Nitrone-oxaziridine photocyclization

Optically active oxaziridines are useful reagents for the enantioselective oxidation of olefins 37 39). The following three preparative methods to make this reagent available have been reported enantioselective oxidation of an imine by (-)-peroxycam-phoric acid 37,38), photocyclization of a nitrone which has a chiral substituent39), and photocyclization of a nitrone in an optically active solvent 39). However, an... 

Nitrones in general undergo a four-electron photocyclization to afford the corresponding oxaziridines. The process is stereospecific,47 proceeds via the excited singlet state, and is in certain instances photochemically reversible.48 Theoretical studies support this proposed pathway49 The nitrones 52, on direct irradiation, afford the oxaziridines 53, which on further irradiation are converted into the isomeric amides 54.so In contrast, triplet... 

Keywords nitrone, photocyclization, inclusion complex, oxaziridine... 

Scheme 6 Enantioselective photocyclization of nitrones to oxaziridines in their host-guest crystals.

Although optically active oxaziridines are useful reagents for enantioselective oxidation of olefins, those of more than 30% ee have not been obtained by any enantioselective synthetic method. Very efficient enantioselective photocyclization of nitrones (27) in the complex with 18 into oxaziridines (28) of high optical purity was found (Table II) [20]. Enantioselectivity in the formation of 28b, 28d, and 28e... 

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