Phosphorus is essential for many reagents in organic synthesis, for ligands of late-transition metals and for phosphonoand phosphanylamino acids, the latter being important isosteres of amino acids. Similar to the Michaelis-Arbuzov and the Michaelis-Becker reaction the phospha-Michael addition, i. e. the addition of a phosphorus nucleophile to an acceptor-substituted alkene or alkyne, certainly represents one of the most versatile and powerful tools for the formation of P-C bonds since many different electrophiles and P nu-