimized conditions constituted azeotropic reflux of a solution in mesitylene or toluene with perrhenic acid (1 mol %; Scheme 10). Scheme 12. Rhenium(VII)-catalyzed synthesis of (a) 1,1-dihydroperoxides and (b) 1,2,4,5-tetraoxanes.

Scheme 10. Dehydration of primary amides and aldoximes to nitriles.

Moreover, the catalyst is also efficient in the Beckmann fragmentation of a-substituted ketoximes, a powerful reaction that allows access to functionalized nitriles.[25b] For example, in the presence of only 0.5 mol % of perrhenic acid under azeotropic reflux in toluene for 30 min, the ketoxime was converted into the nitrile derivative in quantitative yield (Scheme 11).

Synthesis of Tetraoxanes and Dihydroperoxides 1,2,4,5-tetraoxanes are a class of stable peroxides that are of interest as antimalarial therapeutics.[26] However, the synthesis of such molecules remains a challenge. In 2008, Ghorai and Dussault highlighted the remarkable efficiency of Re2O7 as a

Scheme 11. Beckmann fragmentation.

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Re2O7 and 4 equivalents of hydrogen peroxide in acetonitrile at room temperature. In a subsequent study, the same strategy was used for the synthesis of tetraoxanes[28] by the condensation of 1,1-hydroperoxides and carbonyl reagents (Scheme 12 b) and led to the high-yielding formation of tetraoxanes. This method allows access to unsymmetrical tetraoxanes, which are not easily prepared by previously existing methods.

Ring-Opening Reactions of THF The Lewis acidity of rhenium(VII) oxides was exploited in an unprecedented heteroacylative ring-opening dimerization reaction of tetrahydrofuran.[29] Ring-opening reactions of cyclic ethers are of particular interest in chemistry and THF has been widely studied in this regard because of the potential applications in polymer chemistry and organic synthesis.[30] However, the ring-opening examples have resulted in either monomeric products or mixture of oligomers. In 2007, Keinan, Sinha, and co-workers reported that, in the presence of trifluoroacetic anhydride (TFAA), a carboxylic acid, and THF, Re2O7 could be used as a very selective catalyst to produce a nonsymmetrical diester (Scheme 13). The reaction was discovered serendipitously while attempting to expand the substrate scope of the oxidative cyclization of homoallylic alcohols.[31] Typical yields for this reaction have ranged between 80 and 95 % in the presence of 10 mol % of Re2O7 (Scheme 13). The only detected side products were the corresponding monomeric and trimeric analogues of the main product. Interestingly, other cyclic ethers, such as oxetane or THP, were poor substrates and the


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Perrhenate Esters in New Catalytic Reactions Some of these methods have been conducted by using simple perrhenic acid, a water and air-stable rhenium(VII) precursor. These recent examples amply demonstrate the potential of perrhenate esters for the development of new catalytic reactions and surely many more are to come. Keywords: homogeneous catalysis · organic synthesis · oxo ligands · rhenium · synthetic methods [1] a) C. C. Rom¼o, F. E. Khn, W. A. Herrmann, Chem. Rev. 1997, 97, 3197; b) W. A. Herrmann, F. E. Khn, Acc. Chem. Res. 1997, 30, 169–180; c) K. R. Jain, F. E. Khn, J. Organomet. Chem. 2007, 692, 5532–5540; d) J. M. Gonzales, R. Distasio Jr, R. A. Periana, W. A. Goddard, III. , J. Oxgaard, J. Am. Chem. Soc. 2007, 129, 15794–15804; e) B. L. Conley, S. K. Ganesh, Scheme 13. Heteroacylative ring-opening dimerization of tetrahydrofuran. J. M. Gonzales, W. J. Tenn, K. J. H. Young, J. Oxgaard, W. A. Goddard, III. , R. A. Periana, J. Am. Chem. Soc. 2006, 128, 9018–9019; f) B. L. Conley, expected corresponding products were obtained in very low S. K. Ganesh, J. M. Gonzales, D. H. Ess, R. J. Nielsen, V. R. Ziatdinov, J. Oxyields. gaard, W. A. Goddard, III. , R. A. Periana, Angew. Chem. 2008, 120, 7967–7970; Angew. Chem. Int. Ed. 2008, 47, 7849–7852. The authors investigated the role of rhenium oxide by con[2] a) J. H. Espenson, M. M. Abu-Omar, Adv. Chem. Ser. 1997, 253, 99–134; ducting several experiments including isotope labeling with b) B. S. Lane, K. Burgess, Chem. Rev. 2003, 103, 2457–2474; c) F. E. Khn, 18 [29] O. These studies indicated that one rhenium oxo ligand A. Scherbaum, W. A. Herrmann, J. Organomet. Chem. 2004, 689, 4149– was involved in the THF ring-opening step. When the reaction 4164. [3] W. A. Herrmann, A. M. J. Rost, J. K. M. Mitterpleininger, N. Szesni, S. was conducted with labeled benzoic acid (PhC18O2H), only one Sturm, R. W. Fisher, F. E. Khn, Angew. Chem. 2007, 119, 7440–7442; of the two 18O atoms was incorporated in the product. A cataAngew. Chem. Int. Ed. 2007, 46, 7301–7303. lytic cycle could be proposed based on the above observations [4] Perrhenate esters were the object of intensive research in oxidation (Scheme 14). The active catalyst is a carboxylate complex that chemistry in the 1980s and 1990s and, as such, have been widely reviewed; see references [1] and [2]. See also: a) C. Copret, H. Adolfsson, activates the trans oxo ligand to undergo nucleophilic attack J. P. Chiang, A. K. Yudin, K. B. Sharpless, Tetrahedron Lett. 1998, 39, 761– on the adjacent THF ligand, resulting in formation of inter764; b) W. R. Thiel, Coord. Chem. Rev. 2003, 245, 95–106; c) B. S. Lane, K. mediate E. Subsequent coordination of a second THF molecule Burgess, Chem. Rev. 2003, 103, 2457–2473. followed by a nucleophilic attack of the alkoxide ligand led to [5] Wilkinson and Edwards synthesized in 1984 several compounds of general formula O3ReOR by using a transesterification procedure, see: a) P. the second ring-opening step. Finally, cleavage of the Re O Edwards, G. Wilkinson, J. Chem. Soc. Dalton Trans. 1984, 2695—2702; bond with TFAA afforded the desired product. see also: b) W. A. Herrmann, W. R. Thiel, F. E. Khn, R. W. Fischer, M. Kleine, E. Herdtweck, W. Scherer, Inorg. Chem. 1993, 32, 5188–5194; c) W. A. Herrmann, W. A. Wojtczak, G. R. J. Artus, F. E. Khn, M. R. Mattner, Inorg. Chem. 1997, 36, 465–471. Conclusions [6] We note that the perrhenate active species may be generated from ReIn summary, a growing number of efficient catalytic methods O3OSiR3 complexes but also more simply from rhenium oxide Re2O7, as well as from aqueous perrhenic acid ReO3OH. has been developed with the help of rhenium oxides from the [7] Y. Abe, A. Ohsawa, H. Igeta, Chem. Pharm. Bull. 1982, 30, 881–886. perrhenate ester family in recent years. They offer high reactivi[8] P. Chabardes, E. Kuntz, J. Varagnat, Tetrahedron 1977, 33, 1775–1783. ty combined with high selectivity, by use of simple procedures. [9] S. Bellemin-Laponnaz, H. Gisie, J. P. Le Ny, J. A. Osborn, Angew. Chem. 1997, 109, 1011–1013; Angew. Chem. Int. Ed. Engl. 1997, 36, 976– 978. [10] Review: S. Bellemin-Laponnaz, J. P. Le Ny, C. R. Chim. 2002, 5, 217– 224. [11] a) C. Morrill, R. H. Grubbs, J. Am. Chem. Soc. 2005, 127, 2842–2843; b) C. Morrill, G. L. Beutner, R. H. Grubbs, J. Org. Chem. 2006, 71, 7813–7825. [12] R. H. Munday, R. M. Denton, J. C. Anderson, J. Org. Chem. 2008, 73, 8033–8038. [13] Y. Numajiri, T. Takahashi, T. Doi, Chem. Asian J. 2009, 4, 111–125. [14] For other applications in total synthesis of rhenium-catalyzed isomerization of allylic alcohols, see: a) B. M. Trost, F. D. Toste, J. Am. Chem. Soc. 2000, 122, 11262– 11263; b) B. M. Trost, W. Tang, F. D. Scheme 14. Proposed mechanism for heteroacylative ring-opening dimerization of tetrahydrofuran. Toste, J. Am. Chem. Soc. 2005, 127,

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[15]

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14785–14803; c) A. K. Mandal, J. S. Schneekloth Jr, K. Kuramochi, C. M. Crews, Org. Lett. 2006, 8, 427–430. MTO was also found to catalyze the reaction albeit with lower activity; see: a) J. Jacob, J. H. Espenson, J. H. Jensen, M. S. Gordon, Organometallics 1998, 17, 1835–1840; b) G. Wang, A. Jimtaisong, R. L. Luck, Organometallics 2004, 23, 4522–4525; c) J. M. Hutchison, H. A. Lindsay, S. S. Dormi, G. D. Jones, D. A. Vicic, M. C. McIntosh, Org. Lett. 2006, 8, 3663– 3665. E. C. Hansen, D. Lee, J. Am. Chem. Soc. 2006, 128, 8142–8143. S. Bellemin-Laponnaz, J. P. Le Ny, J. A. Osborn, Tetrahedron Lett. 2000, 41, 1549–1552. Note that perrhenic acid and rhenium oxide were found to catalyze the hydrosilylation of aldehydes and ketones and the dehydrogenative silylation of alcohols; see: a) P. M. Reis, B. Royo, Catal. Commun. 2007, 8, 1057–1059; b) B. Royo, C. C. Rom¼o, J. Mol. Catal. A Chem 2005, 236, 107–112. H. H. Jung, J. R. Seiders, II. , P. E. Floreancig, Angew. Chem. 2007, 119, 8616–8619; Angew. Chem. Int. Ed. 2007, 46, 8464–8467. S. Bellemin-Laponnaz, J. P. Le Ny, A. Dedieu, Chem. Eur. J. 1999, 5, 57– 64. P. Chabardes, E. Kuntz, J. Varagnat, Tetrahedron 1977, 33, 1775–1783. I. M. Pastor, M. Yus, Curr. Org. Chem. 2007, 11, 925–957. K. Tadpetch, S. D. Rychnovsky, Org. Lett. 2008, 10, 4839–4842.

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[24] a) A. Sakakura, M. Katsukawa, K. Ishihara, Angew. Chem. 2007, 119, 1445; Angew. Chem. Int. Ed. 2007, 46, 1423—1426; Ishihara et al. also succeeded in phosphoric acid diesters synthesis; see: b) A. Sakakura, M. Sakuma, M. Katsukawa, K. Ishihara, Heterocycles 2008, 76, 657–665. [25] a) K. Ishihara, Y. Furuya, H. Yamamoto, Angew. Chem. 2002, 114, 3109– 3112; Angew. Chem. Int. Ed. 2002, 41, 2983–2986; b) Y. Furuya, K. Ishihara, H. Yamamoto, Bull. Chem. Soc. Jpn. 2007, 80, 400–406; c) For an example of the use of this methodology in synthesis, see: Y. Xu, Z. Wang, Z.-Q. Tian, Y. Li, S. J. Shaw, ChemMedChem 2006, 1, 1063–1065. [26] Y. Tang, Y. Dong, J. L. Vennerstrom, Med. Res. Rev. 2004, 24, 425–448. [27] P. Ghorai, P. H. Dussault, Org. Lett. 2008, 10, 4577–4579. [28] P. Ghorai, P. H. Dussault, Org. Lett. 2009, 11, 213–216. [29] H. C. Lo, H. Han, L. J. D’Souza, S. C. Sinha, E. Keinan, J. Am. Chem. Soc. 2007, 129, 1246–1253. [30] P. Dreyfuss, M. P. Dreyfuss, G. Pruckmayr, Encyclopedia of Polymer Science and Engineering, 2nd ed., Vol. 16, Wiley, New York, 1989. [31] S. C. Sinha, A. Sinha, S. C. Sinha, E. Keinan, J. Am. Chem. Soc. 1997, 119, 12014–12015.

Received: July 24, 2009 Published online on October 6, 2009


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