Monoiodination

Halogenolysis of zirconacyclopentadienes affords 1,4-dihalodienes (Eq. 2.14) [20]. Solvent effects on halogenolysis are remarkable. Indeed, whereas the iodination of zirconacyclopentadienes in THF with 2 equivalents of I2 affords mainly the monoiodinated diene, the diiododiene can be the major product in CH2C12. For example, 2,3,4,5-tetraethylzirco-nacyclopentadiene reacts with 2 equivalents of I2 in THF at room temperature to give the monoiodinated 3-iodo-4,5-diethylocta-3,5-diene 23 in 70% yield along with only an 18% yield of 3,6-diiodo-4,5-diethylocta-3,5-diene 24 (Eq. 2.14). 

When the same iodination reaction is carried out in CH2C12 at room temperature, the diiodination product 24 is obtained in 73 % yield as the major product, accompanied by an 18% yield of the monoiodination product 23 (Eq. 2.15) [20]. 

Transmetalation of zirconacyclopentadienes to copper will be discussed later. However, it is noteworthy here that when the iodination is carried out in THF in the presence of 2 equivalents of CuCl, the product of diiodination (24) is obtained in 95 % yield without any trace of the monoiodinated adduct 23 (Eq. 2.16) [24],... 

Monoiodination of a zirconacyclopentadiene with one equivalent of iodine followed by the addition of one equivalent of CuCl gives the dimer of the cyclobutadiene and the Diels—Alder product in the presence of methyl maleate. This indicates the formation of a l-iodo-l,3-dienyl copper compound and the subsequent elimination of Cul to give a cyclobutadiene equivalent. Direct reductive elimination of zirconacydopentadienes affording cyclobutadienes has not yet been observed. 

Barluenga et al.565 have reported the selective monoiodination of arenes with bis (pyridine)iodonium(I) tetrafluoroborate [I(py2)BF4] in excess superacids (2 equiv.) [Eq. (5.210)]. Comparable results were found for activated compounds with both HBF4 and triflic acid, whereas triflic acid was more effective in the iodination of deactivated aromatics. For example, nitrobenzene and methyl benzoate are unreactive in HBF4 but give the corresponding iodo derivatives in triflic acid (83% and 84% yields, respectively, in 14 h). Iodination of phenol required low temperature (-60°C). 

The effect of temperature is clearly seen in the iodination of alkanes and cycloalkanes with CCI4-AII3-I2, where only monoiodination is observed at — 20°C, but further products are also obtained at 0°C (eq 37).61... 

Halogenolysis. Halogenolysis of zirconacyclopenta dienes (103) affords 1,4-dihalodienes. Whereas the iodina-tion of zirconacyclopentadienes in THF with 2 equivalents of I2 affords mainly the monoiodinated diene, the diiodo diene is the major product in CH2CI2. lodination carried out in... 

As with other halogenation processes, the monoiodination of imidazole has proved to be a difficult process. A number of recent approaches have shown some success. Thus, imidazoles can be monoiodinated at C-2 via the 2-lithio derivative or Grignard reagent. With iodine and iodic acid 5-chloro-l-methylimidazole was converted to a mixture of 12.8% of the 2,4-diiodo compound and 27.5% of the 4-iodo product. The previously undescribed 2-iodoimidazole (119) has been prepared in low yield by the sequence shown in Eq. (27). ... 

I iodine (general) I, iodine) ), monoiodine —I, iodo iodine (general) I+, iodine(l+) iodide (general) I-, iodide) l-) iodide I-, iodido(l—) iodido... 

Release of T4 from the thyroid requires endocytosis of colloid (TG) across the apical membrane and subsequent proteolysis of the TG within the ingestion vacuole by lysosomal enzymes. The liberated T4 then passes across the basal membrane to the circulation. The thyroid may also secrete some T3. This may be formed either by linkage of a monoiodinated tyrosyl residue with a DIT residue within the TG or by intrathyroidal enzymatic 57 - m o n o dc i o d i n a t i o n of liberated T4. The extent of T3 secretion from the fish thyroid is still somewhat controversial and likely species-dependent. Lithium (Li+) inhibits thyroid secretion in humans39. No inhibitor with a direct action on thyroidal secretion has been identified for fish. 

The use of I2 in combination with HIO4 has also been reported for the synthesis of 6 and 7 [9]. In either case, barely a trace of the monoiodinated product was detected. 

The labelling condition using a molar peptide to radionuclide ratio of 2.73 (7.4 MBq/pg of peptide) resulted in one radiochemical species (R = 22.7 min), probably the monoiodinated species (Fig. 3.1(a)). Under this labelling condition, high radiochemical purity (95.53 0.88%) was observed. After the SepPak purification procedure, the radiochemical purity of the ethanol fraction was found to be 99.32 0.09%. When a molar peptide to radionuclide ratio of 0.54 was used, a second radiochemical species R = 24.3 min) was also observed (Fig. 3.1(b)), which could be related to the diiodinated species in the radioiodination of [Tyr Joctreotide, as described by Bakker et al. [3.11]. With... 

Diethyl l-(ethoxycarbonyl)methylphosphonate can be treated with iodine and K2CO3 under phase-transfer catalysis conditions to give the crude monoiodinated derivative in good yield (88%). -> ... 

As with other halogenation processes, the monoiodination of imidazole has proved to be a difficult process. A number of recent approaches have shown some success. Thus, imidazoles can be monoiodinated at C-2 via the... 

Optimum iodinating conditions for monoiodination of histidine use a 1 1 ratio of iodine to azole diiodination requires a 2 1 ratio <83CPB386>. In 1994 ICl in hexane has been used to 5-mono- and... 

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