Reactivity of pyrazolo[4,3-c][1,2,5]oxadiazin-3(5H)-ones toward C-nucleophiles: Synthesis of pyrazolo[3,4-b]pyrazines

The reaction of pyrazolo[4,3-c][1,2,5]oxadiazin-3(5H)-ones 1 with carbanions prepared in situ from compounds containing an activated methylene group afforded pyrazolo[3,4-b]pyrazines 4–13 in good yields. The possible reaction mechanism is proposed and discussed.