Selective iodination with

Treatment of pyrrole, 1-methyl-, 1-benzyl- and 1-phenyl-pyrrole with one mole of A -bromosuccinimide in THF results in the regiospecific formation of 2-bromopyrroles. Chlorination with IV-chlorosuccinimide is less selective (8UOC2221). Bromination of pyrrole with bromine in acetic acid gives 2,3,4,5-tetrabromopyrrole and iodination with iodine in aqueous potassium iodide yields the corresponding tetraiodo compound. 

The silver(I) complexes with the tetrakis(methylthio)tetrathiafulvalene ligand have been reported, the nitrate salt presents a 3D structure with an unprecedented 4.16-net porous inorganic layer of silver nitrate,1160 the triflate salt presents a two interwoven polymeric chain structure.1161 The latter behaves as a semiconductor when doped with iodine. With a similar ligand, 2,5-bis-(5,5,-bis(methylthio)-l,3,-dithiol-2 -ylidene)-l,3,4,6-tetrathiapentalene, a 3D supramolecular network is constructed via coordination bonds and S"-S contacts. The iodine-doped compound is highly conductive.1162 (Methylthio)methyl-substituted calix[4]arenes have been used as silver-selective chemically modified field effect transistors and as potential extractants for Ag1.1163,1164... 

Buchberger et al. [104] carried out a selective determination of iodide in brine. The performance of a potentiometric method using an ion-selective electrode and of liquid chromatography coupled with ultraviolet detection at 230 nm were compared as methods for the determination of iodide in the presence of other iodide species. Satisfactory results were obtained from the potentiometric method provided the solution was first diluted tenfold with 5 M sodium nitrate, and external standards were used. Better reproducibility was, however, achieved with HPLC, provided precautions were taken to prevent reduction of iodine to iodide in the mobile phase, for which extraction of iodine with carbon tetrachloride prior to analysis was recommended. This was the pre-... 

Despite the fact that secondary hydroxyl groups of nucleosides also react with 23 (see later), selective iodination of only the primary hydroxyl group in some unprotected, pyrimidine nucleosides can also be achieved.82 Thus, brief treatment of thymidine with 1.1 mol-equivalents of 23 in N,N-dimethylformamide gave crystalline 5 -deoxy-5 -iodothymidine in 63% yield. It was even possible to effect some selective iodination of the 5 -hydroxyl group of 2,2 -anhydrouri-dine without excessive cleavage of the (quite labile) anhydro linkage. 

On alkylation of 2-(aminomethyl)oxazolines (42) and (43), stereochemical induction is evident for the tertiary carbamates (43), but not the tertiary amines (42) this is apparently a consequence of prior complexation of the carbamate carbonyl group to the base and kinetic preference for ( )-enolate formation on deprotonation 47 4-Alkenylamides (44) having a /1-cliiral centre have been found to undergo syn-selective a-iodination with iodine to give syn-a-iodoalkcnamidcs, via an intermediate... 

Alkenylamides (44) having a /i-chiral centre have been found to undergo syn-selective a-iodination with iodine to give syn - z-i odoa I kcnam i dcs, via an intermediate... 

Should it be necessary to estimate the amount of ozone produced by the ozone generator, the vessel C is charged with 50 ml of a 5 per cent solution of potassium iodide in aqueous acetic acid (1 1 v/v) and the ozonised oxygen allowed to pass for a set period, say 1 hour, at a steady and measured flow rate (e.g. bubbles/second counted by means of the bubbler A). The iodine which is liberated is determined by washing the contents of C into a conical flask and titrating the liberated iodine with 0.1 m sodium thiosulphate solution the yield of ozone may be calculated in mol/hour for the particular flow rate selected. 

The resulting propargylic alcohol is protected as TIPS ether by a standard procedure using the corresponding silyl chloride and imidazole in DMF. Optionally the more reactive silyl triflate and 2,6-lutidine may be employed in order to shorten the reaction time. Under acidic conditions TIPS and TPS are nearly stable protecting groups. Therefore the TBS ether is selectively cleaved with acetic acid even in presence of the acetal moiety.13 Subsequent reaction with iodine and triphenylphosphine, known as the Appel reaction14, provides the desired iodide 4. 

Tris(glycosyl)boranes and dicyclohexylboranes are iodinated with Nal/Chloramine T or brominated with NaBr/Chloramine T to yield iodinated and brominated sugars, respectively946. BC13 is used for the selective chlorination of carbohydrates947. 

Fig. 1. Set-up of the PTB laser system. The Nd YAG laser is frequency stabilized onto a selected iodine absorption line using the phase modulation method. The probe beam is modulated at 2.05 MHz by an electro-optic modulator (EOM), the pumb beam is frequency shifted by an acousto-optical modulator (AOM). The driving AOM rf power is chopped in order to cancel frequency offsets introduced by the Doppler background using a lock-in detection scheme. The transmitted probe beam signal is detected by a photodiode (PD) and mixed with the EOM rf in a double balanced mixer (DBM)...

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