A　divergent　synthetic　strategy　to　1,6-dihydropyridazines　and　pyridazines　through　Cu(II)-catalyzed　controllable　aerobic　6-endo-trig　cyclization　was　developed.　The　selectivity　can　be　rationally　tuned　via　the　judicious　choice　of　reaction　solvent.　It　was　found　that　the　1,6-dihydropyridazines　were　obtained　in　moderate　to　high　yields　with　CH3CN　as　the　reaction　solvent,　whereas　employment　of　AcOH　directly　afforded　pyridazines　in　up　to　92%　yields,　probably　arising　from　the　oxidation　of　the　in　situ　generated　1,6-dihydropyridazines.　©　2019　American　Chemical　Society.