Phosphinidene Oxides and Related Species

The reaction of the relatively unstable phosphine oxide (20) with dimethyl acetylenedicarboxylate gives dimethyl naphthalene-2,3-dicarboxylate. This 

A similar electrocyclic reaction of the oxide with oe-diketones is well documented. This reaction, utilizing benzil, has in fact been recently used to trap phosphinidene oxides and sulphides generated by the action of such metals as magnesium and zinc on phosphonic and phosphonothioic dichlorides. 

The adducts, e.g. (24), react with magnesium in the presence of magnesium 

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