Iodine reagents polymer-supported

Keywords. Hypervalent iodine, Oxidation, Polymer-supported reagents, Rearrangement... 

In 2003, Togo and co-workers described a radical cyclization and ionic cyclization onto the aromatic rings of 2-(aryl)ethanesulfonamides 21 to produce 3,4-dihydro-2,l-benzothiazine 2,2-dioxides with polymer-supported hypervalent iodine reagents in good yields <03ARK11>. 

Scheme 2.4 Polymer-supported oxidations using a hypervalent iodine reagent. 

On the contrary, periodinanes [e.g., iodoxo or iodine(V) reagents] are widely employed in the oxidation of sensitive and complex alcohols, preferably as IBX32 33 or its acetylation product, the Dess-Martin reagent.34 Periodinanes have not been prepared on a polymer support so far, although a sihca-supported IBX has been reported recently.35... 

The isolated solid is a very shock- and friction-sensitive explosive [1], but the preparation and safe handling of dilute solutions in solvents other than ether have been described [2]. The need to use appropriate techniques and precautions when using iodine azide as a reagent is stressed [3], The purer the more explosive explosive properties are characterised (lead-block test, etc.) in a footnote to [4]. A safe way of generating and using it as a polymer supported reagent is advanced [5],... 

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. 

Ley and co-workers applied the polymer-supported hypervalent iodine reagents, poly(diacetoxyiodo)styrene (PDAIS) or polybis(trifluoroacetoxyio-do)styrene (PBTIS) to the above-mentioned spiroannulation reaction. They succeeded in the concise syntheses of ( )-oxomaritidine (40) and ( )-epimari-tidine (41) using this methodology as the key steps [116] (Scheme 26). 

Substrates of this type which afforded ge/n-difluorides are shown in Table 6.2. The yields reported were substantially improved by using a polymer-supported reagent which had the added advantage that no separation from iodobenzene was needed however, fluorination of the iodinated polystyrene requires the use of the expensive xenon difluoride [47, 48]. 

Polymer-supported hypervalent iodine heterocyclic reagents 02SL1966. 

For other polymer-supported hypervalent iodine reagents, see Togo, H. and Sakuratani, K. (2002) Synlett, 1966-75. 

Dichloroiodo)arenes are widely used as reagents for chlorination of various organic substrates. Among (dichloroiodo)arenes, (dichloroiodo)benzene, PhICl2, is the most commonly used reagent, which can be conveniently prepared by direct chlorination of iodobenzene (Section 2.1.3). The preparation and reactions of several recyclable, polymer-supported or nonpolymeric iodine(III) chlorides are discussed in Chapter 5. 

A similar oxidative protocol has been used for the oxidation of (fluoroalkyl)alkanols, Rf(CH2) CH20H, to the respective aldehydes [146], in the one-pot selective oxidation/olefination of primary alcohols using the PhI(OAc)2-TEMPO system and stabilized phosphorus ylides [147] and in the chemo-enzymatic oxidation-hydrocyanation of 7,8-unsaturated alcohols [148]. Other [bis(acyloxy)iodo]arenes can be used instead of PhI(OAc)2 in the TEMPO-catalyzed oxidations, in particular the recyclable monomeric and the polymer-supported hypervalent iodine reagents (Chapter 5). Further modifications of this method include the use of polymer-supported TEMPO [151], fluorous-tagged TEMPO [152,153], ion-supported TEMPO [154] and TEMPO immobilized on silica [148],... 

The first polymer-supported hypervalent iodine reagent, poly[(dichloroiodo)styrene], was prepared by chlorination of iodinated polystyrene in the early 1980s [8]. This method, however, involves the initial preparation of iodinated polystyrene under harsh conditions (160 h, 110 °C), requires the use of hazardous chlorine gas and affords poly[(dichloroiodo)styrene] with a relatively low loading of active chlorine. An optimized one-pot preparation of polystyrene-supported (dichloroiodo)benzene 2 (loading of -ICI2 up to 1.35 mmol g" ) from polystyrene 1, iodine and aqueous sodium hypochlorite (bleach) was reported in 2011 (Scheme 5.1) [10]. 

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]. 

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