Rings containing Two Heteroatoms

Rearrangement. The considerable number of reports associated with the photochemically induced rearrangement of nitrones, oximes, and oxaziridines reflects the continuing interest in this area. The ratio of caprolactam to hexanoamide formed from irradiation of the oxaziridine (659 R = H) was different from that obtained by irradiation of cyclohexanone oxime. Photo- 

Whereas the photochemically induced reactions of pyridine JV-oxides can yield a wide range of products, the substitution of phenyl groups results in the isolation of 1,3-oxazepines (663) and (664), formed via the isomeric oxaziridines (661) and (662), The irradiation of polychlorinated p3rridine 

7V-oxide (665) appears to proceed via a 2-chIoro-oxaziridine intermediate to give an isocyanate (666) this is a rather unusual type of product from photorearrangement of a monocyclic aromatic AT-oxide.  

The isolation of N-substituted pyrroles (669) after photolysis of pyridazine AT-oxides with primary amines in dichloromethane solvent has been inter- 

Among the bicyclic AT-oxides which have been irradiated are the indole JV-oxides (670) and the isoquinoline A -oxides (671). The proportion of each of the products isolated from photoisomerization of (670) was dependent on the nature, position, and number of substituents. The photoisomerization of isoquinoline iV-oxides has been investigated using a range of solvents 

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Details of bond lengths and bond angles for all the X-ray structures of heterocyclic compounds through 1970 are listed in Physical Methods in Heterocyclic Chemistry , volume 5. This compilation contains many examples for five-membered rings containing two heteroatoms, particularly pyrazoles, imidazoles, Isoxazoles, oxazoles, isothlazoles, thlazoles, 1,2-dlthloles and 1,3-dlthloles. Further examples of more recent measurements on these heterocyclic compounds can be found in the monograph chapters. 

As explained in Chapter 3.2, the reactivity of six-membered rings containing two heteroatoms bears the same relationship to six-membered rings containing one heteroatom as do the latter to benzene. Hence many of the methods listed for the preparation of pyridines by substituent introduction and modification in Table 1 of Section 4.2.4.1 are also applicable to the preparation of analogous azines. 

Only few examples were reported related to these ring systems. Moreover, only those fused with three-membered ring mainly containing one heteroatom oxygen were reported. No examples can be found with a four-membered ring containing two heteroatoms. 

Many different rings containing two heteroatoms are known references to many more of them than can be described in detail in the following sections, are given in Table 1. 

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. 

Heteroatom Translocation in Fused Heterocyclic Ring Systems Rings Containing Two Heteroatoms... 

Rings containing Two Heteroatoms.—Direct Insertion. Peroxy-acid oxidation of the cyclic imine (262) yielded the corresponding oxaziridine (263), which rearranged when irradiated with u.v. light (2537 A) to iV-acetylpyrroIidine (264). A study of the proportion of cis- and /rawf-oxaziridines (266) and... 

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