Iodosobenzene, oxidation with

Hydroxy(tosyloxy)iodobenzene 2014 reacts with phenyltrimethylsilane 81 in boiling acetonitrile to give diphenyliodonium tosylate 2015 and trimethylsilanol 4 or HMDSO 7 [184, 185]. Likewise, treatment of 2,5-bis(trimethylsilyl)furan 2016 with 2014 in boiling acetonitrile/methanol affords 78% iodonium tosylate 2017 and trimethylsilanol 4 [185]. In the presence of Bp3-OEt2 iodosobenzene oxidizes allyl-trimethylsilanes such as 2018 to unsaturated aldehydes such as 2019 in 63% yield, with formation of iodobenzene and trimethylsilanol 4 [186]. Analogously, vinyltrimethylsilanes such as (Z)-l-trimethylsilyl-2-phenylethylene 2020 afford, via 2021, acetylenes such as phenylacetylene in 61% yield and iodobenzene and trimethylsilanol 4 [187] (Scheme 12.54). 

The use of iodosobenzene (PhIO) as oxidant with zeolite-encaged phthallocynanines causes supplementary problems. Indeed, PhI02 is produced in the pores of the zeolite by an oxygen transfer reaction between two molecules of PhIO ... 

PhI02 is rather bulky and plugs the pores, thus preventing further access of reactants to the active sites [49-50,63-64]. Therefore turn-overs are quite low when PhIO is used as oxidant. For the oxidation of methyl cyclohexane on TMPcY [49-50,63-64] and of cyclohexane on Fet.BuPcY [67] turn-overs are 5.6 and 7.6 respectively. It should be noted that the reported turn-overs for oxidations with PhIO correspond to conversions of less than 1 substrate molecule per two supercages, or to total conversions of less than 0.1 %. Therefore the observed activities and selectivities may be influenced by sorption effects. Furthermore iodosobenzene is a rather expensive oxidant and not practical to use because of its low solubility in solvents. Therefore some researchers tend to use other oxidantia such as air [65,66] and tertiary butyl hydroperoxide (t-ButOOH) [57]. In the oxidation of n-octane with t-ButOOH turn-overs as high as 6000 have been reported [57]. 

In a related process, l-trimethylsiloxy-2-oxabicyclo[n.l.0]alkanes 72, derived from lactones, were converted to higher, homologous, a,/l-unsaturated lactones 73, by oxidation with hyper-valent iodine, i.e. with iodosobenzene. ... 

Two suitably positioned hydroxylamine groups undergo oxidative cyclization by low-temperature treatment with peracetic acid to give the 4-oxide, but when the diamino-sulphone was oxidized with iodosobenzene diacetate (review of uses [3714]), an azo group is formed to close the ring. 

Reaction of [l,2,5]oxadiazolo[3,4- ]quinoxaline 1-oxides with stable nitrile oxides in refluxing dichloromethane affords l,2,4-triazino[5,6-/>]quinoxaline 1,2,4-trioxides 6 in good yield, which can be reduced by triphenylphosphane or sodium dithionite to the corresponding 5,10-dihydro derivatives 7. Oxidation of 7 with iodosobenzene bis(trifluoroacetate) yields 1,2,4-triazino-[5,6-6]quinoxalines 8.210... 

Kinetic resolution of another allylic alcohol in the Sharpless epoxidation was also employed in the synthesis of (Jl)-lO and fully oxygenated AB building block 35 (Scheme 6) [47]. Epoxidation of alcohol 34 [48] followed by LAH reduction and then oxidation with the Fetizon reagent [41,49] furnished hydroxyketone (Jl)-lO. Ketahzation of the carbonyl group and subsequent stereoselective benzyUc hydroxylation, using iodosobenzene in the presence of [ 5,10,15,20-tetrakis(pentafluorophenyl)-2 lH,23H-porphine ] iron(lll) chlo-... 

A >4 symmetric manganese tetraphenylporphyrin (48) (Figure 1.5) has been employed by Halterman et al. [107] for catalytic oxidation with iodosobenzene. The reaction proceeds with 0.025 mol% of catalyst at room temperature in dichloromethane to give the sulfoxide in less than 2 h. The yield is above 90% and the enantioselectivities range from 40% to 68%. With very reactive substrates, however, the reaction proceeded with low ee, and a large amount of the sulfone was obtained. 

More recently, Katsuki et al. [109] prepared the Salen manganese complex (50) (Figure 1.6), which is efficient in the oxidation of alkyl aryl sulfide with iodosobenzene as oxidant. With 1 mol% of catalyst, they obtained the 2-nitrophenyl methyl sulfoxide in 1 h at -20°C in acetonitrile solution with 90% ee and 88% yield. This is currently one of the best results for catalytic asymmetric sulfoxidation. 

In an analogous approach, the effect of imidazole was also observed by Inoue et al. [114]. When alkyl aryl sulfides were oxidized with a novel iron porphyrin catalyst (52) (0.2 mol% equiv), the reaction proceeded enantioselectively under appropriate conditions. Iodosobenzene was used as oxidant in dichloromethane at -43°C. The turnover number increases to 142, and an ee of 73% was obtained in the presence of a 100 to 600 molar ratio of imidazole to catalyst for the synthesis of (5)-methoxymethyl phenyl sulfoxide. In the absence of imidazole, the enantioselectivity disappeared, giving the racemic sulfoxide. 

Low yields of the 5-acetyl-l0,11-epoxy derivative 11 (R = Me) are also obtained by oxidation of 5-acetyl-5//-dibenz[/>,/]azepine (10, R = Me) with iodoxybenzene and vanadium(lll) acetylacetonate, and with iodosobenzene and iron(lll) porphyrin.220... 

Iodoxybenzene has been prepared by the disproportionation of iodosobenzene,4Hi by oxidation of iodosobenzene with hypo-chlorous add or bleaching powder,7 and by oxidation of iodobenzene with hypochlorous acid or with sodium hydroxide and bromine.8 Other oxidizing agents used with iodobenzene include air,3 chlorine in pyridine,9 Caro s acid,19-11 concentrated chloric acid,15 and peracetic acid solution.13 Hypochlorite oxidation of iodobenzene dichloride has also been employed.14... 

Reaction of N,N-dimethylaniline with 1-cyanobenziodoxol 1783 to afford N-methyl-N-cyanomethylaniline 1784 in 97% yield has been discussed in Section 12.1 [31]. Analogously, oxidation of dimethylaniline with iodosobenzene and trimethylsilyl azide 19 at 0°C in CDCI3 gives the azido compound 2040 in 95% yield, iodobenzene, and HMDSO 7 [194, 195] (Scheme 12.56). Likewise, the nucleophilic catalyst 4-dimethylaminopyridine (DMAP) is oxidized, in 95% yield, to the azide 2041, which is too sensitive toward hydrolysis to 4-N-methylaminopyri-dine to enable isolation [194, 195]. Amides such as 2042, in combination with tri-... 

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