Hydroxylation Camphorylsulfonyl oxaziridines

Chiral Davis oxaziridines allow the oxidation of phosphonates to a-hydroxy-phosphonates in good ee with apparently wide generality and with a sense of induction that is well controlled by the chirality of the reagent used.109 mCPBA oxidation of a bi-cyclic e do-camphorylsulfonylimine surprisingly resulted in an exo-camphorylsulfonyl-oxaziridine, whereas all other camphorylsulfonylimines resulted only in endo-oxaziiidines.110 Asymmetric oxidation of sulfides to sulfoxides and the a-hydroxylation of enolates were predicted by models in which steric interactions are minimized. 

ASYMMETRIC HYDROXYLATION OF TETRALONE AND PROPIOPHENONE ENOLATES USING (CAMPHORYLSULFONYL)OXAZIRIDINES 1 AND 2... 

The product stereochemistry for reagent-induced hydroxylations are under the control of a noncovalently bound chiral reagent which avoids the introduction and eventual removal of the chiral auxiliary as discussed in the preceding section. This method requires an enantiopure N-sulfonyloxaziridine of which (camphorylsulfonyl)oxaziridines (74), (114), and (158) have proven the most useful <92CRV919>. Both epimeric a-hydroxy carbonyl compounds are readily available because the antipodal oxidant controls the absolute stereochemistry of the product (Scheme 25). Oxaziridines (74) and (114) are commercially available. 

Acyclic a-hydroxy ketones of high enantiomeric purity can be prepared by choice of the appropriate conditions and (camphorylsulfonyl)oxaziridine reagent, for example, treatment of deoxy-benzoin (159a) with NaHMDS followed by (+)-(114) at —78°C affords (+ )-(S)-benzoin (160) in 95% ee and 88% isolated yield (Scheme 29) <89JOC202i, 90JA6679). Similarly, (—)-(S)-2-hydroxy-1 -phenyl-1-propanone (161) is produced in 95% ee by hydroxylation of the lithium enolate of... 

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. 

---