(Z)-1-benzyl-3-<2-(ethoxycarbonyl)ethylidene>-2,5-piperazinedione

spiro(3-chlorooxolane-2,3'-(1'-benzyl-2',5'-dioxo)-piperazine)

1-benzyl-5-methoxy-3,6-dihydropyrazin-2(1H)-one

1-benzyl-3-[3'-(diphenyl-t-butylsilyloxy)propyl]-5-methoxy-3,6-dihydropyrazin-2(1H)-one

1-benzyl-3-[3'-(dimethyl-t-butylsilyloxy)propyl]-5-methoxy-pyrazin-2(1H)-one