Oxaziridines, 10-camphorsulfonic acid

Camphorylsulfonyl)oxaziridine described here is prepared in four steps from inexpensive (1S)-(+)- or (1R)-(+)-10-camphorsulfonic acid in 77% overall yield.7... 

Oxaziridines. Davis has developed the use of chiral 2-sulfonyloxaziridines derived from camphorsulfonic acid as chiral auxiliaries in the asymmetric oxidation reactions. Although other oxaziridines may be preferable, the camphor-derived oxaziridines can be used for the oxidation of sulfides and disulfides to sulfoxides and thiosulfinates as well as for the epoxidation of alkenes. On the other hand, the camphoryloxaziridines are the preferred reagents for hydroxylation of lithium enolates of esters, amides, and ketones, as utilized in the synthesis of kjellmanianone (eq 17). ... 

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. " ... 

Asymmetric hydroxylation of etiolates. Davis and Chen1 have reviewed this reaction using in particular (R,R)- and (S,S)-2-phenylsulfonyl)-3-phcnyloxaziridene (1) and (camphorylsulfonyl)oxaziridine (2). Of these reagents, 1 and ( + )- and (—)-2, derived from (lR)-lO-camphorsulfonic acid, provide highest enantioselectivity and in addition are easy to prepare. They are effective for hydroxylatation of ketones, esters, /2-keto esters, amides, lactones, and lactams. 

In 1988 Davis reported the synthesis and properties of (camphorylsulfonyl) oxaziridine, achieving a 77% yield, starting from the inexpensive camphorsulfonic acid. The oxaziridine reported was the first optically active A -sulfonyloxaziridine to be obtained as a single isomer on oxidation of the sulfonimine (Scheme 1.52) [116]. 

In further developments of the method, Davis has crafted a collection of chiral (camphorylsulfonyl)-derived oxaziridines 218-220 (Equation 21). These are readily available from either enantiomer of camphorsulfonic acid, and have proven efficient for a range of enantioselective cx-hydroxyla-tion reactions [23-25, 121]. /i-Keto ester 221 was thus oxidized by oxaziridine 220 to afford tertiary alcohol 222, a key intermediate for the construction of anthracyclinone antibiotics, in >95% ee [122]. 

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