The　oxidant-controlled　divergent　reactivity　of　3-aminoindazoles　is　presented　herein.　Diverse　functionalized　pyrimido[1,2-b]-indazole　derivatives　were　obtained　with　good　yields　via　a　Lewis-acid　promoted　[3　+　3]　annulation　reaction　between　ketene　dithioacetals　and　3-aminoindazoles.　When　the　reaction　was　performed　using　the　Cu/[O]　catalytic　system,　new　reactivity　for　the　ring-opening　of　3-aminoindazoles　via　C-N　bond　activation　was　achieved,　which　enables　the　olefinic　C-H　arylation　of　ketene　dithioacetals　under　mild　conditions.　©　2019　the　Partner　Organisations.