Thermogravimetrical investigations of the dealkoxycarbonylation of N-acyl-α-triphenylphosphonioglycinates

Thermogravimetrical experiments revealed that immediately after the endothermic process of the melting of N-acyl-α-triphenylphosphonioglycinates 1, an exothermic demethoxycarbonylation of phosphonioglycinates commenced, accompanied by the release of CO2. The residues contained the corresponding N-acylaminomethyltriphenylphosphonium salts 2 (18.3–49.5%), methyltriphenylphosphonium salts 7 (21.8–67.9%), and the corresponding 1,2-di(N-acylamino)fumaric acid dimethyl ester 6 (2.1–26.0%). When the reaction was carried out in the presence of Ph3P and the corresponding triphenylphosphine hydrobromide, hydroiodide, or tetrafluoroborate, N-acyl-α-triphenylphosphoniumglycinate bromides and iodides 1a–f underwent demethoxycarbonylation to form the corresponding N-acylaminomethyltriphenylphosphonium salts 2a–f at 95–130 °C in good to excellent yields (79–100%). On the other hand, tetrafluoroborates 1g–i underwent corresponding reactions at about 170–175 °C to give phosphonium tetrafluoroborates 2g–i in much lower yields (34–67%). Plausible mechanisms of the investigated reaction are discussed. It was also demonstrated that the obtained crude α-(N-acylamino)alkyltriphenylphosphonium salts 2 could be applied as valuable α-amidoalkylating agents in spite of their contamination with inert methyltriphenylphosphonium salts 7.