Comparing two models for the selectivity in the asymmetric dihydroxylation reaction (AD)

Becker, H.; Ho, Pui Tong; Kolb, Hartmuth C.; Loren, Stefan; Norrby, Per‐Ola; Sharpless, K. Barry

doi:10.1016/0040-4039(94)85302-9

Cited by 48 publications

(31 citation statements)

References 18 publications

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“…Sharpless compared two models for the selectivity in the asymmetric dihydroxylation and concluded that the aromatic CH/p interaction is important in stabilizing the transition-state leading to the preferred product. 365 Jacobsen found that C2-symmetric 1,2-diimines are effective ligands for Cu(I)-catalyzed enantioselective aziridination and cyclopropanation reactions. 366 The crystal structure of the copper complex bound to styrene was determined.…”

Section: Catalytic Enantioselective Reactionsmentioning

confidence: 99%

CH/? hydrogen bonds in crystals

Nishio¹

2004

CrystEngComm

1,389

781

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The nature and characteristics of the CH/p interaction are discussed by comparison with other weak molecular forces such as the CH/O and OH/p interaction. The CH/p interaction is a kind of hydrogen bond operating between a soft acid CH and a soft base p-system (double and triple bonds, C 6 and C 5 aromatic rings, heteroaromatics, convex surfaces of fullerenes and nanotubes). The consequences of CH/p hydrogen bonds in supramolecular chemistry are reviewed on grounds of recent crystallographic findings and database analyses. The topics include intramolecular interactions, crystal packing (organic and organometallic compounds), host/ guest complexes (cavity-type inclusion compounds of cyclodextrins and synthetic macrocyclic hosts such as calixarenes, catenanes, rotaxanes and pseudorotaxanes), lattice-inclusion type clathrates (including liquid crystals, porphyrin derivatives, cyclopentadienyl compounds and C 60 fullerenes), enantioselective clathrate formation, catalytic enantioface discriminating reactions and solid-state photoreaction. The implications of the CH/p concept for crystal engineering and drug design are evident.

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Section: Catalytic Enantioselective Reactionsmentioning

confidence: 99%

CH/? hydrogen bonds in crystals

Nishio¹

2004

CrystEngComm

1,389

781

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“…Calcd for C 13 H 17 NO 2 : C,71.87;H,6.96;N,6.45. Found C,71.63;H,6.87;N,6. 02, 31.71, 68.17, 77.20, 121.17, 125.65, 127.24, 127.28, 128.44, 136.27, 137.46, 146.26, 162.16. IR (KBr): n = 3387, 3047, 2978, 2936, 2877, 1600, 1583, 1508, 1447, 1080, 1038, 774 cm -1 .…”

Section: (+)-2-ethyl-8-[(1s)2-dihydroxyethyl)quinolinementioning

confidence: 99%

“…Calcd for C 13 H 15 NO 2 : C,71.87;H,6.96;N,6.45. Found C,71.96;H,6.95 N,6. 57, 74.60, 116.77, 121.26 (d, J = 275 Hz), 127.41, 128.60, 129.32, 129.47, 138.57, 139.18, 145.10, 146.58. IR (KBr): n = 3387, 2945, 2868, 1617, 1608, 1472, 1438, 1336, 1191, 1040 18, 77.03, 125.87, 126.59, 127.03, 127.49, 128.45 (2C), 129.39, 129.58, 131.40, 137.29, 137.69, 148.10, 148.32.…”

Section: (+)-mentioning

confidence: 99%

“…5 Considerable attention has been attracted toward a possible mechanism explaining the observed high enantioselectivity. 6 In a recent article dealing with the two proposed models (Corey 7 and Sharpless 8 ) to explain the mechanism of osmium-promoted diol formation, a study 7b on enantioselectivity in the asymmetric dihydroxylation of olefins possessing extended polycyclic aromatic binding groups was presented in support of the CCN (Criegee-Corey-Noe) 7a [3+2] cycloaddition pathway. No such study exists for olefins with heteroaromatic nucleus.…”

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confidence: 99%

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Enantioselective Sharpless Dihydroxylation of Vinylic Aromatic Heterocycles

et al. 2000

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Asymmetric dihydroxylation (AD) with an AD-mix reagent was conducted on a series of terminal olefins possessing an extended heteroaromatic group. Good yields and high enantioselectivities were observed in most instances. However, the steric hindrance resulting from neighboring substituents on the aromatic heterocycle can interfere during the course of the dihydroxylation. The effects of voluminous groups such as t-Boc, t-BDMS or adamantylmethyl were evaluated.The osmium-catalyzed asymmetric dihydroxylation (AD) developed by Sharpless 1 has evolved as one of the most powerful method for enantioselective oxidation of olefins. The broad utility of this reaction relies on the mildness of the oxidizing agent, its high reliability and achieved enantioselectivity and on its simple predictivity using a mnemonic device. 2 Moreover, the reaction can be conveniently run using the commercially available ADmix reagents. The optically active vicinal diol obtained by the asymmetric dihydroxylation (AD) reaction are versatile and convenient building blocks in the synthesis of biologically important compounds. 3 Consequently many researchers are focussing their efforts to bring improvements 4 to make this methodology not only attractive for research laboratories but also to industrial processes. 5 Considerable attention has been attracted toward a possible mechanism explaining the observed high enantioselectivity. 6 In a recent article dealing with the two proposed models (Corey 7 and Sharpless 8 ) to explain the mechanism of osmium-promoted diol formation, a study 7b on enantioselectivity in the asymmetric dihydroxylation of olefins possessing extended polycyclic aromatic binding groups was presented in support of the CCN (Criegee-CoreyNoe) 7a [3+2] cycloaddition pathway. No such study exists for olefins with heteroaromatic nucleus. In fact, a comprehensive search in the literature revealed that only few applications of the AD reaction on vinylic heteroaromatic substrates have been reported to date. In some instances the course of the reaction was seriously altered. 9 This situation prompted us to examine the effect of heteroatoms or substituents of heteroaromatic nuclei fused to styrene in the course of the AD reaction (Scheme) and to report here the experimental details and observations on the preparation of the corresponding chiral diols.The vinylic side-chain was set up via a Stille cross-coupling reaction 10 using commercially available tributylvinyltin and various heteroaromatic bromides or triflates. All asymmetric dihydroxylation reactions were carried out at 0°C using the same procedure. The results are summarized in the Table. In comparison to naphthalene (Entry 1), benzofurans (Entries 2, 3), regardless of the position of the vinyl side chain, behave similarly providing diols with high yields and enantiomeric excesses. Similar effects were observed when application of AD reaction was extended to thiophene, benzoxazole and quinolines (Entries 4-8). To further explore the reliability of the reaction, few substitutions o...

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“…The initial model (Figure 3.2a) for the transition state was based on a [2 þ 2] cycloaddition reaction model and, although NMR studies support this, there is now evidence and consensus that a [3 þ 2] model is followed [123][124][125][126][127][128][129][130]. Computational studies suggest that solvent can play a key role in account for the apparent reversal of reaction stereochemical outcome compared to that predicted by Sharplesss original mnemonic (Figure 3.2a).…”

Section: Mechanismmentioning

confidence: 99%

Cinchona Alkaloids as Chiral Ligands in Asymmetric Oxidations

Ager¹

2009

Cinchona Alkaloids in Synthesis and Catalysis

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For oxidation reactions, the cinchona alkaloids have been mainly employed to control the osmium-catalyzed conversion of an alkene to give a 1,2-diol or vicinal functionalized alcohol. As these are important asymmetric reactions, they have been the subject of a number of reviews [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. This chapter discusses the uses of these alkaloids as chiral ligands in asymmetric oxidation reactions. Oxidation reactions where an alkaloid is used in a phase-transfer sense are discussed in Chapter 5.The use of osmium tetroxide for the conversion of an alkene to a 1,2-diol is a wellestablished reaction [19][20][21][22]. The formation of an intermediate cyclic ester accounts for the cis-stereochemistry [21, 23-32] as reaction occurs on the least hindered face of the alkene [21,30,[33][34][35][36][37][38]. This steric effect is amplified in cyclic substrates [39,40]. The reaction conditions have to be carefully controlled to avoid oxidative cleavage of the diol product [28].There is a marked rate acceleration in the presence of a tertiary amine or pyridine [19,41]. This finding provided the background for the asymmetric dihydroxylation (AD) and, later, the asymmetric aminohydroxylation (AA) reactions as it is this ligand acceleration effect (LAE) that ensures the reaction pathway involving the ligand.The use of a cooxidant can reduce the amount of osmium required for a complete reaction of an alkene from stoichiometric to catalytic; some examples of oxidants that can achieve this are peroxides [20,22,35,37,[42][43][44] including hydrogen peroxide [20,42], chlorates [45], periodate [46,47], hypochlorite [48], N-methylmorpholine-N-oxide (NMMO) [22,34,35,37,49], potassium ferricyanide [50,51], and even air [52,53].Stereoselection for the OsO 4 reactions itself can also be observed when a directing group is adjacent to the alkene, such as in an allyl alcohol. An empirical rule has been devised, where the reagent approaches from the face opposite to the preexisting oxygen functionality. Although the hydroxy group may be protected, the presence of an acyl group reduces stereoselectivity. cis-Alkenes afford better selectivity

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Comparing two models for the selectivity in the asymmetric dihydroxylation reaction (AD)

Cited by 48 publications

References 18 publications

CH/? hydrogen bonds in crystals

CH/? hydrogen bonds in crystals

Enantioselective Sharpless Dihydroxylation of Vinylic Aromatic Heterocycles

Cinchona Alkaloids as Chiral Ligands in Asymmetric Oxidations

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