Oxaziridines

Abstract

N-Sulfonyl oxaziridines 1 have recently been used in the activation of C(sp3)H bonds in an intramolecular aminohydroxylation reaction catalyzed by copper(II) salts. Surprisingly, rather than donation an oxygen atom, a new C-N bond is formed in a highly regioselective manner. The proposed mechanism involves the abstraction of the proton in the δ-position leading to the formation of a six-membered transition state. (B) Dynamic Kinetic Asymmetric Hydroxylation: In the presence of a chiral nickel(II) complex, oxaziridine 2 could perform the α-hydroxylation of racemic malonates. The attack of 2 occurs preferentially on the si face of the malonate, affording the products in excellent enantioselectivities and yields. This methodology was extended to the synthesis of (R)-bicalutamide, an important anti-androgen drug used in the treatment of prostate cancer. (C) [3+2] Cycloaddition: Oxaziridines easily undergo [3+2] cycloaddition with imines, nitriles, alkenes, and alkynes.5 Recently, this transformation catalyzed by chiral N-heterocyclic carbenes was developed with ketenes and oxaziridine 3, affording oxazolin-4-ones in moderate to good yields and excellent enantioselectivities. (D) Oxidation of C-H Bonds: A copper(I)-catalyzed intramolecular oxidation of C-H bonds was developed starting from the oxaziridine 4 to selectively give the corresponding allylic alcohol in moderate to good yields. The proposed mechanism involves the formation of a copper-bound radical anion arising from a single electron transfer, followed by hydrogen atom abstraction. (E) Asymmetric Oxyamination: Chiral iron(II) complexes have been showed to catalyze reactions between alkenes and N-nosyl oxaziridines 5, affording the corresponding substituted oxazolidines with moderate to good yields and high enantiomeric excesses. The cis selectivity of this transformation is explained by a kinetic resolution in which only one of the enantiomers of 5 participates in the oxyamination. As a consequence, 2.5 equivalents of 5 are necessary for high yields. (F) C-H Ethoxycarbonylation: Oxaziridine 6 showed unprecedented reactivity and has been used to transfer an ethoxycarbonyl group to substituted 2-phenylpyridines in moderate yields. The proposed mechanism of this reaction, catalyzed by a palladium(II) complex, involves activation of the ortho C-H bond of the phenyl moiety, followed by oxidative insertion of the metal into the N-O bond of 6, forming an intermediate palladium( IV) species. C-C bond cleavage of 6 followed by reductive elimination leads to the formation of the ethoxycarbonylated product 7 and amide 8 as the by-product. This transformation has been subsequently applied to aryl urea derivatives with moderate yields. © Georg Thieme Verlag Stuttgart New York.