Chiral Hypervalent Organo-Iodine(III) Compounds

Hirt, Urs H.; Schuster, M.; French, Andrew N.; Wiest, Olaf; Wirth, Thomas

doi:10.1002/1099-0690(200104)2001:8<1569::aid-ejoc1569>3.0.co;2-t

Cited by 162 publications

(64 citation statements)

References 39 publications

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“…Of these, the 6-ethylsubstituted iodoarene 5 (entry 2) gives the highest enantioselectivity, a fact also observed in the stoichiometric reaction. 1f, 4 We find that the enantioselectivity obtained in this catalytic reaction is the same as that observed in the stoichiometric reaction performed at the same temperature in the same solvent. We have previously reported that methyl ethers give rise to the best selectivity 1f so we did not test any iodoarenes that did not possess the 1-aryl-1-methoxyethane function seen in 4-11.…”

Section: Scheme 1 Enantioselective Oxytosylation Of Ketonesmentioning

confidence: 99%

Enantioselective α-Oxytosylation of Ketones Catalysed by Iodoarenes

Page¹,

Altermann²,

Paradine³

et al. 2007

Synlett

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The a-oxytosylation of ketones catalysed by enantioenriched iodoarenes using mCPBA as stoichiometric oxidant is reported to give useful synthetic intermediates in good yield and modest enantioselectivity. We believe this to be the first report of an enantioselective catalytic reaction involving hypervalent iodine reagents which should open up a new field for enantioselective organocatalysis of oxidation reactions.The use of enantioenriched hypervalent iodine reagents for asymmetric transformations has emerged as an interesting area of research in recent years. 1 These reagents are attractive because they can replace toxic heavy metal reagents. 2 One example is our report of the enantioselective a-oxytosylation of ketones 1 mediated by chiral Kosertype reagent 2 giving synthetically useful 3 tosylates such as 3 in up to 40% ee (Scheme 1). 1f,4 This reaction suffers the drawback that the l 3 -iodane 2 must be present in stoichiometric quantities and that the preparation of this reagent requires two synthetic steps from the parent iodoarene. We have found the synthesis and isolation of many (especially electron-rich or sterically congested) aryl l 3 -iodanes to be problematic. This includes many of the enantiopure iodoarenes that have been prepared in our laboratory for this purpose and, hence, the enantioinducing power of these reagents remains untested. Scheme 1 Enantioselective oxytosylation of ketonesThe use of hypervalent iodine reagents as catalysts in synthetic transformations has attracted recent attention. 5 Indeed, during the course of this work, the racemic a-oxytosylation of acetophenone derivatives catalysed by iodobenzene using m-chloroperbenzoic acid (mCPBA) as the stoichiometric oxidant has been reported by Togo. 6 It was thought that such catalytic use of iodoarenes should allow a much simplified procedure for the enantioselective aoxytosylation of ketones and, hence, give a significant improvement on current methodology.Initial studies towards identifying efficient iodoarene catalysts were performed using the reaction of 0.5 mmol of propiophenone (1) in acetonitrile with 10 mol% iodoarene 4-19, 1.5 equivalents of commercial 70-77% wet mCPBA 7 as the stoichiometric oxidant and p-toluenesulfonic acid monohydrate (TsOH·H 2 O) as the source of the tosylate nucleophile. The reaction using stoichiometric iodane 2 is usually performed at -30°C to maximise enantioselectivity, 4 but at this temperature we find that the reactions employing catalytic amounts of iodobenzene or chiral iodide 4 and mCPBA as the stoichiometric oxidant proceed very slowly, consistent with the results of Togo. 6 This suggests that the formation of the hydroxy(tosyloxy)iodoarene could be the rate-determining step in the catalytic cycle. To circumvent this problem, we performed our initial reactions at room temperature for two days using a range of iodoarenes (Table 1). In all cases, clean reactions to give tosylate 3 were observed.The results in Table 1, entries 1-4 consist of those iodoarenes that have been previously tested as the...

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Section: Scheme 1 Enantioselective Oxytosylation Of Ketonesmentioning

confidence: 99%

Enantioselective α-Oxytosylation of Ketones Catalysed by Iodoarenes

Page¹,

Altermann²,

Paradine³

et al. 2007

Synlett

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“…Indeed, computational studies of hypervalent iodine compounds have been performed, but have not addressed the questions posed here. 26,27,52 The trouble with this approach is that without some experimental support (kinetics, transition state energies, etc. ), computational results will not be entirely conclusive.…”

Section: Known Unknownsmentioning

confidence: 99%

Asymmetric oxidative dearomatizations promoted by hypervalent iodine(III) reagents: an opportunity for rational catalyst design?

Harned

2014

Tetrahedron Letters

102

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The use of and λ3- and λ5-iodanes in the oxidative dearomatization of phenols is a well-established and general procedure for the construction of cyclohexadienone structures. However, their use in asymmetric dearomatization reactions is quite underdeveloped and, despite work by several research groups over the past several years, a general chiral aryl iodide catalyst has yet to emerge. This article will serve to highlight the significant progress that has been made in this area and will reveal some of deficiencies in the literature that the author believes may be hindering further progress.

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“…This led to finding increased selectivities when R 2 = Et, giving the products in 65% ee (bis-oxytosylation of styrene) and 40% ee (α-oxytosylation of propiophenone). 8 The importance of the ortho-substituent R 2 on the reactivity of the iodine(III) center has recently been shown through further computational evidence. 9 The enhanced catalytic activity of iodoarenes such as 4 has been ascribed to the destabilizing effect of this substituent, with these catalysts giving the products in good yields (70-85%) after several hours at a temperature of -30 °C.…”

Section: Stereoselective Reactionsmentioning

confidence: 99%

Hypervalent Iodine Reagents as Powerful Electrophiles

Brown

Farid

Wirth

2013

Synlett

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109

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Hypervalent iodine reagents have been investigated as very powerful electrophiles in many different reactions. Efficient formation of new carbon-heteroatom bonds as well as carboncarbon bonds can be achieved typically under mild reaction conditions with these metal-free reagents. Enantiomerically pure reagents provide the potential for stereoselective reactions and this aspect is highlighted in this account.

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Chiral Hypervalent Organo-Iodine(III) Compounds

Cited by 162 publications

References 39 publications

Enantioselective α-Oxytosylation of Ketones Catalysed by Iodoarenes

Enantioselective α-Oxytosylation of Ketones Catalysed by Iodoarenes

Asymmetric oxidative dearomatizations promoted by hypervalent iodine(III) reagents: an opportunity for rational catalyst design?

Hypervalent Iodine Reagents as Powerful Electrophiles

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