Polymer-supported hypervalent iodine

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>. 

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). 

Scheme 38. Polymer-supported hypervalent iodine-mediated oxidative cyclization of a maritidine precursor.

Polymer-supported hypervalent iodine heterocyclic reagents 02SL1966. 

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

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]. 

Ley, S.V., Thomas, A.W., and Finch, H., Polymer-supported hypervalent iodine reagents in clean organic synthesis with potential application in combinatorial chemistry, J. Chem. Soc., Perkin Trans. 1, 669, 1999. 

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