Nucleophilic reactivity of amines with an α-formylglycyl enol-tosylate fragment

The E-enol-tosylate of S-3-benzyl-6-formylpiperazine-2,5-dione reacts with 1°- and 2°-amines to yield its respective 3S-benzyl-6E-endiamine products while a 3°-amine, DABCO, exclusively yields a bis-3,6-ylidenepiperazine-2,5-dione product. These competitive reaction pathways with amine electron donors are shown to arise mechanistically via the same intermediate, or its tautomers, with an H-bond assisted nucleophilic substitution process being operative in the former case and an elimination reaction pathway in the latter instance.