With 4 or more hetero atoms

Numbering of the ring starts with the hetero atom and proceeds around the ring so as to give substituents (or other hetero atoms) the lowest numbered positions. When two or more different hetero atoms are present, oxygen takes precedence over sulfur and sulfur over nitrogen for the number one position. Examples follow to illustrate both the heterocycloalkane and the Hantzsch-Widman systems. Trivial names also are included. 

Hetero site reactivity The simplest difference between a cluster and a mononuclear complex is that the cluster can do two or more things where a mononuclear complex can do one. Simple as it is, this difference has hardly ever been verified other than in multiple ligand substitutions. One verification is hetero site reactivity, i.e., different modes of reaction at different sites on one and the same cluster. Two examples of this appear to exist. Different phosphine ligands substitute CO on different metal atoms in H2FeRu3(CO),3 depending on their size and basicity (210), and Ru2Co2 (CO), 3 reacts with H2 at the ruthenium atoms (cf. Section IV, A) and... 

The situation is much more difficult in the case of partially filled valence band(s). Since in this case we cannot easily obtain localized orbitals (only if a commensurable part, e.g. 1/2, 1/4, etc. part of the band is filled which is usually not the case), one usually falls back to homogeneous or inhomogeneous gas methods which are rather questionable in the case of organic polymers with comparatively small densities and large density gradients (if there are hetero atoms). 

We can now look at more specific examples, and see how the principles above can lead to the aromatic heterocycles. In the first of the two broad categories, where only C-hetero atom bonds are needed, and for the synthesis of five-membered heterocycles, precursors with two carbonyl groups related 1,4 are required 1,4-diketones, for example react with ammonia or primary amines to give 2,5-disubstituted pyrroles. 

Our laboratory at Osaka University began studies on catalysis for direct reactions of alkyl halides with tinfoil in 1959. The studies revealed that alcohols and amines show high catalytic activity in these reactions. This catalytic activity is considered to be caused by the coordination of lone electron pair of hetero atoms such as oxygen and nitrogen to a tin atom. That is, metal activation of the tin atom is cansed by these compounds. Two or more reaction products, R SnX4 (R alkyl, X halogen atom n=0, 1, 2, 3, or 4), are always obtained. 

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