Oxidants iodosylbenzene

Similarly, the nitrene transfer reaction from 128 is facilitated by a variety of catalysts, including MTO (136) <01JCS(CC)235>, the lri(pyrazolyl)borate-coppcr(l) complex 137 <01OL1423>, and tetrakis(acetonitrile)copper(I) hexafluorophosphate (138) <01JA7707>. In the latter case, the reaction can be carried out using a sulfonamide and the primary oxidant, iodosylbenzene, whereby the actual nitrene transfer reagent 128 is presumed to be formed in situ. In all cases, acetonitrile appears to be the solvent of choice. 

N—Fe(IV)Por complexes. Oxo iron(IV) porphyrin cation radical complexes, [O—Fe(IV)Por ], are important intermediates in oxygen atom transfer reactions. Compound I of the enzymes catalase and peroxidase have this formulation, as does the active intermediate in the catalytic cycle of cytochrome P Q. Similar intermediates are invoked in the extensively investigated hydroxylations and epoxidations of hydrocarbon substrates cataly2ed by iron porphyrins in the presence of such oxidizing agents as iodosylbenzene, NaOCl, peroxides, and air. 

The observation that addition of imidazoles and carboxylic acids significantly improved the epoxidation reaction resulted in the development of Mn-porphyrin complexes containing these groups covalently linked to the porphyrin platform as attached pendant arms (11) [63]. When these catalysts were employed in the epoxidation of simple olefins with hydrogen peroxide, enhanced oxidation rates were obtained in combination with perfect product selectivity (Table 6.6, Entry 3). In contrast with epoxidations catalyzed by other metals, the Mn-porphyrin system yields products with scrambled stereochemistry the epoxidation of cis-stilbene with Mn(TPP)Cl (TPP = tetraphenylporphyrin) and iodosylbenzene, for example, generated cis- and trans-stilbene oxide in a ratio of 35 65. The low stereospecificity was improved by use of heterocyclic additives such as pyridines or imidazoles. The epoxidation system, with hydrogen peroxide as terminal oxidant, was reported to be stereospecific for ris-olefins, whereas trans-olefins are poor substrates with these catalysts. 

These oxidants have been used rarely. The kinetics of periodate oxidation of sulphoxides have been studied119,124. In an acid medium the reaction proceeds without catalysis but in alkali a catalyst such as an osmium(VIII) or ruthenium(III) salt is required124. Iodosylbenzene derivatives have also been used for the oxidation of sulphoxides to the sulphone level94,125 (equation 39). In order to use this reaction for the synthesis of sulphones, a ruthenium(III) complex should be used as a catalyst thus quantitative yields are obtained at room temperature in a few minutes. However, column chromatography is required to separate the sulphone from the other products of the reaction. 

Imamoto and Koto prepared some interesting chiral oxidants (104) by the reaction of iodosylbenzene with tartaric anhydride. Methyl p-tolyl sulfide (105) was oxidized by 104c to the sulfoxide in 80% yield with 40% e.e. Methyl p-tolyl, o-tolyl and o-anisyl sulfides (105-107) were oxidized by 104a to their sulfoxides with the enantiomeric purities shown. 

A few further general examples of zinc catalytic activity or reactivity include the following. Other zinc-containing systems include a zinc phenoxide/nickel(0) catalytic system that can be used to carry out the chemo- and regioselective cyclotrimerization of monoynes.934 Zinc homoenolates have been used as novel nucleophiles in acylation and addition reactions and shown to have general utility.935,936 Iron/zinc species have been used in the oxidation of hydrocarbons, and the selectivity and conditions examined.362 There are implications for the mechanism of metal-catalyzed iodosylbenzene reactions with olefins from the observation that zinc triflate and a dizinc complex catalyze these reactions.937... 

Dioxo-ruthenium porphyrin (19) undergoes epoxidation.69 Alternatively, the complex (19) serves as the catalyst for epoxidation in the presence of pyridine A-oxide derivatives.61 It has been proposed that, under these conditions, a nms-A-oxide-coordinated (TMP)Ru(O) intermediate (20) is generated, and it rapidly epoxidizes olefins prior to its conversion to (19) (Scheme 8).61 In accordance with this proposal, the enantioselectivity of chiral dioxo ruthenium-catalyzed epoxidation is dependent on the oxidant used.55,61 In the iron porphyrin-catalyzed oxidation, an iron porphyrin-iodosylbenzene adduct has also been suggested as the active species.70... 

What can all these studies suggest to the inorganic chemist interested in the controlled and fAcile catalytic oxidation of hydrocarbons Groves and coworkers have already shown that iron porphyrins in the presence of iodosylbenzene and peracids can be used for such catalytic reactions (37, 38). However, the cost of the oxidants makes such reaction uneconomical at this time. 

In a number of model studies it has been demonstrated that synthetic porphyrin complexes are able to be oxidized to oxo-metalloporphyrin complexes which will, in turn, oxidize organic substrates of the type mentioned previously. Thus, in an early investigation it was shown that a synthetic Fe(m) porphyrin will catalyze oxygenation of hydrocarbons using iodosylbenzene as the reduced-oxygen source (Groves, Nemo Myers, 1979). Following this report, a number of related cytochrome... 

SN]-Labeled 4,6-dimethyl-47/-[l,2,5]oxadiazolo[3,4-rf pyrimidine-5,7-dione 1-oxide 290 is conveniently prepared by nitration of commercially available 6-amino-l,3-dimethyl-l//-pyrimidine-2,4-dione using 15N-enriched nitric acid followed by an intramolecular oxidative cyclization with iodosylbenzene diacetate under mild conditions <2000JOC6670>. 

In a similar manner, 47/-[l,2,5]oxadiazolo[3,4- /]pyrimidine-5,7-dione 1-oxides 344 are conveniently prepared in high yields by the oxidative intramolecular cyclization of 6-amino-5-nitro-l/7-pyrimidine-2,4-diones 343 employing iodosylbenzene diacetate as an oxidant in the presence of lithium hydride (Equation 80) <1998JOG6947>. 

Collman et al.99 reported the asymmetric epoxidation of terminal olefins catalyzed by iron porphyrin complex 129. The catalyst was synthesized by connecting binaphthyl moieties to a readily available aa/ / -tetrakis(aminophenyl)-porphyrin (TAPP). Epoxidation of unfunctinalized olefins was carried out using iodosylbenzene as the oxidant. As shown in Scheme 4-46, excellent results were... 

The synthesis of the manganese(III) complex of the hexaaza macrocyclic ligand (176), derived from 2,3-butanedione and diethylenetriamine, and its use as a catalyst for the epoxidation of olefins using iodosylbenzene as oxidant has been reported." ... 

---