2-Iodo phenols

The synthetic strategies used for the preparation of pyrans on insoluble supports have mainly been hetero-Diels-Alder reactions of enones with enol ethers and ringclosing olefin metathesis (Table 15.33). Benzopyrans have been prepared by hetero-Diels-Alder reactions of polystyrene-bound o-quinodimethanes with aldehydes. The required quinodimethanes were generated by thermolysis of benzocyclobutanes, which were prepared in solution [308]. Other solid-phase procedures for the preparation of benzopyrans are the palladium-mediated reaction of support-bound 2-iodo-phenols with 1,4-dienes (Entry 5, Table 15.33) and the intramolecular Knoevenagel... 

Another Pd-catalyzed carbonylarive Sonogashira cross-coupling gives rise to 2-substituted chromones 44. 2-Iodo phenols are reacted tvith terminal... 

One-electron function, 228, 261 One particle scheme, 210 Ordered configuration, 261 Ortho-iodo-phenol, radiation resistance, 196... 

Phenol is converted to iodo- and di-iodo-phenol In-adding gradually, iodine and mercuric oxide to m alcoholic solution of phenol and agitating VJ... 

Dichloro 4 iodo phenol iodofenphos Dichloro isopropoxy phenyl hydrazine oxadiazon Dichloro maleic anhydride fluoramide... 

The effect of some of the factors mentioned above can be excluded by a proper choice of the type of substance studied. For example, for iodo-phenols and iodoanilines effects of hydration and tautomeric change seem improbable. The effects of adsorption and surface reactions is more difficult to exclude. This type of complication is more frequently encountered with acid-base reactions than with other types of reaction because the former are usually very fast reactions. For such a type of reaction the layer around the electrode in which the chemical reaction takes place is very thin, and the reaction therefore occurs mainly inside the electrical double-layer where the effects of the electrical field are strongest. The slower the chemical reaction the less probable the surface reaction is. 

Another example that has been studied in detail is that of the halogenated phenols. Chloro-, bromo- and iodo-phenols, like their benzene analogues, react rapidly with solvated electrons to undergo dehalogenation and produce hydroxyphenyl radicals (equation 5). 

Alkynylation products of ortho-iodo phenols (32) readily undergo cychzation to give benzofuran derivatives (33) [135, 160, 161]. A reaction involving cychzation occurring with incorporation of CO has been reported by Liao et al. (Scheme 5) [161]. However, an extensive screening of reaction conditions had to be performed to avoid ... 

However, it is possible to produce the furan ring of a benzofuran directly by interaction between an ort/to-iodo-phenol and an alkyne, the two carbon atoms of the triple bond providing C-2 and C-3 of the furan ring and the larger substituent of the alkyne (often SiRs) ending up at the heterocyclic 2-position. ° ... 

If temperature studies are made two useful equations exist between the three unknown Kt, Sc and 8t. The value of the third unknown, 8C, is obtained by extrapolating 8Mao to low temperature, when the equilibrium exclusively favours the cis form. Values of AH = 2356, 2141 and 1651 cal mole-1 are obtained for o-chloro-, -bromo- and -iodo-phenol respectively with an error of 50 cal mole-1. These enthalpies agree very well with those obtained by Baker (1958) from infrared band intensities. 

Resorcin—(OH),—1—3—ia obtained by the faction of fused KHO on parachlor- or iodo-phenol. It is usually prepared by dry distillation of extract of Brazil wood. 

P2i2i2i Z = 4 D, = 1.52 R = 0.07 for 4,811 intensities. This structure is isomorphous with that of the p-hydroxybenzoic acid, p-iodo-phenol, and p-iodoaniline complexes. 

Chloroform and Bromoform are formed if the chloride or bromide of the alkalies is used (comp. Elbs and Herz, who deny this ). Analogous to these substitution reactions is the formation of aristol, a di-thymol-di-iodide, as made by Messinger and Vortmann, by the electrolysis of thymol with the addition of potassium iodide. Similar to this also is the preparation of nosophene, a tetra-iodo-phenol-phthalein (Classen and L6b ). 

Home S, Weeratunga G, Rodrigo R (1990) The Regiospecificp-Deiodination of 2,4-Di-iodo Phenols a New Synthesis of Aflatoxin B2. J Chem Soc Chem Commun 39... 

Potentiometric titration methods have been used to measure equilibrium quotients at 25 for reactions of type l and 2, with X equal to ortho, meta and para nitro-, fluoro-, chloro-, bromo- and iodo-phenol. The medium was in all cases aqueous 0,10 M perchlorate (NaClO /HClO ). 

High yields of coumarin derivatives can be achieved when o-iodo phenolic compounds react with alkynes via domino alkyne addition-CO insertion-nucleophilic acylation reaction (Scheme 64) (130L4834). 

Three different N-heterocyclic carbene (NHC)-Pd-pyridine complexes (A, B, and C), where NHC is 1,2,4-trimethyltriazolyldiylidene, 1,3-dimethylimidazoly-lidene, and 1,4-dimethyltriazolylidene, have been reported to efficiently catalyze a domino sequence of alkyne coupling of an ortho-iodo phenol or an ortho-iodo benzylalcohol and the subsequent cycloisomerization of the intermediate tolane derivative to afford benzofuran 25 or benzoisofuran 26 (Scheme 12.17) [49]. 

Laurent Djakovitch et al. developed an environment-friendly benign heterogeneous catalyst [Pd(NH3)4]/(NH4)Y zeolites and used it for the synthesis of benzofuran by the reaction of o-iodo phenol and terminal alkyne under copper-free condition in the presence of triethylamine in DMF H20 (4 1) at 80 C for 6h (Scheme 45) [67]. 

The [Pd(NH3)4] /NaY was prepared by above procedure (ion exchange method) and Pd/Cald was obtained commercially. After the reaction the [Pd(NH3)4]/NaY and Pd/CALO catalysts were recovered following the above procedure using only DMF instead of mixture of DMF and water for three times and dried for overnight. Both catalysts have shown high recyclability up to fiftii cycle without any significant loss of catalytic activity. However, the reaction between o-iodo phenol and diphenyl acetylene failed to provide benzofuran derivative in the presence of above two catalysts. 

The MgLa mixed oxide-supported Pd catalyst is air and moisture stable and highly efficient for the synthesis of benzofuran derivatives involving Sonogashira reachon between o-halo phenol and terminal alkynes. The reaction was performed in freshly distilled DMF and EtsN at 80°C for 24h to provide the product in more than 60% )deld (Scheme 47) [68]. Though the reactions witii o-iodo phenol provided moderate to high yields, in case of o-bromo and o-chloro phenol very low yields (less than 10%) were obtained. 

Recently it has been observed that NCBs have been used as a support for heterogeneous catalyst due to its hollow core, mesoporous and ball-like structure. Park et al. [70] developed Pd(OAC)2 catalyst supported on NCBs and applied it for the synthesis of 2-substituted benzofuran from u-iodo phenol and various substituted terminal alkynes using Sonogashira cross-coupling reaction under copper and ligand-free condition. 

The reaction between o-iodo phenol and terminal alkynes yielded the expected product in the presence of Pd(OAc)2-NCBs with additive LiCl and base CS2CO3 in DMF at 110 °C for 15 h (Scheme 50). 

Pal et al. have developed a procedure for the synthesis of benzofuran by employing Pd/C as the heterogeneous catalyst in the presence of Cul, PPhs, and S-prolinol for the reaction between substituted o-iodo phenol and terminal alkyne in aqueous medium at 80 °C (Scheme 54) [73]. 

The reaction between aziridine and o-iodo phenol provides 1,4-benzoxazine under the same conditions using K2CO3 instead of CS2CO3 (Scheme 58). This procedure is compahble with a variety of functional groups such as CHO, Cl, Br, C02Et, OMe, etc. present in o-iodo phenol and diversely substituted aziridines and epoxides. 

Thyroxine is derived from two molecules of di-iodo-phenol, and contains an alanine side-chain, thus being related to tyrosine, its precursor in the diet, and to iodogorgic acid. Owing to the asymmetric carbon atom in the side-chain, two forms of thyroxine are known, the natural hormone being the L (—)-isomer, derived from L-tyrosine. 

Synthesis of benzoxazines through aziridine ring opening followed by intramolecular C—N bond formation was reported by Sekar and co-workers. " In this approach, a domino ring opening of A -Ts aziridines 332 with o-iodo-phenols 333 followed by copper-catalyzed intramolecular C(aryl)-N(amide) bond formation in the presence of ethyl-enediamine ligand has been established to afford the resultant product 334 in excellent yield (Scheme 40.73). The trans selectivity was confirmed by H NMR spectroscopy and single crystal X-ray analysis. 

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