3- Alkylidene-2,5-piperazinedione

Shin, C., M. Fujii, and J. Joshimura The General Synthesis of 3-Alkylidene-2,5-piperazinediones. Tetrahedron Letters 1971, 2499. 

Stereoselective formation of 3-alkyl-6-methoxy-2,5-piperazine-dione derivatives by the addition of methanol in the presence of NBS to 3-alkyl-6-alkylidene-2,5-piperazinediones was recently reported by Shin et al. 232 The asymmetric induction in this reaction was accomplished by the chiral center of a derivative of the natural proteinogenic chiral amino acid threonine. 

This is a general method, leading to either 3-hydroxypiperazine-2,5-diones, or to the corresponding alkylidene derivatives (74CB2804). Thus A-pyruvoylproline methylamide cyclizes in water at pH 7.5 to yield the piperazinedione the cyclization appears to be highly stereoselective, leading to the kinetically controlled product (26). The scope of the method has been considerably expanded by Dutch workers, who have used it for the synthesis of l-hydroxypiperazine-2,5-dione derivatives (see Section VI). 

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