Iodination of ketones

Iodination of ketones (1, 499). The cyclization of 1,3-dibenzoylpropane by reaction with iodine and sodium hydroxide in methanol involves iodination at the position a to one carbonyl group and elimination of the acidic hydrogen adjacent to the second carbonyl group.1 A mixture of 35 g. (0.14 m.) of 1,3-dibenzoylpropane and a solution of 11.2 g. (0.28 m.) of sodium hydroxide in 0.4 1. of... 

Diiodosilane (DIS) reagent for mild hydrolysis of ketals, acetals or reductive iodination of ketones and aldehydes (see 1st edition). 

Needles from dioxane - - carbon tetrachloride, mp 200-201°. Sol in acetone, methanol moderately sol in dioxane practically insol in CCI4. ether. Dec in water. Protect from light and avoid contact with skin and mucous membranes. use Iodination of ketones and aldehydes. 

Let us consider the determination of iodides as an example. The reaction method of iodide determination was proposed by Hasty [137, 138]. It is based on iodination of ketones in an acidic medium followed by determination of the resulting iodoketone by gas-liquid chromatography using an electron-capture detector. The method was later improved by using butanone-2 instead of acetone, which made it possible to increase the detection sensitivity [139]. A similar method for determining the total content of inorganic iodine in milk was proposed by Bakker [140]. The detection limit does not exceed lOmg/1. It is a sufficiently accurate method with a relative standard deviation of 1.9%. 

One method for the a-iodination of ketones calls for the assistance of selenium dioxide. Heterocyclization. A new route to a-iodo boronic acids consists of iodoethe-rification. p-Iodobutenolides that are useful for carbon chain extension at the P-position (via Pd-catalyzed coupling) are readily accessible by iodolactonization of allenic acids ... 

Oxidative Halogenation. Benzylic bromination and a-iodination of ketones and uracil derivatives can be achieved with CAN as in situ oxidant. 

The reaction of ketones 107 with [hydroxy(4-nitrobenzenesulfonyloxy)iodo]benzene and subsequent treatment with samarium iodide has been used for a one-pot preparation of a-iodoketones 108 (Scheme 3.43) in high yields [118]. 2-Iodosylbenzoic acid can also be used as a convenient recyclable hypervalent iodine oxidant for the synthesis of a-iodoketones by oxidative iodination of ketones [119]. 

Iodosylbenzoic acid (85) is also a convenient recyclable hypervalent iodine oxidant for the synthesis of a-iodo ketones by oxidative iodination of ketones [88], Various ketones and p-dicarbonyl compounds can be iodinated by this reagent system under mild conditions to afford the respective a-iodo substituted carbonyl compounds in excellent yields. The final products of iodination are conveniently separated from by-products by simple treatment with anionic exchange resin Amberlite IRA 900 HCOs" and are isolated with good purity after evaporation of the solvent. The reduced form of the hypervalent iodine oxidant, 3-iodobenzoic acid (59), can be recovered in 91-95% yield from the Amberlite resin by treatment with aqueous hydrochloric acid followed by extraction with ethyl acetate [88]. 

Although there has been significant development of this type of transformation during the recent past, there are stiU some unreported transformations, such as the a-iodination of ketones. Moreover, improvement of the reaction conditions, especially aiming to reduce catalyst loading and increase catalyst recyclabiUty, would enhance the possibiUties of application of these procedures to large-scale synthesis. 

This latter method consists in treating 2 moles of thiourea and 1 mole of ketone, having a methylene group adjacent to the carbonyl, with 1 mole of iodine overnight on a steam bath. Unreacted products are then extracted with ether after alkalinization of the reaction mixture. 

Iodine in functionalization of C 19 meth> 1 group of 3d acetoxy 20/3 hydroxy 5 pregnene 46, 58 Iron powder in preparation of ketones from carboxylic acids, 47, 75 Isobutene, 45, 49... 

The reaction shows a first-order dependence on substrate concentration but, except at very low concentration, is zero-order with respect to oxidant moreover, the zero-order rate coefficient is the same as that observed with oxidations by iodine, cupric chloride and silver nitrate. The reaction is acid-catalysed. The oxidation is completely analogous to the halogenation of ketones and involves a slow tautomeric equilibrium followed by rapid oxidation, viz. 

Reduction to Halocarbons. The best conditions for the reductive chlorination of ketones use the reagent combination Me2ClSiH/In(OH)3 (Eq. 241).331 Examples include conversions of aryl ketones to benzyl chlorides, ethynyl ketones to propargyl chlorides, and alkyl ketones to alkyl chlorides (Eq. 242).331 Addition of lithium iodide to the reaction mixture yields the corresponding iodide product. The combination of TMDO/I2 reductively iodinates aryl ketones and aldehydes in good yields (Eq. 243).357... 

Iodine has been reported to possess a mild Lewis acidity and can activate carbonyl groups. It can for example catalyze the addition of pyrroles to cf,]3-unsaturated ketones (Scheme 85) [224], A mixture of pyrrol and 3 equiv. of ketone gave disub-stituted products in up to 92% yield in 10 min with 10 mol% of iodine. In cases when only 1.1 equiv. of ketone was apphed in the reaction, mono- and disubstituted products were isolated in few minutes in up to 95% yield in a ratio between 1 1 and up to 1 5. A-Alkylated pyrroles also participated in the reaction in good yields. 

Key K1 - Oxidation of Alcohols K2 - Iodination of a Ketone Cl - Protonization of Imidazole CT - Charge Transfer GC - Free Energy Relationships... 

Ketones can be a hydroxylated in good yields, without conversion to the enolates, by treatment with the hypervalent iodine reagents162 o-iodosobenzoic acid163 or phenyliodoso acetate PhI(OAc)2 in methanolic NaOH.164 The latter reagent has also been used on carboxylic esters.165 02 and a chiral phase transfer catalyst gave enantioselective a hydroxylation of ketones, if the a position was tertiary.166... 

The homolysis of iodonaphthalene can be photosensitized in the presence of ketones.216 Homolysis of phenyl-iodine and phenyl-bromine bonds is a general photochemical reaction217,218 but even in the case of aromatic ketones,217 it is not as yet known whether the triplet state is involved in the direct photolysis. 

Interferences may occur with samples that contain iodine-reducing components. Samples that contain high levels of ketones or aldehydes, especially where low moisture levels are to be measured, may present a problem as these compounds may generate water. 

Several reactions of carbonyl compounds that have one or more a hydrogens proceed through the enol form. Reaction of ketones with chlorine, bromine, and iodine result in substitution of halogen for a hydrogen rates are typically first-order in ketone and independent of halogen concentration and even of which halogen is used. Racemization of ketones with asymmetric centers adjacent to the... 

Using 2 c.c. of the spirit, the excess of unabsorbed iodine is 0-1657 gram, so that the amount combining with the ketones is 0-3939 —0-1657 =0-2282 gram. The weight of ketones, expressed as acetone, in too c c. of the spirit is thus ... 

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