Systems with Two Heteroatoms

Syntheses Using 1,3-Bielectrophiles 4.03.3.5.1 Ring Systems with Two Heteroatoms... 

A fairly large number of protocols have been successfully applied to the synthesis of compounds with heterocyclic rings fused (5 5 5). Synthetic methods of this particular class of heterocycles reported in the literature vary widely. These heterocycles have been classified as shown in Tables 1-7 depending on structural pattern along with the number of heteroatoms present. Thus, the discussion starts with the synthesis of linearly fused (5 5 5) systems with two heteroatoms presented in Table 1, followed by Tables 2-7, respectively. 

D. Systems with Two Heteroatoms 1. One Heteroatom in Each Ring... 

The discovery of metallic conductivity in organic solids stands as a major scientific discovery of the twentieth century <1995S215>. From a total of several organic 7t-donors described in the literature, five (438a-c, 439, and 440) are four-heteroatom bicyclic 5 6 systems with two heteroatoms in each moiety. 

This chapter is designed to build on the excellent previous two chapters in CHEC(1984) and CHEC-II(1996) on bicyclic 6-6 fused ring systems with two heteroatoms <1996CHEC-II(7)527, 1984CHEC(2)581>. Therefore, this contribution has been written in the same style and format as the previous editions, in order to make the information as accessible to the reader as possible, and also to keep the continuity between the editions. 

The present chapter builds on the review of diazinodiazine chemistry in CHEC(1984) < 1984CHEC(3)329> and the expanded review of bicyclic 6-6 systems with two heteroatoms per ring, which appeared in CHEC-II(1996) < 1996CHEC-II(7)737>. The scope of the present review is essentially that of the corresponding chapter in CHEC-II(1996). 

As a t rpical example. Scheme 3 shows the possible formation of five-membered ring systems with two heteroatoms in the aceto-in-ammonium sulfide model system (Barone, R., Universite d Aix-Marseille III, unpublished results, 1986). Similar predictions can be made for the formation of substituted pyrrolidones and for additional five- and six-membered rings. 

The literature contains examples of virtually all heterocyclic systems with two heteroatoms of nitrogen, sulfur and oxygen. However, in some cases simple derivatives of the parent... 

Five-membered systems with two heteroatoms 3.3.1. Imidazoles, pyrazoles and benzimidazoles... 

Figure 19 13C chemical shifts for systems with two heteroatoms. 

A. 6-Ring Systems with Two Heteroatoms 6. Monocyclic (or Annulated) 6-Ring Systems with Two A -Atoms... 

---