Ring Systems Containing Three-coordinate Chalcogen

3 Ring Systems Containing Three-coordinate Chalcogen 

Tellurium chemistry is often significantly different in comparison with selenium chemistry owing to the larger size and metallic character of tellurium (Section 1.1). As an illustration, the cyclocondensation of 

The treatment of 13.19 (R = Ph) with secondary amines produces the corresponding dialkylamino derivatives 13.20. The electron-donating 

The ring system 13.18 (R = Cl) is a source of hybrid PN/SN polymers containing three-coordinate sulfur via a ring-opening polymerization process. This polymerization occurs upon mild thermolysis at 90°C (Section 14.4).  

Eight-membered rings of the type (R2PN)2(NSR)2 (R = alkyl, aryl) can be synthesized in two ways. The S,S, -dimethyl derivative 13.25 is 

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