Synthesis and decarboxylation of N-acyl-α-triphenylphosphonio-α-amino acids: a new synthesis of α-(N-acylamino)alkyltriphenylphosphonium salts

4-Phosphoranylidene-5(4H)-oxazolones 1 undergo hydrolysis in THF in the presence of HBF4 at room temperature to give N-acyl-α-triphenylphosphonioglycines 3 (R2 = H) in very good yields. 4-Alkyl-4-triphenylphosphonio-5(4H)-oxazolones 2 react with water in CH2Cl2/THF solution without any acidic catalyst at 0–5 °C in a few days yielding N-acyl-α-triphenylphosphonio-α-amino acids 3 (R2 = Me) or α-(N-acylamino)alkyltriphenylphosphonium salt 4 (R2 = CH2OMe). α-Triphenylphosphonio-α-amino acids 3, on heating up to 105–115 °C under reduced pressure (5 mmHg) or on treatment with diisopropylethylamine in CH2Cl2 at 20 °C undergo decarboxylation to give the corresponding α-(N-acylamino)alkyltriphenylphosphonium salts 4, usually in very good yields.