Heteroatoms oxidations

Since dioxiranes are electrophilic oxidants, heteroatom functionalities with lone pair electrons are among the most reactive substrates towards oxidation. Among such nucleophilic heteroatom-type substrates, those that contain a nitrogen, sulfur or phosphorus atom, or a C=X functionality (where X is N or S), have been most extensively employed, mainly in view of the usefulness of the resulting oxidation products. Some less studied heteroatoms include oxygen, selenium, halogen and the metal centers in organometallic compounds. These transformations are summarized in Scheme 10. We shall present the substrate classes separately, since the heteroatom oxidation is quite substrate-dependent. 

Colonna S, Del Sordo S, Gaggero N, Carrea G, Pasta P (2002) Enzyme-Mediated Catalytic Asymmetric Oxidations. Heteroatom Chem 13 467... 

In basic solution, Ura and Thy undergo a series of reactions as depicted in reactions (72)—(76) for Ura as an example (Fujita and Steenken 1981). Ura dissociates athighpH [equilibrium (72) for pfCa values see Table 10.11], Its OH-adductscan also be deprotonated at nitrogen leading to an oxidizing heteroatom-centered radical [reaction (76)]. 

Backvall and co-workers have demonstrated that m-annulated furans are obtained in excellent yields from 7-hydroxy alkenes by Pd(ll)-catalyzed oxidative heteroatom cyclization (Equation 83) <1995TL7749>. The scope of the Pd(ll) catalyst system with O2 in DMSO as reoxidant has been demonstrated with ring sizes five to seven (n = 1-3). 

Colonna, S., Del Sordo, S., Gaggero, N., Carrea, G. and Pasta, P. (2002) Enzyme-mediated catalytic asymmetric oxidations. Heteroatom Chemistry, 13, 467 73. 

One key aspect in the study of toxicity is the ability to predict the products of metabolism. In this respect P450s have been the major area of research for many years. The P450s have been shown to catalyze an almost bewildering number of reactions [6], In addition to the common hydroxylation reactions at aliphatic and aromatic carbon centers, they can directly oxidize heteroatoms... 

Huang K, Emge TJ, Zhang X (2014) Synthesis of a novel F-chiral 1,3-oxaphospholane from optically pure propylene oxide. Heteroatom Chem 25 131-134... 

Heteroatom heteroatom oxide heteroatom oxidation fiavin-de pendent... 

E. Jablonkai, L. Drahos, Z. Drzazga, K.M. Pietrusiewicz, G. Keglevich, 3-P(0)< Fimctionalized phospholane 1-oxides by the Michael reaction of l-phenyl-2-phospholene 1-oxide and dialkyl phosphites, H-phosphinates or diphenylphosphine oxide. Heteroatom Chem. 23 (2012) 539-544. 

T. Kortvelyesi, M. Sipos, G. Keglevich, A theoretical study on the conformation of 3-phosphinoxido- and 3-phosphono-l,2,3,4A6-hexahydro-phosphinine 1-oxides, Heteroatom Chem. 16 (2005) 520-524. 

Animal metaboHsm is based on the reactions of oxygen and organic compounds containing carbon, hydrogen, oxygen, and nitrogen and other heteroatoms. Enzymes catalyze these biochemical oxidations, which are accompHshed at about 30—40°C and frequendy proceed stepwise to produce... 

Biodegradable polymers and plastics are readily divided into three broad classifications (/) natural, (2) synthetic, and (J) modified natural. These classes may be further subdivided for ease of discussion, as follows (/) natural polymers (2) synthetic polymers may have carbon chain backbones or heteroatom chain backbones and (J) modified natural may be blends and grafts or involve chemical modifications, oxidation, esterification, etc. 

The formation of acids from heteroatoms creates a corrosion problem. At the working temperatures, stainless steels are easily corroded by the acids. Even platinum and gold are not immune to corrosion. One solution is to add sodium hydroxide to the reactant mixture to neutralize the acids as they form. However, because the dielectric constant of water is low at the temperatures and pressure in use, the salts formed have low solubiHty at the supercritical temperatures and tend to precipitate and plug reaction tubes. Most hydrothermal processing is oxidation, and has been called supercritical water oxidation. 

Hydroxyindole (181) represents a well known example of a compound in which the hydroxyl group is to the ring heteroatom. The equilibrium mixture again contains mainly the carbonyl form (182), indoxyl. Deprotonation gives a reactive ambident anion which can be methylated either on oxygen or C-2 (Scheme 73). Indoxyl is easily oxidized to indigo (184), which may be formed by dimerization of the radical (183) produced by electron loss from the anion. 

As shown in Scheme 2, two heteroatom-carbon bonds are constructed in such a way that one component provides both heteroatoms for the resultant heterocycle. By variation of X and Z entry is readily obtained into thiazoles, oxazoles, imidazoles, etc. and by the use of the appropriate oxidation level in the carbonyl-containing component, further oxidized derivatives of these ring systems result. These processes are analogous to those utilized in the formation of five-membered heterocycles containing one heteroatom, involving cyclocondensation utilizing enols, enamines, etc. 

Although some of the oxidative ring closures described above, e.g. reactions with lead tetraacetate (Section 4.03.4.1.2), may actually involve radical intermediates, little use has been made of this reaction type in the synthesis of five-membered rings with two or more heteroatoms. Radical intermediates involved in photochemical transformations are described in Section 4.03.9. Free radical substitutions are described in the various monograph chapters. 

Joining two heteroatoms to a ring by radical combination is not presently a common route to heterocycles. It might become more important if the art of metal-catalyzed redox reactions keeps advancing at the present pace. Current examples are the conversion of 1,5-dithiols to 1,2-dithiepanes by oxidants such as FeCla, and the oxidation of 1,3-propane-bis-hydrazines to 1,2,3,4-tetrazepines (Sections 5.18.4.1 and 5.18.10.1). 

Acrylate polymers also have fully saturated polymer backbones free of any heteroatoms in the main chain. This makes the polymers highly resistant to oxidation, photo-degradation and chemical attack. The acrylate groups are esters, which could be hydrolyzed under severe conditions. However, the hydrophobic nature of most acrylic polymers minimizes the risk for hydrolysis and, even if this reaction happened to some extent, the polymer backbone would still be intact. Other desirable acrylate properties include the following ... 

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