A discussion of switching in polyvinyl difluoride copolymers is given (see L. Zhang, EPL 2010, 91, 47001) in terms of the general history of ferroelectric switching with and without domain wall participation.

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...

Ketones Q 0350Enantioselective α-Oxytosylation of Ketones Catalyzed by Iodoarenes. -Various chiral iodoarenes are examined as catalyst for the conversion of ketones to α-tosyloxyketones. Even under optimized conditions A), only low enantioselectivities are observed. -(RICHARDSON, R. D.; PAGE, T. K.; ALTERMANN, S.; PARADINE, S. M.; FRENCH, A. N.; WIRTH*, T.; Synlett 2007, 4, 538-542; Sch. Chem., Cardiff Univ., Cardiff CF10 3AT, UK; Eng.) -Mais 27-073

A modified procedure for the direct synthesis of hypervalent [bis(trifluoroacetoxy)iodo]arenes is described. It avoids the use of hazardous reagents with the workup being only an aqueous extraction.Hypervalent iodine compounds are now established reagents in organic synthesis. Their use as mild and efficient oxidants is important, but many more applications of these compounds have emerged recently. They range from the formation of carbon-carbon bonds in phenolcoupling reactions or as benzyne precursors in the generation of carbon-heteroatom bonds to the activation of carbon-hydrogen bonds. Depending on the substrate, rearrangements or fragmentations can also be induced by these reagents. 1 They are an alternative to metal-containing reagents due to their low toxicity, stability, ease of handling, and high efficiency. Although first reports on the catalytic use of hypervalent iodine reagents have recently appeared in the literature, 2 most of the applications still rely on stoichiometric quantities of these compounds. Of practical importance are hypervalent iodine compounds with halides (chloride, fluoride) and acetoxy or trifluoroacetoxy groups as ligands. Among the growing library of hypervalent iodine compounds are [bis(trifluoroacetoxy)iodo]arenes 1, ArI(OCOCF 3 ) 2 , originally prepared by Yagupolskii et al. 3 They have been applied as potent and often chemoselective oxidants, and have a broad appeal throughout organic synthesis.Several methods have been published for the synthesis of [bis(trifluoroacetoxy)iodo]arenes. These reagents (1) can be prepared either by an indirect route, usually by a ligand-exchange reaction on an already-oxidized iodine(III) compound, or by direct oxidation from aryl iodide precursor molecules.A commonly used procedure is the ligand-exchange reaction using (diacetoxyiodo)arenes and trifluoroacetic acid. 4 The success of this method is related to the electronic properties of the (diacetoxyiodo)arene -the reaction rate of electron-poor substrates can be very low. Other indirect methods include the reaction of (dichloroiodo)arenes with silver trifluoroacetate 5 or the reaction of iodosylarenes with trimethysilyl trifluoroacetate. 6

9-Diazofluorene reacts with /rans-dibenzoylethylene to give £rans-2,3-dibenzoylspiro(cyclopropane-l,9'fluorene) (1)2 3in quantitative yield. Cyclopropane 1 was reported to undergo various transformations which were not understood and which led to crystalline products of unknown structures.2 Of special interest is the reaction of 1 with hot excess methanolic potassium hydroxide (Scheme I) to form a red potassium salt, tenta-