Oxaziridines derivatives

According to a kinetic study which included (56), (56a) and some oxaziridines derived from aliphatic aldehydes, hydrolysis follows exactly first order kinetics in 4M HCIO4. Proton catalysis was observed, and there is a linear correlation with Hammett s Ho function. Since only protonated molecules are hydrolyzed, basicities of oxaziridines ranging from pii A = +0.13 to -1.81 were found from the acidity rate profile. Hydrolysis rates were 1.49X 10 min for (56) and 43.4x 10 min for (56a) (7UCS(B)778). O-Protonation is assumed to occur, followed by polar C—O bond cleavage. The question of the place of protonation is independent of the predominant IV-protonation observed spectroscopically under equilibrium conditions all protonated species are thermodynamically equivalent. 

Five configurationally known oxaziridines derived from imines of PEA display nonequivalence behavior that is in general accord with this model, though occasional unpredictable deviations attributed to internal magnetic anisotropic effects were noted (41). 

Direct conversion of diol 395 to cytisine 31a was accomplished by a one-pot procedure. Oxidative cleavage to give the dicarboxylic acid, followed by treatment with aqueous ammonia and catalytic reduction provided racemic cytisine 31a in good yield <20000L4205>. Photolysis in benzene at 254 nm of the nitrone 396 afforded smooth rearrangement to 17-oxosparteine 195 likely through the intermediacy of an oxaziridine derivative (Scheme 80) <2002OL2577>. 

Until quite recently the isolation of optically active seienoxides has been limited to those contained in steroids (isolated as diastereoisomeis). < The difficulty in obtaining these compounds was attributed to the racemization through the achiral hydrated intermediates. Simple optically active sel enoxides (S-11% ee) were first prepared by kinetic resolution. Direct oxidation of selenides to seienoxides was first reported using optically active oxaziridine derivatives under anhydrous conditions, but the extent of the asymmetric induction was somewhat unsatisfactory with methyl phenyl selenide as substrate (8-9% Recently much improved enantiomeric excesses (45-73%) were achieved with new oxaziridine reagents such as (70). An attempt at the asymmetric oxidation of more bulky selenides was independently carried out using Bu OCl in the presence of (-)-2-octanol (equation 55), but resulted in unsatisfactory enantioselectivities (ee 1%). Much better results were obtained by the oxidation of p-oxyalkyl aryl selenides (ee 18-40% equation 56) 27 gjyj selenides (ee 1-28%) using... 

The oxidation of imines continues to be the most common method for the preparation of oxaziridines. Page et al. recently described the preparation of enantiomerically pure chiral NH-oxaziridines derived from camphor and fenchone <2000JOC4204>. Treatment of camphor imine 303 with 1 equiv of MCPBA at —30 to —40°C in dichloromethane gave NH-oxaziridine 50 in 94% yield. The fenchone-derived oxaziridine 305 was obtained similarly... 

Preparative Methods the enantiopure (+)- and (—)-(cam-phorylsulfonyl)oxaziridines (1) and [(8,8-dichlorocam-phor)sulfonyl]oxaziridines (2) are commercially available. They can also be prepared on a large scale via the oxidation of corresponding camphorsulfonimines with buffered Potassium Monoperoxysulfate (Oxone) or buffered peracetic acid. Since oxidation takes place from the endo face of the C=N double bond, only a single oxaziridine isomer is obtained. The precursor camphorsulfonimines can be prepared in 3 steps (>80% yield) from inexpensive (+)- and —yiO-Camphorsulfonic Acids. A variety of (camphorylsul-fonyl)oxaziridine derivatives such as (2)-(4) are also readily available via the functionalization of the camphorsulfonimines followed by oxidation. " ... 

By choice of the appropriate reaction conditions and (cam-phorylsulfonyl)oxaziridine derivative, acyclic a-hydroxy ketones... 

Oxaziridines with no substituent on the ring nitrogen may be stabilized as the fV-acyl derivatives. Indeed, the presence of an acylating agent, that is, benzoyl chloride, is necessary for the trapping of such oxaziridines derived from aliphatic aldehydes (Table 2). ... 

Brief reports have been made about two unusual oxaziridine derivatives. A quaternary oxaziridinium salt apparently reacts with nucleophiles at oxygen in any case, this salt suffered deoxygenation by some process. Finally, the per-fluorinated oxaziridine 59, undergoes attack exclusively at nitrogen to produce amide derivatives ... 

Pyrazine Al-oxides and 2,3-dihydropyrazines also rearrange photochem-ically into imidazoles. From 2,5-disubstituted pyrazine 1-oxides (73) two products, 2-acyl(or aroyl) 4-substituted imidazole (74) and 2,4-disubstituted imidazole (75), result. " " The reaction (Scheme 16) presumably takes place through two isomeric oxaziridine derivatives. 

The oxidation of imines derived from substituted cyclohexanones occurs predominantly from the equatorial direction. However, the product oxaziridines can undergo subsequent equilibration to favor a more stable conformation which places the bulkier nitrogen substituent in an equatorial conformation (Scheme 24). A particularly useful oxaziridine derived from camphor was formed exclusively via exo approach of the reagent (equation 42). ... 

Davis, F. A., Nadir, U. K., Kluger, E. W. 2-Arylsulfonyl-3-phenyloxaziridines a new class of stable oxaziridine derivatives. J. Chem. Soc.,... 

Wolfe, M. S., Dutia, D., Aube, J. Stereoselective Synthesis of Freidinger Lactams Using Oxaziridines Derived from Amino Acids. J. Org. Chem. 1997, 62, 654-663. 

An alternative to the base-catalyzed rearrangement of oxaziridines to ketones, discussed in Section 1.12.3.2.1, is the acid-catalyzed hydrolysis of oxaziridines derived from amines and acetone <75AJC2547>. Oxidation of C,A-diarylaldimines (Ar CH=N-Ar2) with sodium perborate in... 

The (camphorsulfonyl)oxaziridine derivatives, for example (74), generally give lower ees for the asymmetric oxidation of sulfides to sulfoxides than A-(phenylsulfonyl)(3,3-dichloro-camphoryl)oxaziridine (69) <88JA8477,88JCS(P1)1753,92JOC7274). 

The isomerization of oxaziridines derived from conanine, under basic or acidic conditions, has been studied. The hydrolysis of oxaziridines gave either a hydrox-ylamine and a carbonyl compound, or an amine (or ammonia) and two carbonyl compounds (Scheme 1). The first step in this hydrolysis was base- or acid-catalysed isomerization of oxaziridines to iminocarbinols or nitrones. 

The enantioselectivity for sulfide oxidation depends strictly on structural features of the ubstrates, and therefore, variations can be substantial. Oxaziridines derived from camphor, >uch as 56A and 56B" , give acceptable, and in some cases, superior results. The sultam precursor of 56B can also be used as a catalyst in combination with hydrogen peroxide in the presence of DBU. ... 

There are several reaction sequences that use a chiral auxiliary to produce chiral, nonracemic GABOB, but are rather di arate in their approaches. In one, cyclobuta-none 6.5553 reacted with R-phenethylamine to give an imine, and this was oxidized with m-chloroperoxybenzoic acid to give spiro-oxaziridine derivative 6.59.54 Photolysis of 6.59 led to a mixture of lactams 6.60 and 6.61. Separation of these... 

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