With 4 or more hetero

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... 

Hetero-Diels-Alder reactions have also been conducted with aldehydes (Scheme 10) <2003JOC2803>. The reaction is very sensitive to the substitution pattern on the aldehyde and on the phosphole. Reaction of 1-phenyl-3,4-dimethylphosphole with benzaldehyde or its ra-derivatives afforded the corresponding adducts 55 in quantitative yields (Scheme 10). An increase in the steric demands of the aldehydes or of the phosphole results in a dramatic decrease in the yield. For example, with 2,4,6-trimethylbenzaldehyde, no reaction takes place and only 30% conversion is observed with 2,6-dimethoxybenzaldehyde. Similarly, using the more sterically hindered 1-phenyl-2,3,4,5-tetraethylphosphole, no cycloadduct formation is observed with benzaldehyde. Note that with decanal, the yield reaches only 40%. The reaction affords a mixture of endo- and o o-phosphinites 55, the major component being the OT o-derivative. With /ra t-cinnamaldehyde, a mixture of adducts 56 and 57 was obtained (Scheme 10), showing that the 1-phosphadiene can react either via the C=0 or via the C=C moieties of a,/3-unsaturated aldehydes <2003JOC2803>. 

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. 

---