3-Ylidenepiperazine-2,5-diones as versatile organic substrates

3-Ylidenepiperazine-2,5-diones and 3,6-diylidenepiperazine-2,5-diones are c yclic dipeptides consisting of one or two didehydroamino acid moieties, res pectively. Some compounds of this series occur in nature. They can easily b e synthesised by several methods also in optically active form and are pron e to addition reactions to the C-C double bond by electrophiles (enamine re activity), nucleophiles (Michael reactivity), radicals, oxidising reagents or 1,3-dipoles, usually in a stereoselective manner. The resulting adducts can further be transformed to natural products and analogues or serve as pr ecursors for interesting alpha-amino or alpha-keto acid derivatives by clea vage of the diketopiperazine ring.