Iodine compounds polymer-supported

Polymer-supported hypervalent iodine compounds in general are readily prepared and they have gained recently considerable popularity as reagents for clean oxidations. However, they are not newcomers since they have been known since 1961. A detailed procedure for the iodination of polystyrene and its conversion to poly[(diacetoxyiodo)styrene] appeared in 1972 [85]. However, this and other related methods were time consuming and despite encouraging results did not gain popularity. 

Oxidative iodination of aromatic compounds by the combination of a hypervalent iodine reagent with iodine is a synthetically important reaction (Section 3.1.4) [34]. Polymer-supported diacetate 4 is a particularly convenient reagent for oxidative iodination since it can be regenerated and reused many times. Reagent 4 gives the best results for the iodination of electron-rich arenes 13, with predominant formation of the para-substituted products 14 (Scheme 5.8) [12,21]. 

Hypervalent iodine compounds, in stoichiometric amounts, are also known to oxidize alcohols and the use of iodosyl benzene or a polymer-supported iodine(III) reagent, in combination with KBr as a cocatalyst, for the oxidation of alcohols in water has been described. More recently a related catalytic system, consisting of PhI02 (2 mol%), Br2 (2 mol%) and NaN02 (1 mol%), for the aerobic oxidation of alcohols in water at 55°C has been described. ... 

The monomers needed for the polymer support synthesis were prepared as depicted in Scheme 3.15. Compound 11 was converted to the diazonium intermediate which was captured with 2-(ethylamino)ethanol, to form the hydroxytriazene according to Moore s protocol. Silylation to form 47 followed by acetyl conversion to the silylalkyne afforded 48. Compound 48 was divided into two portions the first portion was desilylated to form 49, the anchor unit to be attached to the polymer support. The second portion was iodinated to form the iodoarene 16. 

The ester models, as stated above, were all LC, but two of the ether model compounds, the methoxy- and ethoxy-substituted derivatives, were not, despite the fact that each of these mesogens yielded some liquid-crystallinity in the poly(ether) form. Therefore it seems that the polymers in this system tend to be "more liquid crystalline" than the related small molecules. This hypothesis is supported by the fact that Memeger(H) found liquid crystallinity in allhydrocarbon polymers incorporating the distyrylbenzene mesogen, even in cases where the cis/trans ratio of the unsaturations was as large as 0.3, while Campbell and McDonald (10) noted that iodine isomerization to the all-trans form was essential for the observation of an LC phase in the small-molecule derivatives which they prepared. 

---