Special Issue Reviews and Accounts ARKIVOC 2009 (i) 1-62
O
PhI (5 mol%), Bu4NI (1.1. equiv.)
R1
R1 CO2H
NaBO3•H2O (2 equiv.), AcOH, CH2Cl2, 40 oC O
80-97%
I
R2
R2
177 R1 = H, Me, Et, Bn; R2 = H, Me, Et 178
Scheme 75
Togo and Moroda have reported a DIB-mediated cyclization reaction of 2-aryl-Nmethoxyethanesulfonamides using iodobenzene as a catalyst (5-10 mol%) and mchloroperoxybenzoic acid as the stoichiometric oxidant.66f Very recently, Ochiai and coauthors have reported an efficient iodomesitylene-catalyzed oxidative cleavage of alkenes and alkynes using mCPBA as a terminal oxidant.66g
6.2. Polymer-supported and recyclable hypervalent iodine reagents The preparation and applications of polymer-supported hypervalent iodine reagents, bearing (diacetoxy)iodo, (dihalo)iodo, [hydroxy(tosyloxy)iodo], [hydroxy(phosphoryloxy)iodo], aryliodonium, 1,2-benziodoxol-3-one, and hypervalent iodine groups as counter anions, was reviewed by Togo and Sakuratani in 2002.1g More recently, in 2008, the polymer-supported and reusable monomeric hypervalent iodine reagents were overviewed by Ochiai and Miyamoto.1l These efficient and environmentally benign reagents can be used for various oxidative functional group conversions of substrates and can be recovered quantitatively by simple filtration, and then regenerated and reused. Recent representative examples of synthetic applications of the polystyrene-supported DIB and BTI are discussed in this section.
Polymer-supported [bis(acyloxy)iodo]arenes have been used for the oxidation of alcohols catalyzed by TEMPO67a,b or in the presence of KBr.67c In a specific example, primary alcohols 179 are readily oxidized to methyl esters 180 upon treatment with polystyrene-supported DIB in the presence of KBr in the acidic aqueous methanol solution (Scheme 76).67c Likewise, organic sulfides are selectively oxidized to the respective sulfoxides by DIB or the polymer-supported DIB in water in the presence of KBr.67d
(polystyrene)–I(OAc)2, KBr (1 equiv.),
MeOH, H2O, HCl, rt, 3-12 h O
R
OH
61-76% R
OMe
179
180
R = C5H11, cyclohexyl, Ph, EtO2C(CH2)4, etc.
Scheme 76
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