Synthesis, structure and reactivity of acyclic and heterocyclic α-phosphino amino acids

Abstract

Acyclic α-phosphino amino acids can be conveniently synthesized by a one-pot three-component reaction, but are limited to N-secondary derivatives with N-alkyl, aryl or heterocyclic substituents, provided these are not too bulky or electron-withdrawing. Phosphino-bis(amino acids), stable with a P-aryl group, undergo spontaneous lactamization in the case of a P-alkyl group to five-membered heterocyclic α-P amino acids. Closely related compounds without C(O)-group, by the diagonal relationship to proline named “(phenyl)phosphaprolines”, were obtained by cyclocondensation of 2-aminoethylphosphines with glyoxylic or α-keto carboxylic acids, in this case also furnishing N-tertiary derivatives. N-Tertiary 1,3-benzazaphospholine-2-carboxylic acids are available analogously. However, the reactivity and the ability to form active nickel catalysts for ethylene oligomerization differ for the various types of α-amino phosphino acids and depends on structural aspects. Acyclic and cyclic N-aryl derivatives, in the latter case particularly those with P-tert-butyl group and sufficiently bulky N-substituents to suppress interfering amine-Ni interactions, gave the highest activities.