APPLICATIONS OF THREE-MEMBERED RINGS WITH TWO HETEROATOMS

5 APPLICATIONS OF THREE-MEMBERED RINGS WITH TWO HETEROATOMS 

Since syntheses of three-membered rings with two heteroatoms almost always proceed under mild conditions with good yields and from simple starting materials, they are useful intermediates in synthesis. The easy formation of N—O and N—N bonds offers synthetic potentialities. Furthermore, the three-membered ring may serve as a protecting group during additional operations of substitution. 

Even the trivial decomposition of oxaziridines may have some importance. In the oxidation of s-alkylamines to ketones conversion to the Schiff base of 2-pyridinealdehyde was proposed, followed by peracid oxidation to the oxaziridine (295). Decomposition by alkali yields the ketone added excess acetone suppresses condensation of pyridinealdehyde with dialkyl ketone (75AJC2547). 

By working in anhydrous solvents even aldimines like (296) could be prepared (79TL3201). 

One-electron cleavage of the oxaziridine ring is especially useful in the case of the oxaziridine (114), easily obtained from cyclohexanone, methylamine and hypochlorite. The radical formed from (114) by uptake of one electron from the iron(II) ion can be trapped, for example, by acrylonitrile to form products derived from radical (297) (68TL5609). 

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The first authentic three-membered rings with two heteroatoms were synthesized only after 1950. Because they became available at once by simple and generally applicable procedures, oxaziridines (1) (64HC(19-1)624,68HOU(10-4)449), diaziridines (2) (67HOU(10-2)7l) and diazirines (3) (68HOU(10-4)895) are now extensive, well investigated classes of compound. 

In this section we will consider the asymmetric epoxidation of unactivated olefins. Three membered-rings containing two heteroatoms (dioxiranes, oxazidines, and oxaziridinium salts) are usually employed for the epoxidation of this type of olefin. Especially goods results in the field of the asymmetric epoxidation have been obtained with chiral ketone catalysis and iminium salts. In this section, the landmarks of these two significant areas and some applications of these methodologies will be presented. 

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