Amines A -oxidation

Amine A-oxides 56 were reduced to amines by carbon disulfide (62CPB969). Tire proposed mechanism involved the formation of amines and dithiiranone (57) from the initial adducts 58 the latter is finally hydrolyzed to CO2 and H2S2 (82BCJ3000). 

Rosenau, T. Mereiter, K. Jager, C. Schmid, P Kosma, P. Sulfonium ylides derived from 2-hydroxy-benzoquinones crystal and molecular structure and their one-step conversion into Mannich bases by amine A-oxides. Tetrahedron 2004, 60(27), 5719-5723. 

The use of m-CPBA allows the formation of nitrones in the oxidation of tertiary amines. The resulting amines A-oxides are subject to either Cope or Meisenheimer rearrangements, providing formation of nitrones. Thus, the generated corresponding nitrones in the oxidation of bicyclic aziridines give nitrones as a result of a Meisenheimer rearrangement (Scheme 2.14) (93). 

A low field shift of proton signals of the OH-group in A-(salicylidenephenyl-amine-A-oxides H-12.7-13.6 ppm) indicates the presence of an intramolecular hydrogen bond. The value of this shift depends on the pK value of the parent phenol (400). While studying solvation effects of 11 NMR spectra in a-(2-hydroxy-l-phenyl)-A-(4-substituted-phenyl)nitrones, a Koppel-Palm three-parameter correlation was detected (401). 

Nitrones and amine A-oxides are deoxygenated by a stoichiometric amount of benzyltriethylammonium tetrathiomolybdate to yield imines and amines, respectively (>80%) [7]. Nitro groups and sulphoxides are not reduced under these reaction conditions. 

Sigmatropic rearrangement of tertiary amine A -oxides to hydroxylamines ... 

Amine A-oxides, possessing the property of Lewis basicity, have also been exploited in an enantioselective allylation. Maikov and Kocovsky prepared a series of chiral A-oxide catalysts and found, that ligands 23 and 25 afforded good yield and stereoselectivity (Scheme 17) [49-51]. 

Finally, a very simple way to deoxygenate aliphatic or aromatic amine A-oxides involved the sameNiCl2-2H20/LiyDTBB (10%) combination, so, for instance, compounds 546-550 are examples of this reaction in 66-80% yield °. 

Azomethine ylides such as 64 can be generated from tertiary amine A-oxides (63) by reaction with lithium diisopropylamide (EDA) (Scheme 12.22) (97). Several different chiral A -substituted azomethine ylides were prepared in this manner. The best results were obtained when using 64 in 1,3-dipolar cycloaddition with alkenes, but the de values obtained of the product 65 were <60%. 

The beneficial effects of amine A-oxide promoters are well documented in the example given in Equation (1). While the aromatized product 12 instead of the PKR product was obtained from the reaction of diethylacetylene 10 and compound 11 under thermal conditions, the desired PKR product 13 was formed only by the aid of amine A-oxide. 

Recently, Kerr introduced a promoter anchored to a solid support to facilitate workup after the reaction. For example, the PKR proceeds to completion by use of the amine A-oxide anchored on solid support 14, and then the polymeric amine is recovered by simple filtration. The recovered polymer is cleaned by washing with a THF-aqueous 2 M HGl mixture (2 1 mixture), followed by washing of hydrochloride salt with a 10% solution of Pr2NEt in DMF. The resultant resin is oxidized again and then used without loss of activities.Kerr and Pauson also successfully employed sulfide promoters anchored on the solid support 15 for this cycloaddition (Figure 1). ... 

One of the conceptually appealing approaches for enantioselective PKR with cobalt-alkyne complexes is the use of chiral promoters. It is expected that a sterically biased promoter can approach to one of the two equivalent cobalts preferentially, and effect oxidation of GO to make a vacant coordination site. Early attempts were marginally successful, and there remained much room for improvement. Recently, enhanced enantioselectivity has been obtained by using a bulky amine A -oxides like brucine 7V-oxide 44 under carefully controlled conditions (Scheme... 

Second, Garretero and his co-workers introduced 1,6-enynes bearing a sulfoxide group at C-1 position. The cobalt-complexed enynes readily afford the desired PKR products either by heating in GH3CN at 80 °G or by using amine A -oxide promoters (NMO) in GH2GI2 at room temperature. 

Amine A-oxides, phosphine oxides and other phosphoryl compounds and analogous arsenic derivatives, and sulfoxides all give well-defined complexes with scandium. In many cases, authors deal with several of these classes of ligand in the same paper, so it will be most convenient to consider them together here. 

Added CO2 allows the synthesis of substituted maleic anhydrides. According to a novel aminomethylation, ethane or propane is reacted with /V./V-di alkyl methyl-amine A-oxides in the presence of trifluoroacetic acid and a catalytic amount of Cu(OAc)2 to afford A,A-dialkylaminomethylated alkanes in good yields 321 337 338... 

POLONOVSKI REACTION. Demethylation of tertiary (or Heterocyclic) amine A-oxides on treatment with acetyl chloride or acetic anhydride 1o give A-acylated secondary amines and formaldehyde, along with (9-acylated aminophenols as a result of a side reaction. 

Ozonolysis of alkenes in the presence of amine A-oxides resulted in reductive ozonolysis, i.e, the direct formation of aldehydes in high yields, avoiding the generation and isolation of ozonides or other peroxide products. Use of DMSO and tertiary amines improved the yield of aldehydes but some amount of ozonides remained. This... 

Amine A-oxides (34a-e) were resolved very efficiently by complexation with 14b. In this case, both enantiomers of 34 were obtained in an optically pure form.16 For example, when a solution of 14b (1.0 g, 3.6 mmol) and rac-34b (1.2 g, 7.2 mmol) in THF (20 ml)-hexane (10 ml) was kept at room temperature for 5 h, a 1 1 complex of 14b and (+)-34b was obtained as colorless prisms. The crystals were recrystallized from THF-hexane to give pure crystals (0.85 g, 53%, mp 167-169 °C). The complex was separated to its components by column chromatography on silica gel. Firstly, 14a (0.5 g) was recovered from a fraction eluted by ethyl acetate-benzene (1 4). Secondly, (+)-34b of 100% ee (0.29 g, 48%) was obtained from a fraction eluted by MeOH. Evaporation of the filtrate left after separation of the complex between 14b and (+)-34b, gave crude (-)-34b. Treatment of the crude (-)-34b with 14c by a similar manner to that described above, followed by column chromatography, yielded finally (-)-34b of 100% ee in 40% yield.16 Compounds 34a and 34c-e were also resolved effectively by complexation with 14b, and the corresponding (+)-enantiomers were obtained in the optical and chemical yields indicated, (+)-34a (100% ee, 21%), (+)-34c (73% ee, 39%), (+)-34d (100% ee, 30%), and (+)-34e (100% ee, 68%).16... 

Metal complexes of aromatic amine-A-oxides. (N. M. Karayannis, L. L. Pytlewski and C. M. Mixulski, Coord. Chem. Rev., 1973, 11, 93). 

Fig. 14.30. A /e//-amine — amine A-oxide oxidation as preparation of the oxidizing reagent NMO (see Figures. 14.14 and 14.16 for synthetic applications).

One of the most commonly employed methods to promote the reaction is to add an amine A-oxide, such as triethylamine A-oxide or A-methylmor-pholine A-oxide.10-12 These A-oxides act by oxidising a CO ligand to C02 and creating a vacant site into which the alkene is able to bind. 

Hayashi, E., private communication to Ochiai, E., in Aromatic Amine A-Oxides, Elsevier Publishing Co. Amsterdam, 1967, p 24. 

The effect of the oily component on the phase behavior of o/w ME-forming systems formulated with nonionic surfactants was reported [23].The authors showed that it is possible to formulate cosurfactant-free o/w ME systems suitable for use as drug delivery vehicles using either polyoxyethylene surfactants or amine-A-oxide surfactants. The major advantage of these ME systems is their ability to be diluted without destroying their integrity however both classes of surfactants were shown to be sensitive to electrolytes. 

Figure 16 Intermediates involved in alkane oxidation by cytochrome P450. Catalytic cycles involving either O2 and electrons (from NADPH), or a single oxygen atom donor (AO) are shown. Model reactions often use single oxygen atom donors AO such as iodosylbenzene, amine A-oxides and organic or inorganic hydroperoxides or peroxy acids ...

Asymmetric intermolecular Pauson Khand reactions have been reahzed using a number of chiral auxiliaries chelating to the metal and/or attached to the alkyne. One example using a camphor-derived hgand is seen in Scheme 253. Moderate asymmetric induction has been observed using chiral amine A-oxides as the promoter. For example, (-F)-indohzino[3,4-b]quinoline A-oxide gave up to 53% ee. 

Oxo-rhenium complexes can catalyze various OAT reactions between suitable oxo-donors (XO = sulfoxides (R2SO) tertiary amine A-oxides (R3NO) pyridine A-oxide (C5H5NO, PyO) triphenyl-phosphine, -arsine, or -stilbene oxide (R3AO) (A = P, As, Sb) peroxides (Bn OOH, H2O2) ... 

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