In this study, Michaelis-Arbuzov-type reaction of 1-imidoalkyltriarylphosphonium salts with phosphites, phosphonites, and phosphinites was used in the synthesis of a wide range of phosphorus analogs of α-amino acids such as 1-imidoalkylphosphonates, 1-imidoalkylphosphinates, and 1-imidoalkylphosphine oxides. Large differences were observed in the reactivity of substrates depending on their structure, especially on the type of phosphonium moiety and N-protecting group. The conditions under which the expected products can be obtained in good to excellent yields have been developed. Mechanistic aspects of the transformation have been provided.
Herein, we discuss the formation and reactivity of 1-imidocarbenium
cations in Friedel–Crafts-type reaction between 1-imidoalkylphosphonium
salts and arenes. The observed weakening of C
α
–P
+
bond is described qualitatively and quantitatively. The determination
of rate constants and activation energies of C
α
–P
+
bond cleavage enabled systematic reactivity investigations
of a series of phosphonium salts with different structures. Finally,
the application scope for the imidoalkylation of aromatic hydrocarbons
was explored. The results confirm that the generated 1-imidocarbenium
cations are reactive enough to alkylate strongly activated, less-activated,
or even inactivated aromatic compounds.
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