Département de chimie moléculaire

The feasibility of the cyclization of gamma-alkylthiobutyric acid derivs. to form previously unknown five-membered-ring acyl sulfonium cations was studied. Exptl. results were in good agreement with our DFT calcns. that predicted such cyclizations to be easy if starting with acyl iodides and mixed anhydrides of triflic acid. Particularly efficient were the reactions of gamma-alkylthiobutyryl fluorides with trimethylsilyl triflate in CDCl₃ soln., which led to cyclic acyl sulfonium triflates. In some cases, the obsd. acyl sulfonium salts were stable enough to be characterized by NMR spectroscopy. They were found to be both alkyl-transfer reagents and acylating agents. They react with amines to form amides. These findings lend some wt. to our hypothesis that the acyl sulfonium derived from methionine may have played a major role in the prebiotic synthesis of the first peptides on the primitive Earth.