Five-membered heterocycles with more than one heteroatom

Section 3.1 is a brief overview Section 3.2 deals with six-membered heterocycles, including those with more than one heteroatom in the ring Section 3.3 deals with five-membered heterocycles with one heteroatom Section 3.4 deals with five-membered heterocycles with more than one heteroatom in the ring Section 3.5 covers small (three- and four-membered) and large (>six) ring heterocycles. 

Table 34 Operating Conditions for GLC Separation of Five-membered Heterocycles with More Than One Heteroatom" ...

III. Dewar Isomers of Five-Membered Heterocycles with More than One Heteroatom... 

Space restrictions mean that the reactivity of multiheteroatom systems or fused systems where both rings are heterocyclic cannot be covered in this section - the reader is referred to the relevant CHEC volumes. Space again dictates that the chemistries of oxygen- and sulfur-containing six-membered heterocycles, and the chemistry of monocyclic six-membered heterocycles with more than one heteroatom, are only briefly indicated alongside the description of pyridine/quinoline/isoquinoline chemistry, but especially where these are not shown by the pyridine prototypes, but again the reader should study the CHEC volumes for a full discussion. The inclusion of an extra heteroatom in a six-membered system exaggerates the effect of the first and so often it is possible to predict properties by extrapolation however, the same is not true for the five-membered systems, so these heterocycles with more than one heteroatom are considered in detail and separately. 

This chapter reviews the systems where account is taken of the size of the central carbocyclic ring, the relative orientation of the fused five-membered heterocyclic rings, the types of heteroatoms, their number, and, in rings with more than one heteroatom, their relative situations. 

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