Saturated Rings with Two or More P Atoms

Derivatives of all the parent ring systems indicated in Tables 6.20 and 6.21 have been prepared. The best-known group of compounds are the 1 4 diphosphorinanes, which can be obtained by reacting certain diphosphines with phenyllithium and heating with methylene chloride (6.839). These 

Saturated Rings Based on Carbon and Three or Four P Atoms 

Phosphonium derivatives may be made directly by reacting ethylene dibromide with an appropriate phosphine. Either cis or trans isomers may be obtained, depending upon whether the starting material is a meso or a racemic phosphine (6.840, 6.841). 

The cis and trani -chair forms of 1 4 diphenyldiphosphorinane probably correspond to 

Diphosphiranes can be obtained from potassium polyphosphides (6.843, 6.845) or diphosphines and carbenes (6.844). Some three-membered rings will dimerise or form spiro compounds (6.845) [27-31]. 

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