Oxidations diacetoxyiodo benzene

As an alternative to the lead tetraacetate oxidation, (diacetoxyiodo)benzene can be used to initiate a fragmentation reaction which leads to unsaturated medium-sized lactones [110]. The structures of the starting materials are similar to those of compounds VII/157, VII/160, and VII/163. The same stereochemical consequences are observed as mentioned above. 

Recently, one general route was proposed that involves oxidation of the starting neutral molecule by (diacetoxyiodo)benzene in the presence of strong acids. The resulting salt is highly soluble. Thus, oxidation of TTF in acetonitrile follows this scheme (Giffard et al. 2001) ... 

A very simple synthesis of coumestrol (228) has been described by Kappe and coworkers (Scheme 46) (74ZN(B)292). It is based upon dehydrogenation of 4-hydroxy-3-phenyl-coumarins to coumestans (720PP233). A number of 2 -hydroxy 3-phenylcoumarins were oxidized with lead tetraacetate to the corresponding coumestans 3-(l-acetoxy-4-methoxy-2-oxo-3,5-cyclohexadienyl)coumarins were obtained as by-products (76BCJ1955). Coumes-tan itself (226) has been obtained by photolysis of the phenol ether (232), which is in turn available from 4-hydroxycoumarin (229) and (diacetoxyiodo)benzene (Scheme 47) (78CB3857) via an iodonium ylide (231). 

In contrast to the (E)-isomer, (Z)-alkenyl(phenyl)-A3-iodane 41 is labile and decomposes with a half-life time of 20 min to terminal alkynes in chloroform solution at room temperature [64]. Stereo electronically preferable reductive anti / -elimination accounts for this facile decomposition. In fact, the kinetic results for E2-type dehydrohalogenation of vinyl halides show that the relative rates of elimination decrease in the order anti /3->syn / - a-elimination [65]. Similar anti -elimination of vinyl-A3-iodane was proposed in the oxidation of methoxyallene with (diacetoxyiodo)benzene 4 to 3-acetoxy-3-methoxypropyne [66]. 

The best known member among the various classes of these iodanes is undoubtedly [hydroxy(tosyloxy)iodo]benzene (HTIB), sometimes called Koser s reagent. It is prepared readily from (diacetoxyiodo)benzene and p-toluenesul-fonic acid monohydrate in acetonitrile. The same method using p-nitroben-zenesulfonic acid or 10-camphorsulfonic acid leads to the corresponding sul-fonyloxy analogs [41,42]. Of special interest are some iodanes of this type coming from a chiral ether. Their preparation was effected by direct oxidation with sodium perborate and the isolated diacetoxy derivatives were separately treated with p-toluenesulfonic acid in acetonitrile (Scheme 8) [43]. 

In changing the oxidant to a mixture of (diacetoxyiodo)benzene 3 and a sulfonamide 25 the direct transformation of sulfides 23 to the corresponding N-sul-... 

Mainly iodine(v) reagents have been used for such oxidations, but some iodine(III) reagents have also been successfully applied. The radical TEMPO (2,2,6,6-tetramethyl-l-piperidinyloxyl) is necessary in the oxidation of alcohols with (diacetoxyiodo)benzene 3. With this combination highly selective oxidations of primary alcohols to the corresponding aldehydes in high yields are possible, Scheme 12. Secondary alcohols are not attacked under the reaction conditions providing a useful alternative to the widely used Dess-Martin reagent [71 ]. 

However, longer reaction times can lead to the corresponding carbonyl compounds as well. An activation of (diacetoxyiodo)benzene 3 with boron trifluoride is also possible and can be used for a direct oxidation of carbazolylmethyl alcohols [72]. 

Although the mechanism of the transformation of single into double bonds has not been investigated in detail, a heteroatom attached to the single bond is necessary for an efficient introduction of the double bond. Trisubstituted pyrazo-lines 46 can be oxidized with (diacetoxyiodo)benzene 3 to the corresponding pyrazoles 47 in good yields [98]. Two double bonds can be introduced in easy accessible proline derivatives 48 [99] by an oxidative decarboxylation with [bis(trifluoroacetoxy)iodo]benzene 4 yielding tetrasubstituted pyrroles of type 49, Scheme 22 [100]. 

Tetrahydroquinolones can be transformed also by (diacetoxyiodo)benzene 3 to the aromatic arylquinolines, a structure found in various alkaloids [101]. Depending on the reagent, it is possible to oxidize flavanones 50 either into flavones 51 or into rearranged isoflavones 52 [102, 103]. (Diacetoxyiodo)-benzene 3 or the polymer-supported reagent 18 were also efficient reagents for the oxidation of 1,4-dihydropyridines 53 to the corresponding pyridine derivatives 54, Scheme 23 [104]. 

Step 1. Chemoselective oxidation of the primary alcohol (diacetoxyiodo)benzene (DIB) is the stoichiometric co-oxidant. 

Palladium-catalysed directed C-H oxidation with (diacetoxy)iodobenzene of a series of meta -substituted aryl pyridine and aryl amide derivatives resulted in the formation of the corresponding acetoxy compounds. The reactions generally proceed with high levels of regioselectivity for functionalization of the less sterically hindered ortho-C-H bond.144 The mechanism shown in Scheme 4 has been proposed for the oxidation of 2,6-dimethylphenol with (diacetoxyiodo)benzene for the formation of 3,5,3, 5 -tetramethyl-biphenyl-4,4 -diol, via C-C coupling.145... 

Polymer-supported (diacetoxyiodo)benzene (PSDIB) can promote an oxidative rearrangement of 2 -benzyloxy-chalcones to form the intermediate acetal 748, which can be isolated or directly treated with aqueous base to afford... 

Although several methods are available for the preparation of the title compounds, in practice the starting material is (diacetoxyiodo)benzene (DIB). The standard method for its preparation is direct oxidation of iodobenzene with either peracetic acid [ 1 ] or sodium perborate in acetic acid [2], The first method appears to be preferable it requires great care in maintaining temperature at exactly 40°C at a lower... 

Diacetoxyiodo)benzene (DAIB) is well-suited for the synthesis of azoles from bifunctional substrates via cyclodehydrogenation pathways. Such oxidations occur with C-heteroatom or heteroatom-heteroatom bond... 

Saccharin 218 is obtained by KMn04 oxidation of o-methylbenzenesulfonamide 217 (Scheme 126). Various V-alkylsaccharins 219 (n = 2) and A-alkyl-l,2-benzisothiazolin-3-one A-oxides 219 (n= 1) are conveniently prepared in moderate to good yields by the reaction of A-alkyl(0-methylarene)sulfonamides with (diacetoxyiodo)benzene in the presence of iodine under irradiation with a tungsten or mercury lamp <1999T14885, CHEC-III(4.05.9.1.2)599>. 

---