Zopiclone Impurity 13; 6-(5-chloro-2-pyridinyl)pyrrolo[3,4-b]pyrazine-5,7-dione; 6-(5-Chloropyridin-2-yl)-5H-pyrrolo[3,4-b]pyrazine-5,7(6H)-dione; 6-(5-Chloropyridin-2-yl)- 6,7-dihydro-5H-pyrrolo[3,4-b]pyrazin-5,7-dione