Iodobenzene, oxidation

Complex M(AAOPD), (18) (M = Co or Cu), catalyses the oxidation of aldoximes, ketoximes and carboxylic acids by dioxy iodobenzene (oxidant) in the presence of imidazole to corresponding carbonyl products in high yields. The rate of oxidation of oximes in the presence of Cu(AAOPD) is higher than that with Co(AAOPD) no such effect is observed in the oxidation of carboxylic acids. " ... 

As a typical example, the catalytic reaction of iodobenzene with methyl acrylate to afford methyl cinnamate (18) is explained by the sequences illustrated for the oxidative addition, insertion, and /3-elimination reactions. 

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... 

Iodobenzene, conversion to iodosoben-zene diacetate, 43, 62 oxidation to iodoxybenzene, 43, 65 Iodosoarenes from iodosoarcne diacetates, 43,61... 

Sodium cyclopentadienide, 41, 96 Sodium dichromate for oxidation of alkylarcncs to aromatic carboxylic acids, 43, 80 Sodium iodide, in conversion of 2,4-di-nitrochlorobenzene to 2,4-dinitro-iodobenzene, 40, 34 reduction of peroxide with, 41,... 

Triphenylphosphine oxide (and PhsAsO or Ph2SeO) are reduced by MesSiNs 19, via the labile diazidophosphines 1780, to triphenylphosphine (triphenylarsine or diphenylselenide), nitrogen, and HMDSO 7, whereas iodosobenzene gives, via 1781, iodobenzene, nitrogen, and HMDSO 7 [30] (Scheme 12.9). 

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). 

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-... 

Quinoxalines 85 have been prepared by the reaction of diols with benzene-1,2-diamines in the presence of a ruthenium catalyst <06TL5633>. Iodobenzene diacetate has been suggested as a less toxic alternative to lead tetraacetate for the oxidative cyclisation of iminooximes to quinoxaline iV-oxides 86 <06TL4969>. 

Several organohypervalent iodine reagents have been used for the oxidation of alcohols and phenols such as iodoxybenzene, o-iodoxybenzoic acid (IBX), bis(trifluoroa-cetoxy)iodobenzene (BTI), and Dess-Martin periodinane etc. But the use of inexpensive iodobenzene diacetate (IBD) as an oxidant, however, has not been fully exploited. Most of these reactions are conducted in high boiling DMSO or toxic acetonitrile media that results in increased burden on the environment. 

Scheme 6.33 Oxidation of alcohols using alumina-supported iodobenzene diacetate.

The second most popular method of oxadiazole preparation starts from acylhydrazones 110, which undergo cyclization usually under the action of oxidizing agents (Br2, PhN02, HgO, iodobenzene diacetate). Also, the use of acetic anhydride can lead to cyclization of compound 110. The cyclization can be supported by microwave irradiation. In particular cases, heating is sufficient to accomplish the reaction. 

The oxidation of acetylthiourea and phenylthiourea to afford the corresponding 1,2,4-thiadiazoles has been reported using [bis(acyloxy)iodo]arenes as the oxidants. The proposed mechanism involves the formation of a polyvalent iodine compound 74. After the elimination of iodobenzene, the 1,6-dip he nyl-dithioformamidine 75 is formed, which is set up to undergo a further oxidation to give the bis 3,5-diamino-l,2,4-thiadiazole 76 (Scheme 7) <2003T7521>. 

Partially or fully reduced thiadiazoles can be oxidized to yield 1,3,4-thiadiazoles. The 2,5-disubstituted 3-acyl-l,3,4-thiadiazole 157 can be deacylated by numerous methods <2004H(63)2243>. The oxidative deacylation of compound 157 to thiadiazole 158 can be achieved using oxidants such as KMn04, cerium(iv) ammonium nitrate (CAN), and (diacetoxy)iodobenzene (Equation 58). Better yields and cleaner products are obtained using CAN as oxidant. 

Several approaches to the 1,2,3-triazole core have been published in 2000. Iodobenzene diacetate-mediated oxidation of hydrazones 152 led to fused 1,2,3-triazoloheterocycles 153 <00SC417>. Treatment of oxazolone 154 with iso-pentyl nitrite in the presence of acetic acid gave 1,2,3-triazole 155, a precursor to 3-(W-l,2,3-triazolyl)-substituted a,P-unsaturated a amino acid derivatives <00SC2863>. Aroyl-substituted ketene aminals 156 reacted with aryl azides to provide polysubstituted 1,23-triazoles 157 <00HC387>. 2-Aryl-2T/,4/f-imidazo[43-d][l,2,3]triazoles 159 were prepared from the reaction of triethyl AM-ethyl-2-methyl-4-nitro-l//-imidazol-5-yl phosphoramidate (158) with aryl isocyanates <00TL9889>. 

Finally, Cristau and coworkers have reported on a quite efficient preparation of triphenylphosphine oxide (Figure 2.13) by a similar addition-elimination reaction of red phosphorus with iodobenzene in the presence of a Lewis acid catalyst followed by oxidation of an intermediate tetraarylphosphonium salt.42 This approach holds the potential for the preparation of a variety of triarylphosphine oxides without proceeding through the normally used Grignard reagent. Of course, a variety of approaches is available for the efficient reduction of phosphine oxides and quaternary phosphonium salts to the parent phosphine, including the use of lithium aluminum hydride,43 meth-ylpolysiloxane,44 trichlorosilane,45 and hexachlorodisilane.46... 

The intramolecular arylation of sp3 C-H bonds is observed in the reaction of l-/ r/-butyl-2-iodobenzene under palladium catalysis (Equation (71)) 94 94a 94b The oxidative addition of Arl to Pd(0) gives an ArPdl species, which undergoes the electrophilic substitution at the tert-butyl group to afford the palladacycle. To this palladacycle, another molecule of Arl oxidatively adds, giving the Pd(iv) complex. 

In one possible mechanism, oxidative addition of iodobenzene to Pd(0) gives Pd(II) intermediate 74, which subsequently inserts into thiazole regioselectively at the C(5) position to form the a-adduct of arylpalladium(II) 75. The order of reactivity is similar to the electrophilic substitution, which is known to be C(5) > C(4) > C(2) [74]. Treatment of the insertion adduct 75 with a base regains the aromaticity after deprotonation, giving rise to 73 along with Pd(0) for the next catalytic cycle. 

Free or benzo-fused 1,2,3-triazoles 286 have been prepared by iodobenzene diacetate-mediated oxidation of hydrazones 285 (Equation 37) <2000SC417>. 

Iodine isocyanate, 0524 Iodine(V) oxide, 4627 Iodine(VII) oxide, 4628 Iodine pentafluoride, 4355 Iodine(III) perchlorate, 4140 Iodine triacetate, 2394 Iodobenzene, 2249... 

Several examples have been reported of the use of palladium-mediated oxidation reactions of alcohols and alkyl halides. Palladium(II) acetate in the presence of iodobenzene converts primary and secondary alcohols into carbonyl compounds under solid-liquid two-phase conditions [20], However, other than there being no further oxidation to carboxylic acids, the procedure has little to commend it over other methods. It is relatively slow with reaction times in the order of 2 days needed to achieve yields of 55-100%. 

Buchwald-Hartwig amination of iodobenzene 92 with 2-benzyloxy-4-methyl-aniline 93 affords the diarylamine 94 in high yield (Scheme 32). In this case the Goldberg coupling gives poor yields. Oxidative cyclization of compound 94 using stoichiometric amounts of palladium(II) acetate in acetic acid under reflux leads to the carbazole 95, which by reductive debenzylation provides... 

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