Iodide exchangeable

Cyclohexenones 34 also undergo a highly diastereoselective dihydroxylation to give cii-diols 39 (Scheme 11).22 These diol amides are converted to hydroxylactones 40 by an acid-catalyzed process involving retro aldol-realdolization prior to transacylation. The enantiomers of hydroxylactones 40 are obtained from iodolactones 35 by iodide exchange with 2,2,6,6-tetramethylpiperidin-l-yloxy free radical (TEMPO) followed by reductive cleavage of the TEMPO derivative with Zn in ElOAc. The enantiomeric purity of the hydroxylactones prepared by either route is 95-98% ee. 

Conversion of 2-chloroacetamides 17 into iodoacetamides by iodide exchange followed by reaction with BusSnH in the presence of AIBN affords 7,12-dihydro-indolo[3,2-d][l]benzazepin-6(5H)-ones 18 as products of free radical cyclization (Equation (4) (2005T5489)). Low (8-25%) yields of azepinones 18 are observed in toluene medium, and they are usually accompanied with the product of spiro cyclization 19 and isomeric compound 20. Yields of the paullone 18 can be increased to 25-52% at higher temperatures (boiling mesitylene). 

Polymer supports different from polystyrene show different response to % RS in triphase catalysis of nucleophilic displacements. Poly(4-vinylpyridines) 66-71 % alkylated with C8, C12, and C16 chains (6) give high yields of cyanide displacement on 1-bromooctane and on 1-iodooctane and of bromide/iodide exchange of the 1-halooctanes81,87). An 81.6% RS n-butyl-quaternized poly(4-vinylpyridine) (6)... 

The lower-melting dimethylene compound was resistant to periodate treatment and its ditosyl ester did not participate in the sodium iodide exchange reaction thus it was probable that the diacetal was of the 1,2,4,6-, 1,3,4,6- or 1,3,5,6-type. For theoretical reasons the authors48 favored tentatively the 1,3 4,6-pattern. Since the other dimethylene-D-talitol (m. p. 261-262°) did not react with periodate and since its ditosyl ester could be converted into a didesoxy-dimethylene-hexitol by sodium iodide exchange and hydrogenation, it was designated as 2,3,4,5-dimethyl-... 

In the presence of molar amounts of catalyst, the chloride/iodide exchange reaction is more effective as has been shown by Brandsrom178 for the conversion of chloroaceto-2,6-xylidide into the corresponding iodide. The Finkelstein reaction is also catalyzed by phos-phonium and arsonium salts1. 

Although the direct iodine-to-Zn-exchange allows cyclizations of functionalized molecules, the iodine-to-organolithium and iodine-to-organozinc iodide exchanges were studied on the simple l-iodo-5-hexene, and the tremendous importance of the nature of the lithium halides present in solution was noticed. Indeed, as shown in Scheme 7-44, the cyclization that is somewhat similar to that of Scheme 7-41 does not operate any more, although performed in ether The only difference lies in the presence of Lil (foimed in the first step) and LiBr (formed in the transmetallation step). 

Examples of allylation [39a] and vinylation [39b] are shown in Scheme 24. The dichlorovinylation is especially interesting since the products are immediate precursors of alkynes via the Corey-Fuchs reaction. The process is also applicable to aliphatic iodides, exchange of iodine replacing the exchange of xanthate in the mechanistic manifold in Scheme 22 [39b,c[. 

I ions and I ions must take place considerably more rapidly than the diffusion controlled rate limit for the reaction I + I J I3. Genser and Connick propose that iodide exchange actually takes place through the direct bimolecular reaction... 

Ruff, I. Friedrich, V. J. Csillag, K. 1972. Transfer Diffusion. III. Kinetics and Mechanism of the Triiodide-Iodide Exchange Reaction, J. Phys. Chem. 76, 162-165. 

Copolymers of 4-Vinylpyridine. Acrylonitrile improves the tensile strength of these reverse-osmosis membranes. Cross-linking qnatemization of the copolymers with diiodobutane improves the performance of the membranes, achieving salt rejection of 95% and hydraulic water permeabihty of up to 30 x 10 cm /(s Pa). The quaternized membranes also are anion exchangeable more than two-thirds of iodide exchanges with chloride (162). 

Previous studies of the iodide-tri-iodide exchange reaction have beat discussed in terms of a dissociation-formation model ... 

The use of this model leads to derived rate constants which exceed the diffusion-controlled limit. Further n.m.r. studies and a reconsideration of earlier published experimental data lead to a new proposal of an associative mechanism for iodide exchange, in which iodide attacks at one end of the tri-iodide. It is possible, from the observed kinetic pattern, that the I so generated has a sufficient lifetime to be considered an intermediate rather than a transition state. A transfer diffusion investigation of the same reaction also culminates in the proposal of an associative mechanism, with a linear transition state. Allowing for the non-spherical nature of the tri-iodide, it is possible to calculate a diffusion-controlled rate constant, which turns out to be the same as the experimentally determined (by this method or from n.m.r.) second-order rate constant. Some calculations on the transition state have been made in connection with this transfer diffusion study of the iodide-tri-iodide exchange reaction. Further study of the iodide-thiocyanate reaction has resulted in an estimate of the association constant for the initial rapid association of the reactants to give the intermediate charge-transfer complex la.SCN-. ... 

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