Hypervalent iodine compounds halogenation

Chemical oxidation of silyl enolates has been performed with a variety of inorganic and organic oxidants such as ozone, copper(II) salts, Pb(OAc)4, Ag20, hypervalent iodine compounds such as iodosobenzene in methanol, (NH4)2[Ce(N03)6], xenon difluoride, tetranitromethane, halogens, nitronium-, diazonium- and triphenylmethyl salts, chloranil and ddq. 

Iodine in combination with [bis(acyloxy)iodo]arenes is a classical reagent combination for the oxidative iodination of aromatic and heteroaromatic compounds [99], A typical iodination procedure involves the treatment of electron-rich arenes with the PhI(OAc)2-iodine system in a mixture of acetic acid and acetic anhydride in the presence of catalytic amounts of concentrated sulfuric acid at room temperature for 15 min [100,101]. A solvent-free, solid state oxidative halogenation of arenes using PhI(OAc)2 as the oxidant has been reported [102]. Alkanes can be directly iodinated by the reaction with the PhI(OAc)2-iodine system in the presence of f-butanol under photochemical or thermal conditions [103]. Several other iodine(in) oxidants, including recyclable hypervalent iodine reagents (Chapter 5), have been used as reagents for oxidative iodination of arenes [104-107]. For example, a mixture of iodine and [bis(trifluoroacetoxy)iodo]benzene in acetonitrile or methanol iodinates the aromatic ring of methoxy substituted alkyl aryl ketones to afford the products of electrophilic mono-iodination in 68-86% yield [107]. 

The condensation of two molecules of primary selenoamides proceeds with bromine under extrusion of selenium to give selenadiazoles [93]. The reaction of selenocarbonates, selenothiocarbonates [94], and selenourea [95] with bromine and iodine has been widely tested. The products depend on the amount of halogen used. For example, in the reaction of N-methylthiazoline-2(3H)-selone, the use of one equivalent of bromine gives hypervalent lO-Se-3 complexes 44, whereas two equivalents of bromine cleave the carbon selenium double bond to give product 45. A similar hypervalent compound is formed from 4-imidazolin-2-selone,but the iodination of bis(imidazolin-2-selone)methane gives iodinated product 46. The availability of some of halogen adducts has been tested as a conducting material. 

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