Oxaziridines oxidation with

The mechanism of this reaction involves an activation of the ammonia and hydrogen peroxide because these compounds do not themselves react (118—121). It appears that acetamide functions as an oxygen transfer agent, possibly as the iminoperacetic acid (41) which then oxidizes the transient Schiff base formed between MEK and ammonia (40) to give the oxaziridine (42), with regeneration of acetamide ... 

Oxaziridines are powerful oxidizing agents. Free halogen is formed from hydrobromic acid (B-67MI50800). Reduction by iodide in acidic media generally yields a carbonyl compound, an amine and two equivalents of iodine from an oxaziridine (1). With 2-alkyl-, 2-acyl and with N-unsubstituted oxaziridines the reaction proceeds practically quantitatively and has been used in characterization. Owing to fast competing reactions, iodide reduction of 2-aryloxaziridines does not proceed quantitatively but may serve as a hint to their presence. 

The enantioenriched sulfoxide intermediate 72 (R = CH2OH), obtained by asymmetric 5-oxidation with a chiral oxaziridine (89 11 enantiomeric ratio), has provided a highly enantioselective synthesis of the benzothiepin derivative 71 (4R, 5R). The aldehyde intermediate 72 (R = CHO) was cyclized asymmetrically to 71 (4R, 5R) with >98 2 enantiomeric ratio. Base treatment (f-BuOK, -10°C, THF) of the racemic benzothiepin 73... 

Enantioselective synthesis of a-hydroxy phosphonates can also be achieved by asymmetric oxidation with camphorsulfonyl oxaziridines (Scheme 2-60).156 Reasonable yields can usually be obtained. (+)-147a or (+)-147b favors formation of the (S )-product, as would be expected, because these oxidations proceed via a transition state that parallels that previously discussed for the stereoselectivity observed with ketones.157... 

Oxidation of silyl enol ethers. Oxidation of silyl enol ethers to a-hydroxy aldehydes or ketones is usually effected with w-chloroperbenzoic acid (6, 112). This oxidation can also be effected by epoxidation with 2-(phenylsulfonyl)-3-( p-nitrophenyl) oxaziridine in CHC1, at 25-60° followed by rearrangement to a-silyloxy carbonyl compounds, which are hydrolyzed to the a-hydroxy carbonyl compound (BujNF or H,0 + ). Yields are moderate to high. Oxidation with a chiral 2-arene-sulfonyloxaziridine shows only modest enantioselectivity. 

The Reformatsky type of reaction with Zn(0) was performed in situ and led to somewhat unstable phosphonodiamidite (step a) which was coupled with 5 -DMTr-thymidine to give the intermediate mononucleoside phospho-noamidite (step b). The latter was further coupled with 3 -acetyl-thymidine (step c). Couplings described in steps b and c were activated by tetrazole. The intermediate dinucleoside phosphonite was oxidized with (lS)-(+)-(10-camphorsulphonyl)oxaziridine (step d) or sulfurized with Beaucage reagent. The phosphonoamidites mentioned above were used in the solid-phase chemical synthesis of phosphonoacetate and thiophosphonoacetate oligonucleotides. 

The cycloaddition of an oxygen atom to the CN double bond, analogous to the epox-idation of CC double bonds, is rare. For example, when the imine 17 is oxidized with in-situ-generated dioxirane (equation 15), the oxaziridine 18 is obtained as the major... 

The unstable dibenz[c,/][l,2]oxazepines (312 R = CN, Cl) have been isolated as the major products of the UV irradiation of 9-cyano- and 9-chloro-acridine 10-oxides (310) in benzene (c/. the analogous Af-imide to 1,2-diazepine conversion on p. 598). Although none of the oxaziridine tautomer (311) was detectable by UV spectroscopy, the subsequent deoxygenation of (312) to acridine suggests the existence of a thermal equilibrium between (311) and (312) (79T1273). These dibenzo compounds (312) are the only fully unsaturated oxazepines yet isolated but the 2,3-benzoxazepin-l-one system (314) has recently been prepared by the reaction of benzonitrile oxide with the benzopyranone (313) (80JCS(Pl)846). 

Sulfoxides and sulfones can be prepared on cross-linked polystyrene by oxidation of thioethers. The most commonly used reagent for this purpose is MCPBA in DCM [8,12,32,57,80-82] or dioxane [50,83] (Table 8.6), but other oxidants such as H2O2 in acetic acid [34], oxone (Entry 7, Table 8.6), or oxaziridines [84] have also been used. PEG-bound thioethers have been converted into sulfones by oxidation with MCPBA in DCM [52,54] or with Os04/NMO [85], The oxidation of thioethers to sulfoxides requires careful control of the reaction conditions to prevent the formation of sulfones. Sulfones have also been prepared by S-alkylation of polystyrene-bound sulfi-nates (Entries 8 and 9, Table 8.6), by a-alkylation of sulfones (BuLi, THF, alkyl halide [86]), and by addition of sulfinyl radicals to resin-bound alkenes or alkynes (Entry 11, Table 8.6). 

The permanganate ion oxidation of imines to nitrones is very much dependent on the reaction conditions. For the investigation of this dependency, reactions with benzylidene-r-butylamine, la, were carried out (equation 8). la was oxidized with m-chloroperbenzoic acid to give the corresponding oxaziridine 3a. As byproduct traces (<3%) of the nitrone 2a, amine 4a and benzaldehyde were formed. The permanganate ion and m-chloroperbenzoic acid may then oxidize the imine in two different ways. 

Acetalization of thiochroman-3-one gives a 1 1 diastereomeric mixture and subsequent oxidation with Davis reagent, W-(phenylsulfonyl)(3,3-dichlorocamphoryl)oxaziridine, yielded the sulfoxides each with a 4 1 enantioselectivity. Chiral chromatographic separation of the diastereomers preceded isolation of the major enantiomers. (3-Elimination and isomerization of the double bond then produced the individual thiochromene 1-oxide diastereomers. The generation of an a-sulfinyl carbanion effects the cleavage of one of the acetal C-O bonds with the protected diol released in a final ozonolysis step. The stereochemical results indicate that it is the C-O bond syn to the sulfoxide function that is cleaved (Scheme 63) <1996TA29>. 

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. 

Polyfluoro Af-aryl imines underwent oxidation with MCPBA to give polyfluoro A -aryloxaziridines < 1996JFC(77)175>. The MCPBA-mediated oxidation of 1,5-benzodiazepins 345 gave the corresponding oxaziridines 346 in good yields <1999PS(152)1, 2000HAC158>. 

SMP amides have been used in vanadium(II)-promoted pina-col cross-coupling and in asymmetric oxidations with chiral oxaziridines, The diastereoselective addition of thiocar-boxylic acids to 1 -(2-methylacryloy 1) SMP amides and the stere-ocontrolled addition of various organometallics to a-keto SMP amides have been studied. 

Oxaziridines oxidize sulfides to sulfoxides. Again, the A -sulfonyl derivatives seem to be the best oxidizing agents. They react with sulfides at room temperature to produce sulfoxides uncontaminated with sulfones chiral oxaziridines produce chiral sulfoxides. In addition, chiral thiolsulfinates can be obtained from... 

The method is also successful for carboxyhc esters , and A,A-disubstituted amides, and can be made enantioselective by the use of a chiral oxaziridine. Dimethyldioxirane also oxidizes ketones (through their enolate forms) to a-hydroxy ketones. Titanium enolates can be oxidized with tert-butyl hydroperoxide or with dimethyl dioxirane and hydrolyzed with aqueous ammonium fluoride to give the a-hydroxy ketone. Ketones are converted to the a-oxamino derivative (0=C CH2- 0=C CHONHPh) with excellent enantioselectivity using... 

The first total synthesis of (-)-fumiquinazoline A and B was accomplished by B.B. Snider and co-workers using a Buchwald-Hartwig Pd-catalyzed cyclization of an iodoindole carbamate to construct the imidazoindolone moiety. In order to set up the stereochemistry at the benzylic position of the indole fragment, the double bond was oxidized with the saccharine-derived Davis oxaziridine in the presence of methanol to give the major diastereomer in 65% yield. 

Davis oxaziridine oxidation Oxidation of electron-rich substrates (e.g. alkenes, enolates, enol ethers etc.) with oxaziridines. 130... 

The oxidative deamination of amines to ketones, via oxaziridines, was reported as a model for the process found in oxidative deamination of a-amino-acids to pyruvic acids in biochemical systems." The primary amine, such as (58) or (59) with pyridine-2-carboxaldehyde, was converted into the imine (60) which was oxidized with m-chloroperbenzoic acid to the oxaziridine (61). Ring opening of (61) was effected with KOH in MeOH or in DMF (Scheme 8). Acetone was added to trap regenerated pyridine-2-carboxaldehyde. When other bases were used a competing reaction resulting in (62) occurred. 

Triethoxy-l,2A5-oxaphospholene (112) reacts at room temperature with 2-(p-tolyl)-3-phenyl-oxaziridine (63d) to give a /Miydroxy-y-ketophosphate (113) in 82% yield (Equation (26)) (91TL5313). It seems likely that an oxirane intermediate is initially formed which rearranges on work-up to (113). Asymmetric oxidation with (+ )-[(8,8-dichlorocamphoryl)sulfonyl]oxaziridine (74) gave (113) in 49% ee and 88% isolated yield. The absolute configuration of (113) was not established. 

The potassium enolate of camphor (130) is oxidized with oxaziridine (63a) at — 78 °C to afford a-hydroxyketone (131) in 85% yield (Equation (29)) <84JOC324i>. As mentioned earlier lower yields were observed for the lithium enolate because of the imino-aldol side-reaction. The exclusive formation of the endo product is consistent with attack of the oxaziridine from the sterically least-hindered face of the enolate and is a general phenomena for these reagents. 

The synthesis of the 4 -spiroannulated ribonucleoside was aceomplished by elimination of the 2 -phenylthio group of compound 132 via a controlled oxidation with Davis oxaziridine reagent. 

Mukaiyama and coworkers [1378] have performed such oxidations with molecular oxygen in the presence of pivaldehyde under catalysis with related salen 3.70 Mn(lH) complexes however, lower enantioselectivities were obtained. The use of various manganese or iron porphyrins as catalysts also gives lower enantioselectivities [971, 1379, 1379a], as do the oxidations with chiral oxaziridines in stoichiometric amounts [741],... 

Davis and coworkers [506, 744] performed the asymmetric oxidation of pro-chiral sulfides with chiral oxaziridines, and reagents bearing the bomane skeleton 2.82 or 2.83 (X = Cl) were the most efficient. The chiral oxaziridine oxidations are... 

Oxidative desulfonylotion a-diketones.1 The potassium enolatc of an a-sulfonyl ketone on oxidation with a typical oxaziridine of this type, 2-[(/>-chlorophenyl)sulfonyl]-... 

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