Iodine-catalyzed

In a similar manner, 10-methyldibenz[Z>,/ oxepin (4) can be obtained from dibenz[6,/]oxepin-10-(1 l//)-one after addition of methyllithium and subsequent iodine-catalyzed dehydration.161... 

The iodine-catalyzed photoisomerization of all-trans- a- and (3-carotenes in hexane solutions produced by illumination with 20 W fluorescence light (2000 lux) and monitored by HPLC with diode-array detection yielded a different isomer distribution (Chen et al. 1994). Four cis isomers of [3-carotene (9-cis, 13-cis, 15-cis, and 13,15-cli-r/.v) and three cis isomers of a-carotene (9-cis, 13-cis, and 15-ri.v) were separated and detected. The kinetic data fit into a reversible first-order model. The major isomers formed during the photosensitized reaction of each carotenoid were 13,15-di-d.v- 3-carotene and 13-ds-a-carotene (Chen et al. 1994). 

ILLUSTRATION 3.1 USE OF A DIFFERENTIAL METHOD TO DETERMINE A PSEUDO REACTION RATE EXPRESSION FOR THE IODINE CATALYZED BROMINATION OF m-XYLENE... 

Dvorko and Shilov [Kinetics and Catalysis, 4 (212), 1964] have studied the iodine catalyzed addition of HI to cyclohexene in benzene solution. 

The reagent is obtained as a fairly pure oil by reaction of phenylsilane with iodine catalyzed by a trace of an organic ester. After removal of volatile side products (benzene and HI), the oil can be purified by fractional distillation. 

Iodine is known to catalyze the condensation of aldehydes, benzyl carbamate and allyltrimethylsilane to homoallylic amines. However, in this case the involvement of an in sitn prepared [MejSi] species was suggested to be the active catalyst [235], An iodine catalyzed acetalization of carbonyl compounds was reported, where the active catalyst was believed to be hydroiodic acid [236],... 

Akbari JD, Tala SD, Dhaduk MF, Joshi HS (2008) Molecular iodine-catalyzed one-pot synthesis of some new Hantzsch 1,4-dihydropyridines at ambient temperature. Arkivoc... 

Wang RZ, Zhang LF, Cui ZS (2009) Iodine-catalyzed synthesis of 12-aryl-8,9,10,12-tetra-hydro-benzo a xanthen-ll-one derivatives via multicomponent reaction. Synth Commun 39 2101-2107... 

Lin XF, Cui SL, Wang YG (2006) A highly efficient synthesis of 1,2,3,4-tetrahydro-quinolines by molecular iodine-catalyzed domino reactions of anilines with cylci enol ethers. Tetrahedron Lett 47 4509 1512... 

Appel s salt (54) is exhaustively chlorinated by chlorine with ring opening to sulfenyl chloride (55). In the presence of Ij as catalyst the sulfenyl chloride (56) is produced (Scheme 5) <85CB1632>. The similar iodine catalyzed chlorination of chlorodithiazolinone (57) occurs less readily (Equation (6)) <85CB1632>. Without the iodine catalyst, chlorination proceeds slowly to give a mixture containing chlorodisulfides of the type (55). 

SCHEME 12. Iodine catalyzed formation of organozinc bromides... 

Iodine catalyzes the isomerization of a variety of A.A -dichloropolyfluoroanilines to A, 4-di-chlorocyclohexadienimines,43-45 as illustrated by the rearrangement of jV.A-dichloropenta-fluoroaniline (51) to A. 4-dich]oropentafluorocyclohexa-2,5-dien-1-imine (52).43... 

When position 4 of perfluoropyridine is blocked with a poor leaving group, ammonia replaces the fluorine in position 2 in good yield. Oxidation of the products obtained with hypochlorite, followed by iodine-catalyzed rearrangement, yields interesting fluorodienes [78] (equation 41) Ultraviolet irradiation can be used to assist reactions in which substitution is difficult [79]... 

Carotenoids can be converted into mixtures of geometrical isomers under appropriate conditions, the most common being iodine catalyzed photoisomerization. This produces an equilibrium mixture of isomers, in general the all-trans isomers predominates. These isomers in an isomeric mixture cannot be measured separately by simple spectrophotometric determination. The usual method of subsequent measurement would be chromatographic separation, diode-array detection, and spectral analysis. In the absence of any definitive data on extinction coefficients for cfv-isomcrs, they are quantified against the all-trans isomer. Modem procedures involve the direct synthesis of c/.v-carotcnoids. 

The iodine-catalyzed reaction of aziridines with carbon dioxide leads to 2-oxazolidinones (251). Because carbon dioxide effectively polymerizes ethyleneimine, only low yields are obtained when unsubstituted ethyleneimine reacts with C02. However, direct insertion of carbon dioxide [124-58-9] into aziridines can be accomplished, with better yields, by ethoxycarbonylation of aziridines with subsequent elimination of ethylene under flash vacuum conditions (252). 1- Phenyl aziridine [696-18-4] can react with C02 under antimony [7440-56-0] catalysis to give AI-phenyl-2-oxazolidinone in good yields (253). At low temperatures and with the exclusion of atmospheric humidity, the reaction of ethyleneimine with carbon dioxide produces the unstable ethyleneiminium salt [51645-58-2] of IV-vinylcarbamic acid (254,255). 

Iodine catalyzes the conversion of amorphous selenium to the black, semiconducting metallic modification, and is used for this purpose in the manufacture of photoelectric cells and electric rectifiers (see Seleniumand SELENIUM compounds). 

The first step in the biochemical analysis of the receptor, isolation from the cell membrane, was difficult the membrane-associated protein is present in only small amounts and is insoluble in aqueous solution. Sensitivity and selectivity would be improved by radiolabeling under conditions that maintain cell viability so that only proteins associated with the surface and not those within the cell become labeled. A procedure that met these conditions was iodination catalyzed by lactoperoxidase in the presence of hydrogen peroxide (Marchalonis, 1969 Phillips and Morrison, 1970 Marchalonis et al., 1971). It was also necessary to find conditions for solubilizing membrane proteins that would not interfere with subsequent specific immunoprecipitation. 

Scheme 4 The catalytic cycle for peroxidative iodination catalyzed by c .v-V02. ...

Several iodine-catalyzed organic transformations have been reported. Iodine-catalyzed reactions are acid-induced processes. Molecular iodine has received considerable attention because it is an inexpensive, nontoxic and readily available catalyst for various organic transformations under mild and convenient conditions. Michael additions of indoles with unsaturated ketones were achieved in the presence of catalytic amounts of iodine under both solvent-free conditions and in anhydrous EtOH (Scheme 19) [85,86]. l2-catalyzed Michael addition of indole and pyrrole to nitroolefins was also reported (Scheme 20) [87]. 

Although the reaction in Scheme 10 is a highly efficient procedure, a two-step process was required to prepare aziridines from olefins. Two more convenient methods for the one-step aziridination using CT were discovered by the authors in 1998, one of which involves the iodine-catalyzed aziridination of unfunctionalyzed olefins with CT trihydrate [7b] (Scheme 11). The bromine-catalyzed aziridination of unfunctionalyzed olefins and allylic alcohols with anhydrous CT was reported at the same time [7c], though in this case phenyltrimethylammonium tribromide (PTAB), and not Br2, was used as a catalyst (Scheme 12). These two reactions are applicable to a wide range of olefins, and are considered to proceed by almost the same pathway. 

Scheme 11. Iodine-catalyzed aziridination of olefins with CT.

Helferich, Bohm and Winkler1 have reported that the use of iodine catalyzed the Koenigs-Knorr reaction, which was exceedingly slow when calcium chloride was used as an internal desiccant. This catalyst has since been used by a number of other workers.79 111-114 The work of Talley, Reynolds and Evans79 on the synthesis of the orthoester type of oligosaccharides, indicated that the presence of iodine favored the formation of a normal biosidic linkage, whereas the absence of iodine favored the formation of an orthoester linkage. 

Furan is more reactive than thiophene by factors of 11.9 (acetylation), 107 (formylation in phosgene), and 140 (trifluoroacetylation), under the conditions given in Table 6.6 iodine-catalyzed acetylation gave a rate... 

Either formulation CCLXV or CCLXVI for methiodide A requires that the iodine catalyzed rearrangement involves migration of methyl from oxygen (in CCLXI) to nitrogen. This takes one back to earlier controversies associated with the structure of pseudostrychnine quaternary salts. More work is required. 

Much the same sequence leads to a protease inhibitor that incorporates a somewhat more complex fiiryl function-linked oxygen heterocychc. This fused bis(tetrahydrofuryl) alcohol (16) was designed to better interact with a pocket on the viral protease. The first step in preparing this intermediate consists of reaction of dihydrofuran (13) with propargyl alcohol and iodosuccinimide to afford the iodoether (14). Free radical displacement of the iodine catalyzed by cobaloxime leads to the fused... 

A different pathway (two-electron transfer via bridging iodide) has been proposed for the iodine-catalyzed transformation of MoCareneXCO), into Mo(CO)s. 

At room temperature, 247 very rapidly shows an uptake of iodine corresponding to the complete oxidation of one thiol group. The oxidation product, the dimeric pyranose 249, is also formed by air oxidation of 247 on long standing of solutions thereof. Obviously, there exists, in addition to the favored thiofuranose form 247, a small proportion of the pyranose form 250 as an equilibrium component, and this has an easily oxidizable thiol group. By oxidation to the disulfide 249, this minor component of the equilibrium mixture is removed and, on rapid reattainment of the equilibrium, all of 247 becomes oxidized. The ready oxidizability of the thiol group of a 4-thiopyranose is likewise shown by the formation of bis(methyl 4-deoxy- 8-D-ribopyranoside-4-yl) 4,4 -disulfide by the air oxidation (iodine-catalyzed) of methyl 4-thio-)8-D-ribopyranoside. ... 

In contradiction to Bairstow and Hinshelwood , Gantz and Walters found that iodine catalyzes the thermal decomposition of acetone between 470 and 517 °C. The rate is roughly proportional to the square root of the acetone pressure. Inhibitors, such as NO, C2H4 or C3H6, retard the reaction. 

It is likely that the iodine-catalyzed decomposition is a chain reaction initiated by iodine atoms. The iodine-catalyzed decomposition has also been studied with mixtures of acetone and acetone-c/g. The isotope distribution of the acetone in the pyrolyzed sample has been found to approach the composition expected on statistical grounds. The rapid isotope mixing indicates the presence of chains. 

A closely related reaction is equilibration of a dicarboxylic acid and its diester to produce monoesters The reaction of a carboxylic acid with ethyl acetate, in the presence of NaHS04 Si02, was shown to give the corresponding ethyl ester. Iodine catalyzes the transesterification of p-keto esters. 

Yamashita, S. (1961). Iodine-catalyzed cis-trans isomerization of azobenzene. Bull. Chem. Soc. Japan 24, 842-845. 

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