Amines dioxirane oxidation

Preservatives, pharmaceutical preparations, 623 PRESS technique, NIR spectrophotometry, 624 Primary amines, dioxirane oxidation, 1151 Primary ozonides (POZ), 716, 717 dialkyl peroxide formation, 706 IR spectroscopy, 718, 719-20 microwave spectroscopy, 721 molecular model, 750 NMR spectroscopy, 709, 723-4 octaUn ozonation, 165 ozone water disinfection, 606 7r-complexes with ozone, 732... 

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Sulfur compounds with divalent sulfur functionalities are much more prone to dioxirane oxidation on account of their higher nucleophilicity compared to the above-presented oxygen-type nucleophiles. Examples of this type of dioxirane oxidation abound in the literature. Such a case is the oxidation of thiols, which may be quite complex and afford a complex mixture of oxidation products, e.g. sulfinic acids, sulfonic acids, disulfides, thiosulfonates and aldehydes , and is, therefore, hardly useful in synthesis. Nevertheless, the oxidation of some 9i/-purine-6-thiols in the presence of an amine nucleophile produces n >( -nucleoside analogs in useful yields (equation 19). This reaction also displays the general chemoselectivity trend that divalent sulfur functionalities are more reactive than trivalent sp -hybridized nitrogen compounds P. 

C-H bond unreactive to insertion, 1160 nitrile hydrolysis, 701-2 selective dioxirane oxidation, 1152 Amines... 

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Ferrer M, Sanchez-Baeza F, Messeguer A, Adam W, Golsch D, GOrth F, Kiefer W, Nagel V. The release of singlet oxygen in the reaction of dioxiranes with amine N-oxides. Eur J Org Chem 1998 2527-32 ... 

Messeguer and coworkers reported the use of dioxiranes for the oxidation of amines to N-oxides [94]. Oxidation of various tertiary aromatic amines with di-methyldioxirane (DMD) afforded amine N-oxides in quantitative yields. A few examples are given in Eq. (19). 

In general, peroxomonosulfates have fewer uses in organic chemistry than peroxodisulfates. However, the triple salt is used for oxidizing ketones (qv) to dioxiranes (7) (71,72), which in turn are useful oxidants in organic chemistry. Acetone in water is oxidized by triple salt to dimethyldioxirane, which in turn oxidizes alkenes to epoxides, polycycHc aromatic hydrocarbons to oxides and diones, amines to nitro compounds, sulfides to sulfoxides, phosphines to phosphine oxides, and alkanes to alcohols or carbonyl compounds. 

All classes of primary amine (including primary, secondary, and tertiary alkyl as well as aryl) are oxidized to nitro compounds in high yields with dimethyl dioxirane." Other reagents that oxidize various types of primary amines to nitro compounds are dry ozone, various peroxyacids," MeRe03/H202,"" Oxone ," ° tcrt-butyl hydroperoxide in the presence of certain molybdenum and vanadium compounds, and sodium perborate." ... 

Aliphatic primary amines are known to be oxidized by dimethyl dioxiranes to various products such as oximes, nitroso dimers, nitroalkanes, nitrones and oxazrridines under various conditions depending upon the oxidation reaction . In contrast, when secondary amines lacking a-hydrogens are allowed to react with Oxone and PTC in buffered acetone solution at 0 °C, nitroxides are obtained in good yields in a few minutes (equation 61) . 

The oxidation of secondary amines with no a-hydrogen atoms leads to hydroxy-lamines, but excessive dioxirane may further oxidize the hydroxylamines to the corresponding nitroxyl radical. For example, when a slight excess of isolated DMD is employed, 2,2,6,6-tetramethylpiperidin-4-ol (15) is quantitatively transformed into the hydroxylamine... 

In the case of tertiary amines, the DMD treatment produces cleanly the A-oxides thus, from A,A-dimethylaniline the A-oxide is quantitatively obtained (equation 12). In this context, it must be pointed out that the A-oxide may catalyze the decomposition of the dioxirane (vide infra), so that complete conversion of the amine is not always possible even with an excess of DMD. 

AMI and PM3 calculations reveal that epoxidations by DMDO and TFDO involve peroxide-bond cr at a very early stage and that TFDO is the most reactive dioxirane as the CF3 group in it stabilizes this cr level. In accord with previous calculations a spiro transition state is predicted. Furthermore, allene is predicted to be less reactive than alkenes toward epoxidation by DMDO.192 DFT calculations on the oxidation of primary amines by dimethyldioxirane predict a late transition state with a barrier of 17.7 kcal mol-1 which is drastically lowered by hydrogen bonding to the O—O bond to just 1.3 kcal mol-1 in protic solvents.193... 

The chemoselectivity of the dioxirane oxyfunctionalization usually follows the reactivity sequence heteroatom (lone-pair electrons) oxidation > JT-bond epoxida-tion > C-H insertion, as expected of an electrophilic oxidant. Because of this chemoselectivity order, heteroatoms in a substrate will be selectively oxidized in the presence of C-H bonds and even C-C double bonds. In allylic alcohols, however, C-H oxidation of the allylic C-H bond to a,/ -unsaturated ketones may compete efficaciously with epoxidation, especially when steric factors hinder the dioxirane attack on the Jt bond. To circumvent the preferred heteroatom oxidation and thereby alter the chemoselectivity order in favor of the C-H insertion, tedious protection methodology must be used. For example, amines may be protected in the form of amides [46], ammonium salts [50], or BF3 complexes [51] however, much work must still be expended on the development of effective procedures which avoid the oxidation of heteroatoms and C-C multiple bonds. 

The vast majority of organocatalytic reactions proceeds via covalent formation of the catalyst-substrate adduct to form an activated complex. Amine-based reactions are typical examples, in which amino acids, peptides, alkaloids and synthetic nitrogen-containing molecules are used as chiral catalysts. The main body of reactions includes reactions of the so-called generalized enamine cycle and charge accelerated reactions via the formation of iminium intermediates (see Chapters 2 and 3). Also, Morita-Baylis-Hillman reactions (see Chapter 5), carbene-mediated reactions (see Chapter 9), as well as asymmetric ylide reactions including epoxidation, cyclopropanation, and aziridination (see Chapter 10), and oxidation with the in situ generation of chiral dioxirane or oxaziridine catalysts (see Chapter 12), are typical examples. 

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