Oxaziridines spirocyclic

In a related reaction, treatment of spirocyclic oxaziridines with MnCl(TPP), where TPP = m o-tetraphenylporphyrinate (2 — ), or photolysis leads to a lactam. 

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. 

More recently, Usuki etal. studied, using NMR techniques, the conformation of spirocyclic oxaziridines 3 derived from substituted cyclohexanones <1995JOC8028>. Depending on substitution and on the stereochemistry, these compounds exhibit a substantial upfield shift of the cyclohexyl methylene or methane protons with a 1,3-diaxial relationship to the oxaziridine N-substituent. This effect is ascribed to a conformation that places an aromatic group over the plane of the cyclohexane ring. This conformation has also been observed in the solid state by X-ray crystallography and is further supported by molecular mechanics calculations. 

The same research group also explored a transannular nitrone-olefin [3 + 2] dipolar cycloaddition approach to the spirocyclic core of pinnaic acid, an inhibitor of phospholipase A2 (CPLA2) that was isolated from the Okinawan bivalve Pinna muricata The nitrone 34 was prepared by acidic hydrolysis of the ethylene ketal and the oxaziridine of 32 to generate transiently the keto... 

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