1-(N-Acylamino)alkyltriphenylphosphonium salts as synthetic equivalents of N-acylimines and new effective α-amidoalkylating agents

1-(N-Acylaminoalkyl)triphenylphosphonium salts 2a–f on reaction with DBU in MeCN are transformed into 1-(N-acylaminoalkyl)amidinium salts 3a–f. Amidinium salts 3d–f with a proton at the β-position undergo slow tautomerization into the corresponding enamides 6d–f. The same 1-(N-acylamino)alkyltriphenylphosphonium salts 2d–f in the presence of Hünig’s base are transformed directly into the corresponding enamides. Phosphonium salts 2, amidinium salts 3, and enamides 6 react with dialkyl malonates in the presence of DBU to give the corresponding amidoalkylation products. α-Amidoalkylation of dialkyl malonates is not observed in the presence of (i-Pr)2EtN, yet proceeds well under these conditions with more acidic nucleophiles, for example, phthalimide or benzyl mercaptan.