2-Sulfonyl oxaziridine

Davis et al.111 developed another method for reagent-controlled asymmetric oxidation of enolates to a-hydroxy carbonyl compounds using (+)-camphor-sulfonyl oxaziridine (147) as the oxidant. This method afforded synthetically useful ee (60-95%) for most carbonyl compounds such as acyclic keto esters, amides, and a-oxo ester enolates (Table 4-20). 

S,8aR )-[(8,8-Dimethoxycamphoryl)sulfonyl]oxaziridine 4H-4a,7-Methanooxazirino[3,2-i](2,1]benzisothiazole, tetrahydro-8,8-dimethoxy-9,9-dimethyl-,... 

R,8aR )-[(8,8-DIMETHOXY-CAMPHORYL)SULFONYL]OXAZIRIDINE AND (+)-(2R,8aR )-[(8l8-DICHLORO-CAMPHORYL)SULFONYL]-OXAZIRIDINE... 

Dihydro-2-hydroxy-2-methyl-l(2//)-naphthalenone (7), a model for many natural products, is obtained in >95% ee via oxidation of the sodium enolate of 3,4-dihydro-2-methyl-1 (2f/)-naphthalenone (5) with ( + )-[(8,8-dichlorocamphoi)sulfonyl]oxaziridine (6)88. This material was obtained in less than 16% ee using (j-)-(camphorsulfonyl)oxaziridine 26. 

Tabic 9. Enantioselective x-Oxygcnation of Prostereogcnic Enolates with Enantiomerically Pure rV-Sulfonyl-oxaziridines ... 

As discussed previously, treatment of thiolates generated from thiols and MeLi with sterically hindered A -sulfonyl-oxaziridine 116 gave the corresponding sulfenate intermediates which were alkylated to afford sulfoxides 118 (Equation 4) <1997JOC8626, 1999PS(153)381, 2004JOC6916>. Oxidation of thiolates generated from aryl thiols... 

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. " ... 

Hydroxylation of the sodium enolate of lactone (16) with (+)-( ) gives a-hydroxy lactone in 77% ee (eq 17). Kinetic resolution and asymmetric hydroxylation with (camphor-sulfonyl)oxaziridines has been applied to the synthesis of enantiomerically enriched a-hydroxy carbonyl compounds having multiple stereocenters, which may otherwise be difficult to prepare. Thus hydroxylation of the enolate of racemic 3-methylvalerolactone with substoichiometric amounts of (—)-(l) affords (25,3/J)-verrucarinolactone in 60% ee (eq 18) which on recrystallization is obtained enantiomerically pure. ... 

A reaction model for the S-oxidation of 3-amino-substituted isothiazoles with (-f)- or (—)-((8,8-dichlorocamphor-yl)sulfonyl)oxaziridines (see Section 4.05.55, compound 70) was obtained by B3LYP/6-31G(d,p),S(3df) calculations. Transition states relative energies are in concordance with the experimental reaction outcome and the analysis of the geometrical parameters allows a description of the reasons governing the observed enantioselectivity <2006UP1>. 

The reported synthesis and properties of an oxaziridine by the thermal isomerization of the C7-trityl ester of 3-ac/nitrocamphor bears reinvestigation, particularly in view of the recent report that irradiation of nitronate salts yields hydrox-amic acids but that oxaziridine intermediates could not be detected.) A -Sulfonyl-oxaziridines also rearrange, thermally to nitrones that further decompose to products, but photochemically they yield amides. ... 

For the preparation of (R)-C-6 sulfoxytetrahydromevinic acid lactone (73), a precursor of a potent HMG-CoA reductase inhibitor, optimal results were obtained with (—)-[(8,8-dichloro-camphoryl)sulfonyl]oxaziridine (74) <94TL346l>. 

Thiones (Ar2C=S) are oxidized to thiones 5-oxides (Ar2C=S=0) by A-sulfonyloxaziridine (78) (Scheme 14) <87JCS(Pl)l 113). The oxidation is fast and quantitative, exhibiting second-order kinetics. Thiocamphor 5-oxide (79) and thiofenchone 5-oxide (80) were prepared in 91% and 76% yield, respectively by oxidation of the corresponding thiones with (78b). Earlier attempts to prepare these materials with other oxidants resulted in low yields and the products were difficult to purify. Phosphorothionates (R2P(S)OPh) are oxidized to phosphates (R2P(0)0Ph) by A-sulfonyl-oxaziridines <88MI 112-01). 

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. 

R) -( + )-2-Acetyl-5,8-dimethoxy-l,2,3,4-tetrahydro-2-naphthol (173) is a key intermediate in the asymmetric synthesis of anthracycline antitumor agents demethoxyadriamycin (174 X = Y = OH) and 4-demethoxydaunomycin (174 X = Y = H) <94JOCli84>. The crucial step in a highly efficient asymmetric synthesis of (173) involves the enantioselective hydroxylation (>95% ee) of the potassium enolate of (171) with (—)-[(8,8-dimethoxycamphoryl)sulfonyl]-oxaziridine (158) to afford (172). Conversion to (173) was accomplished in three steps in 50% overall yield from (171) without racemization (Scheme 32). 

Hydroxylation of steroids and amino acids Third Successful Method Hydroxylation with A-Sulfonyl Oxaziridines... 

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