Iodination with -Iodine Reagents

Caution 125-Iodine may he liberated during iodination even when solutions are used. Work in a special hood Check your thyroid gland after 6 and 24 h if you have worked with iodination reagents. 

Iodine becomes incorporated into proteins either oxidatively, or enzymatically, or electrochemically. Oxidative incorporation uses organochemical oxidants, such as, for example, chloramine T or lodo-gen (l,3,4,6-tetrachloro-3a,6a-diphenyl glycouril). Enzymatic incorporation is done by means of lactoperoxidase. By these methods iodine is introduced into phenyl (tyrosyl) residues of the protein. 

Conjugation of a protein with the radiolabeled Bolton-Hunter reagent in the first place modifies lysine side chains. 

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Dichloro and dibromo-compounds give a precipitate with the reagent and also liberate free iodine ... 

The iodoform test. Dissolve 0 -1 g. or 5 drops of the compound in 2 ml. of water if it is insoluble in water, add sufficient dioxan to produce a homogeneous solution. Add 2 ml. of 5 per cent, sodium hydroxide solution and then introduce a potassium iodide - iodine reagent dropwise with shaking until a definite dark colour of iodine persists. Allow to... 

When unsubstituted, C-5 reacts with electrophilic reagents. Thus phosphorus pentachloride chlorinates the ring (36, 235). A hydroxy group in the 2-position activates the ring towards this reaction. 4-Methylthiazole does not react with bromine in chloroform (201, 236), whereas under the same conditions the 2-hydroxy analog reacts (55. 237-239. 557). Activation of C-5 works also for sulfonation (201. 236), nitration (201. 236. 237), Friede 1-Crafts reactions (201, 236, 237, 240-242), and acylation (243). However, iodination fails (201. 236). and the Gatterman or Reimer-Tieman reactions yield only small amounts of 4-methyl-5-carboxy-A-4-thiazoline-2-one. Recent kinetic investigations show that 2-thiazolones are nitrated via a free base mechanism. A 2-oxo substituent increases the rate of nitration at the 5-position by a factor of 9 log... 

Recently, the ring enlargement of 4-hydroxy-2-cyclobutenones 5 was promoted by PhI(OAc)2, a popular and accessible hypervalent iodine reagent (99JOC8995). Thus, when 5a-c (R = Me, Bu, Ph) were treated with a slight excess of PhlfOAcja in dichloromethane at room temperature, the 5-acetoxy-3,4-diethoxyfuranones 13... 

A cursory inspection of key intermediate 8 (see Scheme 1) reveals that it possesses both vicinal and remote stereochemical relationships. To cope with the stereochemical challenge posed by this intermediate and to enhance overall efficiency, a convergent approach featuring the union of optically active intermediates 18 and 19 was adopted. Scheme 5a illustrates the synthesis of intermediate 18. Thus, oxidative cleavage of the trisubstituted olefin of (/ )-citronellic acid benzyl ester (28) with ozone, followed by oxidative workup with Jones reagent, affords a carboxylic acid which can be oxidatively decarboxylated to 29 with lead tetraacetate and copper(n) acetate. Saponification of the benzyl ester in 29 with potassium hydroxide provides an unsaturated carboxylic acid which undergoes smooth conversion to trans iodolactone 30 on treatment with iodine in acetonitrile at -15 °C (89% yield from 29).24 The diastereoselectivity of the thermodynamically controlled iodolacto-nization reaction is approximately 20 1 in favor of the more stable trans iodolactone 30. 

For the determination of small amounts of water, Karl Fischer (1935) proposed a reagent prepared by the action of sulphur dioxide upon a solution of iodine in a mixture of anhydrous pyridine and anhydrous methanol. Water reacts with this reagent in a two-stage process in which one molecule of iodine disappears for each molecule of water present ... 

Introduction of iodine by Sandmeyer processes has been discussed [84AHC(35)83], Direct electrophilic iodination is also observed in the 3-position with reagents such as iodine monochloride, iodine-iodic acid-acetic acid, or molecular iodine. With excess reagent, or when C-3 is blocked, 6-iodination follows [84AHC(35)83 84MI15]. 

Under certain conditions, amides can add directly to alkenes to form N-alkylated amides. 3-Pentenamide was cyclized to 5-methyl-2-pyrrolidinone by treatment with trifluorosulfonic acid. Acylbydrazine derivatives also cyclized in the presence of hypervalent iodine reagents to give lactams. When a carbamate was treated with Bu3SnH, and AIBN, addition to an alkene led to a bicyclic lactam. 

An alternative preparation of aziridines reacts an alkene with iodine and chloramine-T (see p. 1056) generating the corresponding A-tosyl aziridine. Bromamine-T (TsNBr Na ) has been used in a similar manner." Diazoalkanes react with imines to give aziridines." Another useful reagent is NsN=IPh, which reacts with alkenes in the presence of rhodium compounds or Cu(OTf)2 to give N—Ns aziridines. Manganese salen catalysts have also been used with this reagent. ... 

Iodine is enriched to a greater extent in chromatogram zones coated with lipophilic substances than it is in a hydrophilic environment. Hence, iodine is only physically dissolved or adsorbed. Occasionally a chemical reaction also takes place, such as, for example, with estrone [19] (cf. Iodine Reagents ). In general it may be said that the longer the iodine effect lasts the more oxidations, additions or electrophilic substitutions are to be expected. 

This reaction is catalyzed by the presence of divalent sulfur — e.g. sulfur ions, substances with S-S links, thioethers, thiazoles. If such substances are present in a chromatogram zone then the iodine applied with the reagent is consumed by reaction with sodium azide according to the above reaction. It is no longer available for the for-... 

Ridomil, with which the treatment with starch solution was not carried out, is said to yield brown chromatogram zones on a pale yellow background [14]. Hence, it may be assumed that this detection is based not on the iodine azide reaction but on the physical adsorption and enrichment of iodine in the lipophilic chromatogram zones (cf. Iodine Reagents ). 

The preparation of Pans-1,2-cyclohexanediol by oxidation of cyclohexene with peroxyformic acid and subsequent hydrolysis of the diol monoformate has been described, and other methods for the preparation of both cis- and trans-l,2-cyclohexanediols were cited. Subsequently the trans diol has been prepared by oxidation of cyclohexene with various peroxy acids, with hydrogen peroxide and selenium dioxide, and with iodine and silver acetate by the Prevost reaction. Alternative methods for preparing the trans isomer are hydroboration of various enol derivatives of cyclohexanone and reduction of Pans-2-cyclohexen-l-ol epoxide with lithium aluminum hydride. cis-1,2-Cyclohexanediol has been prepared by cis hydroxylation of cyclohexene with various reagents or catalysts derived from osmium tetroxide, by solvolysis of Pans-2-halocyclohexanol esters in a manner similar to the Woodward-Prevost reaction, by reduction of cis-2-cyclohexen-l-ol epoxide with lithium aluminum hydride, and by oxymercuration of 2-cyclohexen-l-ol with mercury(II) trifluoro-acetate in the presence of ehloral and subsequent reduction. ... 

Nitrous fiunes reagent 225, 226 Nondestructive detection 42 ff -with fluorescent reagents 44 -with iodine 46 -with pH-indicator 45 Noradrenaline 76, 240, 393 — 396 Norephedrine 76 Norfenefnne 76 Norfenfluramine derivatives 45 1 l-Nor-d -THC-9-carboxy lie acid 289,292 Novonal 339 Nucleosides 364... 

Place iodine crystal in a closed tank place the plates in the tank nntil color appears Prepare a 2% aqneons solntion of resorcinol add 10 ml of this solntion to 80 ml of HCl containing 10.5 ml of 0. l-MCnS04 solntion spray the plates with the reagent and heat for few min at 110°C... 

Electrophilic iodine reagents are extensively employed in iodocyclization (see Section 4.2.1). Several salts of pyridine complexes with 1+ such as bis-(pyridinium)iodonium tetrafluoroborate and b/.s-(collidine)iodonium hexafluorophos-... 

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