Chemistry and catalysis advances in organometallic chemistry and catalysis
BAEYER– VILLIGER OXIDATION OF KETONES
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22.5 BAEYER– VILLIGER OXIDATION OF KETONES The BV oxidation by aqueous H 2 O
in 1,2-dichloroethane of cyclic and linear ketones to the corresponding lactones and esters (Scheme 22.5) is catalyzed by Re(III or IV) complexes bearing C-scorpionate or pyrazole ligands, which conceivably allow the involvement of coordinative unsaturation at the metal in view of their lability [Hpz, η 3 - or η 2 -HC(pz) 3 toward lower denticity] and/or proton-transfer steps on account of their basic character—features that are favorable to the occurrence of oxidation catalysis with H 2 O
[9]. 292 CARBON–SCORPIONATE COMPLEXES IN OXIDATION CATALYSIS TABLE 22.3 Baeyer–Villiger Oxidation of Several Ketones Catalyzed by Tris(pyrazol-1-yl)methane or Pyrazole Re Complexes [9] a Substrate Catalyst Yield
b , %
TON c Conv.
Select. Product
[ReCl 2 {N 2 C(O)Ph
}(Hpz) 2 (PPh 3 )] (26) 54 537
99 54 [ReClF {N 2 C(O)Ph }(Hpz) 2 (PPh 3 )] (24) 18 178
65 28 [ReCl 3 {HC(pz)
3 }] (11) 33 329
78 42 [ReCl 4 {η 2 -HC(pz) 3 }] (27) 33 334
100 33 [ReCl 2 {N 2 C(O)Ph }(Hpz)
2 (PPh
3 )] (26) 23 231
63 37 [ReClF {N 2 C(O)Ph }(Hpz) 2 (PPh 3 )] (24) 11 109
58 41 [ReCl 2 {N 2 C(O)Ph }(Hpz)
2 (PPh
3 )] (26) 22 223
28 80 [ReClF {N 2 C(O)Ph }(Hpz) 2 (PPh 3 )] (24) 10 102
40 26 [ReCl 3 {HC(pz)
3 }] (11) 21 209
37 57 [ReCl 4 {η 2 -HC(pz) 3 }] (27) 19 192
37 52 [ReCl 2 {N 2 C(O)Ph }(Hpz)
2 (PPh
3 )] (26) 16 158
24 69 [ReClF {N 2 C(O)Ph }(Hpz) 2 (PPh 3 )] (24) 7 74
16 [ReCl
3 {HC(pz)
3 }] (11) 18 180
44 41 [ReCl 4 {η 2 -HC(pz) 3 }] (27) 5 53 46 12 [ReCl
2 {N 2 C(O)Ph }(Hpz)
2 (PPh
3 )] (26) 31 307
77 39 [ReClF {N 2 C(O)Ph }(Hpz) 2 (PPh 3 )] (24) 22 223
79 28 [ReCl 3 {HC(pz)
3 }] (11) 18 177
74 24 [ReCl 4 {η 2 -HC(pz) 3 }] (27) 24 241
65 37 [ReCl 2 {N 2 C(O)Ph }(Hpz)
2 (PPh
3 )] (26) 6 64
81 [ReClF
{N 2 C(O)Ph }(Hpz) 2 (PPh 3 )] (24) 7 74
67 [ReCl
3 {HC(pz)
3 }] (11) 12 118
69 17
a Reaction conditions (unless stated otherwise): rhenium catalyst (1.7 μmol, used as a stock solution in 1,2-dichloroethane), 1.7 mmol of substrate, H 2 O 2 (1.7 mmol, i.e., 1000 : 1 molar ratio of oxidant to Re catalyst), 1,2-dichloroethane (3.0 ml), 6 h, 70 ◦ C, under dinitrogen. Yield and TON determined by GC analysis. b Molar yield (%) based on the ketone substrate, that is, moles of lactone (or ester) per 100 mol of ketone. c TON (moles of product per mole of Re catalyst). Hence, [ReCl 3 {HC(pz) 3 }] (11), [ReCl 4 {η
-HC(pz) 3 }] (27), [ReClF{N 2 C(O)Ph
}(Hpz) 2 (PPh 3 )] (24), and [ReCl 2 {N
C(O)Ph } (Hpz) 2 (PPh
3 )] (26) catalyze the BV oxidation of 2-methylcyclohexanone, 2-methylcyclopentanone, cyclohexanone, cyclopentanone, cyclobutanone, and 3,3-dimethyl-2-butanone into the corresponding lactones or esters in the presence of aqueous H 2 O
, allowing to achieve conversions, for example, up to 79% in the case of 2-methylcyclohexanone or 100% in the case of cyclobutanone [9]. In general, these rhenium compounds are more active for the oxidation of cyclic (four-, five-, and six-membered rings) than acyclic ketones, consistent with the common lower reactivity of the latter ketones. The Re(III) tris(pyrazol-1-yl)methane compound [ReCl 3 {HC(pz) 3 }] (11) is the most active one for 2-methylcyclopentanone and cyclohexanone or pinacolone BV oxidations, whereas the most effective oxidations are observed for cyclobutanone with [ReCl 2 {N 2 C(O)Ph
}(Hpz) 2 (PPh 3 )] (26) (54% yield, 99% conversion, TON of 537) (Table 22.3) [9]. REFERENCES 293 O O O O O O n n Re catalyst aq. H 2
2 Ester
Lactone Scheme 22.5 Baeyer–Villiger peroxidative oxidation of cyclic and linear ketones to the corresponding lactones or esters. The use of 1,2-dichloroethane as solvent leads to the highest activity for all ketones, but water can be used as the only solvent, which is particularly important for the development of a green BV system [9]. 22.6 FINAL REMARKS The application of tris(pyrazol-1-yl)methane-type scorpionate (or related pyrazole) complexes of several transition metals (V, Fe, Cu, and Re) as catalysts or catalyst precursors for alkane and BV ketone oxidation reactions directed toward single-pot organic synthesis proved to be a promising strategy. Moreover, the hydrosolubilty of the scorpionate complexes bearing suitably C-functionalized moieties that allows the uncommon use of water as the only solvent, together with the mild operation conditions, is particularly significant in terms of developing a green catalytic process for alkane and ketone oxidations.
We gratefully acknowledge the coauthors cited in our publications. This work has been partially supported by the Fundac¸˜ao para a Ciˆencia e a Tecnologia (FCT), Portugal, and projects PTDC/QUI-QUI/102150/2008, PTDC-EQU-EQU-122025-2010, and PEst-OE/QUI/UI0100/2013. REFERENCES 1. (a) Shul’pin, G. B. Mini-Rev. Org. Chem., 2009, 6 , 95; (b) Derouane, E. G.; Haber, J.; Lemos, F.; Ramˆoa Ribeiro, F.; Guinet M. Eds. Catalytic Activation and Functionalization of Light Alkanes; NATO ASI Series, Vol. 44; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1998; (c) Hill, C. L., Ed., Activation and Functionalization of Alkanes; John Wiley & Sons, Inc.: New York, 1989; (d) Wolf, E. E., Ed., Methane Conversion by Oxidative Processes: Fundamental and Engineering Aspects; Van Nostrand Reinhold: New York, 1992; (e) Shilov, A. E.; Shul’pin, G. B. Activation and Catalytic Reactions of Saturated Hydrocarbons in the Presence of Metal Complexes; Kluwer Academic Publishers: Dordrecht, The Netherlands, 2000; (f) Jia, C. G.; Kitamura, T.; Fujiwara, Y. Acc. Chem. Rev. 2001, 34 , 633; (g) Crabtree, R. H. J. Chem. Soc. Dalton Trans. 2001, 17 , 2437; (h) Shul’pin, G. B. C. R. Chimie. 2003, 6 , 163; (i) Shul’pin, G. B. J. Mol. Catal. A Chem, 2002, 189 , 39; (j) Shilov, A. E.; Shul’pin, G. B. Chem. Rev. 1997, 97 , 2879; (k) da Silva, J. A. L.; Fra´usto da Silva, J. J. R.; Pombeiro, A. J. L. Coord. Chem. Rev. 2011, 255 , 2232; (l) Pombeiro, A. J. L. In Vanadium: The
DC, 2007, p 51. 2. (a) Michelin, R. A.; Sgarbossa, P.; Scarso, A.; Strukul, G. Coord. Chem. Rev. 2010, 254 646; (b) ten Brink, G.-J.; Arends, I. W. C. E.; Sheldon, R. A. Chem. Rev. 2004, 104 , 4105; (c) Seiser, T.; Saget, T.; Tran, D. N.; Cramer, N. Angew. Chem. Int. Ed. 2011, 50 , 7740; (d) Jin, P.; Zhu, L.; Wei, D.; Tang, M.; Wang, X. Comput. Theor. Chem. 2011, 966 , 207. 3. (a) Kaneda, K.; Ueno, S.; Imanaka, T.; Shimotsuma, E.; Nishiyama, Y.; Ishii, Y. J. Org. Chem., 1994, 59 , 2915; (b) Li, X.; Wang, F.; Zhang, H.; Wang, C.; Song, G. Synthetic Commun. 1996, 26 , 1613; (c) Chrobok, A. Tetrahedron 2010, 66 , 2940.
294 CARBON–SCORPIONATE COMPLEXES IN OXIDATION CATALYSIS 4. (a) Greggio, G.; Sgarbossa, P.; Scarso, A.; Michelin, R. A.; Strukul, G. Inorg. Chim. Acta 2008, 361 , 3230; (b) Sgarbossa, P.; Scarso, A.; Pizzo, E.; Sbovata, A.M.; Tassan, A.; Michelin, R.A.; Strukul, G. J. Mol. Catal. A Chem. 2007, 261 , 202; (c) Conte, V.; Floris, B.; Galloni, P.; Mirruzzo, V.; Scarso, A.; Sordi, D.; Strukul, G. Green Chem. 2005, 7 , 262; (d) Uchida, T.; Katsuki, T. Tetrahedron
(f) Brunetta, A.; Sgarbossa, P.; Strukul G. Catal. Today 2005, 99 , 227. 5. (a) Silva, T. F. S.; Luzyanin, K. V.; Kirilova, M. V.; Silva, M. F. C. G.; Martins, L. M. D. R. S.; Pombeiro, A. J. L. Adv. Synth. Catal.
J. L. Adv. Synth. Cat. 2008, 350 , 706; (d) Silva, T. F. S.; Silva, M. F. C. G.; Mishra, G. S.; Martins, L. M. D. R. S.; Pombeiro, A. J. L. J. Organomet. Chem. 2011, 696 , 1310; (e) Silva, T. F. S.; Mishra, G. S.; Silva, M. F. G.; Wanke, R.; Martins, L. M. D. R. S.; Pombeiro, A.J.L. Dalton Trans. 2009, 42 , 9207; (f) Alegria, E. C. B. A.; Kirillova, M. V.; Martins, L. M. D. R. S.; Pombeiro, A. J. L. Appl. Catal. A Gen. 2007, 317 , 43. 6. Mishra, G. S.; Silva, T. F. S.; Martins, L. M. D. R. S.; Pombeiro, A. J. L. Pure Appl. Chem. 2009, 81 , 1217. 7. Mishra, G. S.; Alegria, E. C. B. A.; Martins, L. M. D. R. S.; Fra´usto da Silva, J. J. R.; Pombeiro, A. J. L. J. Mol. Catal. A Chem.
8. (a) Ullmann’s Encyclopedia of Industrial Chemistry, 6th ed.; Wiley-VCH Verlag GmBH: Weinheim, 2002; (b) Whyman, R. Applied Organometallic Chemistry and Catalysis; Oxford University Press: Oxford, 2001. 9. Alegria, E. C. B.; Martins, L. M. D. R. S.; Kirillova, M. V.; Pombeiro, A. J. L. Appl. Catal. A Gen., 2012, 443–444 , 27. 23 TOWARD CHEMOSELECTIVE BIOCONJUGATIVE DESULFITATIVE CATALYSIS Lanny S. Liebeskind and Ethel C. Garnier-Amblard Department of Chemistry, Emory University, Atlanta, Georgia 23.1 INTRODUCTION Metal-catalyzed desulfitative transformations of sulfur-containing molecules are both challenging and significant. The challenge resides in the fact that many of the catalytic systems that carry out desulfitative transformations require the use of polarizable metal catalysts or precatalysts that can form especially strong bonds to sulfur. Strong metal-to-sulfur bonding, however, inhibits efficient catalytic turnover, particularly when mild reaction conditions are required. The significance rests in the important opportunities, some partly realized, some untapped, for desulfitative transformations. As depicted in Fig. 23.1, these are found in energy-related research with metal-catalyzed desulfurization of carbon-based fuels [1], in the detoxification of chemical warfare agents with metal-catalyzed transformations of phosphonothioate and phosphorothioates [2, 3], as well as in the synthesis of fine chemicals through highly chemoselective desulfitative transformations [4–6]. Of the native carbon– heteroatom bonds that are biologically relevant (C–O, C–N, C–S), the C–S bond is particularly polarizable, and it therefore has the potential to engage in highly selective transformations catalyzed by thiophilic metals in the presence of C–O- and C–N-based functional groups. As a consequence, given its inherent chemoselectivity, the desulfitative catalysis could also play an important role in highly selective bioconjugative reactions where a biomolecule is coupled to another biomolecule, to a probe or therapeutic molecule, or to a nanomaterial (dot, tube, particle, etc.) or surface [7]. Nevertheless, developing effective bioconjugative desulfitative catalytic systems will be especially challenging. Not only must a unique C–S bond within a complex biomolecule be targeted for reaction in the presence of numerous O- and N-based moieties and other S-containing groups, but bioconjugative desulfitative catalysis demands the efficient turnover of a strong M–S bond in water at or near neutral pH and at or near ambient temperature, as required by functionally complex, thermally and pH-sensitive biomolecules such as proteins. This article provides a brief overview of the development of the pH-neutral, desulfitative coupling of thioorganics with boronic acids and describes the evolution of the original process into two new fully catalytic reaction systems that are now poised for bioconjugative desulfitative applications.
The literature on metal-catalyzed “desulfitative” cross-coupling of thioorganics extends back into the 1970s beginning with the early work of Wenkert [8–10] and Okamura [11] and then Ronzini [12–15] who first showed that thioorganics participate
First Edition. Edited by Armando J. L. Pombeiro. © 2014 John Wiley & Sons, Inc. Published 2014 by John Wiley & Sons, Inc.
296 TOWARD CHEMOSELECTIVE BIOCONJUGATIVE DESULFITATIVE CATALYSIS Desulfitative catalysis Energy research Chemical warfare agents Chemoselective synthesis Metal-catalyzed production of hydrocarbon-based fuels (desulfurization of coal and oil or desulfitatively enhanced deoxygenation of biofuels) Destruction and decontamination of phosphonothioate and phosphorothioate nerve gas agents Fine and functionally complex chemical synthesis through chemoselective catalytic desulfitative transformations Figure 23.1 Desulfitative catalysis overview. in Ni- and Fe-catalyzed Kumada-like cross-coupling with Grignard reagents. Such desulfitative cross-couplings were then further developed using basic and nucleophilic coupling partners such as Grignard and organozinc reagents by Lu [16], Fukuyama [17–19], Jacobi [20, 21], and others [6]. In contrast to Grignard and organozinc reagents, nonbasic and non- nucleophilic boronic acids offer the unique potential for metal-catalyzed desulfitative cross-coupling with thioorganics at neutral pH potentially in water, an operational condition required in many bioconjugative applications. The investigation of chemoselective thioorganic– boronic acid couplings began by studying sulfonium salts as participants in a variety of Pd- and Ni-catalyzed coupling protocols, with the sulfonium salts either preformed [22, 23] or generated in
with boronic acids was unknown (Scheme 23.1), a situation primarily thwarted by an unfavorable transmetalation from a neutral boronic acid to an organopalladium thiolate intermediate (Scheme 23.2). The challenge associated with the development of a palladium-catalyzed, pH-neutral desulfitative coupling of a thioorganic and a boronic acid rests with uncovering reaction conditions that would facilitate the unfavorable transmetalation step without perturbing the pH. As a design strategy for accomplishing this goal, we conceived of the incorporation into the reaction system of a pH-neutral, dual thiophilic/borophilic cofactor, M–X, that would simultaneously lower the kinetic barrier and address the thermodynamic deficit implicit in the transmetalation step, all while maintaining pH neutrality (Fig. 23.2). Using this design strategy, copper(I) carboxylates, such as Cu(I) thiophenecarboxylate (CuTC) and Cu(I) 3-methyl- salicylate (CuMeSal) proved to be uniquely effective facilitators of the pH-neutral, palladium-catalyzed desulfitative coupling of thioorganics with boronic acids and their pH-neutral transmetalation partners, organostannanes (Fig. 23.3) The literature is now replete with many examples of this chemistry (Fig. 23.4) [4, 5, 25–42]. All “first-generation” palladium-catalyzed desulfitative couplings of thioorganics and boronic acids highlighted in Fig. 23.4 require the use of stoichiometric quantities of a copper(I) carboxylate cofactor. This requirement is implicit in the mechanism of the transformation (Scheme 23.3). R 1 SMe + R 1 R 2 + “MeS B(OH) 2 ” Catalyst Neutral pH R 2 B(OH) 2
Desulfitative coupling of boronic acids and thioorganics. Pd SMe
L L R 1 R 2 + Pd R
2 L L R 1 + MeS B(OH) 2 B(OH) 2 Poorly electrophilic Poorly nucleophilic A weak bond? Kinetic variables Thermodynamic variable A strong bond? Thermodynamic variable Weak preassociation of "S" with "B" Scheme 23.2 Unfavorable transmetalation THIOORGANIC-BORONIC ACID DESULFITATIVE CROSS-COUPLING 297 M L L S R ′ Pd R 2 B X M S OH L R ′ R 1 L OH L L Thiophilic Borophilic Pd B
R 2 OH R 1 L HO L Kinetic activation Thermodynamic bookkeeping Figure 23.2 Dual thiophilic–borophilic activation of transmetalation. (See insert for color representation of the figure.) R 1
R ′ R 2 B (OH) 2 +
+ R 1 R 2 + R ′ S Cu Cu - OCOR ′′ + R ′′CO 2 B (OH) 2 Pd cat O O OH Cu O O HO Cu Me Me O O Cu O O Cu S S CuTC Cu(I) thiophene-2-carboxylate CuMeSal Cu(I) 3-methylsalicylate Pd R 2 B OCOR
′′ Cu S OH L R ′ R 1 L OH L L Thiophilic borophilic
cofactor enhanced kinetics and thermodynamics
Pd-catalyzed, Cu(I) carboxylate-mediated desulfitative catalysis. (See insert for color representation of the figure.) cat. Pd(PPh 3 ) 4 Het
S R cat. Pd 2 dba
3 Het R
2 R 1 S R ′ R 1 R 2 N N SR R O Br cat. Pd(PPh 3 )
S NC R 2 CN Cyanation Alkynylation Heteroarylation Amidination Switchable catalysis + BocN
O NBoc
S SiMe
3 Me cat. Pd 2 dba
3 H 2 N NH R 2 + cat. Pd 2 dba
3 + + + N N R 2 R O Br S R 1 equiv CuTC 1 equiv CuTC 1 equiv CuTC 1 equiv CuTC cat. Pd(PPh 3 )
R 2 R 2 B(OH)
2 R 2 B(OH) 2 R 2 B(OH)
2 R 2 B(OH) 2 R 2 B(OH)
2 R 2 B(OH) 2 + O R 1 Acylation R 1 O Download 11.05 Mb. Do'stlaringiz bilan baham: 
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