Deiodination, selective

Treating imidazole with iodine in an NaOH solution afforded the complete ring iodination product, 2,4,5-triiodoimidazole. 4-Iodoimidazole was then produced in 75% yield upon selective reductive deiodination, [5]. The same procedure converted 2-methylimidazole and 1-methylimidazole to 4(5)-iodo-2-methylimidazole [6] and 4(5)-bromo-l-methylimidazole [7], respectively. 

By carefully monitoring the pH of the reaction, regioselective diiodination was achieved. Treating imidazole with iodine at pH 12 furnished 2,5-diiodoimidazole. Selective reductive deiodination secured 2-iodoimidazole, which upon bromination afforded 4,5-dibromo-2-iodoimidazole [6],... 

The inversion in selectivity between the insertion into an H—Si bond favored by the intermediate in the dehalogenation and the addition to a triple bond favored by the intermediate formed upon silirane pyrolysis suggests that different reactive intermediates are formed. Since free silylene is implicated in the silirane pyrolysis, the lithium-induced deiodination probably involves a silylenoid such as a complex of the silylene with Lil or with THF. For a further discussion of this possibility, see Section II.E. 

Another interesting application of microwave irradiation is found in the selective dehalogenation of the iodinated indole alkaloid Plakohypaphorine F, described by E. Fattorusso et al. [117,118] (Scheme 32). The bis-halogenated compound was treated with potassium formate and palladium acetate under controlled microwave irradiation, resulting in selective deiodination. The choice of the solvent, in this case DMSO, was found to be crucial. 

Following isolation of the m/z 220 ions by using the first three sectors and deceleration from 8 keV to some 20-30 eV, collisional deiodination was performed in the Qcell and the product ions reaccelerated up to 8 keV. Mass-selected m/z 93 products were thereafter collisionally activated with nitrogen collision gas and the resulting CA spectrum is... 

The regiospecific deiodination of diiodophenols in the dihydrobenzofuran series by n-butyllithium has been used as an important step in the synthesis of aflatoxin 62 (ref.60). Thus, 3-(2-hydroxyethyl)-4-hydroxy-5,7-diioclo-6-methoxy-dihydrobenzofuran as the phenate formed with sodium hydride has been selectively deiodinated at the 7-position by means of butyllithium. 

JV,JV-dimethylacetamide dimethyl acetal. Under the control of the hydroxy-group, the Claisen rearrangement yields a ds-disubstituted cyclopentene. lodo-lactonisation takes place selectively with the amide function after deiodination and reduction of the lactone to the lactol, re-lactonisation and a cis-selective Wittig reaction lead to the desired intermediate, which must then merely undergo re-esterification, oxidation and epimerisation. 

Applications of the selective sonolysis of transition metal complexes are not numerous despite the obvious synthetic potential (Fig. 25). The palladium catalyzed addition-oxidation of halides to olefins (the Heck reaction) in its intramolecular version is improved by sonication. The sonochemical reaction can be conducted at lower temperatures than the silent one, and the usual deiodinated by-products are formed in smaller amounts (see p. 343). ... 

Preparation by selective deiodination of 2,4-dihy-droxy-3,5-diiodoacetophenone with stannous chloride in refluxing acetic acid (40%) [1923]. 

Attempts to deoxygenate the tertiary alcohol of 16 failed, so instead, selective reduction followed by protection delivered 17. Reduction to the axial alcohol followed by dehydration with the Martin sulfiirane then installed the trisubstituted alkene of 18. The C-N bond was re-estabUshed by exposure of 18 to NIS, leading to the crystalline 19. Activation of the derived ketone with Mander s reagent followed by reductive deiodination (Et SiH/Pd) gave 20, Michael addition of which with 21 led to 3. 

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