Alkenes iodosylbenzene

Asymmetric epoxidation. With a chiral (salen)Mn(III) complex to mediate the epoxidation of alkenes, iodosylbenzene supplies the active oxygen atom. 

The epoxidation of alkenes using iodosylbenzene, with tetra-n-butylammonium bromide and a manganese or cobalt polytungstate as co-catalysts [24], appears to have little advantage as a synthetic procedure over other methods. n-Hexene produces the oxirane (58%), when catalysed by the manganese salt, whereas norbornene is more readily converted (96%) into the oxirane with the cobalt salt. 

Chromium complexes in general are poor catalysts for the epoxidation of alkenes with TBHP due to the decomposition of the oxygen donor with formation of molecnlar oxygen . Epoxidation reactions with this metal are known with other oxygen transfer agents than peroxides (e.g. iodosylbenzene) and will not be discnssed here. 

Reaction of iodosylbenzene with the dimethylformamide sulfur trioxide adduct in dichloromethane at room temperature produces phenyliodosulfate 153 in quantitative yield. Phenyliodosulfate (PhlOSOs) reacts with alkenes to form cyclic sulfates. For example, reaction with 2,5-dihydrofuran 154 in dry CH2CI2 at room temperature produced tetrahydrofuro[3,4-r/][l,3,2]dioxathiole 2,2-dioxide 155 (Equation 28) <2003TL1655>. 

Thus far, enantioselective intramolecular aziridination via metal nitrene intermediates has not been successful. Bromamine-T has recently been shown to be a viable source of nitrene for addition to alkenes in copper halide catalyzed reactions, " and so has iodosylbenzene (Phl=0) that forms 44 in situ. Conceptually, aziridination does not necessarily fall between cyclopropanation and epoxidation, as some have suggested. Instead, metal nitrene chemistry has unique problems and potential advantages associated with the electron pair at nitrogen that are yet to be fully overcome. 

The Mn(III) complex 31b was tested as a catalyst for the epoxidation of various alkenes using sodium hypochlorite or iodosylbenzene as oxidants. Although oxidation took place, no selectivity was observed. For example, allylresorcinol was not epoxidized with rates higher than that of allylbenzene. Presumably, the substrate is not bound in the cleft of 31b because the latter is occluded by methoxy groups. It is possible that the reaction occurs on the outside of the metalloclip, which cannot discriminate between guest molecules. 

Many transition-metal complexes have been widely studied in their application as catalysts in alkene epoxidation. Nickel is unique in the respect that its simple soluble salts such as Ni(N03)2 6H20 are completely ineffective in the catalytic epoxidation of alkenes, whereas soluble manganese, iron, cobalt, or copper salts in acetonitrile catalyze the epoxidation of stilbene or substituted alkenes with iodosylbenzene as oxidant. However, the Ni(II) complexes of tetraaza macrocycles as well as other chelating ligands dramatically enhance the reactivity of epoxidation of olefins (90, 91). 

Chromium(III) salen will form chromium(V) derivatives in much the same way as porphyrin complexes do. By reaction of iodosylbenzene with chromium(III)salen oxochromium(V) complexes are obtained (equation 74) which will effect oxygen atom transfer to phosphines and alkenes such as norbornene (equation 75) in stoichiometric and catalytic systems.1270 The... 

Some attempts to use simple Cu and Ag salts as catalyst for alkene epoxidation have been performed. Both silver nitrate and triflate in acetonitrile as the solvent were unsuccessful (ref. 9). However, we have found that Ag20 as well as AgN03, the latter in the presence of tertiary amines, can catalyze the oxidation of alkenes with iodosylbenzene as oxygen donor (ref. 10). The results for the epoxidation of different alkenes catalyzed by Ag20 and with iodosylbenzene as oxygen donor at 60 0 C in CHCI3 are given in Table 3. 

Epoxidation of different alkenes with Ag20 as catalyst and iodosylbenzene as oxygen donor. 

Manganese(V)-oxo-porphyrinato complexes have been presumed to be the active species in the epoxidation of alkenes by iodosylbenzene or hypochlorite catalyzed by manganese(III) porphyrins. This and related oxidations will be examined in more detail in Section 61.3.6.2.2. 

Epoxidation of alkenes and hydroxylation of alkanes can be achieved under mild conditions with iron porphyrin catalysts and iodosylbenzene as the oxidant.497 499,488... 

Tertiary amine oxides can be used instead of iodosylbenzene for the epoxidation of alkenes in the presence of Fe(TPP)Cl.500 p-Cyano-N,IV-dimethylaniline IV-oxide (p-CN-DMANO) has... 

Cu2+ ions, e.g. Cu(N03)2, catalyze the epoxication of alkenes by iodosylbenzene.664 Oxidation of alcohols to aldehydes can be effected by 02 in the presence of Cu2 ions and Tempo (2,2,6,6-tetramethylpiperidinyl 1-oxide).665 Arene hydroxylation of the binucleating ligand (206)... 

Diederich et al. had postulated that the highly reactive iron-oxo species, arising from oxygen transfer from the oxidant to the Fem site [87], should be greatly stabilised by enclosure within a dendritic superstructure. The catalytic potential of the dendrimers 6 a-c was determined in the epoxidation of alkenes [83 a, 88] (1-octene and cyclooctene) and the oxidation of sulphides [83 a] ((methylsulphanyl)benzene and diphenyl sulphide) to sulphoxides - in dichloro-methane with iodosylbenzene as oxidising agent. Compared to the known metal-porphyrin catalysts, 6a-c exhibit only low TON (7 and 28, respectively, for... 

The formation of aziridines using bromamine-T was catalysed by cobalt porphyrins.77 Yields range from the mid-50% level to >90% with aliphatic and aromatic alkenes. Sulfonimidamide also yielded aziridines when treated with iodosylbenzene diacetate in the presence of dirhodium tetraacetate.78... 

To demonstrate the flexibility of the approach to catalyst design that we set out in this paper, the epoxidation of alkenes using iodosylbenzene has also been studied. Initial studies focused on MnHY salen catalysts for the epoxidation of styrene, however, the reaction was slow, and low yields of styrene oxide were observed. Analysis of the reaction mixture revealed the breakdown of the salen ligand within a few turnovers. Subsequently Mn-Al-MCM-41 was used with iodosylbenzene as the oxygen donor and cis -stilbene was used as substrate, and the results, together with those of control experiments, are shown in Table 3. 

Oxidation of ]V-MeTTPFenCl (46, 52). Catalytic alkene oxidation by iron N-alkylporphyrins requires that the modified heme center can form an active oxidant, presumably at the HRP compound I level of oxidation. To show that iron N-alkyl porphyrins could form highly oxidized complexes, these reactive species were generated by chemical oxidation and examined by NMR spectroscopy. Reaction of the (N-MeTTP)FenCl with chlorine or bromine at low temperatures results in formation of the corresponding iron(III)-halide complex. Addition of ethyl- or t-butyl-hydroperoxide, or iodosylbenzene, to a solution of N-MeTTPFenCl at low temperatures has no effect on the NMR spectrum. However, addition of m-chloroperoxybenzoic acid (m-CPBA) results in the formation of iron(III) and iron(IV) products as well as porphyrin radical compounds that retain the N-substituent. 

The observation that iron porphyrins can catalyze, under mild conditions, epoxidations of alkenes when iodosylbenzene is used as the oxidant has been followed up by a number of studies on metallopor-phyrins as models for cytochrome P-4S0 enzymes. Cytochrome P-4S0 enzymes catalyze epoxidation of alkenes by molecular oxygen in the presence of a hydrogen donor, NAOPH cofactor. This has led to the study of a number of systems based on a metalloporphyrin/02/reducing agent, to bring about epoxidation of alkenes. 

Cobalt-catalyzed epoxidation of alkenes has been carried out with the cobalt derivative of (174), employing iodosylbenzene as the oxidant. Epoxidation of cfa- -methylstyrene furnishes exclusively the cis-epoxide (equation 62). The reaction proceeds through an active oxo-cobalt(IV) species, and is mote selective than reactions proceeding through oxo-chromium or oxo-manganese species. The catalyst can be recovered unchanged by simple filtration. 

The oxidative decarboxylation of aliphatic carboxylic acids is best achieved by treatment of the acid with LTA in benzene, in the presence of a catalytic amount of copper(II) acetate. The latter serves to trap the radical intermediate and so bring about elimination, possibly through a six-membered transition state. Primary carboxylic acids lead to terminal alkenes, indicating that carbocations are probably not involved. The reaction has been reviewed. The synthesis of an optically pure derivative of L-vinylglycine from L-aspartic acid (equation 14) is illustrative. The same transformation has also been effected with sodium persulfate and catalytic quantities of silver nitrate and copper(II) sulfate, and with the combination of iodosylbenzene diacetate and copper(II) acetate. ... 

Porphyrin hgands also allow the preparation of Cr complexes. For example, reaction of [(TPP)CrCl] with iodosylbenzene provides [(TPP)Cr(0)Cl], a six-coordinate complex, which is stable in solution for several hours. Its reaction with alkenes involves oxygen atom transfer and yields alcohols and epoxides. Another Cr porphyrin complex is the nitride [(TPP)CrN]. A crystal-stmcture determination has confirmed the square pyramidal structure with a very short bond distance to the apical lutrido ligand (Cr N, 156.5 pm). 

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