Spirocyclic oxaziridines, synthesis

In another example, the cumulative effect of equatorial attack in prochiral cyclohex-anoneimines with diastereoselectivity induced by a chiral nitrogen substituent allowed the synthesis of spirocyclic oxaziridines with a high induction of axial dissymmetry. The major oxaziridine isomer results from both the favored equatorial attack and oxidation anti to the chiral nitrogen substituent (equation 45)204... 

In all the following examples, the targeted double bonds were activated by suitable substituents to increase the efficacy of the desired cyclization mode. For the total synthesis of acutumine (26), an activated a,p-unsaturated ketone 27 was chosen as precursor (Scheme 10) [74, 75], Aryl radical additions to this type of alkenes are known to proceed about ten times faster than to comparable allylic alcohols. In a radical-polar crossover reaction, the spirocyclic product 28 was obtained in the presence of triethylaluminum as promoter and an oxaziridine as hydroxylating agent. The fact that even the efficient hydrogen donor tetrahydrofuran could be used as solvent nicely demonstrates the high efficacy of the cyclization step. 

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